2nd story not cooling off

[lynn comstock]

You have some very good points above and I agree with everything you wrote EXCEPT the statement above, which is 100% wrong. The problem you don't understand is that it does not just magically get delivered and evenly distributed. You get some mixing out of the supply registers and then normal physics takes over and cold air sinks and hot air rises. When the fan is off, stratification due to the differing densities of cold air and warm air takes over. However when the fan is on the fan driven mixing of the air overwhelms the density effect. My house had the exact same condition you describe with adequate supply vents and a 90% crippled air return on the 2nd floor. You actually said no return in your claim. This led to all the cold air staying near the floor level and exiting quickly down the stairs in my open foyer (nothing but a huge air duct) to the first floor. This sounds as though the supply grilles are in the floor or at the wall near the floor. In addition, the supply air may have lacked the velocity to throw or push the air up into the room beyond the 3 foot level. In that case a high return vent would make up for the poor volume and velocity of the supply air. The choice of grilles on the supply duct may well be a factor, especially if the grilles are mounted low on the walls. I should use the words "pulled downstairs" as the return duct downstairs was doing just that. The result was a perfect stack Stratification rather than stack, effect with hot stagnent air trapped above 3' as well as an A/C system cooling already cooled air leading to 30% more energy being spent on A/C. Try to get that kind of return on investment with a 20SEER $10k system added onto an already screwed up duct system.

What you did obviously worked. What I say, with proper design of the supply duct and grille selection, would work equally as well. I would choose a one-way ceiling grille with curved blades to deliver air upward from a low sidewall location. The air would be directed up instead of outward into the room. Post 59 confirms my position on the supply ducts but your more complete description of the Stratification problem while running needed further explanation.

[cherokee180c]

My supply registers are actually at floor level and I do have a ceiling fan in my master bedroom that mixed the air. I still ended up with a 6 degree temperature difference between that bedroom and directly below it in the open foyer. I am sorry to disagree with you guys a bit, but a single ceiling fan in a master bedroom with a cathedral ceiling is not going to adequately mix air so the density effect with no return register does not exist. This was proven by my 6 degree temperature differential, which is now 2 degrees since I have tripled (estimate) the return air flow from the 2nd floor hallway return which is located up high in the hallway. The ceiling fan, does provide considerable comfort from the evaporation effect of moving air over the skin. I could not even imagine how bad my problem would have been with no return at all on the second floor.

I don't doubt that is I had double the airflow from the supply registers upstairs that the problem would be reduced, as my parents have that case with an isolated A/C system upstairs that delivers tons of cold air, but a normal open foyer house where they have not zoned the upstairs properly and have not designed the house a bit around a proper HVAC system will have these types of problems.

[Xavier]

First the great news, the part I designed for my Jag works great.

I also updated the alternator to a new design that I discussed with someone who builds and repairs them (Expert) and “we” came up with a Chevy alternator that we/he modified. Last night after talking with an HVAC poster on how I can cool my home with only 2 tons, I went cruising to confirm what I had done WORKS!

The car is running great for being 46!

The point of this story is I do and have done what I post! Not sure how many posters can make that claim.

PTSU if you remember many years ago when you first posted with your question, I stated you had leaking duct work in non-conditioned spaces. (this was before it bacame a popular respnse on HVAC!) Since that time you have spent time and money trying to better understand your home. You also know that my son and I redid his home in Texas to a “X” design and reduced his energy costs significantly and improved his IAQ. I have sent you the drawings of the duct design, but I am not sure you understand them as they do not agree with manual D. Finally, not sure what your career was, but it is clear it was not in negotiations, because when you (& Carnak) turn to personal attacks it is a sign you have lost the discussion. You may want to reread your posts. By the way, what size is your AC?

Lynn, to explain your statements, have you ever taken a bath and after a short while the water cooled off? So you turn on the faucet (any DESIGN you want!) and out comes all this hot water, BUT how long does it take for the NEW HOT WATER to get to the other end of the tub and raise the temperature? With this process you are constantly “averaging” the temperature. Now imagine you opened a drain on the other side of the faucet and let the “OLD” cold water out. Would the temperature change more quickly in the tub?

Furthermore, while the air is going down the stairs it is raising the temperature in that area, -- less efficient. Also, it is extremely difficult to blow/push air into a bottle no matter what the nozzle looks like

I suggest that when a poster recommends a solution they should include if they have used it or are merely quoting from the manufacturer’s ad or stating their opinion. How many of you when you go to the Doctor ask him “Have you done this before”, I DO!

Time for cruising with the top down so I can get better air exchange; in and OUT!

X

[lynn comstock]

...Lynn, to explain your statements, have you ever taken a bath and after a short while the water cooled off? So you turn on the faucet (any DESIGN you want!) and out comes all this hot water, BUT how long does it take for the NEW HOT WATER to get to the other end of the tub and raise the temperature? With this process you are constantly “averaging” the temperature. Now imagine you opened a drain on the other side of the faucet and let the “OLD” cold water out. Would the temperature change more quickly in the tub? Analogies are fickle. I would compare it to a whirlpool spa rather than a bathtub because the mixing is forced by a pump.

Furthermore, while the air is going down the stairs it is Only if the air in the upper floor was warmer than the lower floor. raising the temperature in that area, -- less efficient Neutral efficiency. . Also, it is extremely difficult to blow/push air into a bottle no matter what the nozzle looks like The upper floor has an open stairwell usually and air flows freely down the stairwell as the OP noted. However, if the stairwell is sealed of with a door, you are correct about pushing air into a bottle as an analogy....

I have plenty of field experience on airflow and design. I did not object to the high return. It worked for the OP and I acknowledged that it worked. "There is more than one way to skin a cat." Another analogy, sorry.

Note that I was correct about the supply grilles being at floor level (post 62). The OP did not confirm that they are in the side wall and that the air is directed out into the room instead of up along the wall. His description of stratification is classic for a poor choice of grille and/or grille location.

[Brian GC]

Cherokee,
You have a very good understanding of the subject because of your background and the fact that you have seen it work. I believe it will be hard to dissuade you now.

Lyn,
Perfect air distribution is very effective as you point out but how often do you see supply registers in hallways or foyers circulating that air? These areas are often large “return ducts” that “pull” the densest air downstairs (during cooling when return is downstairs). Of course anything can be overcome by more supply volume and velocity but hat comes at an energy price. Cherokee overcame his problem without increasing volume, velocity or changing supply location or grille selection.

Mixing supply air is good but it is what Xavier called “averaging”. His bathtub example showed this. If hot water was inputted into one side of the tub and the cooler water was removed from the other side of the tub it would heat faster and more efficiently than if you inputted and removed from random locations in the tub and stirred the water.

Pstu,
We all have different writing styles and levels of frustration. IMO you should interpret and respond a little less personally and stick to the subject, similar to a classroom.

Lyn has seen his approach work and Cherokee has seen his method work. They both will obviously cool a house fairly evenly. The question is which does it with more efficiency and less energy consumption?

[lynn comstock]

...The question is which does it with more efficiency and less energy consumption?

With either method done correctly the efficiency will be a tie. Good supply design and grille location and choice has the advantage of getting air everywhere that is is needed. Return location has far less influence on getting air where you need it. This is easy to prove with a cigarette (gasp) or a smoke pencil. I suppose confetti or powder would work also, but it would be messy.

[Brian GC]

With either method done correctly the efficiency will be a tie. Good supply design and grille location and choice has the advantage of getting air everywhere that is is needed. Return location has far less influence on getting air where you need it. This is easy to prove with a cigarette (gasp) or a smoke pencil. I suppose confetti or powder would work also, but it would be messy.

Do you think you could get the same results Cherokee got by re-locating supply registers, using different grilles, not increasing upstairs supply volume and using one downstairs return at floor level? Remember, he already had perfect air mixing in the mbrm with a ceiling fan and it did not help.

[cherokee180c]

I have plenty of field experience on airflow and design. I did not object to the high return. It worked for the OP and I acknowledged that it worked. "There is more than one way to skin a cat." Another analogy, sorry.

Note that I was correct about the supply grilles being at floor level (post 62). The OP did not confirm that they are in the side wall and that the air is directed out into the room instead of up along the wall. His description of stratification is classic for a poor choice of grille and/or grille location.

To answer the remaining questions:

1. The ducts are not in any exterior walls or attic in my house. The house was certified as a BGE energywise house when it was purchased and after my Energy audit about 3 years ago I have confirmed that it still meets the highest Energy Star ratings for air infiltration. That still doesn't mean that I haven't found and fixed a ton of problems and issue with poor design and construction. It just probably started life a bit ahead of the average home. Since my house was constructed in the late 90's most of the construction techniques have probably surpassed it by now.

2. Air is directed upward instead of out into the room. There are only two registers though in my room, which seems very low to me given the volume of air in there with a cathedral ceiling. Other factors making this room subject to more heat loss/gain then some is that the master bedroom floor is half over the hot garage and part of the wall is exposed to the hot garage attic. Given the cathedral ceiling, part of the upper walls are exposed to the hot attic, as well as all the ceiling area. The energy audit I did exposed all the problem areas where insulation had fallen down etc. and I fixed all of them, including rapping and aditional layer of R-19 unbatted insulation around the walls up in the attic to mostly increase the total R-value, but more imporantly make sure nothing could fall again.

Overall my house is very, very efficient with heat loss and heat gain. It has been 99 degrees here in the last month and when I leave at 7am, I am at 76 degrees in the house on the first floor. I have a setback of 85 degrees and it has never come on before the schedule kicks in around 4pm. In fact, I have never seen it reach over 80 on the first floor before it starts back up to cool the house down at the end of the day. I know this because I have Z-wave control system and can see my temperature on the first floor. It looks like I only used somewhere around 400kWh this month on A/C. Oh yea, I forgot to mention that all my windows have cellular shades that when closed increase the window total R value over 6, and they remain closed while we are not in the house to greatly lower solar gain.

[cherokee180c]

Guys, I am not convinced what both of you are saying is mutually exclusive. I think the supply side location and volume of air is hugely important and probably more so than the return side. This can be proven by how a single return per floor design works, versus a multiple return. I would take a single properly sized return in the halway anyday over a multiple return system where they were dumb enough to run everything in the attic where the air reaches 140 deg F.

I think what the supply side guys are not acknowledging is the fact that any design flaw in the single return airflow, (ie my situation with very poor airflow from the one single return) can have a MASSIVE effect on performance of the entire system (ie 30% wasted energy). The other issue with a single return system is you absolutely can not shut the doors to the rooms if you want cooling unless you have a huge gap under the door, as you have just closed a box and increased SP thereby droping airflow dramatically (the blowing into a bottle analogy). In fact, I have actually verified that closing the doors / registers to unused rooms upstairs is counter productive in two ways. It drops the total CFM delivered to the upper floor considerably and secondly it allows that room to heat up so you now have un-insulated interior walls transferring heat into the rooms you are using.

[Brian GC]

To answer the remaining questions:

1. The ducts are not in any exterior walls or attic in my house. The house was certified as a BGE energywise house when it was purchased and after my Energy audit about 3 years ago I have confirmed that it still meets the highest Energy Star ratings for air infiltration. That still doesn't mean that I haven't found and fixed a ton of problems and issue with poor design and construction. It just probably started life a bit ahead of the average home. Since my house was constructed in the late 90's most of the construction techniques have probably surpassed it by now.

2. Air is directed upward instead of out into the room. There are only two registers though in my room, which seems very low to me given the volume of air in there with a cathedral ceiling. Other factors making this room subject to more heat loss/gain then some is that the master bedroom floor is half over the hot garage and part of the wall is exposed to the hot garage attic. Given the cathedral ceiling, part of the upper walls are exposed to the hot attic, as well as all the ceiling area. The energy audit I did exposed all the problem areas where insulation had fallen down etc. and I fixed all of them, including rapping and aditional layer of R-19 unbatted insulation around the walls up in the attic to mostly increase the total R-value, but more imporantly make sure nothing could fall again.

Overall my house is very, very efficient with heat loss and heat gain. It has been 99 degrees here in the last month and when I leave at 7am, I am at 76 degrees in the house on the first floor. I have a setback of 85 degrees and it has never come on before the schedule kicks in around 4pm. In fact, I have never seen it reach over 80 on the first floor before it starts back up to cool the house down at the end of the day. I know this because I have Z-wave control system and can see my temperature on the first floor. It looks like I only used somewhere around 400kWh this month on A/C. Oh yea, I forgot to mention that all my windows have cellular shades that when closed increase the window total R value over 6, and they remain closed while we are not in the house to greatly lower solar gain.

Was your home in its present condition (as stated above) before you balanced the returns? Did drawing more return from upstairs make the biggest improvement?

[pstu]

Cherokee I admire how methodical you are. Perhaps you have mentioned already, have you had a room-by-room Manual J model done on your house? I am curious how well the cooling load correlates with the airflow supplied. Measuring the airflow may be the more difficult half of this comparison. Or more expensive, flow hoods cost a bundle.

Back when you posted KWH per day for a week before and after your change, did you have any suspicions about that last day being an outlier I wonder. Post #36. While you may have little desire to repeat the "before" scenario, it might add value to do some repetition of the "after" measurements.

Again, thanks for sharing your measurements. I feel we make a whole lot more progress when we do that.

Brian, I will try hard to be impartial in the future.

Best wishes -- Pstu

[cherokee180c]

Yes and Yes!!! But that is coming from a known design flaw issue where the idiots put the two main returns in series within a wall cavity without balancing the airflow. I did not move anything, I just re-balanced (skewing to the upper foor) by blocking off most of 1st floor return. I am not so sure the benefits would have been anywhere near as great had the system been perfectly balanced to start off with.

[cherokee180c]

Yes, unfortunately the last day is an outlier as you pointed out. The day before that was actually even lower though so I took the most conservative contiguous data point. I tried to match average temperature conditions as close as possible between the weeks. The easiest way to tell the savings is real though is that I have 3 more weeks of data now and there are only 2 days above 60kWh at all with the highest being 64.5kWh. Go back and look at the before week and you will see there is no need to re-run. My billing cycle ends today, and it looks like I just had the lowest July electric bill since I finished my basement 6 years ago.

[genduct]

Guys, I am not convinced what both of you are saying is mutually exclusive. I think the supply side location and volume of air is hugely important and probably more so than the return side. This can be proven by how a single return per floor design works, versus a multiple return. I would take a single properly sized return in the hallway any day over a multiple return system where they were dumb enough to run everything in the attic where the air reaches 140 deg F.Watch it you are begining to sound like one of us "supply siders" because I agree with what you just said

I think what the supply side guys are not acknowledging is the fact that any design flaw in the single return airflow, (ie my situation with very poor airflow from the one single return) can have a MASSIVE effect on performance of the entire system (ie 30% wasted energy).
Again I agree if the return is not working then it is not going to work The point is to have the duct (not stud or joist space) install so it does the job it was designed to dop. No conflict with us "supply siders:

The other issue with a single return system is you absolutely can not shut the doors to the rooms if you want cooling unless you have a huge gap under the door, This is where you use ONE stud space to install transfer grills as you have just closed a box and increased SP thereby droping airflow dramatically (the blowing into a bottle analogy). In fact, I have actually verified that closing the doors / registers to unused rooms upstairs is counter productive in two ways. It drops the total CFM delivered to the upper floor considerably and secondly it allows that room to heat up so you now have un-insulated interior walls transferring heat into the rooms you are using. This observation is also in line with the "supply siders point of view as well

So your question is????

[lynn comstock]

1. What is the elevation of the upper return relative to the floor upstairs?
2. The sidewall grilles direct the air both up and out if they have flat blades, probably set at a 45° angle. A one-way curved blade grille is most commonly used in ceilings but will direct the airflow tight to the surface upward when it is installed on a wall. This maximizes the upward throw or distance that the air is pushed.
3. Did you stop using the ceiling fan or change its setting in any way?

You have done a good job by being alert, thoughtful, and observant.

[cherokee180c]

1. The bottom is about 6' off the ground and it is an 18" x 18" grill.

2. I don't have wall supply vents as they are in the floor.

3. Nope, my wife loves cold air blowing on her. Drives me crazy as she keeps it blowing all the time even in the winter.

[Brian GC]

Guys, I am not convinced what both of you are saying is mutually exclusive. I think the supply side location and volume of air is hugely important and probably more so than the return side. This can be proven by how a single return per floor design works, versus a multiple return. I would take a single properly sized return in the hallway any day over a multiple return system where they were dumb enough to run everything in the attic where the air reaches 140 deg F.Watch it you are begining to sound like one of us "supply siders" because I agree with what you just said

I think what the supply side guys are not acknowledging is the fact that any design flaw in the single return airflow, (ie my situation with very poor airflow from the one single return) can have a MASSIVE effect on performance of the entire system (ie 30% wasted energy).
Again I agree if the return is not working then it is not going to work The point is to have the duct (not stud or joist space) install so it does the job it was designed to dop. No conflict with us "supply siders:

The other issue with a single return system is you absolutely can not shut the doors to the rooms if you want cooling unless you have a huge gap under the door, This is where you use ONE stud space to install transfer grills as you have just closed a box and increased SP thereby droping airflow dramatically (the blowing into a bottle analogy). In fact, I have actually verified that closing the doors / registers to unused rooms upstairs is counter productive in two ways. It drops the total CFM delivered to the upper floor considerably and secondly it allows that room to heat up so you now have un-insulated interior walls transferring heat into the rooms you are using. This observation is also in line with the "supply siders point of view as well

So your question is????

Nobody can detract from the importance of the supply side but you are left with one hard question to answer. How did the power consumption drop by 30% and setpoint obtained 60% faster by simply drawing the return from upstairs vs. downstairs? There were no changes to the supply side or the envelope. The most obvious answer to me is that downstairs was not the most ideal location for a return for cooling. In other words return location matters a great deal, up to 30% or more.

[cherokee180c]

Yes, I fully agree. In this case, there is no doubt that a basically crippled single return on the upper floor is 100% responsible for a 30% waste of A/C energy. All I am saying is that if that return had been properly sized and balanced so that there was equal airflow to begin with on both floors, the improvement by skewing more airflow to the upper floor would have been less (maybe 10%, but this is just a guess). Remember I clearly stated in Post#2 that I estimated I had 90% of the air pulling from the first return in series (ie 1st floor) and only 10% from upstairs. When I physically blocked 90% of the first floor return, I flipped that ratio to highly skew to the upstairs.

There was one other benefit here that might have been lost in all the posts. When I blocked off 90% of the first floor return, I also increased the airflow pulled from the basement return as well, which also reduced the differential temperature between the basement and the first floor. The basement was always freezing and now it is only about 2 degrees colder than the first floor. I don't have good data for the basement temps though, but I can tell you it made a huge difference. I think I recall a data point from a few years ago and 4 degrees colder sounds familiar. The entire system is working so much more efficiently it is not even funny. It literally feels like a brand new HVAC system.

[Wrmair]

Closing the downstairs will work but I would try running the fan in the on position to keep circulating the air I aszume it bad duct work and thats the last run to the home

[lynn comstock]

Do you think you could get the same results Cherokee got by re-locating supply registers, using different grilles, not increasing upstairs supply volume and using one downstairs return at floor level? Remember, he already had perfect air mixing in the mbrm with a ceiling fan and it did not help. Not so perfect as the OP reported that cold air was flowing down the stairwell toward the downstairs return.

No, because the supply air volume and velocity was too weak to push the air more than 3 feet upward into the room. That is why the OP reported that the cold air near floor level was flowing down the stairwell instead of cooling the upstairs zone properly. When he increased the airflow from the upstairs return located about 6 ft 9 inches (center) above the floor level, the supply air stoped flowing down the stairwell and moved the stratification layer higher to cover the occupied space in this zone.

Based on the severe change in the balance of the two main returns, I would expect that air from the first floor is now moving up the stairwell and is a factor in the cooling improvement reported.

What the OP did, worked and worked well. What I just said above is my understanding of why it worked. It really is a matter of physics. The huge advantage of his solution is that no duct modifications needed to be made. He only needed to damper the first floor return at the grille. Success speaks for itself.