adding air return

[ace064]

I recently enclosed a back porch and made it a regular room. I need to get an air return installed since the room doesn't maintain temperature although it has double pane windows, insulated walls and insulated floor. I have an air return close to where I want to install a return for the room. It is 12 inch flexduct and is about 10 feet from the main return where it is connected. Can I "T" into that flexduct with the new return and still accomplish my goal of more air return for the new room?

[SkyHeating]

You need to have a pro assess the ductwork otherwise it could create expensive problems.

[cec39466]

Who installed the supply grill for the room? Is the unit sized for the additional load on your a/c? How does it return the air now and were you told that a return could or would be required? Get a professional now instead of later!!!!!

[udarrell]

I recently enclosed a back porch and made it a regular room. I need to get an air return installed since the room doesn't maintain temperature although it has double pane windows, insulated walls and insulated floor. I have an air return close to where I want to install a return for the room. It is 12 inch flexduct and is about 10 feet from the main return where it is connected. Can I "T" into that flexduct with the new return and still accomplish my goal of more air return for the new room?

A lot of relevant data would need to be collected before making more changes.


If it were my home I'd start with a Home Energy Efficiency Audit & do retrofitting to reduce the equipment loads.
I would then do a manual J room-by-room heat-gain/heat-loss load calc
Then a manual D duct system air handler analysis


That might indicate whether the existing equipment, plus air handler & new duct system design will deliver adequately, both heating & air conditioning to every room.

You need experts in those areas to get everything right.

[Brian GC]

…and then there are those here who continually say “you cannot have too much return air”. It seems with that motto you could T-off anyplace along the return ducting and put a return just about anywhere allowed without detrimental effects, right?

Personally, I do not believe a return can go anywhere allowable without bad effects, but plenty here do. I cannot see why anyone here would object to your proposed return re-duct.

[udarrell]

Well Brian, the reason I outlined that procedure is because we don't know enough about the situation he is dealing with. (Just trying to justify my prior post.)

He might install a return & T it to the other Return duct & still have heating & cooling problems in that room.

You are right in that no one is going to have too much Return, & that is especially true of RA filter areas.

[ace064]

House has 2 year old HVAC system. Ran one register into new room 10/20 feet. Only air return is thru door opening into main house. Get decent air flow thru one register, but believe adding another register and an air return would improve situation. House size before adding new room was approximately 1450 sq ft. Could go thru all of the tests but wanna bet that the end result will be to get air out of the room via air return to solve problem. Trying to keep this as simple as possible. By the way, the new system is a 3.5 ton with high efficiency furnace. Furnace natural gas fired. A/C is electric.

[ace064]

Additional info-- House has three air returns. Main return in hallway above HVAC unit. 20/25 size. Second is about 27' from main return 10/10 size. Third is small 4x6 size in den approximately halfway between other returns. All windows in house are double pane, Argon gas, etc. Attic has 12 inches of insulation with new roof. No basement.

[energy_rater_La]

3.5 ton unit on a 1450 sf house...

I wouldn't T-into return duct.
maybe a jump duct in the ceilings
or a transfer grill over door.

hard to tell without seeing.

lots of info needed...
where are you located?
what size room?
what size ducts did you add?
flex duct?
where are the ducts located? attic?
is there room on the plenum to add ducts?
and that's just to start.

did you call a hvac company to do this
or diy?
you do know this isn't a diy site??

best of luck.

[Brian GC]

He might install a return & T it to the other Return duct & still have heating & cooling problems in that room.

Very true about the supply side possibly not being adequate, but re-ducting the return as he described couldn't cause any problems, could it?

[Brian GC]

I wouldn't T-into return duct.


Why not?

Very few pros here seem to use returns to control and regulate airflow patterns? Rather they use them to reduce pressure and as an “air path back to the handler”. That means to most pros here a return could go just about anywhere allowed.

[tedkidd]

3.5 tons. 1450 sf.

Hoboy, here we go AGAIN! What's the furnace, 100,000 btu?

Love to see pictures of the unit.

Doesn't 3.5 tons generally require side/side or bottom/side return to have enough airflow/filter area?

[udarrell]

Doesn't 3.5 tons generally require side/side or bottom/side return to have enough airflow/filter area? - tedkidd
Yes, Ted.

Since furnaces now-days don't have filter racks, that leaves a lot of things to consider:

Is there only one, or even two Returns with a filters close to a 90-ell with no turning vanes, resulting in much higher velocity through portions of the filter.
Is the Return on the blower motor side; increases static & lowers CFM some.
Did they reduce the ducting prior to the 90-ell resulting in a smaller filter area?
Are all of the Return Air grilles large enough?


Willing to bet the equipment is way oversized.

By the way, to keep the electric bills down, we need to go to the most efficient blower motors possible on the smaller sized longer running furnaces.

A smaller condenser furnace requires more airflow to keep the temp-rise within 60-F, some require even lower temp-rises.

I have seen some situations where they had belt-drive blowers on oil furnaces where the new smaller condenser furnace set-ups will use nearly twice the wattage with considerably longer run-times. This is heating only even without an A/C cooling coil. The customer should always be shown the full-disclosure options so they can make an informed decision.

Hopefully those super efficient motors will get less pricey, both initially & when needing repairs.

[kls-ccc]

Contrary to popular beliefs air is not inteligent and doesn't automaticly knkow where it is suppose to go. You can try to force it but it has been my experience if it is fanesed and led to where you want it to go it just works better.

Having said that we are back to what others have said and I paraphrase " DON"T JUST GO CUTTING HOLES ANYWHERE, CALL A PRO". You can take a shot in the dark and get it somewhat right, or you may screw up the whole system. Duct work and airflow is not just a science but also an art. Unless you put smoke in the air you can't see how it reacts so experience gets to be a big deal. Paying someone for that experince can be a whole lot cheaper in the long run than trying to save a buck up front.

[energy_rater_La]

true dat!

op why not T into return air?
most ducts are not sealed properly or
the nationwide average would not be so high
for duct/return leakage.
either the right products are not used, or the ducts
are not air tight, ducts are improperly sized or all of the above.

my climate has problems with high humidity
return air leakage contributes to this a lot.

I've answered your question..
care to answer my questions?

these things matter.
hvac companies charge a lot to go back
and properly fix diy jobs.


best of luck.

[Brian GC]

true dat!

op why not T into return air?
most ducts are not sealed properly or
the nationwide average would not be so high
for duct/return leakage.
either the right products are not used, or the ducts
are not air tight, ducts are improperly sized or all of the above.

my climate has problems with high humidity
return air leakage contributes to this a lot.

I've answered your question..
care to answer my questions?

these things matter.
hvac companies charge a lot to go back
and properly fix diy jobs.


best of luck.

So your short answer seems to be, if sealed properly there’s nothing wrong with it.

And, I’d be happy to answer your questions.

[pstu]

It seems to me the proposed T-ed return has many characteristics in common with a jump duct, is that not right?

If the addition is well sealed, I certainly would be interested in learning what the downside of the proposal could be. Not at all saying it would be a solution to the comfort problem. You should be able to tell from the message header that I am not a professional.

Hope this helps -- Pstu

[bironacad]

In our climate, southern Ontario, a room over an unconditioned space such as a garage seems to always be at odds with the rest of the house. A simple fix may not be there. Someone mentioned louvers to allow for air migration but a cold floor is a cold floor. My first home had a kitchen built on piers, the floor was insulated, the entrance to the kitchen was open so no problem with return but the floor was cold and that affected the comfort levels. I currently own a house that is six years old with blown insulation on the bedroom floor over the garage and it still has different comfort levels to the rest of the house. Crawl spaces unheated have similar challenges to the floors above. So what am I saying? Perhaps it is the room design that is a challenge? How about radiant in floor heating, lol.

[tedkidd]

The load on these spaces is SO out of balance with the load on other more protected spaces, and typically it's the furthest from the furnace and possibly short on supply and return, and leakier than all the other rooms that your handicaps are huge.

Add in typical oversized/short cycling equipment, and the furnace satisfies the thermostat way before that long ductwork even warms up enough to deliver any btu's to the room.

[54regcab]

Add ons have a bad habit of needing different heating/cooling requirements than the main living space. Rarely is does it work right with one system serving both areas unless there is a large opening between.

[genduct]

I recently enclosed a back porch and made it a regular room. I need to get an air return installed since the room doesn't maintain temperature although it has double pane windows, insulated walls and insulated floor. I have an air return close to where I want to install a return for the room. It is 12 inch flexduct and is about 10 feet from the main return where it is connected. Can I "T" into that flexduct with the new return and still accomplish my goal of more air return for the new room?

is flawed! This is said with the full understanding the post #5's author, Brian will vigerously disagree. If you still aren't comfortable with the door open then you clearly have a supply duct problem

[ace064]

The installer told me that all I needed was another register run to the other end of the room. Perhaps this would fix the problem, but air must exit the room in some fashion, right? I guess I could just leave the door cracked a little to let air out, but it seems that putting in an legitimate return would make more sense. I realize that this is a professional site and that, whether you guys admit it or not, calling in a professional is the response you will give most times. That is fine. I will do that, but , since I have been involved in construction for over 35 years, I tend to lean toward solving any probelms I can myself. Thanks , guys, for the help.

[genduct]

The installer told me that all I needed was another register run to the other end of the room.

If you heard right, register means supply.

Unfortunately this area of study has a wide view of what is best, so even if you call several "professionals" it would be like calling several economists ... you would probably get 1.345 X opinions.

The presence of a return grill vs an open duct still gives you the same result. Actually the open door is less resistance than a ducted return so my suggestion is even more indicative of understanding if your real problem is a lack of supply air

[ace064]

Genduct- I heard right. The installer was talking about a supply register. I will get another supply register installed and see what happens. If this doesn't do the trick, would you suggest a return duct or just open the door wider?

[Brian GC]

is flawed! This is said with the full understanding the post #5's author, Brian will vigorously disagree. If you still aren't comfortable with the door open then you clearly have a supply duct problem

I did not say adding a return would help the Op’s problem. I said T-ing off the return could not hurt anything, as some here suggested. Frankly, after all I’ve written on returns, I doubt you’ve followed much of it.

The OP probably has a supply problem, but adding a return along with an additional supply could only make things better, far better than an ugly jump duct.

[ace064]

Genduct- No, I haven't read any of your writings on returns, but I will research more on this. I really appreciate your taking the time to help me with this problem.

[Brian GC]

As per the AOP Rules only Professional Members * can reply with
advice to the OP. Anyone may post and ask questions. They may even
question the * member answer but not give advice or expand on the
advice given. Please read these rules for a complete understanding. AOP Rules (http://hvactalk.
com/vbb/showthread.php?t=853582)
For those in our industry who wish to become a Professional Member, please click here and follow the
instructions. Apply for Professional
Membership (http://hvac-talk.com/vbb/showthread.php?t=116113)

[genduct]

Genduct- No, I haven't read any of your writings on returns, but I will research more on this. I really appreciate your taking the time to help me with this problem.

In this case, Brian is talking about HIS posts and ideas on Return duct installs not mine.

Actually Brian's opinions have evolved somewhat, although he finds it inconvenient to admit it. Either because he has not fully grasped what I have tried to share OR if he does understand but would find himself admitting that he now agrees and can't bring himself to do that... I don't know

Brian, I have offered to speak with you so that there would be a chance for a conversation i.e. Q & A my tele# is in profile. Feel free

[Brian GC]

Actually Brian's opinions have evolved somewhat, although he finds it inconvenient to admit it. Either because he has not fully grasped what I have tried to share OR if he does understand but would find himself admitting that he now agrees and can't bring himself to do that... I don't know


If you were willing to learn something about return location you would have engaged in this thread of over 300 posts
http://hvac-talk.com/vbb/showthread.php?t=855922 but I didn’t see you there. If you care to read it you will find the sharpest posters and very detailed data taken. The HO who was very sharp himself took KW readings before and after he moved his return from downstairs to upstairs. By doing so he documented a 33% savings on his electric consumption from that change alone.

To sum it up even Shophound relented by saying Xavier and I were vindicated about our theory that return location matters. So if you wish to debate the issue further you should take it up with Cherokee, he has the detailed data that is very difficult to refute.

[genduct]

what you find inconvenient to your strongly held theories. see posts below:

Brian GC I find it very strange that... 06-23-2011, 12:11 AM
genduct Brian, have you changed your... 06-23-2011, 06:35 AM
genduct PS Brian 06-23-2011, 06:48 AM

this was in the early stages of the discussion.
Just because I don't need you accept my point of view, and choose not to continue to beat the same drum, doesn't mean I didn't contribute

[udarrell]

If you were willing to learn something about return location you would have engaged in this thread of over 300 posts
http://hvac-talk.com/vbb/showthread.php?t=855922 but I didn’t see you there. If you care to read it you will find the sharpest posters and very detailed data taken. The HO who was very sharp himself took KW readings before and after he moved his return from downstairs to upstairs. By doing so he documented a 33% savings on his electric consumption from that change alone.

To sum it up even Shophound relented by saying Xavier and I were vindicated about our theory that return location matters. So if you wish to debate the issue further you should take it up with Cherokee, he has the detailed data that is very difficult to refute.

I also maintain that Return location matters.
However, claiming a 33% savings is only accurate to the degree that all factors are within the equation.

I would also want a meter on the condenser & air handler; though that is only one part of all the factors. Conditions have to be identical or prorated to adjust for all the differences.

I do question that there would actually be a 32 or 33% savings; I would like to know what the actual real savings was.?

Maybe he can prove that was the actual savings...

I didn't read everything; here is the page with a lot of Cherokee's data:
http://hvac-talk.com/vbb/showthread.php?t=855922&page=3

Cherokee's research is a very important study & may be very close to actual usage differences... Thank you, Cherokee!

[Brian GC]

Udarrell,
You are correct in that an exact 33% figure cannot be attributed to the savings, but it was probably close to that. Multiple watt meters in a perfectly sealed structure and duct system would be required for more accuracy. But heck, even if it was 15% it would be significant.

One thing was for sure. Cherokee was revealing something with his experiment and it had to do with the importance of return location. He was amazed at the two things I have been talking about for years now. That correct return location will improve temp gradients and system efficiency. Those two results were clearly proven.

Genduct,
I forgot you were in that discussion early on, but why did you bail out? Cherokee, as well as the other contributors, were very technical posters with a lot to bring to the table. If you claim to know about these matters you should have stuck around to school everyone there. But I assume the discussion was going in a direction that forced you to open your frame of thinking…something you are not ready to do.

It would be more helpful to not take issue with me, but rather the subject at hand. If you do not accept Cherokee’s findings now is the time for you to explain what he was doing to yield such savings, efficiency and comfort.

BTW - To say that Cherokee was "beating the same drum" indicates closedmindedness IMO.

[Shophound]

I relented to the extent that I understand in Cherokee's case that his return air location was affecting the dynamics of summer reverse stack effect on his house (since his original complaint was poor cooling upstairs). My goal in participating in that thread was to get a better handle on why moving a return air intake location affects the thermal gradiant characteristics of a two story house. My conclusion was that return and supply air duct leakage outside of the thermal and pressure boundaries is a large driver behind why when he covered up one return vs. the other he got better results, comfort and energy-wise.

But that's not what this thread is about, is it? Far as I know it's a single story house, or at least since we're talking about a recently enclosed porch, the room in question is on the ground floor, and communicates with the ground floor when the door to the new room is left open.

What we ARE talking about is a lack of understanding heat load diversity, which is what Darrell and other pros here attempted to address with their responses. The enclosed porch, if there was never any attempt to calculate how much airflow it requires for a design summer heat gain, or a design winter heat loss, is then relegated to "poke and hope". Let's "poke" another supply into there and "hope" for the best. Let's "poke" a return outlet to the room and "hope" that helps. For the latter, I agree that would help for when the door to the new room is closed.

However, if the room is NOT comfortable even with the door wide open, which allows air introduced into the room via the one supply vent to return to the air handler via a common path the house shares with the room, there is not enough supply air being introduced into the room to offset the heat gain through the windows and enclosure. Same for winter...not enough air to offset the heat loss through the structure.

[Brian GC]

Shophound,
You are correct, there is little in common with this thread and Cherokee’s thread. As I also said earlier, this OP probably has a supply problem and it may not be because of a porch like enclosure since it is fully insulated, dual pane w/argon, and 12” in the attic. It’s simply lack of supply airflow. And, I doubt by only adding a return it will suck comfort into that room.

As for Cherokee’s thread, if it’s OK to discuss here, my observation was that there was more at play than just reverse stack effect. That would require a very porous envelope to have a 33% effect. It may be a factor, but the removal of the warmest upstairs air and the prevention of cold air from falling down the stairwell were major factors as well. What percentage each played is open for speculation without further testing…but I doubt it was only one of the three. And, if his return ducting did leak more when the downstairs was covered it would positively pressurize the structure and reduce infiltration/stack.

[ace064]

Hey guys!!! Wow!! Here is my plan. I will have another supply register installed. The room is 10 x 20 and I believe it needs another register regardless. I will get a return placed on the opposite wall from the supply registers and attach it at the air handler with a "Y" with the other return line (the one I was going to "T" into ) on the other side of the "Y". Does this sound like it might work?

[Brian GC]

Hey guys!!! Wow!! Here is my plan. I will have another supply register installed. The room is 10 x 20 and I believe it needs another register regardless. I will get a return placed on the opposite wall from the supply registers and attach it at the air handler with a "Y" with the other return line (the one I was going to "T" into ) on the other side of the "Y". Does this sound like it might work?

It sounds like it would be a big improvement. But when you get it installed I would like to know which arrangement works best:

One supply with a return at the far end of the room vs. one supply with the door open. (as it is now)

Two supplies with a return at the far end of the room vs. two supplies with the door open and the return covered.

[ace064]

Will do Brian. And thanks.

[Brian GC]

I relented to the extent that I understand in Cherokee's case that his return air location was affecting the dynamics of summer reverse stack effect on his house (since his original complaint was poor cooling upstairs). My goal in participating in that thread was to get a better handle on why moving a return air intake location affects the thermal gradiant characteristics of a two story house. My conclusion was that return and supply air duct leakage outside of the thermal and pressure boundaries is a large driver behind why when he covered up one return vs. the other he got better results, comfort and energy-wise.

When Cherokee moved his return from downstairs to upstairs it lowered his electric consumption by 33%. That is a fact. What dynamics that were responsible for the improvement was unproven, beside the point and does not change the basic fact that return location matters. It matters a lot, as some here wrongly refute.

Even if your conclusion was correct, in the real world homes leak and ducting leaks. If the return can be placed in a certain location to counter these effects and save 33% of energy consumed, then that is where they belong (upstairs in the summer and downstairs in the winter).

If you or anyone is inferring that further sealing the thermal envelope and ducting makes return location irrelevant in temp gradient and power consumption improvements I’d like to hear of your experiment or experience that proves that.

[pstu]

Cherokee reports some very surprising observations. There ought to be a VERY publishable paper that could result from a 3rd party visiting the house, repeating the observation, and making enough additional measurements to explain why this could be.

33% from just changing return location, I cannot imagine explaining that by the science I know. I have heard similar outsized claims on other building science topics, for example the earnest local builder/teacher who claims tiny electric bills just from "vent skinning" wall construction. But those claims have not been verified by any 3rd party. There was also the guy (our HVAC tech at the time) who insisted that putting magnets on his gas line improved his Chevy Astro van from 14 mpg to 20 mpg. I need to hear things verified from several sources before I am confident.

Regards -- Pstu

[tipsrfine]

Saying Cherokee reduced his energy consumption by 30% by only moving the return location is taking it out of context, IMHO. Cherokee had floor register with poor air throw which caused air stratification upstairs. The upstairs t-stat would take forever to be satisfied 'cause the cold air took forever to reach it, and once satisfied, that heat line would just build back up and lower,(or the cold line would drop) causing the stat to start it all over.
To me it is the equivelant of hanging the t-stat out the window, taking energy use readings, and then bring the t-stat back into the conditioned area-of course there will be a huge reduction on energy use.
Changing the return location helped to correct a supply side issue.

[Brian GC]

Saying Cherokee reduced his energy consumption by 30% by only moving the return location is taking it out of context, IMHO. Cherokee had floor register with poor air throw which caused air stratification upstairs. The upstairs t-stat would take forever to be satisfied 'cause the cold air took forever to reach it, and once satisfied, that heat line would just build back up and lower,(or the cold line would drop) causing the stat to start it all over.

How did moving the return upstairs make the floor registers cool the upstairs better? How did it cool the house more evenly? How did it satisfy the t-stat up to 5 times quicker, which is the reason for the energy savings?

[tipsrfine]

How did moving the return upstairs make the floor registers cool the upstairs better? How did it cool the house more evenly? How did it satisfy the t-stat up to 5 times quicker, which is the reason for the energy savings?

Pretty much just said it, and I also said it in Cherokee's thread. Kind of a hybrid displacement situation.

[Shophound]

For the sake of the OP of this thread, to my understanding he's dealing with an add-on room on the same floor that likely does not receive enough supply air on hot days with the door to the house open, and becomes worse when the door to the add-on is closed. Increasing the amount of supply will help with the door open, and adding a return will help with the door closed. Short of seeing the house in person I think that's about the extent we can advise the OP on this board.

With the reintroduction of Cherokee's saga over this past summer inserted into this thread, it could be viewed as a hijack/derail, but since I think we've met the OP's needs sufficiently, perhaps notions of a derail aren't warranted now. It's then a matter of whether evolving this thread into a general discussion about supply and return air dynamics is in keeping with the AOP intent of this section. We've answered the OP well enough that he has sufficient info to proceed toward a solution. Add more supply, add return for when the door is closed. Ideally it would be best to know how much supply to add...but from what I've heard it will likely come down to "cut in a supply and return and hope for the best". Without a room to room load calc in hand, that's all that can be expected.

Would be nice if typical approaches residential HVAC design had a more precise aspect to it. But I do dream.

Nevertheless, since the Cherokee matter has resurfaced, let's look at that a bit. About the only relevance I see it having to the OP is that it deals with return air issues, but that's it:


Saying Cherokee reduced his energy consumption by 30% by only moving the return location is taking it out of context, IMHO. Cherokee had floor register with poor air throw which caused air stratification upstairs. The upstairs t-stat would take forever to be satisfied 'cause the cold air took forever to reach it, and once satisfied, that heat line would just build back up and lower,(or the cold line would drop) causing the stat to start it all over.

The floor supply registers certainly aren't the best choice for cooling, that's true. But sometimes, as they say at drag races, you gotta "run what ya brung". In Cherokee's case, he had downstairs and upstairs return air inlets on the same building cavity, that in itself a poor choice for HVAC ducting. Meaning that the downstairs inlet, being closer to the air handler in the basement, would draw the lion's share of return air while the upstairs inlet starved.

A fundamental aspect of successful space conditioning is adequate turnover of air volume within the conditioned space to stay ahead of the heat gain. You must remove air from the space alongside introducing it to the space so the removed air can be cooled and dehumidified. If you introduce cooled and dehumidified air to a space but don't provide adequate means to remove it, either the space becomes overly pressurized and forces air out through walls, ceilings, etc, or in Cherokee's case, the upstairs region being the focus here, the air stagnates as it heats up and does not reach the downstairs return air inlet in sufficient quantity to provide adequate air volume turnover that stays ahead of the heat gain.

When Cherokee blocked most of the downstairs return, the amount of air entering the upstairs return inlet greatly increased. This resulted in a net increase of air volume turnover for the upstairs region. So much so that he reported significant comfort gains and reduced a/c run times. With the thermostat for the entire system being upstairs, that's an expected outcome.



Changing the return location helped to correct a supply side issue.

Partly. In Cherokee's thread I got a bit intensely focused on duct leakage, being he stated there were supply and return duct runs in the interstitial spaces between the first and second floors. Supply leakage would account for any mechanical enhancement of reverse stack effect. A wimpy return air inlet upstairs suddenly made macho would certainly help offset a lot of the outcome of a mechanically induced reverse stack effect, but you can be confident that reverse stack is still there. Enabling the upper level return simply made it and the supplies better positioned to deal with the effects of reverse stack.

Cherokee later reported that he had Aeroseal work done to his supply and return air ducting, with notable performance improvements all over the house following such work. I asked after he reported this if he'd care to repeat the high/low return air experiment, which he was reluctant to do, stating he had additional thermal boundary work done alongside, and that the weather had moderated outdoors. So he didn't think the test was repeatable.

I wasn't out to disprove anyone by asking Cherokee to repeat the test post Aeroseal, but to see whether my own hunches were on track or not. If Aeroseal is effective at reducing duct leakage, I would expect mechanically induced reverse stack effect to be reduced as well, with a concurrent improvement of a/c performance regardless of whether a downstairs return air inlet was covered or not. I would expect some differences between a covered and uncovered inlet to be noticable as in the beginning, but not as pronounced, under similar testing conditions (hot weather, same thermostat settings, etc.).

The only way I'll ever be able to more thoroughly satisfy my own curiosity and knowledge base on this matter is to hope that someday I come across a similar problem and configuration in a residence, and with a patient homeowner run some extensive, minimally invasive data collection and experimentation to reach some repeatable observations. Doing it over the internet is handicapped from the word "go". Nothing beats being on site and responding instantly to subtle whisperings of one's onboard intuition to "go check that out, see if it's so!". I would volunteer my own house as a lab, as I have in many related building science discussions, but alas it is a single story structure with a central return air inlet directly beneath the furnace. Which by the way works fine year round.

[tipsrfine]

We do love this stuff!! I think I remember Cherokee saying the results from the aerosol was so good that he believed he could change that return back to its original position and he still wouldn't have problems. That was a good thread, but I'm ok with putting that one to bed. There will be others.

[Shophound]

We do love this stuff!! I think I remember Cherokee saying the results from the aerosol was so good that he believed he could change that return back to its original position and he still wouldn't have problems. That was a good thread, but I'm ok with putting that one to bed. There will be others.

It's all good, amigo!

I may have missed where Cherokee said that but that's cool if he thinks such is the case. Duct leakage and building infiltration/exfiltration are HUGE drivers behind indoor comfort or the lack thereof.

I also agree we'll certainly have other discussion along these lines....plenty of houses out there like Cherokee's that each person will need guidance on to approach good results like his.

[energy_rater_La]

since we are revisiting the aeroseal thread...
there was something that I thought had a huge impact
and it wasn't the 6% duct sealing.
it was the foam insulation.

cherokee says in post 39:
Unfortunately due to the one week delay in the final test out, the bump out and fireplace spray foam occured inbetween the baseline and final test of the duct sealing, so it is impossible to isolate how much of the 123 CFM reduction was due to either improvment. If you call a 6% improvement very little (ie assuming all was due to Aeroseal), than maybe your statement "Aeroseal reduced leakage to outside very little, if at all." is true. If I were guesing, I would think the large % was due to the return side leakage reduction from the Aeroseal process that went from 350 CFM down to 90 CFM, especially when my return ducts are not really ducts at all, just wall cavities. Your second statement "Aeroseal made a huge improvement in distribution, even temperatures, and overall control and comfort." is 100% true and by far the biggest benefit I have seen so far.

Granted we are only going by information provided, but
I would think that 6% duct leakage reduction is not much.
nor is sealing house leakage 123cfm. I wondered if those
numbers were correct...
His comfort has improved greatly..no doubt about that.
Glad he his comfortable and happy with the work done.

but what is attributed to foam and what to aeroseal?
what is return leakage and duct leakage no longer
being driven by infiltration rates from the areas foam sealed?
we will prolly never know.
but wouldn't it have been nice to have had those numbers to start with?
so that an accurate measure of each upgrade would be reflected for us
nerds..

not to ruffle feathers guys...just an observation.

[tipsrfine]

And in post #37 Cherokee said:

Shophound asked about activent closure question an the answer is simple, my master bath and walk in closest have 3 vents total in them that were open to the same master bedroom, so it appears that the increased airflow is so dramatic that even with the two main vents by our bed shut, we still had more total airflow in the room.

This is what I meant about the changing of the return being taken out of context. The main culprit was a failing of the supply side. All air flow is FROM a higher pressure TO a lower pressure. Add low supplies with poor velocity/throw that barely makes it half-way to the height of the t-stat before gravity overtakes it and that cold air starts to fall back down the steps to the lower return, and you have high energy use caused by a t-stat that takes forever to be satisfied, and a lower level that is overcooled. Putting the t-stat in the attic would have mimicked these symptoms.

I know I said I was ready to put this one to bed, and I lied.

[hvacvegas]

And in post #37 Cherokee said:

Shophound asked about activent closure question an the answer is simple, my master bath and walk in closest have 3 vents total in them that were open to the same master bedroom, so it appears that the increased airflow is so dramatic that even with the two main vents by our bed shut, we still had more total airflow in the room.

This is what I meant about the changing of the return being taken out of context. The main culprit was a failing of the supply side. All air flow is FROM a higher pressure TO a lower pressure. Add low supplies with poor velocity/throw that barely makes it half-way to the height of the t-stat before gravity overtakes it and that cold air starts to fall back down the steps to the lower return, and you have high energy use caused by a t-stat that takes forever to be satisfied, and a lower level that is overcooled. Putting the t-stat in the attic would have mimicked these symptoms.

I know I said I was ready to put this one to bed, and I lied.

I'm not interested in re-reading that old thread, so:
I saw something about the cherokee basing his energy savings off his meter.

Out of curiosity, were the outdoor temperatures recorded?
33% savings make sense when the unit only has to run 2/3 of the time, based on outdoor temp.


If only a 3rd independant party, whos ruling could be considered emperical, would produce some information on the subject of return location impacting comfort level in the home.

Oh...nevermind.

[energy_rater_La]

yeah..kinda moot isn't it?

maybe next time!

[Brian GC]

Shophound gave a good explanation of what was happening in Cherokee’s house. I would like to expand on his findings.

“A fundamental aspect of successful space conditioning is adequate turnover of air volume…” This is true but certain parts of a two story house require more turnover than others. You must take in account where the heat gain and supply air is migrating to. The heat gain was going upstairs and the supply air was flowing downstairs. As Cherokee described, “the stairwell is like a giant chute”. With the return downstairs it created a downward draft in the stairwell that naturally pulled the cooler/heavier air down first. When the return is upstairs it will create an upward draft in the stairwell and pulled the cooler downstairs air up the stairwell. Turning over the upstairs air is far more important than doing it downstairs.

Heat gain and heat loss migrate in different directions within a structure. Cool supply air and heated supply air also migrate in different directions. Cherokee’s findings show that “adequate turnover” must be concentrated where the heat loss/gain collects. He has little-to-no turnover downstairs and it is comfortable. I’d bet that little-to-no turnover upstairs in the winter will also be very comfortable.

[tipsrfine]

The above description of stack effect is very wrong. This is why this site only wants professionals with an * after their name to give advice to "appliance owners".

Here is a brief definition of Stack Effect:

Stack effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, and is driven by buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences.

The taller the building, the more pronounced stack effect is. Generally speaking, stack effect becomes a concern in building over 3 stories high. Reverse stack effect occurs in the cooling season, but it is much less pronounced than the stack effect that occurs in the heating season. This is due to the fact that there is a larger temp split between the outside and inside in winter, than there is in summer.

[Shophound]

The root cause of stack effect:

It will surprise you.

Ready?

It's the atmosphere.

The fact that we plant a building on the ground and then choose to heat or cool it is mere extra detail.

In winter, with variation, the air mass of the atmosphere is sinking. Ever go outside on a cold, clear winter morning with no wind and look out across your fair city? You'd think the air would be pristine, but often it's hazy from overnight fireplace burning, coal power plants, etc. A sinking air mass explains why.

In summer the air mass is rising, due to heating of the earth from much increased sunlight intensity and length of days.

Pretty basic. Colder air is more dense, warmer air is less dense. Air expands as it warms, and contracts as it cools.

Still not sure? Go to wunderground dot com and select your region. Go to weather history for your region and collect a year's worth of barometric pressure data. More than likely you'll see, provided you don't live in Hawaii or such, a difference between average barometric pressure in the summer vs. average barometric pressure in winter.

It was an eye opener for me when I reached this conclusion regarding stack effect. The forces involved to me needed a point of origin. It's one thing to say that, regarding physics, the order of operation is from more to less (greater pressure to lesser pressure, higher moisture to lower moisture, etc). It's another thing to nail down where the greater force originates. Once you have something nailed down, the hurricane seems less chaotic.

Okay, so we have this huge mass of nitrogen and oxygen over our heads, along with countless other gases. It has weight, mass, and density. It heats up and cools down. It expands and contracts. It blocks out sunlight or lets it come down without mercy. It allows moisture to condense and form rain, sleet, or snow. We then look up at the sky and say, "You know, that's a pretty fantastic dance! Mind if my house cuts in?"

Sure, join the dance. But unfortunately that is what most of our houses do...they dance with the atmosphere all too well. It's too good of a partner, letting the atmosphere take the lead at all times. Never a switching of hands on the back and waist... the atmosphere is always waltzing the house across the dance floor. Sometimes it even throws in the twist just to shake things up. :)

Those of us who understand building stack effect and how the atmosphere figures into it will know what we can do to make the house be a less willing dance partner. Knowing how to do that entails knowing who the dancers are, and then working to put each where they belong.

IOW, it's far more than merely a supply and return air discussion.

[genduct]

what happens when you consider that the lighter component of air (the RH) is there in summer and not as much in winter. We know that steam is lighter than dry air

[Shophound]

what happens when you consider that the lighter component of air (the RH) is there in summer and not as much in winter. We know that steam is lighter than dry air

A rising air mass, increased moisture mass = summer condition. Moisture comes from oceans, lakes, streams, plant transpiration, the ground. Heat all that up and rate of evaporation increases. Dew points day to day average higher than in winter.

A sinking air mass, reduced moisture mass = winter condition. Where can moisture come from in the higher reaches of the atmosphere comparable to summer sources? Don't let the higher relative humidity readings fool you. Overall dew points track lower in winter vs. summer. Dew point is directly tied to absolute moisture content. I've been measuring this for several years now in addition to comparing it to local weather data year to year. It's a consistent pattern, at least where I live and for a good chunk of the USA.

Steam may be lighter than dry air, true. Literal steam is >212F and will heat surrounding air along with its own buoyancy, thereby both rise (reduced density, increased volume). That said, what weather events converge to deliver consistently lower dew point/absolute moisture contents over a winter season? Well, a biological factor must also be given, in that winter for most of the USA carries a high dormancy rate for plant life, thereby reducing transpiration significantly. That, and the plants that are evergreen experience reduced transpiration due to colder temperatures and less sunlight. The reduced daylight hours and reduced sun angle also reduce heating of the earth's surface and bodies of water, so evaporation from these sources also goes down.

For a house, while the atmosphere is the principle driver behind stack effect, the fact that we heat or cool the enclosure is the secondary driver. That's the "dance" aspect I was alluding to in my previous post. The atmosphere carries on its own dance regardless of what we do to the interior of a house. If the interior was the same temp and moisture content as the atmosphere surrounding the house, no stack would occur. But we humans seldom like our interiors the same as the atmosphere surrounding our houses, so we heat or cool them.

Heat the interior, its air mass, contained by the building's shell, expands and exerts pressure against the shell. If the shell leaks, portions of the air mass will pass through these leaks and into the atmosphere, seeking equilibrium (ain't that truly the principle behind the physics in question here...a seeking of and an upsetting of equilibrium?). Being that the building shell leaks in more than one location, and being that the atmosphere outdoors is pressing against the earth with increased barometric pressure over a summertime condition, the atmosphere presses into the house toward the floor as heated air exits the house up high. We call this negative and positive pressure planes, pertaining to the study of infiltration/exfiltration.

The basis is that the lower levels of the house are negative to outdoors and the upper levels are positive. This is true, but simultaneously the atmosphere is exerting positive pressure down low and air exiting the house is momentarily at a higher pressure than the atmosphere, until it cools and equalizes with the surrounding air mass (say, in a ventilated attic).

The general winter pattern concerning interior moisture is that infiltrating air from outdoors, being it has a consistently lower absolute moisture content, drives moisture from the house via stack exfiltration. In summer, reverse stack effect brings warm, moist air from high in the structure, where it exfiltrates down low, near the floor of the lower to lowest levels. Hence the need to dehumidify the interior to stay comfortable.

[Brian GC]

The above description of stack effect is very wrong. This is why this site only wants professionals with an * after their name to give advice to "appliance owners".

Here is a brief definition of Stack Effect:

Stack effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, and is driven by buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences.

The taller the building, the more pronounced stack effect is. Generally speaking, stack effect becomes a concern in building over 3 stories high. Reverse stack effect occurs in the cooling season, but it is much less pronounced than the stack effect that occurs in the heating season. This is due to the fact that there is a larger temp split between the outside and inside in winter, than there is in summer.

Please point out where in the forum rules it specifically says only pros with an asterisk can give opinions and advice. I read them and did not find it. And, since most pros here and elsewhere only agree about 80% of the time, who gets the last word...the guy with the asterik? Please.

I’ve read all about stack effect. Though there are many dynamics to it, it is a very simple concept to understand. But maybe I missed something that you could clarify. Since you are a pro (with an asterisk) and you failed to point out my errors, maybe you could answer this question that parallels my “very wrong” statement:

It is 110F outside. A two story building with no windows, doors, interior walls, has R50 insulated exterior walls and every cubic inch of air within that structure is 75F +/- 0.1F. There is no wind outside. The RH is the same inside and outside. There are three golfball size holes in the thermal envelope located at the top, the middle and the lowest level of the structure. Will the building experience noticeable stack effect? If it does, where will it infiltrate air from?

[HeyBob]

Brian GC,

You do not have site permissions to give advice in this forum. Please review forum rules.

Bob

[k-fridge]

Gentlemen,

Some posts have been reported. Please remember that only Professional members with a * by their tiles are allowed to give technical advice.

Thanks

[Shophound]

I’ve read all about stack effect. Though there are many dynamics to it, it is a very simple concept to understand.

Apparently not. I've learned to be wary when someone says, on the borderline of being flippant, "oh it's so simple". Personally, when I've done that, it was only later I would discover how flippant that truly was of me. When you set your mind on "simple", that's all you see. The litmus test is when reality comes along and gives you a wake up call, do you reside obstinantly in "simple" or do you arouse from simple slumber to fathom a larger picture?


It is 110F outside. A two story building with no windows, doors, interior walls, has R50 insulated exterior walls and every cubic inch of air within that structure is 75F +/- 0.1F. There is no wind outside. The RH is the same inside and outside. There are three golfball size holes in the thermal envelope located at the top, the middle and the lowest level of the structure. Will the building experience noticeable stack effect? If it does, where will it infiltrate air from?

Oh that's easy! :D Seriously, with how you've set up this scenario, a few things can be eliminated right off:

A) Three golf ball sized holes spaced at the top, middle, and bottom of the structure will assure, among other factors not mentioned in your outline above but are most certainly in play, that there is no way every cubic inch of air contained in that structure will be within a 0.1 degree variance of 75 degrees. Ain't gonna happen.

B) Exact same humidity indoors as outdoors? Strike that as well. Blame the golfers with precise enough aim to punch the structure through three times in three different locations, but who aren't skilled enough to keep the damn ball on the fairway.

So, let's allow that it's reasonably 75 inside, give or take a few degrees, and there's a small delta in absolute humdity between indoors and outdoors. Along come our errant golfers, precise enough to punch one hole near the top plate of the upper story of our house in question, punch another hole in a common stairwell between first and seconf floors, and the third one near the sole plate of the ground level floor. I guess if it's 110 degrees outside, the heat has messed with these golfer's brains badly. Enough so that rather than be in the house, nice and cool at 75 degrees, give or take a few single integers, they're punching holes in the side of this building.

After this violent piercing of the thermal shell, what do you think the 110 degree air will do right at the vicinity of the holes? "Ah ha! There's a mass of cooler air volume inside! Think I'll go in there." At least the air has more sense than the golfers!

So the air goes inside and cools down. It invites more of its heated brethren to do the same. The bros do so gladly. But wait a minute...there's only so much room for all that hot air outside to fit inside. So some of the air that's already in gets evicted. The hot air says "Hey you guys, we're taking over! You've been in here nice and cool long enough. Take a hike!" Being that air is a pack animal, the beta cooler air submits to the alpha warmer air and beats feet out the lower golf ball hole near the ground floor. This in turn causes alpha not as hot air to call more of his compadres to enter the top golf ball hole.

Little does he know, of course, that at some point he'll get the boot from his brothers and be back out in the heat again. And so it goes on and on ad infinitum ad nauseum.

[grizzzlle]

Shophound, what would be the affect if all three holes penetrated just the top? Sinc there are no lower holes and no place for the cold air to go would the air inside the building remain cold? Now to put that into practice if a person had limited funds and resources to tighten a house up in a warm climate would a person be better spendenig money sealing the lower portion of their home stopping the cold air from leaving? And in a cold climate sealing the top portion of their home?

[Brian GC]

What I meant was the basic concept of hot air rising and cool air sinking within a structure and how that air pushes against the ceiling and floor is pretty easy to visualize and understand. All the dynamics of where that air infiltrates and exfiltrates in a building structure is a little more complicated.

That question about stack effect was meant for Tips. I wanted to hear his technical explanation, not a quote from wikipedia, but since he swung wildly against the other posters he probably won’t be coming back to this thread any time soon.

While we are on stack effect I’d like further clarification of your quote below:

… I understand in Cherokee's case that his return air location was affecting the dynamics of summer reverse stack effect on his house…

You seem to be saying that Cherokee’s downstairs return exacerbated reverse stack effect and when he moved it upstairs it minimized it. If so, how can this be? It seems that when the return is at the lowest level in the structure it will reduce pressure downstairs, thus reducing exfiltration. When he moved it upstairs it reduced pressure upstairs and would cause more infiltration. But what you are saying seems to be the opposite. How can further reducing pressure high in a structure by moving most of the return up there reduce reverse stack effect?

[Shophound]

Shophound, what would be the affect if all three holes penetrated just the top? Sinc there are no lower holes and no place for the cold air to go would the air inside the building remain cold?

Assuming the rest of the structure is airtight, for the sake of this discussion, AND let's assume that the building shell itself is "adiabatic", in that there is no actual heat transfer to or from the interior through the enclosure components, aka "shell". Since all three holes are at the top of the structure, the rest of the structure is otherwise airtight, would there or not be any exchange of air through the three holes?

There would be a transfer of air, being that 110 degree air is warmer than 75 degree air (referring back to Brian's example). Hot flows to cold. If we assume the indoor air is drier than the outdoor air, there is also a moisture delta in effect, meaning the greater source of moisture migrates to the lesser source of moisture.

Depending on the size of the holes the rate of exchange will be small, but enough that if left unchecked, and with no a/c on, eventually the indoor and outdoor air masses will equalize in terms of temperature and moisture content. That's assuming, of course, that I'm still maintaining the same "adiabatic" regard toward the building shell itself. In reality we know such an adiabatic state never exists, as there is ALWAYS heat transfer directly through a building shell.


Now to put that into practice if a person had limited funds and resources to tighten a house up in a warm climate would a person be better spendenig money sealing the lower portion of their home stopping the cold air from leaving? And in a cold climate sealing the top portion of their home?

My vote would be to make the ceiling on the highest level of the house airtight, the ceiling that most of the time adjoins a ventilated attic. This ceiling is where the most flagrant "stack effect offenders" are. Recessed light cans, supply and return air duct boxes, electrical boxes for lighting and ceiling fans, attic access hatches, etc. Can lights and attic access hatches being the worst culprits.

What would this do? Put a real damper on winter stack effect AND summer reverse stack effect. Ventilated attics adjacent to ceilings that are not airtight are a real concern. Of course, making the ceiling airtight is no silver bullet. Depending on how the house is constructed it could have multiple thermal bridging and bypass issues that at some point need to be looked at. But if you want to start somewhere, look up.

Assuming the rest of the structure is airtight, for the sake of this discussion, AND let's assume that the shell itself is "adiabatic", in that there is no actual heat transfer to or from the

[grizzzlle]

Thanks shophound. Good information. To th op sorry for jacking part of the thread.

[Shophound]

What I meant was the basic concept of hot air rising and cool air sinking within a structure and how that air pushes against the ceiling and floor is pretty easy to visualize and understand. All the dynamics of where that air infiltrates and exfiltrates in a building structure is a little more complicated.

Agreed.




That question about stack effect was meant for Tips. I wanted to hear his technical explanation, not a quote from wikipedia


The definition he gave, regardless of source, was adequate to initiate discussion on the topic. I gather Tips is learning more on this subject alongside us, and at some point I'd expect him to become more proficient at explaining his understanding of stack effect in his own words. I won't go into the particular tack he took in this thread, as frankly it left me (and apparently others) a bit baffled.


While we are on stack effect I’d like further clarification of your quote below:


You seem to be saying that Cherokee’s downstairs return exacerbated reverse stack effect and when he moved it upstairs it minimized it. If so, how can this be? It seems that when the return is at the lowest level in the structure it will reduce pressure downstairs, thus reducing exfiltration. When he moved it upstairs it reduced pressure upstairs and would cause more infiltration. But what you are saying seems to be the opposite. How can further reducing pressure high in a structure by moving most of the return up there reduce reverse stack effect?

Having had time to ruminate on the tack I took in Cherokee's thread (time is your friend when you're attempting to parse through something with a lot of apparently disparate factors) I see my circling the wagons around the term "reverse stack effect" could possibly be misleading. More accurately, what I think I did have a good bead on was (going by Cherokee's disclosed info, of course) that he had significant duct leakage outside of the conditioned space, and that was accelerating any already in place natural air exchange between indoors and outdoors.

But you rightly ask how just covering up the downstairs return made the upstairs comfortable. For starters, the two returns were linear in nature, with one being closer to the furnace than the other. That means the one closer to the air handler will draw the lion's share of air, leaving the one further away underserved. By covering the closer one up, the one out further has no choice but to draw more air.

In the two story scenario of Cherokee this worked in his favor because the return upstairs, with both inlets open, could never draw at a rate sufficient to guarantee adequate turnover of air in all the spaces upstairs. Whatever the supplies push in, a return needs to remove. That's basic air conditioning knowledge. If the upstairs return is dragging its butt at the same time supplies are attempting to introduce sufficient air to offset the heat gain, the space conditions will not be favorable for comfort.

In Cherokee's case he apparently had an open stairwell between the first floor and the upper floor. One might think, "Oh, even if the upstairs return is dragging its butt, the air introduced by the supplies into the upstairs room should just fall down the stairs and go back into the air handler at some point." Which it probably did to some extent, but not enough to assure adequate turnover of air on the top floor zones.

Now, getting back to the reverse stack effect, I was going on the notion that when the downstairs return was drawing, combined with the already mentioned leakage, it was in effect drawing down a "plume" of stagnant, warmer air further into the upstairs occupied zones than when the upstairs return was drawing as it should. With the upstairs return drawing and the downstairs return mostly covered, this "plume" would stay closer to the ceiling and have less effect on the upstairs occupied zones (where people live...from floor to around six feet up).

Here's something to ponder. Let's take this same house and rework the return system. Instead of a stacked return, let's hard pipe the upstairs return straight to the air handler, with no other taps into its duct, and let's do the same for the downstairs return. Turn the blower on and find both drawing at their design volumes.

Would this accomplish the same desirable result as when Cherokee covered his downstairs return on his linear return duct configuration? Discuss.

[Brian GC]

My view on the effectiveness of Cherokee’s return re-duct is because it was drawing and removing the warm upstairs air. It also stopped the cool upstairs supply air from falling down the stairwell. IMO infiltration is a distant second, but I could be wrong.

The possibility of reducing infiltration when he covered the downstairs return is still a bit puzzling to me. When he covered the downstairs return it increased negative pressure within the return chase. This would draw more air from outside the conditioned space and more positively pressurize the house throughout. This will reduce infiltration and the negative effects of stack, right? Or are you saying that there was more reverse stack effect and infiltration with the return downstairs? If so, I’m confused.

[Shophound]

My view on the effectiveness of Cherokee’s return re-duct is because it was drawing and removing the warm upstairs air.

That part is correct. Because blocking the downstairs return allowed the upstairs return to draw close to what it actually should vs. be crippled by the downstairs return grabbing the lion's share of air.


It also stopped the cool upstairs supply air from falling down the stairwell. IMO infiltration is a distant second, but I could be wrong. I don't think it prevented air from falling downstairs. Air is moving up and down the stairs all the time. Whatever was warmed lower down is moving up and whatever is cooling down higher up is moving down. Basic convection.


The possibility of reducing infiltration when he covered the downstairs return is still a bit puzzling to me.I don't think it reduced infiltration. Only changed how the mechanical system deals with it.



When he covered the downstairs return it increased negative pressure within the return chase.Probably.



This would draw more air from outside the conditioned space and more positively pressurize the house throughout.Except that you have simultaneous supply loss in the interstitial spaces I've mentioned before. The supply loss may exceed the return gain, depending on the leakage rates of the return ducting. My hunch is that the supply loss exceeds the return gain, since there is typically much more supply ducting outside the conditioned space than return ducting.


This will reduce infiltration and the negative effects of stack, right? Or are you saying that there was more reverse stack effect and infiltration with the return downstairs? If so, I’m confused.No, all I've said is that where the return draws from results in the greatest total turnover of air in that region. Pertaining to reverse stack I posited the notion that the plume of stagnant air is affected by where the return draws from. And that's hinged on an understanding that the supply ducts leak outside of the conditioned space at a greater rate than the return leakage offsets what is lost.

Note I'm not arguing that the return location made no difference, as I have in the past. It obviously did. No sense arguing with facts. What I am exploring is WHY it made a difference, and that while in itself it's an acceptable countermeasure to reduce temperature imbalance concerns in two story structures, I of course am not satisfied to stop there. If a better remedy is available, it should be discussed and pursued, if possible. I think that's what Cherokee did and he reported satisfactory results.

[Brian GC]

… blocking the downstairs return allowed the upstairs return to draw close to what it actually should vs. be crippled by the downstairs return grabbing the lion's share of air.

Then you are saying there is a correct place for a primary return during cooling and that place is high on the second floor?


I don't think it prevented air from falling downstairs. Air is moving up and down the stairs all the time. Whatever was warmed lower down is moving up and whatever is cooling down higher up is moving down. Basic convection.

That is truer while the system is cycled off. Less so while the system is running. While it is running and one return is downstairs all the upstairs supply air is being pushed downstairs causing a downward draft in the stairwell. With one return upstairs it will cause a draft containing the volume of the downstairs supply air to be pushed up the stairwell. This will affect natural convection currents. Upward currents in the stairwell are better for cooling and downward currents are better for heating, wouldn’t you think?


Except that you have simultaneous supply loss in the interstitial spaces I've mentioned before. The supply loss may exceed the return gain, depending on the leakage rates of the return ducting. My hunch is that the supply loss exceeds the return gain, since there is typically much more supply ducting outside the conditioned space than return ducting.

The supply loss may exceed the return gain but the return gain will be more with the downstairs blocked vs. unblocked, right? This would decrease envelope infiltration while blocked and improve Cherokee's system efficiency.


No, all I've said is that where the return draws from results in the greatest total turnover of air in that region.

That is a very important statement that I wish all pros on this forum knew firsthand. When someone says “returns do not affect air in front of them because they will not blow out a match” they are very wrong and need to be schooled on this principle.


Pertaining to reverse stack I posited the notion that the plume of stagnant air is affected by where the return draws from. And that's hinged on an understanding that the supply ducts leak outside of the conditioned space at a greater rate than the return leakage offsets what is lost.

But with the downstairs return blocked that ratio of loss to gain should reduce those supply losses.


Note I'm not arguing that the return location made no difference, as I have in the past. It obviously did. No sense arguing with facts. What I am exploring is WHY it made a difference, and that while in itself it's an acceptable countermeasure to reduce temperature imbalance concerns in two story structures, I of course am not satisfied to stop there. If a better remedy is available, it should be discussed and pursued, if possible. I think that's what Cherokee did and he reported satisfactory results.

Pursuing and dissecting what Cherokee did is definitely a worthwhile venture because we are talking about a 10 – 33% saving of our natural resources, energy bills and comfort all for just a simple ducting setup/modification.

A lot of brain power goes into HVAC and the publishing of the Manuals that govern it. Now we have “building scientists” taking the topic even further. Have you ever seen those authorities study and publish test results for this type of airflow dynamic? If not, how could they have overlooked it when a regular guy like Cherokee just stumbled across it?

[kls-ccc]

I think this is a great discussion that is going on, but I think it goes back to what I have said on many occations "Airflow and duct work is a science and an art."

If you go back to houses that were build in the 1900's you will find that in lue of machanical cooling they built the houe to naturaly cool itself in the summer and spread the heat in the winter through convection currents. As mechanical ventilation became more common place that art was lost to more efficeint building practices. The change in building practices did not change the science it just went to the back burner. Now, after years of the art being lost we are starting to renew interest through the building sciences as energy costs are driving it. To say that a duct opening location, be it supply or return, doesn't matter is closing your eyes to the obvious. The problem is we have become so use to the comfort levels afforded by mass produced houses where the cheapest wins that we forget that it doesn't have to be that way. I for one do not understand all the science behind it, but I do understand quite a bit of the art and work everyday to understand more. I just wish more in our industry would exert the time and effort.

[Shophound]

Re: science vs. art. Here's my take on it:

Science: knowing why something works

Art: knowing how and when to apply the why

Science is knowledge.

Art is wisdom, which is knowledge seasoned by experience.

[Shophound]

Then you are saying there is a correct place for a primary return during cooling and that place is high on the second floor?

So far, in various scenarios we've been discussing with upstairs/downstairs return air locations, there has been only one return doing any real work. In your California cases you've been dealing with returns in the ceiling causing problems with winter heating temperature differences between floors. In Cherokee's case it was a downstairs return, albeit part of a multiple return circuit (upstairs and downstairs inlet on same "duct" aka chase).

What I raised in my last post is a scenario where one could have both returns drawing at consistent flows year round. You can't have that on a linear system like Cherokee's unless the ducting is oversized so that it might be possible to actually damper the returns (imagine that!) so each draws at a correct volume for where it is located and for the amount of air admitted by the supply registers for that location.

And you certainly can't have that with the common two story California return scenario (return in hallway or stairwell ceiling of highest floor). That's only one source and it will only draw from that location...period.



That is truer while the system is cycled off. Less so while the system is running.

Actually, when the system is running is when the greater temperature gradients will be in place. For cooling you're introducing much cooler air into rooms, which must react with air already in those rooms. Leave the system off and all of the air in all of the rooms warm up and I'd dare say the gradient lessens (you don't have 55 degree air being pushed into a 75 degree room).

The cooler air will fall downstairs when the system is running, and as I see it at a greater rate than when the system is off (for cooling). The wider a delta exists between aspects of the same air mass, the greater amount of convective air movement will occur.



While it is running and one return is downstairs all the upstairs supply air is being pushed downstairs causing a downward draft in the stairwell.
With one return upstairs it will cause a draft containing the volume of the downstairs supply air to be pushed up the stairwell.

I see what you're saying, but I don't think it works out precisely that way. Not that what you are saying does not occur at all, but there's always other things going on that make a more simple scenario like you've outlined a bit messier.



This will affect natural convection currents. Upward currents in the stairwell are better for cooling and downward currents are better for heating, wouldn’t you think?

Consider what drives convection in summer. Heat gain through windows and the shell of the structure. The shell will always be warmer than the interior core, away from the shell. So air will flow upward along exterior walls as it warms and continue doing so until it hits an obstacle, like a ceiling. With the introduction of forced cooling, this air will mix with the cooler air and gravity begins taking over from there. However, the process of air being heated has not let up as long as it's warmer outside than inside. So there's this tug of war between factions of the same air mass within the structure. While it may be true that cooled air introduced upstairs may find its way down an open stairwell, air is rising up the stairwell simultaneously due to the structure itself gaining heat through its shell.



The supply loss may exceed the return gain but the return gain will be more with the downstairs blocked vs. unblocked, right? This would decrease envelope infiltration while blocked and improve Cherokee's system efficiency.

If you're trying to lay that down as an iron clad principle, then I'd say no. One would need to conduct component duct leakage testing to determine which section has more leakage...supply or return. In Cherokee's case, like I mentioned above, if the chase/duct was sized to handle both return inlets, but not sized to handle one open and one closed, then closing off one return reduces the net intake of air across the open return inlet. Cherokee repeatedly stated he never completely closed off the downstairs inlet, only most of the way. What that amounts to is return air balancing.

The point I made is that typically supply ducting has many more joints, fittings, runs, etc. that are prone to leak than a return duct run for the same system. And as for how this affects house pressurization depends on how much of the supply ducting is outside of the conditioned space. For many, many houses, most if not all of the supply ducting is outside of the conditioned space.




That is a very important statement that I wish all pros on this forum knew firsthand. When someone says “returns do not affect air in front of them because they will not blow out a match” they are very wrong and need to be schooled on this principle.

We're all here to learn. The only time "schooling" truly occurs is when instructors and students are both willing participants. Force feeding knowledge onto unwilling recipients builds nothing but resentment in both parties.




But with the downstairs return blocked that ratio of loss to gain should reduce those supply losses.

The amount of leaking areas in the return ducting is a fixed quantity. The amount of leaking areas in the supply ducting is a fixed quantity. If the square inches of leakage area in the supply ducting exceeds the square inches of leakage area in the return ducting, net air loss from the structure will exceed net air gain into the structure, even with one of the return inlets partially or completely blocked.




Pursuing and dissecting what Cherokee did is definitely a worthwhile venture because we are talking about a 10 – 33% saving of our natural resources, energy bills and comfort all for just a simple ducting setup/modification.

That would be if his savings are based solely on the return air balancing effort. It was hard for me to keep things straight in that thread. He had a lot of stuff going on and a lot of ideas were flying around that thread. I did ask him to repeat his testing after the duct sealing and envelope improvements were done, but he felt it was not worthwhile.


A lot of brain power goes into HVAC and the publishing of the Manuals that govern it. Now we have “building scientists” taking the topic even further. Have you ever seen those authorities study and publish test results for this type of airflow dynamic? If not, how could they have overlooked it when a regular guy like Cherokee just stumbled across it?

Willis Carrier was a "regular guy" while standing on a train platform at night, watching dew form on surrounding surfaces. That event inspired him to form the very same psychrometric chart that engineers and building scientists rely upon today.

Orville and Wilbur Wright were regular guys, bicycle mechanics at that, who figured out powered flight while other more notables of their time like Otto Lilenthial and others failed.

It's not that building scientists and HVAC engineers have not studied what we are talking about. I'm sure someone within those communities has at least glanced at it. It may be that us "regular guys" have not yet come across any writings proceeding from their studies. It's a big world out there.

That said, I for one would like to take this topic from anectodal to emperical, and subsequently write about it, with the data, so it can be peer reviewed.

[tipsrfine]

My view on the effectiveness of Cherokee’s return re-duct is because it was drawing and removing the warm upstairs air. It also stopped the cool upstairs supply air from falling down the stairwell. IMO infiltration is a distant second, but I could be wrong.
The possibility of reducing infiltration when he covered the downstairs return is still a bit puzzling to me. When he covered the downstairs return it increased negative pressure within the return chase. This would draw more air from outside the conditioned space and more positively pressurize the house throughout. This will reduce infiltration and the negative effects of stack, right? Or are you saying that there was more reverse stack effect and infiltration with the return downstairs? If so, I’m confused.

I agree with the above quote in red, and would like to add to it. I'm gonna use an analogy, that of what is going on in a flue stack of a natually drafting water heater. Colder air enters at the bottom at a higher pressure and pushes the hot air up and out of the flue stack. If you take a pressure reading at any point of this flue stack you will get a negative reading in reference to the house and to the outside.
Now, seal off the top of this flue stack and what happens? Take a pressure reading near the top and you now will read a positive pressure, and the cold air can no longer overcome the hot air-why? because the cap on the flue stack is creating an equal & opposite force to that of the force of colder higher pressure air below that is pushing itself against the hot air.
This is the only reason the top of a home in heating season is at a high pressure.
IMHO, putting a return up high is anologous to removing the flue stack cap. Cherokee has floor registers upstairs with low velocity cold air flowing from them. That cold air not only was fighting gravity in its attempt to flow upwards, but also was fighting that pocket of warmer air, warmer air that was artificially at a higher pressure due to it having the force of the ceiling creating that "equal & opposite" force I mentioned ealier. Take the roof off of the house and the hot air goes back to its natural low pressure state and the colder air from the floor supply will push it out & take its place.
Or, instead of taking the roof off, you put in a high return.

[Brian GC]

Shophound,
You could have two returns of equal flow volume upstairs and downstairs but the key to understanding what was happening in Cherokee’s house would be to fully monitor what type and amount of air passes through the stairwell with the two different return locations. With equal flowing returns some of the downstairs heat gain will flow up the stairwell and some of the upstairs cool supply air will still fall down the stairwell. Only when the majority of return is upstairs will it aggressively pull the heat gain up the stairwell, slow the loss of cool upstairs air from falling down the stairwell, not remove any of the downstairs cool air and target the removal of most of the heat gain from both floors by being at the highest point in the house.

In a test scenario the answers to understanding this dynamic would be in closely monitoring what air (heat gain vs. conditioned air) is moving through the stairwell under different return locations. Cherokee never increased the volume of his unit to decrease the runtime 33%. He possibly reduced volume a bit. He never changed throw patterns to his supply registers. He couldn’t have reduced infiltration enough to account for a 33% improvement without sealing a very leaky structure. IMO, He did it by manipulating, targeting and removing the heat gain via the stairwell.

[hvacvegas]

Shophound,
You could have two returns of equal flow volume upstairs and downstairs but the key to understanding what was happening in Cherokee’s house would be to fully monitor what type and amount of air passes through the stairwell with the two different return locations. With equal flowing returns some of the downstairs heat gain will flow up the stairwell and some of the upstairs cool supply air will still fall down the stairwell. Only when the majority of return is upstairs will it aggressively pull the heat gain up the stairwell, slow the loss of cool upstairs air from falling down the stairwell, not remove any of the downstairs cool air and target the removal of most of the heat gain from both floors by being at the highest point in the house.

In a test scenario the answers to understanding this dynamic would be in closely monitoring what air (heat gain vs. conditioned air) is moving through the stairwell under different return locations. Cherokee never increased the volume of his unit to decrease the runtime 33%. He possibly reduced volume a bit. He never changed throw patterns to his supply registers. He couldn’t have reduced infiltration enough to account for a 33% improvement without sealing a very leaky structure. IMO, He did it by manipulating, targeting and removing the heat gain via the stairwell.

Or from a lower outdoor temperature.

Or from having a lower outdoor humidity.

Or from not watching TV that night, because he was busy adding/tracking his effect on the return.

or, or, or.

[Brian GC]

Or from a lower outdoor temperature.

Or from having a lower outdoor humidity.

Or from not watching TV that night, because he was busy adding/tracking his effect on the return.

or, or, or.

Too bad the Mods don't take away asterisks for inattentiveness. :whistle:

[hvacvegas]

Too bad the Mods don't take away asterisks for inattentiveness. :whistle:

Show me, in this thread, where outdoor temperature was addressed as a possible cause to the savings of 30%.

Shame they don't ban guests for posting advice in the AOP section.....

[tipsrfine]

Show me, in this thread, where outdoor temperature was addressed as a possible cause to the savings of 30%.

Shame they don't ban guests for posting advice in the AOP section.....

It wasn't in THIS thread, it was in that other thread that has been mentioned a lot. A thread started by a poster named "cherokee". He did some detailed testing & kept pretty close to the same before & after outdoor temps. He pretty much recreated the before & after test so that the only thing different was the location of the returns.

[hvacvegas]

I'm not interested in re-reading that old thread, so:
I saw something about the cherokee basing his energy savings off his meter.

Out of curiosity, were the outdoor temperatures recorded?
33% savings make sense when the unit only has to run 2/3 of the time, based on outdoor temp.


If only a 3rd independant party, whos ruling could be considered emperical, would produce some information on the subject of return location impacting comfort level in the home.

Oh...nevermind.

Tips, I said that on page 3 or so.

[tipsrfine]

I'm not interested in re-reading that old thread, so:
I saw something about the cherokee basing his energy savings off his meter.

Out of curiosity, were the outdoor temperatures recorded?
33% savings make sense when the unit only has to run 2/3 of the time, based on outdoor temp.


If only a 3rd independant party, whos ruling could be considered emperical, would produce some information on the subject of return location impacting comfort level in the home.

Oh...nevermind.

If you go back to that old thread and just read Cherokees posts it will be quicker to get through. Cherokee is actually a professional in a related field and he had no pony in the race. He just wanted to find out why changing the return location produced the results it did. He was pretty much a 3rd independent party.
Genduct is also a proponent of the high return increasing comfort & saving energy and is a highly experienced HVAC pro spcializing in commercial duct design systems.
Brian is a contractor who has stated he has seen the difference of moving the return in homes he has worked on. Other experienced HVAC pro's here have stated return location matters.
It just makes basic sense when you think about how for there to be any air flow you have to have a higher pressure & a lower pressure. All air flows from the high to the low.

[Shophound]

It just makes basic sense when you think about how for there to be any air flow you have to have a higher pressure & a lower pressure. All air flows from the high to the low.

Yes indeedy! :)

Perhaps when it is stated that a return air inlet does not have a large sphere of influence, those saying this are thinking in terms of velocity. It's true that a return can never match a supply in terms of velocity. If you have a supply pumping air into a room at 200 CFM, air exiting the supply grill may be initially traveling at 500 feet per minute. Across the room is the return, intaking the same volume of air, but definitely not at the same velocity...IOW air is not traveling toward that return inlet at 500 feet per minute.

Regardless, there is a pressure delta between the supply and return, and this is how air turnover in the room is accomplished. Without sufficient air turnover, the room cannot be adequately conditioned.

[hvacvegas]

If you go back to that old thread and just read Cherokees posts it will be quicker to get through. Cherokee is actually a professional in a related field and he had no pony in the race. He just wanted to find out why changing the return location produced the results it did. He was pretty much a 3rd independent party.
Genduct is also a proponent of the high return increasing comfort & saving energy and is a highly experienced HVAC pro spcializing in commercial duct design systems.
Brian is a contractor who has stated he has seen the difference of moving the return in homes he has worked on. Other experienced HVAC pro's here have stated return location matters.
It just makes basic sense when you think about how for there to be any air flow you have to have a higher pressure & a lower pressure. All air flows from the high to the low.

Ok, sounds like a yes from the constant outdoor temp.

The 3rd independant party sentence was sarcastic. I'm referencing the ACCA's publication on return air not effecting air movement outside of a few feet. Dash produced it awhile back.

[tipsrfine]

Ok, sounds like a yes from the constant outdoor temp.

The 3rd independant party sentence was sarcastic. I'm referencing the ACCA's publication on return air not effecting air movement outside of a few feet. Dash produced it awhile back.

I was not trying to be sarcastic. As to a return not affecting air movement outside a few feet, you have to take it into context as to what they were talking about. Close a return completely off and see what that does to air movement. Take a room with no return and close the door to the room and what happens? The room gets pressurized to that of what is trying to come out of the supply register and ALL air flow stops. Return placement does affect air flow.
I agree with you in regards to a return will not contribute to "mixing" of air- that is a job only the supplies can do, and if they are doing their job, then return placement is not as important-generally speaking. A high return will reduce stratification of air, which could be said to be the result of improper air supply, throw & velocity-and even from an oversized system.
The placement of a return can certainly encourage air to flow into its direction. The ACCA certainly has guidance in regards to that, as I am sure you are aware of. We've all read their guideance in regards to ensuring that your supplies don't short circuit straight to a return. In that context, the ACCA endorses the fact that return placement is important.

[Brian GC]

… the ACCA's publication on return air not effecting air movement outside of a few feet.

…Which is a vague, flat-out wrong statement taken out of context.

A 200cfm supply in a 10x10x10 room can stir all the air in that room, and yes you can feel the air movement. However a 2,000cfm return can outright remove that amount of air every 30 seconds, condition it, and send it out the supplies redistributing it throughout the house. That 1,000cuft of air removed every 30 seconds is immediately replaced by the surrounding air. So yes, a return does move and affect mass quantities of air in front of it far more rapidly than any one supply.

Learning where to put these mass removal ducts (returns) to best deal with heat gain/loss and stratification is key to maximizing the efficiency of a system. Cherokee pretty much proved that and no “ACCA Publicized Study” that anyone has brought forward to date has disproved it.

[tipsrfine]

…Which is a vague, flat-out wrong statement taken out of context.

A 200cfm supply in a 10x10x10 room can stir all the air in that room, and yes you can feel the air movement. However a 2,000cfm return can outright remove that amount of air every 30 seconds, condition it, and send it out the supplies redistributing it throughout the house. That 1,000cuft of air removed every 30 seconds is immediately replaced by the surrounding air. So yes, a return does move and affect mass quantities of air in front of it far more rapidly than any one supply.

Learning where to put these mass removal ducts (returns) to best deal with heat gain/loss and stratification is key to maximizing the efficiency of a system. Cherokee pretty much proved that and no “ACCA Publicized Study” that anyone has brought forward to date has disproved it.

I'm actually starting to wonder where all the other pro's who previously fought you regarding this issue are. I know I was one of them, but then again I am not one of the more experienced pro's here regarding HVAC & especially duct design.
I think the lack of their posting is in fact proof that what Brian has been saying all along is true. I'm not saying I endorse bashing the HVAC pro's on this site because of this. I'm just saying their lack of posting lately is an endorsement to Brians theory.

[Shophound]

A 200cfm supply in a 10x10x10 room can stir all the air in that room, and yes you can feel the air movement. However a 2,000cfm return can outright remove that amount of air every 30 seconds, condition it, and send it out the supplies redistributing it throughout the house. That 1,000cuft of air removed every 30 seconds is immediately replaced by the surrounding air. So yes, a return does move and affect mass quantities of air in front of it far more rapidly than any one supply.

If you're speaking about a central return that communicates indirectly to the 10 x 10 x 10 room, the assumption would be that the central return in question has a much greater volume of air to draw from, found in the rest of the structure, than the 1,000 cubic feet of air contained in the room of your example. In this case the central return is the second half of the pressure differential equation Tips mentioned earlier. The 10 x 10 room sees an inflow of 200 CFM, with 200 CFM leaving through either an open door to the central return, or say a transfer duct (or at minimum the door undercut) if the door is closed.

Otherwise if you could somehow manage to draw air out of a sealed 10 x 10 x 10 room faster than air is introduced, the room would be significantly below atmospheric pressure, similar to pulling a vacuum on an enclosed and sealed vessel (save for the point of evacuation). But with residential HVAC equipment, the same source that introduces air into the room also removes it. Meaning if only this room was being conditioned, and if the return and the blower were sized to flow 2,000 CFM and the supply sized for 200, net flow would likely be around 200, since the volume of air in the room, along with supply duct sizing, would not allow 2,000 CFM of return and only 200 CFM of supply.


Learning where to put these mass removal ducts (returns) to best deal with heat gain/loss and stratification is key to maximizing the efficiency of a system. Cherokee pretty much proved that and no “ACCA Publicized Study” that anyone has brought forward to date has disproved it.

Since you mentioned "context" earlier, let's look at ACCA Manual T, Air Distribution Basics, regarding return air provision. In my version the following quote is on Page 7-2, Section 7-3, first paragraph:


Even though the influence of a return over air motion within a room is negligible, there are preferred return locations. As a general rule, the return should be located inside the stagnant region. The stagnant zone is characterized as an area that is not under the influence of the supply outlet but which is subject to natural convection currents.

Staying within the context of the quote above, referring again to Cherokee's case, he had floor supplies and a poorly functioning high return. The stagnant zone in his case would naturally be at the ceiling. And, true to context, this zone would be subject to natural convection currents. When the high return was made to function better via mostly blocking the low return (which increased the upper return's rate of intake), it was in an optimal location to positively affect air turnover and occupant comfort.

In fact, let's see what Manual T might say about a configuration like Cherokee's:


When perimeter supply outlets are placed low in the room, the largest stagnant zone will occur near the ceiling, during cooling. Therefore when low outlets are used the returns should be placed high in the room.

Moving on from Cherokee in the following quote:


When high supply outlets are used the heating performance is poor and the largest stagnant zone will occur near the floor, during heating. In this case the returns should be placed low in the room.

In the whole of Section 7 there is no mention of a two story structure with a central return located low or high. In all examples quoted above, the context is one room with one supply outlet and one return inlet. I think the two story structure scenario merits delineation similar to what we've seen quoted above.

[Brian GC]

I did not suggest a 2,000cfm return would be in a 10x10x10 room, rather that amount of air, say at the top of a stairwell, just in front of a central return would disappear every 30 seconds. A 100 percent displacement of that amount of air definitely “affects” that air far more than squirting a 200cfm supply at it in a contained room.

The Manual T says the return should be in the stagnant zone, presumably to help remove the stagnant air. It gives two examples of where a stagnant zone could be found, but surely supply placement and throw are not the only causes of stagnant zones. The unintended accumulation of heat gain and loss is a major contributor too.

It would be safe to say that the top of a typically unmixed stairwell or foyer would have a stagnant zone during cooling, and the bottom would be stagnant during heating. To a lesser degree hallways do not have supplies and are unmixed, therefore the ceiling strata is stagnant (or warmer) during cooling and the floor level is stagnant (or cooler) during heating.

Since a central return can remove a 10x10x10 block of stagnant air every 30 seconds and that amount of supply air is constantly being pushed in that direction to fill the ever-created void of removed air, why not put the return where it could do the best work as a “stagnant air removal duct”? That is what Cherokee did. Now the question remains, aren’t these stagnant zones typically high during cooling and low during heating?

[Brian GC]

I'm actually starting to wonder where all the other pro's who previously fought you regarding this issue are.
I think the lack of their posting is in fact proof that what Brian has been saying all along is true. I'm not saying I endorse bashing the HVAC pro's on this site because of this. I'm just saying their lack of posting lately is an endorsement to Brian’s theory.

I often wonder where they are too. Cherokee’s thread was over 300 posts long and some of them must have taken a gander at it. But only a couple responded.

What I think happened is that they never gave a heck about the subject in the first place. They saw that a “regular guest” was giving one revered poster a hard time so they decided to throw a few blows of their own about a subject that they were ill prepared to delve very deeply into. To compound the issue I presume they had been installing returns in less than ideal places for decades and did not want to take a serious look back of how there could have been much better places to install them. Actually, I think that would be a reason many do not want to look very seriously at the subject now. Who wants to first, learn about this subject and second, who want to bid or do more complex and expensive installs?

As I have said all along, there are many who understand this and implement into their installs. But the bulk of the installs will be cost driven and just thrown together until there is a shift of consciousness, natural gas and electricity doubles in cost or city regulations require it. But the “building scientists” lead this industry and it is they who have to skin this union. Until then, very few will listen.

[udarrell]

I have really enjoyed the excellent comments on this thread; I have always been in agreement, that Return placement is an important factor in optimal air distribution to & within all the individual rooms. Except bathrooms & kitchens.:grin2:

[energy_rater_La]

and some of simply read more than we post.

I've found in my hot humid climate
that to supply high and return low works well.

this is your thing Brian..return locations.
we all have things that we have strong opinions
on, this is not one of mine.
I often have to work with what is there rather
than the option of putting it together the way
I'd perfer for it to be.

in new construction I always promote
air tight return chases, but sometimes you
have to work with what you have.

as this is beyond the scope of an energy rating
it is all ot for me. I find it interesting and always
am willing to learn, but have little to contribute
that would make a difference.

[Brian GC]

I've found in my hot humid climate
that to supply high and return low works well.

Then you must be amazed by what Cherokee did by raising his return to the second floor and got such positive results? It being contrary to you’re a/c preference.


in new construction I always promote
air tight return chases, but sometimes you
have to work with what you have.

Wouldn’t airtight supplies be more important than airtight returns? Leaky returns will just positively pressurize the conditioned space. A leaky supply will lower supply volume and promote infiltration. That seems worse to me.


as this is beyond the scope of an energy rating

Seems that dealing with a hot upstairs in an efficient way would interest an energy rater? At least understanding why that hotter air is there in the first place. Infiltration seems presently to get all the focus but it might be a minor cause. We won’t know until many building scientists and the like fully test this.

[energy_rater_La]

Quote:
Originally Posted by energy_rater_La
I've found in my hot humid climate
that to supply high and return low works well.

"Then you must be amazed by what Cherokee did by raising his return to the second floor and got such positive results? It being contrary to you’re a/c preference. "

not amazed... his northern based requirements vary greatly from what works here in the south. I like to learn these things, but they simply don't apply here. supplying the air high, as most installs of ducts are in attics, and returning low via chase provides good circulation of air. I've seen high returns and the problems that are solved by moving
return to where we live...at floor level not at ceilings.


Quote:
in new construction I always promote
air tight return chases, but sometimes you
have to work with what you have.

"Wouldn’t airtight supplies be more important than airtight returns? Leaky returns will just positively pressurize the conditioned space. A leaky supply will lower supply volume and promote infiltration. That seems worse to me."

both are important, I was keeping to the return location being discussed in this thread.
here leaky returns contribute to higher humidity..and we battle humidity levels in the houses during our 8 month cooling season.


Quote:
as this is beyond the scope of an energy rating

"Seems that dealing with a hot upstairs in an efficient way would interest an energy rater? At least understanding why that hotter air is there in the first place. Infiltration seems presently to get all the focus but it might be a minor cause. We won’t know until many building scientists and the like fully test this."

the return location is beyond scope of a rating. I promote what I know works because I work for the homeowner and get my business from referrals. most of the hot upstairs
areas are because they share walls with attic and the heat transfers thru insulation
and sheetrock. we solve this by installing foam sheathing boards with foil facing into attic space, caulking @ top and bottom & taping seams.
continuing the foam/foil sheathing to meet ceiling downstairs between joists stops hot
air movement between floors. foil reflects heat back into attic keeping the walls cooler.
the sealing stops air movement allowing the insulation to perform as spec'd.
or they foam the roofline.
my recommendations are promoted by building science, common sense & experience

thats it for me for now...long day..worn out.
I'd like to let others who have input do so, my pov is different from hvac standpoint.

[Brian GC]

Energy Rater,
I do not discount any of the methods you use to seal up and insulate a house and its ductwork; they are all proven to be very legitimate fixes based in the sciences. You should be very proud of yourself that you can save people money and improve their comfort. Good going.

What I would like to see done someday is to take a house that you were about to do the previously mentioned improvements on and do one thing first. Take a two story house that was nominally leaky, had nominal attic insulation, had an issue with a warmer upstairs and had one return down low on the first floor…similar to Cherokee’s house. If you did one thing first, that is, take a large flex duct (up to 24” to keep static low) and cover the low return and run that ducting all the way to the top of the stairwell so it draws off the upstairs ceiling level with minimal restriction to the unit. Then closely monitor temp transition rates and temp gradients. Then disconnect the 24” flex return and do your improvements and compare the two. Then implement both modifications and take data again.

Results from tests like that should be all over the internet, but they are not. IMO, the building scientists have not done their job.

[Brian GC]

I hope you don’t mind me further discussing your posted causes and methods.


. most of the hot upstairs
areas are because they share walls with attic and the heat transfers thru insulation
and sheetrock.

Hot upstairs can also be because heat gain through the entire house will rise to the second floor if not adequately mixed with supply air, which exists in more houses than not I presume. Or in Cherokee's case, the return was downstairs "short curcuiting" the air exchange by not using methods of air displacement.



We solve this by installing foam sheathing boards with foil facing into attic space, caulking @ top and bottom & taping seams.
Continuing the foam/foil sheathing to meet ceiling downstairs between joists stops hot
air movement between floors.

Do I understand you correctly? You pull back the existing attic insulation, cut rigid foam boards to fit between the ceiling joists, tape the foam boards to the joists, cut around all the framing and electrical wires and drops, extend all the boards to the narrow reaches of the exterior walls, and cut the boarding around all can lights using spray foam and tape to seal all of it? Then probably add more insulation over the top of this afterwards because of the low R-value of solid foam board?

I have to say that seems very labor intensive. Couldn’t you get better results by just sealing electrical drops and can light from the attic and sealing the rest from inside the conditioned space and using thick blown-in insulation? It seems sealing and insulation levels would be better.

[energy_rater_La]

"Do I understand you correctly? You pull back the existing attic insulation, cut rigid foam boards to fit between the ceiling joists, tape the foam boards to the joists, cut around all the framing and electrical wires and drops, extend all the boards to the narrow reaches of the exterior walls, and cut the boarding around all can lights using spray foam and tape to seal all of it? Then probably add more insulation over the top of this afterwards because of the low R-value of solid foam board?"

you misunderstand, I was talking about knee walls...interior walls shared with attic space. not dealing with r/a locations bit cooling off second floors. bonus rooms, family
rooms above garages, and second floors that are smaller than first floors. these walls
are shared with attic space.
in most cases these walls are insulated. what works for clients in the diy world is to add
to the face of these walls that face into attic is what I described above.

this is why I said that
1- return locations are less of an issue...sometimes you have to deal with what is in place, and dont' have the option of designing.
2-my input was not as valuable as others...different climates, energy rater vs hvac vs builder.

of I had to pull back the existing attic insulation, cut rigid foam boards to fit between the ceiling joists, tape the foam boards to the joists, cut around all the framing and electrical wires and drops, extend all the boards to the narrow reaches of the exterior walls, and cut the boarding around all can lights using spray foam and tape to seal all of it? Then probably add more insulation over the top of this afterwards because of the low R-value of solid foam board.
it would be too labor intensive, and foaming the roofline vs the time, labor and cost
would be about the same.
plus who would invest in this?? I wouldn't recommend this...ever, but do recommend the
foam sheathing boards exterior of walls shared with attic. in most cases I have to invest my time to do this.
a simple fix is to foam seal the roofline.
my recommendation depends on complexity of attic, and what homeowner can afford to pay for. diy is sometimes cheaper, and folks around here are very hands on.
I've invested a lot of time in education of foam installers...not company owner, but installer.

you should take a look at the following link.
http://imageevent.com/okoboji_images/deloreshouse
this was a home built by a friend of mine in a cold climate...
his attention to detail is amazing. I was really impressed.

"What I would like to see done someday is to take a house that you were about to do the previously mentioned improvements on and do one thing first. Take a two story house that was nominally leaky, had nominal attic insulation, had an issue with a warmer upstairs and had one return down low on the first floor…similar to Cherokee’s house. If you did one thing first, that is, take a large flex duct (up to 24” to keep static low) and cover the low return and run that ducting all the way to the top of the stairwell so it draws off the upstairs ceiling level with minimal restriction to the unit. Then closely monitor temp transition rates and temp gradients. Then disconnect the 24” flex return and do your improvements and compare the two. Then implement both modifications and take data again.

Results from tests like that should be all over the internet, but they are not. IMO, the building scientists have not done their job. "

finding this type house could happen...but takes extra time, added cost to homeowner
I would have to find the perfect house & client.
as for building scientists...I think that they have done an excellent job. but you know one
study always ends in...more testing would be required. leaves that door open for the next grant. I don't do the grant thing...but work to solve problems for individuals.
that whole grant thing...is not where I want to invest my time & lose money.
many people are much better at grant stuff than I.

[Brian GC]

Energy Rater,
I viewed all the photos of the Delores House and was quite impressed with all the steps they went through to seal and insulate that house. But at the risk of sounding cynical, as I am sure my skepticism comes across as on the site, I’d like to know a few things about that project that were not included in the descriptions.

We do not dig basements in my area. Why, when land is probably cheap in that area, do they go through the expense of digging holes in the ground for basements? Then go through the expense of water sealing it? Why not build wider?

Why build two story houses where land is cheap. When you go higher you introduce stack effect factors that are expensive to curtail.

The living space of that house seemed very small with very small window area. This alone will save on energy costs which do not relate to their sealing techniques.

And my biggest question is what did all of their added endeavors cost? I would say about $100K over standard ranch house building techniques. I wonder if they waved these costs to the HO in hopes of being compensated by the proceeds of their book. In other words, is this type of building feasible to the average person? Even if it was only $50K over typical cost, that is about $350/mo for thirty years.

Cash outlay and actual month-to-month savings seem to be ignored with projects like this. Perfect building practices like that are easy to show but they must be weighed against what percentage of people can afford it and its return on investment. They left out the math.

My gripe with builiding scientists and green people (like Al Gore) is they discover better building methods that cannot be argued against and force people to accept the increased costs while positioning themselves to benefit from that extra cashflow.

[Shophound]

We do not dig basements in my area. Why, when land is probably cheap in that area, do they go through the expense of digging holes in the ground for basements? Then go through the expense of water sealing it? Why not build wider?

Cold climates have a frost line. Basements are done so the footings of the house are below the frost line. Shallow footings can heave when the ground freezes for extended periods of time.


Why build two story houses where land is cheap. When you go higher you introduce stack effect factors that are expensive to curtail.

Land in cold climates may not be cheap. Especially in the northeastern USA.




And my biggest question is what did all of their added endeavors cost? I would say about $100K over standard ranch house building techniques. I wonder if they waved these costs to the HO in hopes of being compensated by the proceeds of their book. In other words, is this type of building feasible to the average person? Even if it was only $50K over typical cost, that is about $350/mo for thirty years.

My response is if that's what the homeowner wanted to do, more power to him. There is no one-size-fits-all way to build more energy efficient building shells across all price points.



My gripe with builiding scientists and green people (like Al Gore) is they discover better building methods that cannot be argued against and force people to accept the increased costs while positioning themselves to benefit from that extra cashflow.

Give a specific example of this, naming a specific building scientist and/or cash income benefit for Al Gore.

[energy_rater_La]

brian,

I don't know what thoughts/costs/plans came to pass in the link I provided.
it is an efficient affordable house for a widowed lady, maybe she had bucks..
I don't know, and its not my business.
I do know Rollie, but I wasn't involved in design.

I really don't want to debate with you. life is too short,
and there are things I need to do other than go over and over
areas covered by others with you.

to do all the return air do and redo you suggested in my
next two story house...who pays for that?

I deal with real world homes, not houses with no windows doors or interior walls... can't remember which thread that was...
but who has time to invent problems when there
are so many already to be solved?
not me.
the time to think up these impossible scenerios..could be spent much more wisely...imo

al gore and bldg scientists are hardly the same thing.
as my favorite bldg scientist says...1-green building is misLEEDing. I agree.
2-efficiency is 80% of green building. 3-build tight ventilate right.

and we don't do basements here...but it is cheaper to build up rather than out.

no offense intended & have a good one.

[Brian GC]

Some are interested in HVAC theory. Some are not - to the point of being irritated by it. Some just want to go out and make money or problem solve. But one thing is for sure, a deep understanding is not a requirement. To each their own.

[Brian GC]

Give a specific example of this, naming a specific building scientist and/or cash income benefit for Al Gore.

Building scientists in general helped form the BPI type organizations that went after state rebate programs and grant money. Persuing state money is the next closest thing to collecting welfare. Now they have had influence in requiring that certain HVAC people be BPI certified, which creates an industry for them.

From what I have read from building scientists on attic ventilation and what the Manual T says about certain aspects of ductwork it is vague, skewed, and incomplete. Though some is very impressive and interesting, some is very disappointing to read.

As for Al Gore, Google will tell you all about him. You can decide where the ethical line should be drawn.

[genduct]

They (BPI) could care less about Man D or T or anything that is involved with duct design/ sizing. They are only concerned about Duct ( and building envelope ) LEAKAGE. If you have been following the recent press, the HVAC Industry through AHRI and including ACCA,RSES, And PHCC have called the Dept of Energy to task for their no-bid contract with BPI that ignores the HVAC people and considering that with the combustion testing and the impact of ducts and equipment on the consumers energy cost is 60% of their program, the fact that the HVAC people were never considered 'stakeholder" in this process is amazing.

As to your comments about not hearing from the "pros" about this issue. I think that is unfair! You have heard from us and have chosen to ignore any point of view that you don't find squares with you. I think you have slowly begun to evolve. Of course you'll need it to be slow so you won't have to admit what we have been trying to share with you, has changed your mind.
Good luck with your journey

[Brian GC]

They (BPI) could care less about Man D or T or anything that is involved with duct design/ sizing. They are only concerned about Duct ( and building envelope ) LEAKAGE. If you have been following the recent press, the HVAC Industry through AHRI and including ACCA,RSES, And PHCC have called the Dept of Energy to task for their no-bid contract with BPI that ignores the HVAC people and considering that with the combustion testing and the impact of ducts and equipment on the consumers energy cost is 60% of their program, the fact that the HVAC people were never considered 'stakeholder" in this process is amazing.

I know very little about BPI and their pull with state and federal programs. What I do suspect is that discoveries of building sciences arm them and greed propels their monopolistic motives. I never thought the HVAC industry was in bed with them, rather they are an obstacle to their monopoly. I recall a poster here who was up to his ears in those programs and was beginning to say too much in a thread. I forget who he was but he realized he said too much too late and was letting the cat out of the bag. He suddenly retracted from that thread.


As to your comments about not hearing from the "pros" about this issue. I think that is unfair! You have heard from us and have chosen to ignore any point of view that you don't find squares with you. I think you have slowly begun to evolve. Of course you'll need it to be slow so you won't have to admit what we have been trying to share with you, has changed your mind.
Good luck with your journey

The dynamics involved when a return is positioned in different places in a house affects high and low pressure zones, pushes supply air from one side of a house to the other, pushes air up or down a stairwell, increases or decreases stack effect, helps or causes stratification and general infiltration and has the ability to remove large quantities of air in front of it very rapidly – it being supply or stagnant air. These are very real aspects of return placement that even someone with your experience is often ill prepared to discuss in detail. I assume that is why many of my questions go unanswered and tend to irritate some. But I am not “coming around” to your “one return location is best” for a/c and heating in a two story house as you suggest. Its way more complicated than that for those who are willing to delve deeper. Cherokee proved that. Now if the building scientists would step up and prove it too.

[Shophound]

They (BPI) could care less about Man D or T or anything that is involved with duct design/ sizing. They are only concerned about Duct ( and building envelope ) LEAKAGE. If you have been following the recent press, the HVAC Industry through AHRI and including ACCA, RSES, And PHCC have called the Dept of Energy to task for their no-bid contract with BPI that ignores the HVAC people and considering that with the combustion testing and the impact of ducts and equipment on the consumers energy cost is 60% of their program, the fact that the HVAC people were never considered 'stakeholder" in this process is amazing.

If true (which I'm not calling into doubt), this makes me even more glad I belong to RSES. No entity, no matter how noble in intent or action, should win on a no competing bid basis when it comes to government money. It could be argued that no other entity but BPI was available for competing bids. What...no input from Comfort Institute or National Comfort Institute? If I'm not mistaken they both deal with HVAC and building leakage. How about RESNET? Maybe Ted and LA Rater can weigh in there.


As to your comments about not hearing from the "pros" about this issue. I think that is unfair! You have heard from us and have chosen to ignore any point of view that you don't find squares with you. I think you have slowly begun to evolve. Of course you'll need it to be slow so you won't have to admit what we have been trying to share with you, has changed your mind.
Good luck with your journey

In fairness to Brian, and in spite of his online manner that at times may be grating, I had to reexamine my own thoughts concerning high and low return air locations in multi-level dwellings. Unless the whole thing with Cherokee was one well engineered troll via those who advocate the high/low return approach, the findings of that poster must be considered.

Of course, perhaps somewhere in my ancestry I have native Missouri relatives, as I'm of the "show me" variety. I would have liked to be at Cherokee's house with data loggers and so forth while his little experiment was conducted. Not to disprove it, but for the data to simply be there one way or another. But I'd also like to think I'm led by reason, and if in spite of a lack of "show me" data, the line of reasoning works out (at least on paper) it merits evaluation and comparison to common thought that may be contrary to it.

This is how we learn and grow as individuals and as an industry. Common assumptions are often seldom questioned, and it is not easy to call same into review without running the risk of being considered a pariah of sorts. But it can be done, with thoughtfulness and tact.

[tipsrfine]

What no-big contract are we talking about?

[genduct]

http://www.ahrinet.org/ahri+update.aspx

Check topic AHRI and NATE Press DOE on Plans for Technician Certification

You need to read between the lines

[genduct]

Cherokee proved that. Now if the building scientists would step up and prove it too.

My take is that the substantial amount of return that was drawn from the high return was responsible for the shorter run times and better temp distribution. I have offered that observation and think that the high pressure differences you speak of are really low pressure diffs of just a few pascals. I don't think it takes much pressure diff to make a difference, only a low resistance path for the air to get back to the unit.
I understand you are looking for a more complicated answer that just that simple thought

[genduct]

In March 2010, the Department of Energy’s Office of Energy Efficiency and Renewable Energy directed the National Renewable Energy Lab (NREL) to establish a “voluntary” set of national standards for worker certification and training program accreditation for home energy retrofit technicians. These guidelines are to be published as the Workforce Guidelines for Home Energy Upgrades that are to become the de facto standards for technicians on all residential energy efficiency projects. The Department’s intention is to require all workers on energy efficiency retrofit projects funded with federal money to be certified to the Workforce Guidelines by an independent, third-party certification body.

North American Technician Excellence (NATE) and AHRI have been working closely with DOE and NREL to ensure that the HVAC industry is appropriately represented in the Workforce Guidelines development and the associated certifications. On September 15 and 28, AHRI, NATE and allied organizations met with DOE staff to express concerns over the process that the Department has employed in developing these Guidelines, but also to propose that DOE separate HVACR products from the weatherization certifications to be established, on the basis that HVACR installation and maintenance work is highly specialized and distinct from the weatherization activities on which the Guidelines are focused. Accordingly, AHRI and NATE have asked the Department to work with NATE to develop other certifications for the HVACR industry.

DOE has committed to work with AHRI and NATE and we expect further dialogue on next steps.

[genduct]

the third-party certification body. they are refering to was the no bid BPI group who has already been deemed the Energy Experts

[energy_rater_La]

http://www.resnet.us/home4
scroll to bottom of home page
8 Most popular categories»
Home Energy Auditors »
Heating and Cooling »
Energy Raters »
Air Sealing »
Ducts & Vents »
Indoor Air Quality »
Insulation »
Electricians

this is the direct link to the hvac part.
http://www.resnet.us/trade/heating-cooling-contractor

read and educate yourself.

best of luck.

[Shophound]

My take is that the substantial amount of return that was drawn from the high return was responsible for the shorter run times and better temp distribution. I have offered that observation and think that the high pressure differences you speak of are really low pressure diffs of just a few pascals. I don't think it takes much pressure diff to make a difference, only a low resistance path for the air to get back to the unit.
I understand you are looking for a more complicated answer that just that simple thought

With how Cherokee's return air duct was described on this forum, it composed of an inlet high on the second floor, and one toward the ceiling of the first floor, both on the same chase. By closing off most of the first floor return inlet, it made the second floor inlet draw at a higher volume, which in turn one would expect improved total air turnover of the upstairs regions due to the improved inlet volume.

The greater heat load is upstairs due to several factors: heat rising from downstairs from internal and external sources; heat gain upstairs from same sources, both via conduction through the building shell and glazing; and reverse stack effect (for the summertime scenario that other thread was concerned with). Therefore the upstairs zones have greater CFM supply needs, overall, which requires a return air inlet that can receive the same volume of air displaced by the supplies. If this return inlet was sized correctly for the upstairs zones but is crippled by the downstairs inlet, being closer to the furnace blower in Cherokee's case, receiving the lion's share of air, well there you are.

[energy_rater_La]

does no one get the foaming of the bump out and around fireplace?
the heat/cold gain is a factor.
the minimal duct/return leakage & minimal house infiltration
contribute.
look at the whole picture...the fact that the foam was done before
duct leakage is important.

just what I know, based on my experience.

[genduct]

I have not followed this as closely as you have. Are you saying that some substantial sealing was done along with the experiments with return locations?

If so, my vote for such a substantial diff would be as you suggest, a really big diff in the infiltration load.
As much as I enjoy having these esoteric conversations about high and low returns. Guess we will need to find another example to start this all over again.
Now its all your fault, Rater

[Shophound]

does no one get the foaming of the bump out and around fireplace?
the heat/cold gain is a factor.
the minimal duct/return leakage & minimal house infiltration
contribute.
look at the whole picture...the fact that the foam was done before
duct leakage is important.

just what I know, based on my experience.

I for one remember the other envelope and duct sealing improvements Cherokee made. I even asked if he could repeat the high/low return experiment, regardless of the stated improvements, to see if returning the return air configuration to how it was prior to the first test, pre envelope/duct improvements, made the performance of his a/c upstairs deteriorate or not. Cherokee felt it was not necessary, and he said the weather at the time was no longer cooperative.

The initial test Cherokee did, covering the downstairs return most of the way, was followed up by positive response that he was more comfortable upstairs. What I do not remember seeing in that thread is if he stated that doing such was solely responsible for his claimed 30% or so reduction in energy consumption. For me, the revelation of his other improvements muddied the waters if hopes were staked on the return air modification being the salient energy saver.

[Brian GC]

My take is that the substantial amount of return that was drawn from the high return was responsible for the shorter run times and better temp distribution.

Could you explain how the increased airflow from a high upstairs return allowed the unit to cool the whole house evenly with a shorter runtime?



I have offered that observation and think that the high pressure differences you speak of are really low pressure diffs of just a few pascals. I don't think it takes much pressure diff to make a difference, only a low resistance path for the air to get back to the unit.

Whether it is a high or low pressure delta makes little difference, supply air will move toward a return. If the return is upstairs, as in Cherokee’s case, the unwanted, warmer air will be pushed up toward it first. When that warmer air reaches the return it is then removed from the conditioned space. Once that warm air is removed and all that is left is condition air, you’ve reached your setpoint.



I understand you are looking for a more complicated answer that just that simple thought

I’m not looking for a more complicated answer; I think there is more going on that you are not considering. When I say return location matters what I am saying is elevation of the return and distance from the conditioned space matters. When a return is high for a/c the warmer air will be pushed toward it and removed first. When a return is low for heating the cooler air will be pushed toward it and removed first. Do you not agree with that?

I think I’ve heard you say a high central return at the top of stairwell will work best for a/c and heating but Cherokee said his low downstairs return worked fine for heating, just as I suspected. Do you think his new high return will heat just as well as his old low return?

If Cherokee comes back during the heating season, as I asked him to, and says his high return does not allow his system to heat evenly, causes a cold downstairs and long runtimes will you still say a high return is best for heating? Will you be able to point out what is causing his high return to not heat properly?

[genduct]

You may call me if you really want to understand. Number in profile

[tipsrfine]

I just don't think enough attention is being paid to on what the difference stratification has on the throw/mixing of floor registers in cooling mode.
I just did a makeshift test in a 5 gallon bucket of water at a temp of 80 degrees. I took two syringes (the kind you give pets oral meds with) and filled them with green dyed water. One syringe was at room temp (70 degrees) and the other I had in my refrigerator for a while.(not the freezer). I released the green dyed water near the bottom of the bucket, and the difference was profound. The green dyed water at 70 degrees mixed fairly well in the bucket, but the green dyed water at the lower temp resisted any flow towards the top of the bucket and quickly fell and lay at the bottom of the bucket.
This is what I have been saying all along in regards to cherokees' house and the return placement. The high return, by removing the hotter air at the top, allowed the colder air from the floor returns to better mix at the higher levels of the upstairs area - where the t-stat is.
The greater the temperature difference between supply air and room air, the greater the tendency for stratification. In cherokees home, the cold supply air never got high enough to mix enough to shut the t-stat off and this resulted in the lower portions of the home to become overcooled.
This is why I said that the original problem was supply related, and Brians' theory of the high return paid off and aleviated that failure.

[energy_rater_La]

dang..are you trying to make me go back to find that post by cherokee??
its not gonna work genduct! its only 9 pages. LOL!

I was following the thread up to a point.
then the numbers just didn't make sense to me.
reduced duct 6% and house infiltration 125 cfm.

if he foam sealed the fireplace opening, and if it was one of those
situations where you stand in the attic and look down into a chase
and see the fireplace with the insulation that fell into the chase..
that is a huge thermal bypass. maybe not so much air is moving
thru it, but the heat/cold gain alone.when the system runs
it draws air thru the thermal bypass (open chase to the attic)
and the attic temps are drawn down the wall.

the other area foam sealed was a 'bump out' don't know the details
like floorplan & orientation of the house. but I've seen some big
open walls in add ons.

these would contribute to comfort improvements.
the numbers are just too low for air sealing & duct sealing
to be the complete comfort package.
is it an exceptionally tight house?? were the numbers squewed/
faulty equipment..wrong readings?? who knows for sure.
neither the foam or the aeroseal is inexpensive.

6% duct leakage reduction isn't anything I'd invest in.
nor sealing a house & reducing cfm's by 125
I wouldn't be pleased if my readings were so minimal
after the work was done.


just my theory. we all understand the difficulty of diagnosing online
with less than complete info. he did test his house, but the
aeroseal and the foam install were tested at the same time.
so there is no % of which added to his comfort.

[genduct]

You caught the reference to the 'big hole that got plugged' while "us guys" were fixated on the high low return debate that will soon be part of the political debates as well. I am waiting for high-low returns being the litmus test for the New Hampshire Primaries.

I like your observation as probably being most responsible for any savings.
Doesn't change my feelings about the impact of high returns since I have seen the results and now believe. Just call me Thomas!

[tipsrfine]

I think you "guys" are misconstrueing the time line here. The 30% energy saving was recorded before the duct sealing & foaming % whatever. The original thread showed a savings of 30% energy reduction simply by sealing up the lower return. The only thing different in the before & after saving was closing off the lower return.
If you don't have the desire or time to read the original thread, you may as well not comment on it. It's just a waste of time & reason to just close this thread.

[Brian GC]

You may call me if you really want to understand. Number in profile.

Your reluctance to answer my simple questions on this thread is telling.

[genduct]

You just don't like answers that don't agree with your own.

By the way, Heat ENERGY can move in and to that second floor without the air moving. That doesn't mean that there isn't convective air moving, it is just that it is not all convection some is conduction.
If you can understand this concept, then you can set aside the pushing/pulling of rising and falling air thing you seem to be fixated on.

Stick to your guns Brian, don't let anyone change your mind

[Brian GC]

Terms are slung around like convection, conduction, stack effect, reverse stack effect, infiltration, exfiltration, stratification, displacement, turnover, short circuiting, specific air movement from supplies, general air movement from returns, rising warm air, sinking cool air, pushing supply air from one side of a house to the other or from one floor the other. It makes things very complicated and allows a person to point to which ever one they are familiar with and call it the cause.

These are all dynamics of conditioning a house that are interconnected and all play a part in the efficiency of a system. Each one must be fully understood before being considered an authority on the subject. Shophound and Tips are two who have opened their perspective to understand each one of those dynamics individually and how much each one affects the efficiency of a system.

Genduct, you should have firsthand experience and be willing to speak in depth about each one of those dynamics before coming across as an authority on the subject. Your shying away from the hard questions is still telling of your all-around experience level.

[genduct]

Terms are slung around like convection, conduction, stack effect, reverse stack effect, infiltration, exfiltration, stratification, displacement, turnover, short circuiting, specific air movement from supplies, general air movement from returns, rising warm air, sinking cool air, pushing supply air from one side of a house to the other or from one floor the other. It makes things very complicated and allows a person to point to which ever one they are familiar with and call it the cause.
Using the correct term is meant to clarify not confuse. If you are not comfortable with these terms it may indicate that you need to do a little more homework and not expect us to dumb it down. Remember Confucius say "first step in wisdom is to call things by same (correct) name"


Genduct, you should have firsthand experience and be willing to speak in depth about each one of those dynamics before coming across as an authority on the subject.
if my remarks don't convince, I am sure my CV wouldn't help you accept or believe so no need to go there
Your shying away from the hard questions is still telling of your all-around experience level.

I don't think I have been bashful or reluctant to share my ideas It has been you who have been "shying away" from considering the thoughts with an open mind. Please note your response completely ignored my thoughts in the last post, about your fixation on stagnate air and moving air masses with the simple observation that the energy can be transfer with less dramatic air motion/ movement then your remarks suggest.
How about taking your own advice and respond to the comments and not continue to ignore what you find inconvenient to your strongly held theories and not accuse someone of evasion.
Sounds like the Al Gore approach to science

[tipsrfine]

I just don't think enough attention is being paid to on what the difference stratification has on the throw/mixing of floor registers in cooling mode.
I just did a makeshift test in a 5 gallon bucket of water at a temp of 80 degrees. I took two syringes (the kind you give pets oral meds with) and filled them with green dyed water. One syringe was at room temp (70 degrees) and the other I had in my refrigerator for a while.(not the freezer). I released the green dyed water near the bottom of the bucket, and the difference was profound. The green dyed water at 70 degrees mixed fairly well in the bucket, but the green dyed water at the lower temp resisted any flow towards the top of the bucket and quickly fell and lay at the bottom of the bucket.
This is what I have been saying all along in regards to cherokees' house and the return placement. The high return, by removing the hotter air at the top, allowed the colder air from the floor returns to better mix at the higher levels of the upstairs area - where the t-stat is.
The greater the temperature difference between supply air and room air, the greater the tendency for stratification. In cherokees home, the cold supply air never got high enough to mix enough to shut the t-stat off and this resulted in the lower portions of the home to become overcooled.
This is why I said that the original problem was supply related, and Brians' theory of the high return paid off and aleviated that failure.

Was my 5 gallon bucket & green dye just too stupid for anyone to comment on? It took a little doing, so even some negative comment is better than no comment.

[energy_rater_La]

we all seem to be picking the part of the long multiple threads to quote/refer to.

without more testing ...during the improvements, monitering the progress..its a
crap shoot.

Brian will stay convinced that it is the return location
I'll believe that the air sealing was the keeper and the aeroseal
was a minimal improvement.

however Brian did make good points:
Terms are slung around like convection, conduction, stack effect, reverse stack effect, infiltration, exfiltration, stratification, displacement, turnover, short circuiting, specific air movement from supplies, general air movement from returns, rising warm air, sinking cool air, pushing supply air from one side of a house to the other or from one floor the other. It makes things very complicated and allows a person to point to which ever one they are familiar with and call it the cause.

These are all dynamics of conditioning a house that are interconnected and all play a part in the efficiency of a system. Each one must be fully understood before being considered an authority on the subject. Shophound and Tips are two who have opened their perspective to understand each one of those dynamics individually and how much each one affects the efficiency of a system.

I find this to be true for folks/guys who haven't had time in the field.

thanks shophound for the following:
For me, the revelation of his other improvements muddied the waters if hopes were staked on the return air modification being the salient energy saver.

and genduct for backing me up.

tips I don't know the deal going on with you and I. is it a remrate bpi thing?
lack of qc?? do I care? (prolly!)

thats my input at the end of a long day.

have a good one everyone.

[genduct]

I don't think there was much disagreement on the cold fluid dropping and warm rising thing. I will say that I was speaking with an instructor buddy last week about what I think was the misuse of a "water board" that was set up to show those "convective" air patterns. This might fit our discussion because from my point of view the dramatic patterns with the dyed water were dramatic because the dyed water is not compressable and had no choice but to move with the obvious dye "vapor trails" left to show its journey.

I think the Man D explanation about the limited effect of the return grill for instance is correct and the effects were are talking about a little more subtle, less dramatic

[tipsrfine]

I don't think there was much disagreement on the cold fluid dropping and warm rising thing. I will say that I was speaking with an instructor buddy last week about what I think was the misuse of a "water board" that was set up to show those "convective" air patterns. This might fit our discussion because from my point of view the dramatic patterns with the dyed water were dramatic because the dyed water is not compressable and had no choice but to move with the obvious dye "vapor trails" left to show its journey.

I think the Man D explanation about the limited effect of the return grill for instance is correct and the effects were are talking about a little more subtle, less dramatic

I understand my 5 gallon bucket experiments are not great science. In regards to your statement about placement of the return grill being a little more subtle, less dramatic: I have to say that a 30% drop in energy use by only changing the place of the return grill is a little more dramatic, and a little less subtle. The cherokee thread did not seem staged by Brian, and Cherokee has a profession that (I forget what it was) made him qualified for being able to conduct the test that he did.
The bottom line is that the test that he performed that resulted in a 30% cut in energy use resulted from changing the placement of the return in his home. Either we assume his testing was flawed & all go home, or we assume his testing was correct, and try & explain the reasons why changing the return location resulted in such a drastic energy savings.
In regards to the dyed water not being compressable, I'm not understanding how this is a player in my experiment on fluids & stratification due to temp differences.

[Brian GC]

Either we assume his testing was flawed & all go home, or we assume his testing was correct, and try & explain the reasons why changing the return location resulted in such a drastic energy savings.


Even though Genduct got Cherokee’s timeline all wrong he claims he explained his experiment/findings to us already. I’m glad I’m not the only one who missed it and is still waiting for it. Actually, I’m waiting for responses to a lot of my questions.

Its true Cherokee only changed return location to achieve a 30% savings. The duct sealing and such were done afterwards.

[genduct]

If the second floor didn't have enough supply air to meet its needs, with the T Stat on the first floor
and the occupants set the temp lower to compensate for the generally higher temps on the 2nd floor and increased the run times
Then the large quantity of return air from the 2nd floor helped remove the HEAT from the 2nd floor And the second floor was satisfied indirectly
which means the lower temps settings on 1st floor T Stat were moved to higher set point
Then the run times were shortened to get a more comfortable condition and some nice savings were experienced Is my theory,

but I also believe that since we haven't seen the "log book" it is very possible that Energy Raters idea of the good sealing job that was done may also have had a real impact. We don't really know and Cherakee hasn't been speaking for themselves, it has only been the guesses and supposition of others and we don't have the facts (log book)
I believe I tried to state this several times. Perhaps I need to go to a persuasive writing class and work on this skill

[Brian GC]

If the second floor didn't have enough supply air to meet its needs, with the T Stat on the first floor and the occupants set the temp lower to compensate for the generally higher temps on the 2nd floor and increased the run times
Then the large quantity of return air from the 2nd floor helped remove the HEAT from the 2nd floor and the second floor was satisfied indirectly which means the lower temps settings on 1st floor T Stat were moved to higher set point then the run times were shortened to get a more comfortable condition and some nice savings were experienced is my theory,

Genduct,
Thanks for going into more detail, maybe now we can find some common ground. I question whether the upstairs did not have enough supply because when Cherokee moved the return to the upstairs he did not increase the upstairs supply and it was enough. So the upstairs supply was adequate if the return was positioned correctly. But to cool the upstairs with a low return you’d have to significantly increase upstairs supply, but that would come at an increased cost. Only when the return was relocated upstairs was the cycle time reduced due to a faster, more even temp transition.

Where we agree is in this statement: “the large quantity of return air from the 2nd floor helped remove the HEAT from the 2nd floor”. Isn’t this what I’ve been saying all along? Tips refers to it as “displacement”. Shophound referred to it as “turnover”. I referred to it as “targeting and removing stratified air”. But either way it is placing the return where heat gain migrates to and the stratified air resides. Where I may part ways with you is if you say the warm upstairs is caused by lack of supply air. To pump more supply air up there is what I consider a “band-aid” because it could be done for free with a return up there.

A comment about t-stat placement: It shouldn’t matter where the t-stat is located if the ducting is supplying and returning correctly because the whole house will temp transition at the same rate.

[tipsrfine]

The t-stat was located at the second floor level during cherokees experiment.
If the upstairs supplies were located high on the walls, I don't think the return placement would have made such a big deal, at least in cooling mode.

[Brian GC]

The t-stat was located at the second floor level during Cherokee’s experiment.
If the upstairs supplies were located high on the walls, I don't think the return placement would have made such a big deal, at least in cooling mode.

I believe he had a remote t-stat that he only took upstairs at night when he went to bed. The hardwired t-stat was downstairs closer to the unit. But once his system cooled evenly with the high return it wouldn’t matter where it was because the whole house cooled evenly.

High registers are better for cooling, and better for heating too because they are less obstructed, but a floor register can easily reach the ceiling. Since the upstairs cooled fine with the high return we know there were enough cfms and maybe throw too.

[Shophound]

This thread has become a meeting of the wonks:

World English Dictionary
wonk (wɒŋk) http://sp.dictionary.com/dictstatic/g/d/dictionary_questionbutton_default.gif (http://dictionary.reference.com/help/luna/IPA_pron_key.html)— n informal a person who is obsessively interested in a specified subject: a return air location wonk; a residential building science wonk; an HVAC air distribution wonk, a residential energy auditing wonk

A little joshin' to lighten up this thread a tad... :D

[udarrell]

A lot of older homes began with gravity flow wood then coal furnaces.
The SA was usually at the interior walls on the floor or baseboards, & RA on the floor under windows at the outside walls.

Many older homes start out with small ducts designed for heating only, many were two story homes with other compromising situations.

When air conditioning was added they had very high free air area SA registers & lack of throw.

A lot of Oil furnaces had evaporators installed directly on top of them causing excess back-pressure thus compromising airflow, also with lack of blower HP.

Not a very good scenario for proper airflow mix...
That makes this interesting thread important to a lot of folks.