attic ventilator [Archive] - HVAC-Talk: Heating, Air & Refrigeration Discussion

tuccillo

06-03-2005, 03:39 PM

Originally posted by old yeller
IT depends on where you live and other factors.

In Dallas, I had the static-type roof vents and I could NOT keep my house below 80 degrees in July and August running constantly. This was not a matter of efficiency, it was a matter of livability and sanity.

I put in an electric roof vent and made sure that I had the required number of soffit vents to allow enough outside air into the attic so I would not have the negative pressure situation you mention.

The vent plus solar screens cut my bill by more than 50% the next year. I really couldn't beleive how much it dropped. I was able to keep the house at a comfortable 77 degrees with normal cycling.

Some people do it to increase efficiency, and then it is a toss-up, but some do it out of necessity. Just make sure you have adequate attic intake air.

Did you add the roof vent and solar screens at the same time? If so, then you dont know which one had the biggest impact?

uktra

06-03-2005, 05:01 PM

OldYeller--no matter how much sq. area of soffit/gable vents you have, you will still have a negative pressure in the attic. This will still pull airconditioned air from room below. Power vents don't save energy or lower cooling bills.

txnoob

06-03-2005, 05:22 PM

Hi eve,

I thought I'd add my input in the hopes that you might find it useful since I went through this exact same thing 1 month ago and live in the north TX area.

I have 3 turbines on my house. I considered replacing all of them with solar powered attic fans. These types of fans are totally enclosed and the solar panel is what powers the fan, so there is no need to wire into your electrical system. Sounds great, but 2 big drawbacks for me:

1. The cost per fan was at least $300!!
2. Like you indicated, there is the possibility of the motor crapping out in a few years. What then? Buy another one? Shell out another $300??

No thanks.

I ultimately decided to simply replace the turbine with new ones. My old ones were at least 30 years old, made of galvanized steel, and those things weighed at least 7 pounds! They would only turn if the wind was around 15MPH. Absolutely terrible, plus they were rusted.

When you replace yours, purchase aluminum turbines only. There are a couple of big reasons for this.

1. Aluminum will not rust.
2. Aluminum is much lighter than steel.
3 Being that aluminum is lighter, the turbine will turn more often.
4. Aluminum is generally a little cheaper.

Attic Aire or Ventmatic are both good companies, but don't buy steel turbines. Place a special order if you have to but just make sure they are aluminum. My turbines now spin if there is just 2MPH worth of wind...they spin all the time now.

old yeller

06-04-2005, 10:34 AM

Originally posted by tuccillo

Did you add the roof vent and solar screens at the same time? If so, then you dont know which one had the biggest impact?

OldYeller--no matter how much sq. area of soffit/gable vents you have, you will still have a negative pressure in the attic. This will still pull airconditioned air from room below. Power vents don't save energy or lower cooling bills.

True, I don't know exactly what worked better- but I would still recommend them both in the right situation. I only had 5 west-facing windows in the whole house.

Uktra- If you want to get picky, of course there is negatve pressure! There is always negative pressure whether it is from static vents, whirly-birds, or power vents. You will even have it from nothing more than a stack effect in the attic.

You are obviously speaking your opinion regarding a different situation than the one I mentioned (did you read it?) I am speaking from PROOF and direct EXPERIENCE. I don't feel like digging up my 4 year old electric bills to show you my bills going from 275 in august to 135 in August the next year. Like I said, the house could not go below 80 degrees before, would stay comfortable at 77 with the attic fan afterwards. The solar screens helped, but I always had my blinds closed anyways. The attic temps went from 150+ to around 110.

Now, if you would like to discuss an already optimal situation where someone wants to shave a few dollars off their already moderate cooling bill, I'm sure you are correct. But in my particular situation- you are wrong.

uktra

06-04-2005, 05:52 PM

Old Yeller--Unless you had an individual meter for your A/C, and you compute the average temps form one year to the next, bills going down don't mean the power vent saved you money. There were are too many other factors involved. So you can believe I am wrong but before you give advise to people,you had better have some research to back it up--which you don't.

eve

06-04-2005, 06:57 PM

thanks everyone for your thoughts on this.

thanks txnoob,
regarding aluminum:
someone on HVAC talk mentioned a company called LOMANCO
http://www.lomanco.com/ProductPAGES/BEBBIB.html
they're aluminum, and seem okay from their description.
anyone have any experience with these?

I put a thermostat in my attic today and if it was accurate it read 104 degrees F
that seems okay
but surely, as we approach August in Houston, that will go up perhaps up a lot.
so
perhaps it makes sense to get the turbine which I think means no electric power, just self propelled.
That sounds great txnoob to have turbines that turn with just a 2 mph wind.

old yeller

06-04-2005, 08:46 PM

Uktra- you need to read my post before you type.

Power vents are good for SOME situations. not all. period.

You ARE correct- someone trying to shave a few dimes off their electric bill is NOT a candidate for a power vent. If their attic temps stay at 104 or near that (<>120), then she is NOT a situation for power vents. period. I did not give advice telling someone what they should do. I said they are good for certain situations and it worked for me. Anyone can use that as they will.

It worked for me because, as I mentioned, I was NOT trying to shave dimes off my bill, I was trying to LIVE in my house. (It was a brand new house with a "professionally" installed HVAC)

I didn't care what my dollar savings were, because I was paying a fortune at any temperature. The simple fact is, that in my proven, researched experince, it was effective in serving it's purpose, screw what any report says for THIS situation.

Now, my current house has 4 whirly-birds and they work great! I have no need or intention of using power vents becaseu this is the WRONG situation.

Try to keep an open mind here- if you go around telling everyone they didn't experience what they experienced just becaseu you read something different in a report somewhere- you are going to miss out on a lot of good information.

cem-bsee

06-04-2005, 09:43 PM

turbins ok if you have wind --

plant some fast growing trees 15ft from hse on south & west!

Uktra -- bet you do not beat $25 for a/c last Sept! I range from 1 to 2.6 kwh/dd or 1.5- 4.14 btu/dd/sf. I have utility billings for about 4yr -- trashed prior 2, because of so many upgrades to hse.

uktra

06-04-2005, 10:59 PM

Ol Yeller--I read before I typed. I also have an open mind. Your experience does not change the facts of heat transfer in attic assemblies. There are NO situations where power vents do anything positive in homes.

uktra

06-04-2005, 10:59 PM

Old Yeller--I read before I typed. I also have an open mind. Your experience does not change the facts of heat transfer in attic assemblies. There are NO situations where power vents do anything positive in homes.

trane

06-04-2005, 11:12 PM

Originally posted by uktra
Ol Yeller--I read before I typed. I also have an open mind. Your experience does not change the facts of heat transfer in attic assemblies. There are NO situations where power vents do anything positive in homes.

I can't agree with you. If I had to choose between a slight neg pressure or a 160 degree attic I would be putting these fans in. I will agree that having the attic vented any other way would be better, but there are times that this does not work. If there are enough openings for outside air the power vents will do a better job of removing the heat.

old yeller

06-05-2005, 09:28 AM

Originally posted by uktra
Old Yeller--I read before I typed. I also have an open mind. Your experience does not change the facts of heat transfer in attic assemblies. There are NO situations where power vents do anything positive in homes.

Your statement "NO situations" clearly exemplifies the fact that you do not have an open mind about these matters.

Keep trying.

uktra

06-05-2005, 03:07 PM

Trane--The air temp. in the attic is not what transfers the most heat to the rooms below. The dominant transfer mechanism is radiant (about 85% of heat), not convective. You cannot flush out radiant transfer with ventilation. The reason the code ventilated the roof assembly was for winter ice damming--not heat. In the 70's hot attics were turned into huge energy transfers by various industries, the HVAC in particular. We as HVAC professionals should give advice like check insulation levels, seal holes in attic, check leaky ducts in attic, that really benefit the customer, instead of power vents that don't work.

trane

06-05-2005, 06:18 PM

Originally posted by uktra
Trane--The air temp. in the attic is not what transfers the most heat to the rooms below. The dominant transfer mechanism is radiant (about 85% of heat), not convective. You cannot flush out radiant transfer with ventilation. The reason the code ventilated the roof assembly was for winter ice damming--not heat. In the 70's hot attics were turned into huge energy transfers by various industries, the HVAC in particular. We as HVAC professionals should give advice like check insulation levels, seal holes in attic, check leaky ducts in attic, that really benefit the customer, instead of power vents that don't work.

So you are saying that it does not matter what the attic temp is your still getting the same amount of tranfer through the ceiling? I wonder what heats the air in the attic then. All of the hot air that comes out of any kind of vent in a roof is radiant and removing it does help stop transfer through the ceiling.

uktra

06-05-2005, 10:00 PM

Trane--hot air coming out of the attic is hot air not radiant heat. The bulk of the heat transfered to the air in rooms below the attic comes from radiant transfer not the hot air by convection. If you want to believe that the hot air in the attic is the problem, or that the earth is flat--go for it--that will be the most "hot air" I have felt in a long time.

trane

06-05-2005, 11:18 PM

Radiant heat is what causes your attic to get hot and by keeping the air moving through the attic space it will help stop radiant heat from transfering to the conditioned space. The way you think, your attic tempature could be 40 degrees and it wouldn't matter because radiant heat bypasses attics and goes straight into the living area.

uktra

06-05-2005, 11:44 PM

Trane--If that were true, explain how heat is transfered from the sun to the earth through space which is close to absolute zero.

trane

06-05-2005, 11:52 PM

Alright I give up if you can answer one question. What does make attic spaces warmer than the outside temp. (ON EARTH)

uktra

06-06-2005, 08:18 AM

Trane--there is no question that the air in the attic is heated by the radiant energy off the underside of the roof sheathing. That same radiant energy is also heating the drywall of the ceilings in the rooms below. This transfers the radiant energy to heat the air in the rooms. This is the dominant transfer mechanism. That is why radiant barriers and reflective roofs make more difference than venting attics. Hot air in the attic transfers little heat through the insulation by conductivity. The worst problem with hot air in attics is when the holes are not sealed and hot air enters the living space. Again when we in the industry and give advice to people, we need to give information that will really make a difference--like check insulation levels, seal holes, check for leaky ducts, ect. Those are the things that cure problems, not power vents that can create problems.

old yeller

06-06-2005, 10:22 AM

I knew it- Uktra has drank the "Radiant Barrier" kool-aid!

Insulation in the attic is there to slow convective action from transferring the heat from the warm air in the attic to the ceiling surface. R values are an exact measurement of this "slowing". It's purpose is NOT to block radiant energy, although if the top surface of a non-conducting insulation get's hot, who cares? It's non conducting!

Now, I AM NOT saying that blocking the radiant energy isn't a good thing. That is what your radiant barrier is "supposed" to do. Only proven through heavily biased and trade association funded "research", of course.

If a home is NOT set up to take advantage of radiant barrier technology, and is instead set up to slow the convective properties of air with insulation, then it makes sense to most of us that removing the main convective medium (hot air) would be the more effective way of helping the insulation serve it's designed purpose.

Once again- try to keep an open mind here. I'm sure there are plenty of really bad power vent situations out there that have made you so negative against them. They can be done properly and used correctly IN THE APPROPRIATE SITUATION. Just like HVAC installations.

fat bob

06-06-2005, 10:43 AM

A big factor is whether whether you have ducts and equipment in the attic, sitting above the insulation. An evaporator coil with 1/2 inch of insulation, and a supply plenum with 1 inch of insulation, sitting in a 150 degree attic, is a problem that ceiling insulation can't help. In that situation attic ventilation and/or radiant barrier is important.
http://homeenergy.org/archive/hem.dis.anl.gov/eehem/96/960704.html

uktra

06-06-2005, 11:32 AM

Old Yeller--You need to learn how heat is transferred. The vast majority of heat transfer fron the attic to the rooms below by hot air is CONDUCTIVE rather than convective. Insulation slows this transfer down. Convective is hot air transfering heat by leaking into the rooms below. This type bypasses or filters through insulation. Again, the majority of energy (85%) that transfers from the sun to the rooms below the attic is radiant, and you cannot flush that transfer with a power vent. I suggest you read the article in the above thread and learn something.

old yeller

06-06-2005, 02:28 PM

now your just getting mean...

Insulation slows the convection/conduction transfer from the attic air to the surface of the ceiling. The limited conduction of the ceiling material then convects/conducts that heat to the inner surface of the ceiling and through convection again dissipates the heat into the cooled space. I will admit that I stretched a bit in my last statement in saying that insulation was "non-conductive".

Now, you are correct in saying that a breach would allow a much faster transfer of this heat into the space. I won't deny that, but contrary to your belief it is NOT the only way heat gets into a space. A theoretically perfectly sealed house would still have a heat load that would be increased as the outdoor temperature increased and as the attic temperature increased. This is a simple fact. IF r-values are calculated using temperature differences among other variables, then that would mean that lowering the temperature difference would lower the amount of transfer. A power vent in the appropriate situation could accomplish this as could a radiant barrier. This is a simple fact.

Why can't someone seal all the air leaks AND have a power vent to bring attic temps down? Then the power vent would work as designed and help to keep the surface temp of the insulation down. This is the open mind part...

I'm sure you are very excited about the "Radiant Barrier" but many people cannot afford to have their roof rebuilt using barrier materials.

keep trying.

amigadude

06-06-2005, 02:59 PM

Good advice from old yeller,

I also can vouch for the attic fan, from personal experience (and pain).

Back track, three years ago in HOTtlanta:
- > 5,000 sf 2 story house + basement
- three systems, 1 per level
- Single Pane windows
- Relatively leaky house
- Three (3) 15 year old Turbines
- Summertime after 5pm, 2nd floor at 78 (best I could get) with system running constantly
...

OK, I decide to follow standard advice and did the following (for differing reasons, after HVAC tuneups)
1) Sealed ductwork in attic
2) Sealed any leaks between attic and 2nd floor (there were some big ones), and cleared soffit inputs
3) Replace windows with Pella double-paned
4) Added layer of insulation where blown-in stuff was matted down

Now system can keep me at 78, and even shuts off from time to time! Progress, but still HOT. Put a remote temperature sensor in the attic, and it gets to 120 or so.

Finally, two years ago, I decided to get fans installed, and roofer suggested that I get ridge vents also. What the hey, I'm desperate, so in they go. 2 Ridge vents, and 2 attic fans, later and I reach nirvana. 76 in the Master!! And get this - The system cuts off! So much in fact, that during moderate times I have to make it 74 to get rid of the humidity.

Wife is happy, so I'm happy, and these babies are staying no matter what any guidelines say. Had a new roof installed, and they had the nerve to suggest that I remove the fans and install turbines. I probably was a little harsher on the estimator than need be, but I think he got the point. Not in this life time...

By the way, scientifically I understand that the power fan and the ridge vents contradict each other, but it works here!

old yeller

06-06-2005, 03:07 PM

Good stuff- very rewarding tackling a problem like that and winning, eh?
My house was 2 months old when my problems started. It was so bad that the bulder had to go check their records to make sure the insulation contractor had actually put insulation in the walls.

Did you measure the attic temps with the fans and vents?

uktra

06-06-2005, 04:04 PM

Old Yeller--I never said that radiant is the only heat transfer mechanism in attic assemblies! If you lower the temperature in the attic, this will lower the transfer to the rooms below through the insulation. The problem is that for the umpteeth time--this is NOT the majority of heat transfered from the sun to the rooms under the attic. So using a power vent (that uses power) will not save money on the small amount of heat transfered caused by hot air. In addition, how many air tight attic assemblies have you seen? I haven't seen any. In tests in NC they tested about 25 homes with power vents and found the average air infiltration rate doubling with the vent on. Does that save money? does that lower humidity levels in the home?--I don't think so.

The big question is, if they really saved energy, why won't Florida Power, Dominion resources and many other utilities recommend power vents? In fact they recommend against them.

old yeller

06-06-2005, 06:00 PM

Originally posted by uktra

The big question is, if they really saved energy, why won't Florida Power, Dominion resources and many other utilities recommend power vents? In fact they recommend against them.

I digress, that is a very good question.

Maybe it's because they didn't have to live in my house before I put my power vent in? Maybe it's because they didn't pay the other gentleman with a similar story a visit before he installed 3 of them?

I truly do not care if the vent transfers the air in my house 200 times per hour. I could not LIVE in my house before I installed the power vent and I lived comfortably with it and saved hundreds of dollars in one summer (for the umpteenth time).

Uktra- Tear down this wall! You are being so stubborn about this. I have readily agreed that radiant barriers are good and sealing breaks in the thermal barrier is good, but in the face of now mounting evidence you refuse to accept the reality that SOMETIMES power vents can do good in the RIGHT SITUATION. Stop relying on biased non- real-world reports for all your information.

uktra

06-06-2005, 08:35 PM

Old yeller--Lets just say we agree to disagree.

trane

06-06-2005, 09:24 PM

Originally posted by uktra
Old yeller--Lets just say we agree to disagree.

I will agree with that

54regcab

06-06-2005, 10:05 PM

Make sure there is plenty of open ventilation for cool air to come in. Turbine vents are especially sensitive to the amount of intake area they have.

old yeller

06-07-2005, 09:12 AM

Originally posted by uktra
Old yeller--Lets just say we agree to disagree.

ok, and for the extension of the proverbial olive branch- I do agree with the sealing holes and radiant heat issues that Uktra raised. No disagreement there at all.

robnjr

06-13-2005, 12:54 AM

Hi folks, I’ve been lurking here for a while, and thought I would add my 2 cents on power ventilators. For the record, I’m not an HVAC person, but an Electrical Engineer who lives in the Dallas area.

I had a power ventilator installed after we moved into our home 12 years ago. It has made a noticeable difference in my electric bills, and more than offsets the cost of running it. However, it took a little work to get the most efficient use of the ventilator. I won’t go into details, but I analyzed this issue in-depth. Besides checking my power usage, I’ve also installed a wireless thermometer in my attic (an extra sensor from my weather station), that connected to my computer. This lets me make graphs of attic temps throughout the day, with an overlay of outside and inside temp graphs, so in essence I can SEE the relationships between the three variables (as well as read my meter). I’ve compared graphs with the ventilator at various thermostat settings, and disconnected completely, on similar days. Here are my conclusions:

1)The ideal setting (for me at least) is with the fan ON at 110 deg, and OFF at 95. My unit (a “4000 sq ft” model) has a 15 deg ON/OFF differential.

2)As you can guess, this turns the fan off about 30-60 minutes after sunset. After this, the decrease slope of the graph doesn’t change much if the fan is on or off. It’s about the same as the natural cooling and venting.

3)The OFF setting is more important than the ON. The rise slope of the graph is so steep after 105 deg that the fan would turn on about the same time if set for 110 ON or 120 ON, but would run for too long after the sun has set. Not all thermostats have a 15 deg ON/OFF differential, so set yours for the OFF temp. Use a thermometer (ideally a wireless one) to confirm.

4)Note that your attic will never get cooler than the air it sucks in (during the summer)! Therefore, you should set your OFF temp accordingly for your climate.

5)INTAKE VENTILATION IS CRITICAL. Not only will it make the power ventilator more efficient, it will cut down on the negative pressure effect it causes on your living space. My unit recommended 900 free sq inches of intake space. That was 16 of the 8x12 soffit (under eave) vents, which have an equivalent free area of 56 sq in. I had to add 6 vents. Not only that, the builder didn’t cut the holes full size for the existing ones, and I had to open them up!! (as well as unclog them with the blow in insulation).

6)CHANGE/CLEAN YOUR SOFFIT VENTS REGULARLY. It only takes about 2-3 years (again, for me) for them to get pretty clogged with dirt, bugs, spider webs, etc (it gets caught in the bug mesh on the vents). I just change mine every two years, well worth the 30 bucks and couple of hours. It's hard to clean them, and not worth it IMO. BTW, I have pics of clogged vents that look OK from outside, but can't post them for some reason...

That’s my experience, in my climate. Like they say, your mileage may vary, but I believe that following the above items makes an attic power ventilator well worth the cost of running it. Not only will you save money, you’ll have less wear and tear on your equipment and a more comfortable home. The bottom line is the ventilator should not be run more than necessary, and needs plenty of free intake ventilation. My unit has a thermostat that goes from 50 to 120 deg, and I’m set at 110…what does that tell you? Of course a power ventilator will not solve a severe cooling problem caused primarily by other ills (and may actually make things worse in a house that is poorly sealed, and lacks adequate soffit intake venting!), but all things being equal, it is an asset that will assist your cooling system, and save you money. Like all equipment, it just needs to be set up right, and needs the proper support and maintenance. It’s more than a simple fan, but a system with several components.

[Edited by robnjr on 06-13-2005 at 01:48 AM]

tuccillo

06-13-2005, 08:31 AM

Under identical (or nearly identical) conditions, say summer, sunny, same outside temperature, how much impact does running the venitilator have on your attic temperature? In other words, run it one day and record the max attic temperature and then leave it off (unplug) the next day and record the max attic temperature.

Originally posted by robnjr
Hi folks, I’ve been lurking here for a while, and thought I would add my 2 cents on power ventilators. For the record, I’m not an HVAC person, but an Electrical Engineer who lives in the Dallas area.

I had a power ventilator installed after we moved into our home 12 years ago. It has made a noticeable difference in my electric bills, and more than offsets the cost of running it. However, it took a little work to get the most efficient use of the ventilator. I won’t go into details, but I analyzed this issue in-depth. Besides checking my power usage, I’ve also installed a wireless thermometer in my attic (an extra sensor from my weather station), that connected to my computer. This lets me make graphs of attic temps throughout the day, with an overlay of outside and inside temp graphs, so in essence I can SEE the relationships between the three variables (as well as read my meter). I’ve compared graphs with the ventilator at various thermostat settings, and disconnected completely, on similar days. Here are my conclusions:

1)The ideal setting (for me at least) is with the fan ON at 110 deg, and OFF at 95. My unit (a “4000 sq ft” model) has a 15 deg ON/OFF differential.

2)As you can guess, this turns the fan off about 30-60 minutes after sunset. After this, the decrease slope of the graph doesn’t change much if the fan is on or off. It’s about the same as the natural cooling and venting.

3)The OFF setting is more important than the ON. The rise slope of the graph is so steep after 105 deg that the fan would turn on about the same time if set for 110 ON or 120 ON, but would run for too long after the sun has set. Not all thermostats have a 15 deg ON/OFF differential, so set yours for the OFF temp. Use a thermometer (ideally a wireless one) to confirm.

4)Note that your attic will never get cooler than the air it sucks in (during the summer)! Therefore, you should set your OFF temp accordingly for your climate.

5)INTAKE VENTILATION IS CRITICAL. Not only will it make the power ventilator more efficient, it will cut down on the negative pressure effect it causes on your living space. My unit recommended 900 free sq inches of intake space. That was 16 of the 8x12 soffit (under eave) vents, which have an equivalent free area of 56 sq in. I had to add 6 vents. Not only that, the builder didn’t cut the holes full size for the existing ones, and I had to open them up!! (as well as unclog them with the blow in insulation).

6)CHANGE/CLEAN YOUR SOFFIT VENTS REGULARLY. It only takes about 2-3 years (again, for me) for them to get pretty clogged with dirt, bugs, spider webs, etc (it gets caught in the bug mesh on the vents). I just change mine every two years, well worth the 30 bucks and couple of hours. It's hard to clean them, and not worth it IMO. BTW, I have pics of clogged vents that look OK from outside, but can't post them for some reason...

That’s my experience, in my climate. Like they say, your mileage may vary, but I believe that following the above items makes an attic power ventilator well worth the cost of running it. Not only will you save money, you’ll have less wear and tear on your equipment and a more comfortable home. The bottom line is the ventilator should not be run more than necessary, and needs plenty of free intake ventilation. My unit has a thermostat that goes from 50 to 120 deg, and I’m set at 110…what does that tell you? Of course a power ventilator will not solve a severe cooling problem caused primarily by other ills (and may actually make things worse in a house that is poorly sealed, and lacks adequate soffit intake venting!), but all things being equal, it is an asset that will assist your cooling system, and save you money. Like all equipment, it just needs to be set up right, and needs the proper support and maintenance. It’s more than a simple fan, but a system with several components.

[Edited by robnjr on 06-13-2005 at 01:48 AM]

cem-bsee

06-13-2005, 04:24 PM

the heat source for attics may be due to radiation, but that which is transferred into the living space is NOT maily due to radiation! --

and, if one has blow- in chopped insulation, that seals most holes against air transfer --

probably the biggest source is holes around boxes & pipes -- at recessed lighting fixtures, all outlets & switches, ceiling fixtures, HVAC supply boxes

next would be the HVAC piping out of the conditioned space-- with poor sealing and poor insulation. especially after it is crawled over 3- 4 times.

per GOOGLE: per Engr BRSteward @ Texas A&M: one air change per minute of 95F air will lower 155F attic to 101F; one air change per 2 minutes of 95F air will lower 155F attic to 106F. use 0.1 of this for winter. Having less than 4inch thick insul on ceiling will probably contribute 30% of a/c needs, more will cut this in half.

Ridge vents need baffels to direct wind over the vent; having wind to pass thru ridge vents greatly decreases their preformance..

Most moisture comes into attics from crawlspaces -- thru pipe penetrations --

[Edited by cem-bsee on 06-13-2005 at 05:41 PM]

uktra

06-13-2005, 07:16 PM

Wrong on both counts.

thewoodman

06-13-2005, 08:04 PM

hey old yeller, I have been reading this string, because I believe attic heat is a big issue in an ongoing problem we are having. I take care of 48 duplexes, and the ACs can be working great but the tennants are very unhappy with the electic bills and they can't get thier homes comfortably cool. I have looked the buildings over and discoverd they have no turbines and no soffits. Only a single vent on the gable ends. I started working here last summer, and fought this problem the whole time. I believe soffits and turbines would help lower the temp. inside. What do you think?
BY THE WAY.. I LIKE YOUR AGRUMENTS OVER THE OTHER GUY, WHO JUST DON'T SEEM TO GET IT...i won't say who,,,but common sense ain't so common, I have been told.

robnjr

06-13-2005, 10:19 PM

Tuccillo:

Worse case day, attic is about 20 deg hotter than outside air with the power ventilator ON, it’s more than 45 deg hotter with it OFF. The power ventilator cuts the maximum Delta-T by more than half…

Uktra:

I understand what you are trying to say, but you don’t think hot air radiates heat???? Like all matter, it will absorb, and then reradiate heat, so take that into account when you say something like “the majority of heat transfer from the attic to the house is through radiation, not convection”….Hot air is ALSO a source of radiated heat….the cooler the air, the less it will radiate….ask a physicists….

uktra

06-13-2005, 11:37 PM

Yes hot air has a very small amount of radiant transfer. What we are talking about is what is the doninant heat transfer mechanism to the rooms below. All you have to do is go into the same size attic (with No openings to the outside) with a metal roof and then go into the same structure with a shingle roof, with the outside temperature the same. Why is the shingle roof space so much warmer than the metal roofed space? The temperature is the same on the outside.

All the folks who have said the bills have gone down haven't eliminated all the variables in a scientific way. No one can claim fact without eliminating the variables like: seperate electric meters, not combining power vents with window solar screens, average temperature readings, exact same performance from the HVAC equipment, and on and on. People selling products and health cures, and gadets you can put on your car to get 60 mpg by personal endorsements have been with us for years.

My profession is to help people design and build comfortable, energy efficient, quality IAQ, durable homes. I recommend ways to do this by learning from the best people in the business who have researched and proven ways to do this based on science, not personal endorsements.

[Edited by uktra on 06-13-2005 at 11:40 PM]

robnjr

06-14-2005, 12:07 AM

Uktra:

If you actually read my post, you would see that I have only changed one variable: the power ventilator thermostat setting (as well as turning it off)…

You claim that the majority of heat transfer from the attic to living space, 85%, is through radiant heating. There seems to be a difference of "opinion":

http://homeenergy.org/archive/hem.dis.anl.gov/eehem/96/960716.html

From the link:
"Radiant Barriers Test Well. Radiant heat gain is an important contributor to a house's cooling load-a single-story ranch home typically gains 30%-50% of its cooling load from rooftop radiant heating"

That's for a single story house. A two story should do better, since the ratio of floor/atic living area is greater. Do you have a source for your 85% claim????

uktra

06-14-2005, 12:15 AM

robnjr--you have a house with no walls or windows?

plano ak

06-14-2005, 01:55 AM

I too live in North Texas and have a adjustable power vent on my roof and yes it saves me money plus one thing noboby mentions is you roof will last longer since the shingles won't have 150F below them...Thanks Tuccillo I'll try your settings I believe mine are very close to yours. I had no whirly birds before the power vent and my AC would run almost nonstop during the 95F+ days and I had a hard time getting below 75F inside now I get well below that until I have to put on a coat!!!

robnjr

06-14-2005, 02:34 AM

Uktra:

Of course I do. Now you're being obtuse, and comparing apples to oranges. I had the same walls and windows before I installed and adjusted the power ventilator thermostat, and the same ones now.....I thought we were talking about the attic, and the power ventilator effect on assisting the AC system. I spent a few weeks collecting data, and the benefit of the PV was obvious. Bottom line is that IF the power ventilator thermostat is set up correctly, and IF there is the proper isolation of the attic/living space, AND adequate soffit vents, it will help your cooling system, not hinder it. I believe that PVs have a bad rap because people don't follow instructions on soffit ventilation, and don't change/clean them (I'll try and post some pics). I would also guess most of them run too much, as I mentioned in my first post. I certainly wouldn't argue that a PV can make things worse in some cases, especially if there is poor attic/living space isolation and lack of clean soffits.

I'm sure a new home can be designed to eliminate the need for the PV, but most of us with existing homes have to make do with a cheaper solution! Also, I'm not saying EVERYONE will get a big benefit from a PV, but saying they NEVER have merit is very close minded IMO.

Plano-AK:

I agree with the roof observation, but wanted to stick to the issue at hand. BTW, Tuccillo was quoting my experiences in adjusting the thermostat, not his....I've collected lots of data to support this (graphs, power meter readings, system usage numbers from the thermostat), and you live close to me, so try the 95 OFF 110 ON setting....only on the worse days will the attic get over 125, and the fan won't run longer than necessary when the sun sets. CHECK YOUR SOFFITS!!!

robnjr

06-14-2005, 03:33 AM

Here are pics of the same soffit vent, about 2.5 years old. Notice that it doesn't look too bad on the outside, and that's close up, not 20 feet up under the eave!!!

http://hometown.aol.com/robnjr/index.html

PS: Please let me know if the link does not work....

[Edited by robnjr on 06-14-2005 at 03:36 AM]

uktra

06-14-2005, 07:33 AM

If I am being obtuse, I sincerely opologise. You are missing the point. If you take what the article stated as fact, (30-50% of the heat load of the home, in a ranch type house is from the roof), how can you sit there and tell me that the dominant transfer mechanism in an attic assembly is not radiant? In a 30x50 ranch you have 1500 sq. ft. of transfer area with an average R-20 to 30 and in the walls you have 1280 sq. ft. (8 ft. high walls) with maybe an average R-8 to 9. If 50% of the total load comes from the roof with better insulation, how much comes from the walls with less insulation? Whatever the exact percentage of transfer of energy by radiant depends on all the details--but it is dominant and you can't flush it with a power vent.

To the other expert on shingle life. Shingle life is only reduced about 5-7% on UNVENTED roofs compared to vented roofs---so just lowering the temperature from 120 or 130 to 100 won't have much affect on shingle life.

tuccillo

06-14-2005, 07:49 AM

Originally posted by robnjr
Tuccillo:

Worse case day, attic is about 20 deg hotter than outside air with the power ventilator ON, it’s more than 45 deg hotter with it OFF. The power ventilator cuts the maximum Delta-T by more than half…

Uktra:

I understand what you are trying to say, but you don’t think hot air radiates heat???? Like all matter, it will absorb, and then reradiate heat, so take that into account when you say something like “the majority of heat transfer from the attic to the house is through radiation, not convection”….Hot air is ALSO a source of radiated heat….the cooler the air, the less it will radiate….ask a physicists….

Thanks for the info on the temperature change with the PV on vs. off. In my previous home (2 story), I had 2 PVs with plenty of soffits and one large, screened gable so I had plenty of venting for the PV. I never got around to doing the on vs. off experiment to see how effective they are. In my current house (a new ranch), I went with a non-ventilated attic - completely sealed with sprayfoam insulation on the underside of the roof sheathing. The attic never gets above 90F even on a hot sunny day. This is the only insulation in the attic. In retropsect, I believe I should have done a radiant barrier (aluminum on the underside of the roof sheathing), traditional blown-in insulation on the attic floor, made sure that every attic penetration was sealed to prevent air from escaping from the inside of the house to the attic, and PVs. I suspect it would have produced the same attic temperatures but cost less money.

uktra

06-14-2005, 08:06 AM

tuccillo--what ever the price difference, if you are now able to put the ducts and air handler in conditioned space, this will save you more on utility bills than the amount of mortgage increase to do this---smart move.

tuccillo

06-14-2005, 09:22 AM

Originally posted by uktra
tuccillo--what ever the price difference, if you are now able to put the ducts and air handler in conditioned space, this will save you more on utility bills than the amount of mortgage increase to do this---smart move.

Hi Uktra,

Yes, that was the reason for doing the sprayfoam - the airhandler and ducts are all in the attic. It is nice to go up there in the middle of the day when it is 85F instead of 140F. There are a number of homes in our area that have also done the non-ventilated attic with sprayfoam. I originally spec'd out a radiant barrier (GP product with foil on OSB) but switched to the sprayfoam instead - the difference was probably about $3K. I would love to see an objective, scientific comparison of non-ventilated with sprayfoam compared to a radiant barrier and either passive ventiation of PVs. Do you know of any? Thanks so much.

uktra

06-14-2005, 09:44 AM

What I recommend doing to create unvented attics is to net and dense pack cellulose. By doing this, the attic is air sealed and insulated--and it is not much more expensive than vented attics. Putting the ducts and air handler in conditioned space is critical.

cem-bsee

06-14-2005, 10:09 AM

better get the facts straight!
little transfer of heat from any attic is via radiation!

if one retofits radiation barriers into an attic, such must be spaced from the roof by at least one inch and have a ventilation path to draw away the hot air transfered from the barrier to the above air space -- one must be careful as to radiation barriers and the roofing materials -- it would be a shame to cause accelerated deterioration just because one did not understand the inner actions.

having soffit vents on opposite sides of a house to allow the prevailing wind to create a negative pressure across the attic space is quite effecient and cheap.

having tall trees to provide shade is also cheap and quite effective -- no spot of my 2100 sf roof has sun more than 2 hours on ANY given day due to 148 tall (~ 40-60ft) trees on my 0.73 acre lot. trilevel house. at 3:30p, all my roof in shade-- I looked while checking my gable vent size & clogging (= NONE on the 0.25 inch hardware cloth of 5 yr ago)

I cooled yesterday with one 5000 btu/hr window shaker in office due to having 2 computers + 17" CRT monitor running from 2:30am onward = have to wear T-shirt & have redirection baffel to keep cold air from me.

uktra: are you doing better/ cheaper? what are YOUR a/c costs per sq ft/ per DD? how long have you kept such records?

BTW, we only reached 89F at the airport 20miles away. --

[Edited by cem-bsee on 06-14-2005 at 10:18 AM]

uktra

06-14-2005, 10:17 AM

Wrong again! I suggest you do a google search on radiant barriers. Manufacturers are seathing foil on the underside of plywood/OSB.

tuccillo

06-14-2005, 10:32 AM

Originally posted by uktra
What I recommend doing to create unvented attics is to net and dense pack cellulose. By doing this, the attic is air sealed and insulated--and it is not much more expensive than vented attics. Putting the ducts and air handler in conditioned space is critical.

I havent looked into the emissivity of the sprayfoam on the underside of the roof sheathing but I suspect it is fairly low but not as low as a radiant barrier. The house is also constructed with ICF and has a two-speed Bryant compressor. I live in SE Georgia and most of the time the compressor runs at 1/2 speed with is 1.5 tons of AC for roughly 3000 sq. ft. Overall, the combination of ICF and the sealed attic seems to work out well.

uktra

06-14-2005, 11:02 AM

ICF construction, while expensive, is an execellent way to build a home. The roof is usually the weak spot in this type of construction to save energy. With your foam sealed roof--that is not the case. Congratulations on building a better home!

P. S. Did you mechanically ventilate?

[Edited by uktra on 06-14-2005 at 11:06 AM]

tuccillo

06-14-2005, 11:24 AM

Originally posted by uktra
ICF construction, while expensive, is an execellent way to build a home. The roof is usually the weak spot in this type of construction to save energy. With your foam sealed roof--that is not the case. Congratulations on building a better home!

P. S. Did you mechanically ventilate?

[Edited by uktra on 06-14-2005 at 11:06 AM]

Hi Uktra,

We decided not to add an ERV at this time. We can add one later on if we decide we need more fresh air. The Bryant Evolution control will seemlessly integrate an ERV into its operation. So far we havent had any issues.

The ICF did cost us some extra - never asked for a breakdown of the cost difference compared to framed construction - perhaps a few percent of the price of the home if I had to guess. We would have done 2x6 framed if we didnt do ICF and that would have cost some extra also. I am quite happy with the ICF and think it is a good way to go in the southeast US because of the termite problem - less wood to eat.

robnjr

06-14-2005, 03:28 PM

Uktra:

You said in the beginning of this thread that "There are NO situations where power vents do anything positive in homes". Then you justify that statement, and dismiss the experiences of others, by saying that radiant heat is the dominate effect, and that air infiltration increases from PVs. Something can be 40%, and still not dominate. That doesn't change the fact that reducing the 40% has no effect....whatever the action of the heat transfer, do you have a SOURCE for your claims that PVs don't work, or make things worse? Of course PVs would not be good if there were other abnormal factors in the home that need correction, like excessive infiltration before the PV was installed.

Despite what others have experienced, you stick with that claim. I guess we''re all hallucinating, and you magically know the conditions of our homes and electric bills!!! Or maybe we're just lying for some reason....

There are some things that make much bigger differences, but what do they cost? I think you miss the point when you compare building a better designed home to improving an existing one that has inherent limitations.....I can't economically move my ducts to a conditioned living space!!! I had to live with what I have, and make econimical tradeoffs in improving it.....

cem-bsee

06-14-2005, 04:04 PM

BTW, my best friend, Tom, a retired rocket engineer, reminded me that the transfer of heat via radiation varries with the fourth power of absolute temperature -- degrees Rankin.

so, going from 155F to 100F has a 3% Rankin temp change = not much driving force.

you asked if one person had isolated the influence of the variables? I ask you, uktra, do you stop & decide which item most influences the apparence of a room when redecorating = painting the ceiling? painting the walls? new carpet? new trim?

I did track some for 2 years, but stopped when the economics were not great individually -- still keep making improvements; eg: cauling above & below baseboard to stop air infiltration, keep dirt from going under the baseboard, stop bugs from coming in -- sealing around all electrical boxes -- biggest influence = adding attic insulation, next = closing the 4x5.5ft gap under family rm windows & insulating that block wall --

uktra

06-14-2005, 05:12 PM

I suggest you folks do some research on the computer. Check out Building Science corp.--Advanced Energy corp.--Florida Power.--Dominion Resources.--Home Energy magazine.

If you want to get technical, you can figure the radiant heat transfer to the attic floor by this formula:
Q=s x(T1 to 4th power-T2 to the 4th power.)

old yeller

06-15-2005, 10:29 AM

Originally posted by tuccillo

Thanks for the info on the temperature change with the PV on vs. off. In my previous home (2 story), I had 2 PVs with plenty of soffits and one large, screened gable so I had plenty of venting for the PV. I never got around to doing the on vs. off experiment to see how effective they are. In my current house (a new ranch), I went with a non-ventilated attic - completely sealed with sprayfoam insulation on the underside of the roof sheathing. The attic never gets above 90F even on a hot sunny day. This is the only insulation in the attic. In retropsect, I believe I should have done a radiant barrier (aluminum on the underside of the roof sheathing), traditional blown-in insulation on the attic floor, made sure that every attic penetration was sealed to prevent air from escaping from the inside of the house to the attic, and PVs. I suspect it would have produced the same attic temperatures but cost less money. [/B]

Wow- leave for a few days and look what happens! I thought for sure I would get accused of re-registering as Robjr and posting that VERY informative temperature data.

Uktra- you said yourself that you help design and build better houses. I think we could all do that just fine. What is more difficult and requires somebody to think outside the box is what to do with an older, as in ALREADY built home.

Tucillo was extremely smart in selecting the "Hot Roof Theory" method of insulation, which, in my opinion, is by far the best method if attic/roof insulation.
My brother in law built a NEW house this year, and when he told the HVAC bidder that he was thinking of going hot-roof (which I begged him to do) the HVAC calculation dropped from 3 AC units for a 7 ton total down to 2 AC units for a 4.5 ton TOTAL!! This single calculation 100% paid for the extra insulation costs and would pay him back every month of his living in that home. I was shocked!

now the downside: The contractor is either stupid or a crook. He must have realized that he would lose money this way, so he then told my BIL that there are NO 80% outside ventilation furnaces. Paying for 90% furnaces in Texas is unbeleivably wasteful. That change increased the HVAC cost and ate up all the savings. My BIL is kind of "tight" so he opted not to go with the hot roof and spend the extra 3-4k to live comfortably and cheaply.

The moral of the story- go build your NEW house however you want and Uktra will give lots of good, informed advice (seriously- no sarcasm). Otherwise- talk to uktra and you may end up tearing off your entire roof and replacing it to the tune of tens of thousands of dollars- only to avoid running a PV at a few dimes per day. This is where the common sense usually kicks in.
Until Uktra goes to every older home mentioned and addresses on a cost-effective basis how to make them all comfortable- the personal experience will trump all studies. For new homes- the sky is the limit.

robnjr

06-15-2005, 01:23 PM

Old Yeller:

Gee, I didn't know I had a clone!!!

I think the main "evil" Uktra sees in PVs is the extra negative pressure, not the "few dimes a day" to run the fan. I agree with him in this regard, BUT if one makes sure soffits are adequate, and the attic is well sealed, the benefits of the PV assisting the cooling system should outweigh the small increase in infiltration. Also, my tests have shown the best ON/OFF thermostat settings, for my home at least....

Whatever the mechanism really is, it works for me: seeing is believing. Probably most people have clogged soffits, and set the thermostat WAY too low, so the PV does make things worse....as you can see, my soffit vents were pretty dirty after only 2.5 years....imagine never changing them???

uktra

06-15-2005, 02:40 PM

Sorry to bust your bubble again boys, but I have delt with exising homes for over 10 years as well as helping folks build new ones. As I have stated before, rather than spend money on a PV that can cause problems and not solve any, one should invest in things like sealing ducts in the attic, sealing holes in the attic, making sure you have enough insulation in the attic. These things will save money and add to comfort, and are much better investments. Again do your research in the locations I mentioned. All of us can learn.

old yeller

06-15-2005, 04:22 PM

Originally posted by uktra
Sorry to bust your bubble again boys, but I have delt with exising homes for over 10 years as well as helping folks build new ones. As I have stated before, rather than spend money on a PV that can cause problems and not solve any, one should invest in things like sealing ducts in the attic, sealing holes in the attic, making sure you have enough insulation in the attic. These things will save money and add to comfort, and are much better investments. Again do your research in the locations I mentioned. All of us can learn.

Dude- talk about learning....

I will repeat myself AGAIN for your benefit.

My house was NEW, with lots of blown in insulation to code.
My house was NEW, with attic gaps sealed w/EF as per CODE.
My house was NEW, with a brand new AC system and double strapped and mastic coated joints.

I covered 5 medium sized double-pane low-e windows with solar screens, 3 of which where under an awning already.

My house would not stay under 80 degrees under any circumstances during the day in August. No kids opening doors, just one person. The house would cool to 78 at about midnight after running 100%.

Again- I don't care about the power meter, so let's leave that out of this. It REALLY didn't matter to me. I was trying to live indoors.

With the PV, The house easily stayed at 78 WITH cycling. I could drop it to 75 at night and it would get there by 10pm. This shoots holes in the solar screen being a large part of the solution. If it was the screens, it would be easier to cool down after sunset, but it wasn't.

My E bills went from max 275 (1440 sq feet!!) one year to no more than 135 the next. I don't need meter readings to tell me how brutally obvious it is that the PV I installed helped tremendously. According the Robnjr's numbers, I even had my thermo set too low at 105. I could climb into my attic and barely break a sweat, although I didn't take temperatures. I didn't need to. My problem was solved, and pretty darn well I might add.

Now you have other examples that DO have specific temperatures and meter readings, and you won't admit that you may not ALWAYS be right.

Trust me on this, we will have much more respect for someone that can admit they are wrong. Maybe a few more days of people telling you are wrong will help.

Also- please pick one dog for your fight. You keep going back and forth between your radiant heat issue and air leaks in the system/house depending on which one you get called out on. Which one is it?

If it's radiant heat, then we have to replace our roofs, which most folks aren't in the mood for. A PV will solve the problem for 2% of that cost.

If it's leaky air, then what if you know there are no/very few leaks? doesn't it still make sense to go ahead and get most of the heat out?

Both arguement are full of holes with absolutley no proof for either one. You haven't been to any of our houses to confirm that we are wrong, so why do you insist we are all hallucinating about our comfort/savings?

[Edited by old yeller on 06-15-2005 at 04:28 PM]

robnjr

06-15-2005, 05:53 PM

uktra

06-15-2005, 06:50 PM

The problem you have is between what you think you have saved by a PV, vs what you can prove you have saved by using a a PV. Like I have said before, there are too many variables that can cause a utility bill to go up or down. Unless you have a separate meter and eliminate the other variables, what you may believe and what is fact are two different things. Too many tests have been run under scientific conditions by too many people with all the variables accounted for, that shows that PV's do NOT save energy. In fact test have proven that they can and do increase energy use in many cases as well as the back drafting problems they can cause. Not only that but they have been a source of fires in the attic. Again, you need to research the web sites I gave you.

old yeller

06-16-2005, 08:46 AM

Originally posted by uktra
The problem you have is between what you think you have saved by a PV, vs what you can prove you have saved by using a a PV. Like I have said before, there are too many variables that can cause a utility bill to go up or down. Unless you have a separate meter and eliminate the other variables, what you may believe and what is fact are two different things. Too many tests have been run under scientific conditions by too many people with all the variables accounted for, that shows that PV's do NOT save energy. In fact test have proven that they can and do increase energy use in many cases as well as the back drafting problems they can cause. Not only that but they have been a source of fires in the attic. Again, you need to research the web sites I gave you.

I my gosh you are a broken record.

I DON'T CARE WHAT I SAVED! I could live comfortably AT ANY COST for the PV! I already had all of your "magic fixes" handled and they did not solve the problem. The PV did. At ANY energy cost. Until you go to that house and prove it didn't- you are dead wrong.

You MUST sell radiant barrier, otherwise you wouldn't be so hardheaded as to tell people that the sky is not blue right in front of them.

We have touched and seen the results. You have read loaded research reports that conveniently support your Radiant barrier sales but have no real world examples of proof like we do. "Setup" houses in the desert don't count, either.

This is called PROOF versus THEORY, and your theory loses in these situations.

uktra

06-16-2005, 09:10 AM

I don't sell radiant barriers--but you need to learn more about them. If doctors used your form of "proof" we would all be dead at an early age.

tuccillo

06-16-2005, 09:43 AM

Just out of curiousity, you didnt happen to have your AC serviced and perhaps the improvement was do to service on your AC that made it perform better?

Originally posted by old yeller

Originally posted by uktra
The problem you have is between what you think you have saved by a PV, vs what you can prove you have saved by using a a PV. Like I have said before, there are too many variables that can cause a utility bill to go up or down. Unless you have a separate meter and eliminate the other variables, what you may believe and what is fact are two different things. Too many tests have been run under scientific conditions by too many people with all the variables accounted for, that shows that PV's do NOT save energy. In fact test have proven that they can and do increase energy use in many cases as well as the back drafting problems they can cause. Not only that but they have been a source of fires in the attic. Again, you need to research the web sites I gave you.

I my gosh you are a broken record.

I DON'T CARE WHAT I SAVED! I could live comfortably AT ANY COST for the PV! I already had all of your "magic fixes" handled and they did not solve the problem. The PV did. At ANY energy cost. Until you go to that house and prove it didn't- you are dead wrong.

You MUST sell radiant barrier, otherwise you wouldn't be so hardheaded as to tell people that the sky is not blue right in front of them.

We have touched and seen the results. You have read loaded research reports that conveniently support your Radiant barrier sales but have no real world examples of proof like we do. "Setup" houses in the desert don't count, either.

This is called PROOF versus THEORY, and your theory loses in these situations.

uktra

06-16-2005, 09:56 AM

That is one of the "variables" I mentioned.

old yeller

06-16-2005, 09:57 AM

oops

[Edited by old yeller on 06-16-2005 at 10:01 AM]

old yeller

06-16-2005, 09:59 AM

Originally posted by old yeller
[QUOTE]Originally posted by tuccillo
[B]Just out of curiousity, you didnt happen to have your AC serviced and perhaps the improvement was do to service on your AC that made it perform better?

Nice try... no. The PV was put in after 4 visits from the AC installer and the builder accomplished nothing. They just kept looking at each other going "Well, the calculation says it's correct, and it's running the way it's supposed to.." Couple of inbred crooks. probably married each others sister or something.

You can't really think I would get into this converstaion and then go "oh yeah.. I did replace my entire AC system..duh"

Don't be ridiculous. If you are losing the arguement, don't try to change the subject. My wife does that.

tuccillo

06-16-2005, 10:54 AM

Originally posted by old yeller

Originally posted by old yeller
[QUOTE]Originally posted by tuccillo
[B]Just out of curiousity, you didnt happen to have your AC serviced and perhaps the improvement was do to service on your AC that made it perform better?

Nice try... no. The PV was put in after 4 visits from the AC installer and the builder accomplished nothing. They just kept looking at each other going "Well, the calculation says it's correct, and it's running the way it's supposed to.." Couple of inbred crooks. probably married each others sister or something.

You can't really think I would get into this converstaion and then go "oh yeah.. I did replace my entire AC system..duh"

Don't be ridiculous. If you are losing the arguement, don't try to change the subject. My wife does that.

Whats this "nice try" crap? It was a legitimate question. I am not losing any arguments cause I didnt start any arguments. I dont know what your problem is but you are acting like a jerk.

uktra

06-16-2005, 11:25 AM

Maybe he is a power vent salesman coming out of the closet!

robnjr

06-16-2005, 11:53 AM

Originallyposted by tuccillo
Just out of curiousity, you didnt happen to have your AC serviced and perhaps the improvement was do to service on your AC that made it perform better?

What about my findings??? AGAIN, I clearly stated the ONLY thing I changed was my PV thermostat setting, as well as turn it off..I did this for several weeks, in midsummer, weather almost exactly the same day to day (those hot Texas doldrum days) with my computer graphing the results. I also made clear that the PV has optimal settings (they should not run more than necessary), and need maintenance, but I guess all my points about PVs and my pictures of clogged vents fell on deaf ears....

Uktra:

What's this BS about separate meters?? If my total system USAGE dropped, as shown by my thermostats, and my ONE meter (the only one that the power company uses to bill me!!!) shows a drop, why do I need another meter?? What does that prove....please explain, as I'm only an EE....

Source of fires?? How exactly?? Any electrical equipment can cause fires if not maintained, or installed correctly.... I'm sure I can find a link showing toasters burning down homes....the question is, why would a PV pose any more risk than other equipment in my attic???

old yeller

06-16-2005, 01:00 PM

That wasn't directed at you, tucillo. Read uktras post in reference to yours and put down the gun :) I would at least hope that you would think that I took that into consideration before having this conversation.

I won't deny that I could be a PV salesman, but at least I would know when it is a wrong situation and when it can help. Your PV equivalent would be: "Nothing else works, power vents are proven beyond any reasonable doubt to cool your house down and save you money. I won't hear any other information about it"

Does that put it in perspective for you?

pstu

06-16-2005, 01:53 PM

I admire the heck out of Robnjr for being methodical in measuring what works with his power vent situation. Not many people are logical enough to take measurements, let alone try one variable at a time.

I *have* been measuring my attic temperature, and have extreme trouble believing any of the "150 degree" statements that are thrown out so casually. If it were that hot, you could literally do without the hot water heater so long as there is enough piping run (or tank) in that attic. And it would be hot enough to scald. Really I don't think that is the case. My own temperatures seldom if ever exceed 115 in this locale west of Houston TX. This is still hot enough to be a hazard to the working men who sometimes have to go up there in the summer. I won't claim this is typical but certainly do not believe it to be abnormally low. Again, if anyone wants to back up that 150 degree claim, I would appreciate seeing a link so I can learn more.

Damn few things can produce a 50% reduction in electric consumption. With Old Yeller it seems more reasonable to believe in magic, than to believe here was a situation where a power vent made a big difference in energy use. I have seen electric customers get very confused as to measuring what they use and pay for, and would want to look very closely for external factors that affect Yeller's billing. I'm not closed minded here but very skeptical -- it seems to contradict all published research that I have seen.

Best wishes all -- P.Student

[Edited by perpetual_student on 06-16-2005 at 09:22 PM]

robnjr

06-16-2005, 02:23 PM

Perpetual Student:

I posted a pic of one of my attic temp graphs for this week. I have slowly been turning the PV thermostat up, to see what the max attic temp will be....I haven't unplugged it yet this year (actually, its been some time since I last have done any of this stuff), but I thought after reading this link I would try experimenting again, and reevaluating the PV:

http://hometown.aol.com/robnjr/index.html

Scroll down past the vents to the graph...You can see how the slope of the graph decreased yesterday after the vent came on....look at the top graph: you can see the temp level out as the fan came on at 119.1....I had the same thermostat setting yesterday, and the max attic temp was 124.3.....what would it have been if the fan was off??? Stay tuned for more tests.....

PS: Its 100 deg today, with extreme UV index, +10....
PPS: Top graph is really last 42 minutes, not 24..

[Edited by robnjr on 06-16-2005 at 02:28 PM]

uktra

06-16-2005, 02:26 PM

I hear the closet door opening now.

Attic temps are not the point--the point is how much energy is transfered to the air in the rooms below. That is what the HVAC has to control and how much energy is used.

[Edited by uktra on 06-16-2005 at 02:34 PM]

old yeller

06-16-2005, 02:37 PM

Originally posted by perpetual_student
I admire the heck out of Robinjr for being methodical in measuring what works with his power vent situation. Not many people are logical enough to take measurements, let alone try one variable at a time.

I *have* been measuring my attic temperature, and have extreme trouble believing any of the "150 degree" statements that are thrown out so casually. If it were that hot, you could literally do without the hot water heater so long as there is enough piping run (or tank) in that attic. And it would be hot enough to scald. Really I don't think that is the case. My own temperatures seldom if ever exceed 115 in this locale west of Houston TX. This is still hot enough to be a hazard to the working men who sometimes have to go up there in the summer. I won't claim this is typical but certainly do not believe it to be abnormally low. Again, if anyone wants to back up that 150 degree claim, I would appreciate seeing a link so I can learn more.

Damn few things can produce a 50% reduction in electric consumption. With Old Yeller it seems more reasonable to believe in magic, than to believe here was a situation where a power vent made a big difference in energy use. I have seen electric customers get very confused as to measuring what they use and pay for, and would want to look very closely for external factors that affect Yeller's billing. I'm not closed minded here but very skeptical -- it seems to contradict all published research that I have seen.

Best wishes all -- P.Student

That's totally cool that you question it- you see, the difference here is you are skeptical, and uktra is calling myself and Robnjr liars. I am waiting for him to tell me the sky I'm looking at isn't blue.

I have tried to give every bit of information about my situation that can be given, including windows counts.

Please don't focus so much on my dollar savings. Please read the posts where I am trying to explain that I really wasn't trying to save money. That was just a side benefit. I didn't care if it made my bill go up!

I was trying to live in a home that would not cool off, and with the PV, it would cool off quite easily. The numbers and temps I gave are not exaggerations, and are not scientific as Robnjrs are, but I was there and I lived in that house and paid the bills.

uktra

06-16-2005, 02:45 PM

Old Yeller --please come out of your PV seller closet, but please don't put words in my mouth. I never called anyone a liar. Just because there is no provable cause-effect doesn't meen you don't believe what you believe--many reputable scholars thought the earth was flat and no one called them liars--just wrong.

old yeller

06-16-2005, 03:04 PM

Originally posted by uktra
Old Yeller --please come out of your PV seller closet, but please don't put words in my mouth. I never called anyone a liar. Just because there is no provable cause-effect doesn't meen you don't believe what you believe--many reputable scholars thought the earth was flat and no one called them liars--just wrong.

You make a good point, but you keep trying to tell me I didn't experience what I experienced: A decent living environment. You keep trying to say the PV doesn't work, when it DID in my situation, even in light of some other small problems it may have caused and regardless of energy consumption. I truly don't know of any problems in my situation, but I didn't care- I know it can cause problems- I never arugued that.

If you want to say that they are not efficient and can "amplify" other problems, I will stand behind you 100%. That is not what I am arguing, but you still won't listen.

Good analogy- if columbus got back to spain and you said the earth is flat no matter what he saw, you would be calling him a liar. Just because the word liar doesn't come from your mouth doesn't mean anything. This is the exact same situation. You are trying to tell me I didn't live what I lived. You are calling me a liar. Are you going to call Robnjr a liar by telling him his attic temperatures didn't decrease even in the face of his scientific evidence? I am not putting that word in your mouth, I am just asking.

robnjr

06-16-2005, 03:07 PM

Uktra:

In Engineering there is a method called "the principle of extremes." If you're not sure if something has an effect, you do a thought experiment, and then measure to confirm. Something like this:

1) If attic air temps were 1000 deg (no matter what the source of the heat), would that affect my AC efficiency??? Most likely yes!!!
2) If they were 75 deg, the same as inside temps, would they? Probably not...
3) Therefore there must be SOME temp in-between where it does matter....what is that temp??
4) Experiment, measure, observe....first do a control with PV OFF, and then try various thermostat settings, and correlate. I did that, and attic temps above (about)115 **DO** increase AC USAGE (for me at least...the AC thermostat usage-hours go UP): More power is now consumed by my AC system than that used by the fan...significantly more than the fan uses, in fact...

Do I need to post more pics to prove it? Pics of my meter, usage numbers, etc, etc....

I'm not claiming any 50% reductions in my bill, but I calculate (and see on the usage hours!!) the PV saves about 5% of my cooling costs....not a huge amount, but it is there....That is MY experience, but maybe it won't be the same for others (who don't have their blowers and ducts in the attic, for example)....certainly a PV is of minimal value if the PV thermostat is not set correctly, or creates excessive negative pressure due to lack of clean soffit vents....Since it works for ME, and others who have posted here, your statement that "they never do any good" is FALSE....that's it in a nut shell....

robnjr

06-16-2005, 03:27 PM

Old Yeller:

""Are you going to call Robnjr a liar by telling him his attic temperatures didn't decrease even in the face of his scientific evidence? I am not putting that word in your mouth, I am just asking.""

I think Uktra's point is that Attic air temps don't effect the inside temps, but whatever they effect, I have proved to myself that they do (again, for my home) have an influence on AC ***USAGE-HOURS*** You don't even need a thermometer or to graph it like I did....if your AC system has a thermostat with a "usage-hours" function, just look at those numbers with the PV OFF, or at various PV thermostat settings, while maintaining the same inside temps on days with similar weather...keep a log, and you'll see the obvious usage variations as you play around with the PV...an attic thermometer is not even needed....adjust your PV for the minimal AC usage-hours if saving money is your goal.....if comfort is the goal, just set it accordingly......Personally, my family is perfectly comfortable with the PV set for minimal AC usage-hours..

I rest my case in this subject!!!

uktra

06-16-2005, 03:32 PM

I never said there was no energy transfer from hot air to the rooms below--there is. The energy is transfered by both conduction and convection. Convection depends on total holes size and temp difference. The problem with PVs is that the amount of energy saved by lowering the attic air energy transfer is more than offset by the cost of electricity to run the fan and the amount of infiltration increase the fan will produce. And please, dont't tell me about the free soffit-gable sq. area vs the sq. ft. area of the roof. The fan puts a negative pressure on ANY hole from the lower rooms to the attic. Tests on many homes by many people have shown that the infiltration rate goes up by 30 to 100%. Again there are too many variables one has to account for in YOUR situation to say you saved 5 % from the PV. You sound like an educated person, I emplore you to do the research on the sites I mentioned.

old yeller

06-16-2005, 03:38 PM

Originally posted by robnjr
Old Yeller:

""Are you going to call Robnjr a liar by telling him his attic temperatures didn't decrease even in the face of his scientific evidence? I am not putting that word in your mouth, I am just asking.""

I think Uktra's point is that Attic air temps don't effect the inside temps, but whatever they effect, I have proved to myself that they do (again, for my home) have an influence on AC ***USAGE-HOURS*** You don't even need a thermometer or to graph it like I did....if your AC system has a thermostat with a "usage-hours" function, just look at those numbers with the PV OFF, or at various PV thermostat settings, while maintaining the same inside temps on days with similar weather...keep a log, and you'll see the obvious usage variations as you play around with the PV...an attic thermometer is not even needed....adjust your PV for the minimal AC usage-hours if saving money is your goal.....if comfort is the goal, just set it accordingly......Personally, my family is perfectly comfortable with the PV set for minimal AC usage-hours..

I rest my case in this subject!!!

I understand his point, but it is possible that with your proven reductions in static air temperature you have managed to reduce the extremes of your AC systems working environment. Which in your case has helped, it sounds like.
It is also possible that the same reduction helped my AC system among other things, but I didn't measure temps, so I can't prove that.

robnjr

06-16-2005, 04:01 PM

Holy Cow, Uktra, you are stubborn!!!

Lets boil everything down to POWER USAGE, and ignore everything else (attic temps, holes in the attic to living space, etc):

1) My PV uses 1/8 the power of ONE of my compressors....throw in the condenser coil fan, and indoor blower, and its now about 1/10.....so 1 hour of ONE of the AC system running equals 10 hours of the PV being on....
2) On a typical hot summer day my PV runs about 8 hours....
3) If I disconnect my PV, my total AC usage-hours goes up by about 1.5 hours (.8 for upstairs system, .7 for down)....this equals 15 hours of the PV running, but it only ran for 8.....the cost of running the PV has paid for itself almost twice over.....
4) I have confirmed this over and over, on more than just one day, but many days with similar weather....

CASE CLOSED.....I'M DONE.....

pstu

06-16-2005, 09:53 PM

We seem to have a case here where something is not *supposed* to deliver results, but at least in one or two cases it does deliver. As in the bumblebee which legend says, is not supposed to fly but obviously does. Robnjr's information seems unlikely to be faulty, the amount of detail and the background in engineering makes me a believer of this experiment.

Yet in general there is a concensus that a power ventilator is voodoo, something with a price tag which does not deliver. I respect all of the links that Uktra has shown us. What is the difference between Robnjr's case and the typical one? This is so much effort that it may have to remain a rhetorical question, but I would find it very interesting to list all the differences that we think exist. Something in there apparently makes the difference so that the power ventilator saves more energy than it consumes.

Robnjr has given careful attention to the thermostat temperatures, and learned that the lower one is the more important. Is that sufficient to explain his success?

The observation that infiltration typically rises 30% or so when using a power ventilator, is an important one. But I would be cautious to think that applies in every case. Since so many houses are built with deliberately leaky ceiling cannister lamps, that factor alone ought to result in a noticeable leakage rate in the average house. But some houses have tons of those lamps and some have sealed ones, or no cannister lamps at all. I submit that if we knew the infiltration rate of each house under controlled conditions, that would help us make sense of the results. But since that implies a blower door test for each house, we are unlikely to get such results -- unless they are in a designed experiment such as certain research institutions are doing.

Anyhow, if we don't have some *really* thorough professionals help us figure out what factors make the difference... I am not likely to have enough education and brainpower to figure it out myself.

I always am intrigued when someone credibly reports something that does not fit my world-view. It shows me that more learning is needed and gives a hint as to what.

Best wishes -- P.Student

P.S. I cannot bring myself to use the "PV" abbreviation for "power ventilator" since I have always seen it refer to "photovoltaic".

old yeller

06-17-2005, 05:32 AM

wow- very well put.

For the record, I agree with all of the reasons why PVs can be wrong. But I think you are correct- it isn't "supposed" to help, but despite itself, it did in a few cases.

eve

06-26-2005, 03:50 PM

Thanks everyone for the interesting and helpful comments.

For the record I replaced my broken power vent with a Lomanco aluminum turbine. First thing in the morning it isn't turning. But as the outside temperature rises, it starts turning and continues to spin throught the heat of the day on its very functional ball bearings.
I bought it at West End Lumber. One of the guys there said that it's the best attic turbine available and that Houston's too hot to have a power vent because they burn out so fast.

Anyway, my attic seemed to only reach about 104 degrees F. I'll have to check it again since I had the turbine installed.

If I were building a new home I'd sure look into some of the suggestions here on reflecting roof material and better insulation.

I hope to get up the initiative to clean the soffit vents if I can get to them and perhaps to lay more insulation in the attic. The house stays cool enough but I'd love to get my A/C bills down. I have reflective film on all windows which does a great job.

Thanks, again, everyone.

Xavier

06-26-2005, 06:00 PM

Eve, it is me who recommends Lomanco Turbines. I have been using them for a long time since they meet the Florida Dade Country Hurricane specs. I have also been using Turbines on my homes since the early 60”s.

You made a good choice in using Lomanco Turbines rather then power or solar vents, better ROI!

My understanding of how the floor of the attic changes temperature in the summer is: Radiation heats the roof shingles, then conduction through the roof shingles and wood, then convection to the floor. Therefore, if you exchange the air in the attic, it will reduce the heat transfer to the floor! With my three Lomanco Turbines at 5 MPH wind, there is an air exchange in the attic every seven minutes.

I agree with the comments on soffit vents getting dirty and must be cleaned. This also applies to ridge vents. Another reason for Turbines.

eve

06-26-2005, 07:57 PM

Thanks, Xavier.
I am very satisfied with this Lomanco aluminum turbine.
I love saving energy for ecological reasons too. So a wind driven (breeze driven) turbine is cool...no pun intended!

tuccillo

06-27-2005, 08:26 AM

I believe the primary mechanism of heat transfer to the floor of the attic is radiative transfer. The hot underside of the roof radiates. If also transfer heat to the air of the attic through conduction.

Originally posted by Xavier
Eve, it is me who recommends Lomanco Turbines. I have been using them for a long time since they meet the Florida Dade Country Hurricane specs. I have also been using Turbines on my homes since the early 60”s.

You made a good choice in using Lomanco Turbines rather then power or solar vents, better ROI!

My understanding of how the floor of the attic changes temperature in the summer is: Radiation heats the roof shingles, then conduction through the roof shingles and wood, then convection to the floor. Therefore, if you exchange the air in the attic, it will reduce the heat transfer to the floor! With my three Lomanco Turbines at 5 MPH wind, there is an air exchange in the attic every seven minutes.

I agree with the comments on soffit vents getting dirty and must be cleaned. This also applies to ridge vents. Another reason for Turbines.

old yeller

06-27-2005, 02:03 PM

Tucillo,

I completely agree with you on turbine ROI, but we should keep in mind that in some situations, comfort comes at a price.

Some people are concerned about efficiency and savings.

Some are just trying to be comfortable at any (reasonable)price. As in, they can't just replace a 7k HVAC to try and solve a problem. They have to live with most of what they have; roof, HVAC, poor construction, etc...

It sounds like Eve is in really good shape with a turbine for the situation. 104 seems VERY good for a Houston attic. I would love to have that in Dallas. Mine are about 120-130 with new turbines.

smp7015

06-28-2005, 01:41 AM

Squashing the quam's of heat transfer.

Based on the study of thyrmodynamics and fire science.

I believe everyone is missing the point about attic temp.

Everyone that lives up north just think about the principle of layer's: You dress in layer's to block air which act's as an insulator.

Your attic work's the same way. Radiant heat from the sun or a fire travel's as waves such as infared light. That wave will go through a water curtain or window. It doesn't stop until it hits a solid object. (I.E. your roof) From there the heat is transfered to the attic through conduction. Radiant heat doesn't go through your decking it is transfered. Radiant barrier's help reduce this by "reflecting" back the heat produced by the radiant heat hitting the shingle's on your roof. Through the course of the day the heat that is transfered by conduction raises the one good insulator in your attic, "The Air". Your insulation is there to keep the heat from the attic air being transfered to your house. This will only happen as long as the insulation doesn't absorb its full amount of heat. Once the insulation absorbs the total amount it is voided.

You can use this same princple with the gear fire fighter's use. If you are in a building and you sit right in front of a fire your gear will heat up much faster because of the radiant heat "light" coming from the fire compared to if you are behind a wall which blocks the radiant heat.

To me replacing the attic air with cooler air makes since. This would allow the "new" cooler air to absorb more heat off the roof before it is transfered to your insulation or duct's, or plenum.

Now what is the temperature at which your attic has to get to affect all these facet's I don't know. If you live in a hot weather climate I would believe that increasing your attic venilation would make perfect since but just as my mother said when I was a kid "too much of a good thing is bad." How is that you say? Because if you don't have a proper balance of the use of electicity or pressure you could negatively affect your desired outcome.

For all the HVAC pro's out there just think of it as putting a 5 ton system in where a 3 ton will do the job. Sure it will cool faster but you will have a humidity problem and use to much energy.

As for my house I am having serious problems with not being able to get to design temp during the middle of the day. It's probable a combination of the system being designed at or bellow the desired capacity, high attic temperature's, cooling loss from the duct's.

"Everything is a balance and is in a sybiotic relationship"

Just basing my thought's from my studies as an engineer and a professional firefighter.

uktra

06-28-2005, 07:55 AM

Smp7015--You need to go back to class. The best insulator in an attic is not moving air. The best insulator in your attic is insulation that traps air. The problem with your explanation is the fact that the roof sheathing and support framing emit radiant energy to the cooler attic floor below and that this is the dominant source of heat transfer through the insulation.

old yeller

06-28-2005, 03:47 PM

You're WAY off- heat radiates from everything- including us humans. Not just things that are burning.

Try solar screens to ease your heat load.

Carnak

08-01-2005, 07:25 PM

Uktra, if you are still following this thread, drop me an email, address is in my profile.

Looking at some cases of a power venter creating a negative leading to some major condensation

[Edited by Carnak on 08-01-2005 at 09:29 PM]

old yeller

08-02-2005, 08:56 AM

Condensation where? On the unit? In the house?

Just curious.

Carnak

08-02-2005, 08:59 AM

Inside building cavities

08-03-2005, 01:47 AM

Hey, Uktra, can you point me to some unbiased scientific evidence to support your contention that the primary transfer from roof deck to attic floor is through radiation?

I'm no genius, but I figure if this is true, I better start putting up some mirrors up there...:)

Carnak

08-12-2005, 09:50 PM

Its looking like attic exhaust fans are causing depressurization of small buildings. Serious condensation occuring.

[Edited by Carnak on 08-12-2005 at 09:52 PM]

old yeller

08-13-2005, 12:21 AM

That's understandable around here. In some areas the big new McMansions have 5 or 6 PVs running at one time. This is the kind of situation I said was BAAAD news.

They can vacuum the carpet by holding a hose up to the wall plug outlet- sucks it right up...

pstu

08-13-2005, 12:43 AM

Dx said:
>>Hey, Uktra, can you point me to some unbiased scientific evidence to support your contention
>>that the primary transfer from roof deck to attic floor is through radiation?

>>I'm no genius, but I figure if this is true, I better start putting up some mirrors up there...

The "mirror" part is almost true. It is called "Radiant Barrier" and the most efficient form looks a lot like aluminum foil on a paper backing. Blocks around 98% of the heat energy and would be irresponsible to build a new house in Texas without this stuff or equivalent.

You can also spray on a paint form which is less efficient but far less labor for a pre-existing house. If you are building new, the right thing to do is just specify radiant barrier combined with the roof sheathing, that way there is no added labor cost and little material cost.

This is a long summary of attic research, compiled by Florida Solar Energy Center:
http://www.fsec.ucf.edu/bldg/pubs/literature/DCA_sealed_attic_5_31.pdf

I believe somewhere in this 60-odd page report is unbiased scientific evidence, documenting that radiation from roof sheathing is a primary mechanism of transferring heat to conditioned space. Not convection. However if HVAC ducts are in the attic, they also provide a large amount of undesired heat transfer. There is a ton of info in this report and I am in the process of perusing it myself.

Hope this helps -- P.Student

08-13-2005, 01:32 AM

No, people, the fans are not causing depressurization of buildings. That was caused by the idiot who forgot to plug the holes in the ceiling. Now, if you don't want to plug the holes, just provide a second fan blowing an equal CFM of air into the attic. And yes, the admission fan has to be installed so it doesn't blow rain water into the attic. Otherwise we're going to read how fans are causing rust, wood rot and mold.

Perpetual student, keep studying. Let me know when you find that data in the 67-page report:) I'm guessing if uktra had any data, he would have presented it by now. My hat is off to Robnjr. When it comes to engineering, data talks and BS walks.

By the way, uktra, you don't even need an experiment. You can easily calculate the radiant, convective and conductive transfer in a simple attic space. The thermal properties and emmissivities of the materials involved are easily found. Pick some temperatures, some air speed/no speed and show us the calculations. I'll even let you use a flat roof so you don't have to do trigonometry.

Carnak

08-13-2005, 10:58 AM

Well given that the main purpose of attic ventilation is to prevent ice dams and I am in a year round cooling environment, I do not believe the fans are a good idea.

A vapour barrier in the north especially a well sealed one, stops airflow as well. Easy to apply - poly on the under side of truss chords. Use proper electrical boxes that are sealed or covers that seal them off. Seal all holes for wiring in top plates of walls. Pot lights are a little more challenging.

Except in a year round cooling environment, vapour barrier on the underside of trusses is a disaster waiting to happen. Pretty hard to seal above the truss chords on top of the insulation.

We could try to seal every penetration of the sheet rock ceiling, and as well as all holes through the top plates of the walls, just so we could power vent the attics (to avoid all these tropical ice dams).

It is sort of analogous tho to wearing a condom and screwing a hooker with aids. Maybe it is better to avoid the infected skank in the first place.

The ceiling holes will be sealed, to reduce the pathways that allow natural infiltration of humid air. This will be retrofitted sealing on pre-manufactured modular buildings, factory built and imported from the USA.

In my situation the attic fans were causing the indoors to be on average,-0.009" with respect to the outdoors, as I measured with a Shortridge micromanometer.

-0.009" sounds like peanuts but this exceeds levels that have been published and proven to have repeatedly caused millions of dollars of water damage to hotel walls. See ASHRAE's Humidity Control Design Guide where I just plagerized this comment from.

Pre-manufactured buildings, majority of the load was internal, lights and occupants. Humidity was high due to constant infiltration of humid air due to negative pressure and occupants were lowering thermostat settings down so that the AC system ran constantly to try and be comfortable. In many situations the thermostats were turned all the way down.

Supply duct leakage doubled the depressurization level compounding problem. With space occupied during the day, systems running steady could only pull temperatures down to low 70s. Occupants uncomfortable still, with 75% RH.

With space un-occupied, the majority of the load (people and lights) is gone and at night, the space would get down into the low 60s with the AC cycling off. Humid air was still trickling in all the time from cheap atttic fans with stuck thermostats changing the attic air 12 times an hour.

Easy to get water in building cavities when ambient dewpoint is near 80F. High indoor RH slows down mositure diffussion through walls to room air so water flows down into floor space and collects in vapour barrier in crawlspace on underside of floor. Only gallons collected and floor tiles lifting up.

Attic fans a good idea? Not here!!! Let the insulation do its job on the sensible heat, stop the fans to eliminate latent heat.

I investigated another situation where massive condensation was occuring and was a result of negative pressure. The owners recycled a design that "Worked great in Arizona", but is just a little more humid here. Each cliamte has its own problems, but in a humid climate you do not want negative pressure.

Radiation, well lets say and attic with insulation on the bottom of the truss chords gets a 140 air temp. Still with no air moving through the fiberglass insulation, let insulation do its job.

Put reflective bubble wrap below roof sheathing, and maybe attic gets up to 105F. R-value of bubble wrap the big factor or the reflection. My vote is reflecting away the radiant heat. Not read about, just experienced.

You guys need to cut uktra some slack, beacause I think he is right on target.

pstu

08-13-2005, 12:42 PM

I can see how it is burdensome to read through a 67-page paper, here is a shorter one. These I located using a Google search "FSEC ATTIC RADIATION CONVECTION".

From the University of Florida, first published in 1986:
http://edis.ifas.ufl.edu/BODY_EH245 or
http://edis.ifas.ufl.edu/pdffiles/EH/EH24500.pdf

A 5-page paper in PDF format. On page 3 it says "most of the solar gain absorbed by the roof is transmitted down to the attic floor by radiation."

From the City of Austin TX, Sustainable Building Sourcebook:
http://www.ci.austin.tx.us/greenbuilder/srcbk_4-12.htm

"In hot weather, almost all of heat gain in buildings is from radiation, and most of this is from radiation striking the roof. This heat is absorbed by the attic insulation and eventually moves through the ceiling into the occupied space. A roof radiant barrier system keeps the attic up to 30 degrees cooler, and reduces heat transfer into the occupied space up to 40 percent in the hottest part of the day."

Hope this helps -- P.Student

[Edited by perpetual_student on 08-13-2005 at 02:00 PM]

08-13-2005, 12:52 PM

Carnak, the main purpose af attic ventilators is NOT to prevent ice dams. It is to ventilate the attic (duh!) and try to get it to close to the same temp as OAT. For whatever purpose you want. If you don't need or want the attic at OAT, don't use them.

Nobody is arguing with you about depressurization. It's not good. So just put some supply fans in the attic to push equal CFM in. Is that concept too difficult for you? I could install a fan in less time than it took you to write that long post.

08-13-2005, 01:49 PM

Student, yes it does say that. Then they produce experimental data that flatly contradicts it. Look at Figure 3. Check out the "temperature at the ceiling" (diamonds) graph. That's what heats the interior of the house. Notice how they are almost identical, but the continuous line (radiant barrier) shows a HIGHER temperature than the dotted line (standard roof) both during the day and at night. Translation for you: the radiant barrier side did WORSE than the standard roof in a side-by-side experiment.
The University of Florida is not exempt from the first law of engineering: data talks and BS walks.

[Edited by dx on 08-13-2005 at 01:52 PM]

pstu

08-13-2005, 02:03 PM

So DX, you are alleging that a radiant barrier INCREASES cooling load?

I found a 2nd reference and edited the prior post to include it. It is from the City of Austin TX, supports the original statement. They in turn trust the info from FSEC and reference it. If you are saying what I think you are saying, there are a whole lotta builders, scientists, engineers and homeowners who are using radiant barrier based on an unfounded myth. Over and over I hear stories from people who have personally felt the benefits of RB on their skin. Myself included.

Analyzing convection effects in attics is *not* a simple problem. I have found one good FSEC paper studying this, but the math and engineering models they use are just too far over my head.
http://www.fsec.ucf.edu/bldg/pubs/stratified/

One observation I would make is, they found important air temperature differences in different parts of the attic. On the order of 21 degrees F. That would seem to argue against convection being an important factor in moving heat energy from the roof to the attic floor. At least it strikes me that way.

Hope this helps -- P.Student

Regards -- P.Student

[Edited by perpetual_student on 08-13-2005 at 02:19 PM]

08-13-2005, 02:42 PM

No, student, I am not alleging anything. The study you quoted does. Before you brush it aside, answer how Figure 3 (their data) supports radiant barriers.

08-13-2005, 03:24 PM

Nobody disputes the usefulness of radiant barriers, when properly applied. We simply dispute the assertion that they are a cure-all. Uktra states that radiant is dominant. To me dominant means 90%. If to you dominant means 30% or 40% then we agree (although remedial English may be in order for one of us).
Here is a case in point. I have done a house with flat roof. EPDM is flat black, so plenty of solar absorbtion. But it gets dirty, i.e. lighter than black. EPDM must be installed on iso board, pretty good insulator. 2" is about R13. The attic space is ventilated with simple soffit and top vents, no power vents or turbines. Underside of roof deck is only about 10deg above OAT on hot days. So radiant is close to zilch. Radiant needs delta T.
By ventilating (power or otherwise), you move ambient air through the attic. This cools the underside of the roof deck by convection. Once cooler, the underside of the deck radiates less. Remember, if the underside of the deck is at the same temp as the top of the ceiling insulation, radiation gain is zero.

Carnak

08-13-2005, 06:53 PM

Originally posted by dx
Carnak, the main purpose af attic ventilators is NOT to prevent ice dams. It is to ventilate the attic (duh!) and try to get it to close to the same temp as OAT. For whatever purpose you want. If you don't need or want the attic at OAT, don't use them.

Nobody is arguing with you about depressurization. It's not good. So just put some supply fans in the attic to push equal CFM in. Is that concept too difficult for you? I could install a fan in less time than it took you to write that long post.

I commented on attic ventilation being implemented to stop ice dams, which it was. Research the concept, attic ventialtion was developed in the north. Ventilation and can be passive or induced. I have no threat of ice dams down here, therefore no requirement to vent an attic.

Not venting the attic and blowing icynene on the under side of the roof pitch and down the walls, looks like they way to go in a humid climate such as mine.

All attic ventilation does in a humid climate is allow humidity in.

I understand many concepts DX including the path of least resistence. Good luck with your balanced fan ventilation scheme.

Carnak

08-13-2005, 07:09 PM

Originally posted by dx
I could install a fan in less time than it took you to write that long post.

Probably could install two in the time it took you to read. Next time try not moving your lips when you read or sounding out the long words :)

08-13-2005, 07:39 PM

Carnak, it took surprisingly little time to read. I just scanned it. Yada-yada, there are all these terrible problems caused by those big, bad PVs. The end is near. Wait a second, what's this about hookers? I better read this part slowly a few more times and do some research...:) Glad it all had a happy ending for you. You're my hero. Say, how did you get that data about hookers with aids...?

Carnak

08-13-2005, 07:49 PM

You must be from Livonia

pstu

08-14-2005, 01:41 PM

I have tried to look at that notorious "Figure 3" and just cannot see in it what DX says he sees. The physical graph just does not have the resolution to be completely legible. There are 10 lines plotted on that one graph, which probably is wonderful if you are looking at the original in color.

I do know what the text says, and will try to keep an open mind as to any weirdness when I read future papers on the subject.

Regards -- P.Student

old yeller

08-14-2005, 08:54 PM

It's funny how nobody seem to bring up the simple fact that IF radiant barriers work, then they work BOTH ways.

What this means, very simply, is that when the heat gets through, and it eventually will, the radiant barrier acts to HOLD IT IN!

Radiant barrier roofs are very well known (by those who pay attention) to cause extended heat gain into the interior space AFTER the roof heat load goes away (sun).

Basically, the RB slows down the radiation and heat gain, but when it is time for the RB to quit working at sundown, it is too stupid to do so- holding the heat in the attic.

So let's all get along here and realize that everything has a drawback of some sort, with the exception of icynene foam to make a cold-attic setup.

pstu

08-14-2005, 10:00 PM

Old Yeller, where do you get this info? Could you possibly find a reference to support it, for the benefit of my education? Where are these BTUs stored which come out late at night, in the roof decking perhaps? To some degree that would occur when the roof decking is hotter, as it is with a radiant barrier. But I fully would expect the radiant barrier to continue to block (reflect back) 97-98% of the heat energy, and so most of the BTUs would be re-radiated into the night sky.

The behaviour you are describing might better apply to insulation, it is contrary to my own observation and most of what I have read about radiant barriers.

I'm all ears, but just don't try to sell me on the magnets which soften my water and boost my car's fuel economy by 50%<g>. Honestly one of my years-ago AC techs did try that.

Regards -- C44

08-15-2005, 12:02 AM

Perpetual, Fig. 3 does make the authors of that study look stupid. This is nothing new, people were laughing at it 20 years ago. You must be new to this. We are willing to accept that radiant barriers do help when engineered and deployed intelligently. Then the authors go out and produce data that shoots down their own assertions. It's called shooting yourself in the foot.
Now to walk you through the graph. Look at the bottom 2 traces, one continuous (barrier) and one dotted (no barrier). Both marked with diamond shapes. Those are the temps at the ceiling throughout the day. Note how they are within about a degree of each other, but the one for the barrier is always higher. Which part of that don't you understand?
What this means you will have to ask the clowns who wrote the paper. The consensus is that they screwed up either the experiment itself or the data, so it is meaningless.

08-15-2005, 12:40 AM

Perpetual, old yeller does state the limitations correctly, although the effect he talks about is not so great as to make radiant barriers useless. You need to let go the sarcasm and concentrate on learning. Here is what he is talking about:

During the day, the barrier stops some radiant energy. Nevertheless, the attic is hotter than the ceiling. The top of the insulation is at attic temp, the bottom of the insulation is at ceiling temp. There is a linear temperature distribution in the thickness of the insulation. Some of the heat energy leaks into the house and some is stored in the insulation, particularly the top layer.

At night, the outside air is cooler than the attic. Without the barrier, the top layer of insulation (hot) will radiate and the underside of the roof deck (cooler) will absorb energy. This energy is conducted through the deck to the outside shingles, which are cooled by convection (breeze). It's just the reverse of what happens during the day. The radiant barrier stops this process, just like it stops the opposite process during the day.

As I said, the benefit from the barrier during the day is larger than the detriment at night. We are also ignoring any convection in the attic, as barrier systems are generally specified with sealed attics.

pstu

08-15-2005, 07:37 AM

There was no sarcasm intended. The remark about magnets was intended to be funny rather than sarcastic.

I have trouble with you rejecting FSEC published data since no other source I can find, is its equal and no other publication echoes your criticism. With an illegible graph I cannot see what you see. Not to mention that you have picked out 2 lines out of 10, with the minimum difference possible, and used that to reject the entire study. The phrase "dwelling on trivia" comes to mind.

The argument you have described with the attic insulation, I have a couple observations:

1) Having the insulation top at attic air temperature, is quite an accomplishment since attic air temp is much reduced with RB.
2) Ditto since without RB, radiant energy would make that insulation material *hotter* than attic air temperature.
3) All of the heat transfer you have described, would happen in much larger quantities if RB were not present.
4) The energy savings using RB is well documented, and nowhere but in your post have I seen any description of moving the heat load to later in the day. I have asked you to provide a link to research which supports your ideas, and you have not. I will tend to think such research cannot be found.

You stated that RB is generally applied with unvented attics. That is contrary to everything I have read and seen. In my region unvented attics are very much the norm and RB is normally installed except in the cases where the builder wants the absolute cheapest construction.

I am done with this thread. You may have the last word but I will not reply.

Regards -- P.Student

[Edited by perpetual_student on 08-15-2005 at 09:29 AM]

tuccillo

08-15-2005, 09:18 AM

I thought the main reason the RBs were effective is the low emmisivity - essentially the RB doesnt radiate to the attic. This is different than the mechanism you suggested. Anyone have any thoughts?

Originally posted by old yeller
It's funny how nobody seem to bring up the simple fact that IF radiant barriers work, then they work BOTH ways.

What this means, very simply, is that when the heat gets through, and it eventually will, the radiant barrier acts to HOLD IT IN!

Radiant barrier roofs are very well known (by those who pay attention) to cause extended heat gain into the interior space AFTER the roof heat load goes away (sun).

Basically, the RB slows down the radiation and heat gain, but when it is time for the RB to quit working at sundown, it is too stupid to do so- holding the heat in the attic.

So let's all get along here and realize that everything has a drawback of some sort, with the exception of icynene foam to make a cold-attic setup.

08-15-2005, 09:25 AM

Somebody take this guy (Perpetual student)by the hand and explain some basic high school physics to him. Also teach him how to read a simple graph.

08-15-2005, 09:33 AM

Tucillo, you are correct, low emissivity. Also low absorbtion.
At night the process is reversed. The floor of the attic (insulation material) is warmer than the roof so it radiates to the roof. The aluminum foil barrier will reflect radiation instead of absorbing it at night when it is on the receiving end.

fat bob

08-15-2005, 10:59 AM

Originally posted by tuccillo
I thought the main reason the RBs were effective is the low emmisivity - essentially the RB doesnt radiate to the attic. This is different than the mechanism you suggested. Anyone have any thoughts?

In the case of aluminum which is the radiant barrier material, it has a very high reflectivity and a very low emissivity. For aluminum foil, R + E = 1 for all practical purposes. Radiation always goes from the warmer to cooler object, so in the evening some heat will radiate from the floor of the attic and be reflected back, but this effect is far outweighed by the ability of the RB during the day to stop radiation from the shingles to the insulation on the floor of the attic.

You could say the same thing about insulation. At dawn in the summer it may be a little cooler outside that inside, so the insulation is trapping the heat inside the house. But I wouldn't want to tear out all my insulation for that reason.

Carnak

08-15-2005, 12:43 PM

Originally posted by dx
Somebody take this guy (Perpetual student)by the hand and explain some basic high school physics to him. Also teach him how to read a simple graph.

Physics as in heat transfer is directly proportional to temperature difference?

How to read the bigger temperature difference shown on the graph between top of insulation and underside of ceiling for the attic without radiant barrier?

Carnak

08-15-2005, 01:28 PM

http://edis.ifas.ufl.edu/EDISImagePage?imageID=1162866237&dlNumber=EH245&tag=IMAGE%20EH:EH245F3&credits=

old yeller

08-15-2005, 02:08 PM

Originally posted by perpetual_student
The argument you have described with the attic insulation, I have a couple observations:

1) Having the insulation top at attic air temperature, is quite an accomplishment since attic air temp is much reduced with RB.
2) Ditto since without RB, radiant energy would make that insulation material *hotter* than attic air temperature.
3) All of the heat transfer you have described, would happen in much larger quantities if RB were not present.
4) The energy savings using RB is well documented, and nowhere but in your post have I seen any description of moving the heat load to later in the day. I have asked you to provide a link to research which supports your ideas, and you have not. I will tend to think such research cannot be found.

Response to question #:

1. I'm sorry, are we talking about attic temps or radiation here? RB is for radiation, PV is for attic temps. The arguement has been made here that radiation is the leading cause of heat load into the interior space. This being true, RB would slow it down, but it WOULD get in, somehow, someway- and when it does, the RB will be more reluctant to let it out. Particularly since we have "removed" our active ventilation from the equation.
2. Huh?
3. Very true grasshopper- but at least it will get out faster after the heat load is gone. Roof surface temps are shown to go down to ambient in as little as a few minutes after sundown. SO, 80 degree roof surface with a 120 degree attic would allow for a decent amount of outward radiation, but the RB would slow it down significantly.
4. It was research from a Radiant barrier website that tested real-world style the effect of different placements of RB. Floor, rafters, and none. Worked better on the floor, but got dusty quicker. See, everything has a drawback. There is no free lunch.

http://www.savenrg.com/1placemnt.htm

I am not selling anything and I am not against RB. I am FOR RB, but I wanted to bring up a fact that nobody had mentioned. PV's have their problems, and so does RB.

uktra

08-15-2005, 02:33 PM

no one brought it up because that sentence doesn't make sense. PV's don't have benefits and cause problems. Radiant barriers wll save the homeowner money.

Carnak

08-15-2005, 11:07 PM

Originally posted by Carnak

Originally posted by dx
Somebody take this guy (Perpetual student)by the hand and explain some basic high school physics to him. Also teach him how to read a simple graph.

Physics as in heat transfer is directly proportional to temperature difference?

How to read the bigger temperature difference shown on the graph between top of insulation and underside of ceiling for the attic without radiant barrier?

I guess there will be no physics or graph reading lessons from dr dx tonight

08-16-2005, 12:09 AM

No, Carnak, there won't be. Go back and read the posts carefully. The answers are there.

Now here is the other pearl from that study, right below that infamous Fig. 3:

"In a typical Florida home, a radiant barrier roof could cut annual cooling loads by 4-8% and peak cooling loads by 9% depending on the level of attic ventilation. Good ventilation requirements, to meet the upper end of these savings, can normally be provided by continuous soffit and ridge vents".

Oh, so we need lots of ventilation to make RB work better???? Well, duh! If you convection cool the attic to lower and equalize the temps, there is little radiation and the RB doesn't need to do much, does it? Sheesh, didn't we just agree that RB works better with sealed attics? Didn't we just agree that Florida is too humid to ventilate the attic?

I think the article was really written by Homer Simpson.

Carnak

08-16-2005, 01:25 AM

You were commenting on how the two ceiling temperatures were close, with the ceiling below the attic without a radiant barrier being in reality a fraction of a degree cooler and claiming that proved something.

The graphs show that there is less temperature differential across the insulation in the attic section with the radiant barrier. So physics suggests that there is less heat transfer from the attic to the space below with the radiant barrier.

In each scenario, meaning attic with and without a radiant barrier, compare the areas enclosed in each pair of 'temperature at top of insulation' to 'temperature of ceiling surface' lines.

Are my 'physics' wrong here?

Am I graphically challenged?

Or does the chart not show that there is more heat transfer from the attic without the radiant barrier?

'Splain it to me Lucy, I can eat some humble pie if I am wrong.

Properties of matter change with temperature, so I am wondering if I have been ignorant of a dramatic increase in R-Value when insulation is heated?

The ceiling temperature is as much a function of the room air temp below as the temperature at the top of the insulation. In the attic section without the radiant barrier, the graph showed that the top of the insulation was hotter than the attic air suggesting some radiant flux.

They may have divided an attic up, but who is to say what the air temperature was in the areas where they measured the ceiling temperatures. This room air temperature could be influenced by the walls, windows and numerous other factors besides the ceiling. So if there is any flaw in this data, it would have been with not showing the room air temperature below the ceiling.

Yet you slam p-student like a pompous a$$hole and you have not demonstrated the best 'physics' or 'chart reading' yourself. That attitude is uncalled for.

I think you need to lighten up in here. You seem to have a hard on for people in the hvac business.

Figure 3 was comparing radiant barriers vs no radiant barriers. The attic was vented.

I was not arguing venting vs not venting an attic as I have already stated my opinion not to vent them in the first place so there is no need to change the subject.

[Edited by Carnak on 08-16-2005 at 01:28 AM]

08-16-2005, 09:39 AM

By golly, Carnak, you almost got it. Look again, the ceiling on the side with the RB is warmer. Not by much, but clearly warmer.

There is clearly less heat transfer on the side with the RB. Quite a bit less. So why is the ceiling warmer? The ceiling needs to be colder by quite a bit. Do a simple experiment. Take a piece of drywall and put it on sawhorses. Put a heater on top of one side, blowing at the drywall. Put a small blower under the drywall and blow ambient air across the underside of the drywall. Can you keep the drywall at the same temperature at the heated and unheated sides? Not on your life, unless:
1. Your drywall is a perfect insulator (in which case you dont need insulation, RB or even a job).
2. Your blower can move an infinite amount of air.
3. Somebody screwed up the experiment.

I vote for #3:)

Carnak

08-16-2005, 10:57 AM

Originally posted by dx
By golly, Carnak, you almost got it. Look again, the ceiling on the side with the RB is warmer. Not by much, but clearly warmer.

There is clearly less heat transfer on the side with the RB. Quite a bit less. So why is the ceiling warmer? The ceiling needs to be colder by quite a bit. Do a simple experiment. Take a piece of drywall and put it on sawhorses. Put a heater on top of one side, blowing at the drywall. Put a small blower under the drywall and blow ambient air across the underside of the drywall. Can you keep the drywall at the same temperature at the heated and unheated sides? Not on your life, unless:
1. Your drywall is a perfect insulator (in which case you dont need insulation, RB or even a job).
2. Your blower can move an infinite amount of air.
3. Somebody screwed up the experiment.

I vote for #3:)

1. Maybe R=0.55 or 0.56 for some 5/8ths
2. A pair of blowers could almost be treated as infinite when compared to still air films
3. Somebody did not look at the whole picture, yet tells others to take high school physics or learn to read a chart. Who now back peddles when he should be apologizing.

Talk to that PE that charges you $75/hr.

Learn about temperature drops through composite building sections and how the indoor air temperature factors into the equation. Learn about the resistance when heat flows down and then has to convect from a horizontal surface to the air beneath it.

The room air temperatures were not the same in the two scenarios plotted in Figure 3. There would not have to be that much difference in air temperature to cause you to jump to incorrect conclusions.

The surface temperature of the ceiling depends as much on the air temperature below it as the temperature at the top of the insulation. I mentioned this to you before but perhaps you scanned by and missed that part.

Consider this Lucy, a house where exterior walls have a combined R value of 20, which includes indoor air flims with a value of R=0.68.

Its forty below zero outside as an overnight low and the room air is 72F. There is a temperature differential of 112F across an exterior wall. The inside surface temperature of an exterior wall would be approximately 68.19F.

Now assume the weather warmed up to an overnight low of 0F, and after you got the gas bill from the period of extreme cold, you lowered your thermostat setting to conserve energy. The air in the same room is now only 70F and the temperature differential across the same exterior wall is now only 70F.

The inside surface temperature of that wall would now be about 67.62F.

What a miracle or is it physics?

The wall that is exposed to a 112 temperature differential has a warmer surface temperature, by a fraction of a degree compared to the wall exposed to only a 70 degree temperature differential. The wall is exposed to air 40 degrees colder in one scenario , yet it's surface temperature is slightly warmer.

This all due to a small change of 2 degrees in room air temperature.

In Figure 3, the indoor air film resistance would be higher than 0.68 and the changes in temperature differentials in the attic section with and without radiant barriers are a lot lower than 42 degrees.

A small difference in room air temperature could confuse some one only looking at the ceiling surface temperature and not the whole picture.

uktra

08-16-2005, 12:51 PM

Carnak-Carefull with all that information, dr. dx could blow his roof (sorry), top!

[Edited by uktra on 08-16-2005 at 12:53 PM]

Carnak

08-16-2005, 02:15 PM

Definitely an "X" factor here, maybe this one is junior?

rich pickering

08-16-2005, 08:11 PM

I dunno, I kinda like X. :)

uktra

08-16-2005, 09:11 PM

Rich--were you getting a "piece of the action" on those wonderful Equalized-Air units? I understand Home Depot was buying 'em like crazy and placing them next to the PV's on the shelf.

[Edited by uktra on 08-16-2005 at 09:28 PM]

08-17-2005, 02:29 AM

Carnak, thank you for that heartfelt story. Now lesson #2: conducting and reporting an experiment.

The two attic spaces were side-by-side according to the writer. Same day, same house, same planet, same everything except the RB on one side, which was the ONLY VARIABLE. Thant means no liquid nitrogen being discharged on either side and no blow torches were run on either side. So air temps at the ceiling should have been only a function of the ambient below (equal) and the heat load above (not equal). End of story.

Since we all agree the heat transfer was not equal, clearly there is something else not equal that they haven't told us about. What it is, I don't know. Ask them. Point is they get a D on runnning and reporting experiments, which IS their main business. Sorta like an hvac tech who charges a new system and forgets to pull a vacuum. They simply lose any credibility.

Now take uktra with you and go get some of that good ole RB foil for that -40F Florida weather you're all having. Say, are the ski runs open yet?

rich pickering

08-17-2005, 02:30 AM

nah, no cut on anything.:(

But I would put a pv in if I ever build a new house. The caveat is that our houses are tight. Think a zip lock bag.Bath room exhaust fans are more of a problem. Last house I worked on had a 6" combustion air and we still had problems. Had to add a second one.

Customers ask about a pv in an old house, I recomend against it. My concern is co problems.

08-17-2005, 02:47 AM

Rich, you hit it on the head. If you want it, you do it and provide the air for it. Whining does not supply the air. I do many kitchens with 1600CFM hood fans. They are required with grills. Talk about depressurization! You can suffocate the family if you don't provide supply air, never mind the humidity and infiltration.

uktra

08-17-2005, 08:18 AM

Rich--I understand your "caveat" being from Canada. Creating a nearly air tight ceiling would cut down on increased infiltration caused by the PV. The other part of the "caveat" is that attic insulation in Canada is R-30 or better. That being the case, the energy to run the PV still offsets the energy saved in cooling the home. So, if you want to put another hole in your roof--be my guest.

Carnak

08-17-2005, 08:58 AM

Originally posted by dx
Carnak, thank you for that heartfelt story. Now lesson #2: conducting and reporting an experiment.

The two attic spaces were side-by-side according to the writer. Same day, same house, same planet, same everything except the RB on one side, which was the ONLY VARIABLE. Thant means no liquid nitrogen being discharged on either side and no blow torches were run on either side. So air temps at the ceiling should have been only a function of the ambient below (equal) and the heat load above (not equal). End of story.

Since we all agree the heat transfer was not equal, clearly there is something else not equal that they haven't told us about. What it is, I don't know. Ask them. Point is they get a D on runnning and reporting experiments, which IS their main business. Sorta like an hvac tech who charges a new system and forgets to pull a vacuum. They simply lose any credibility.

Now take uktra with you and go get some of that good ole RB foil for that -40F Florida weather you're all having. Say, are the ski runs open yet?

You were asking others for numbers before but so far you seem to be incapable of providing any yourself. You still cannot do much better than liquid nitrogen stories or anecdotes about sheet rock on a saw horse with infinite air flow blowers.

I will give you a chance to redeem yourself. Previously you stated "The ceiling needs to be colder by quite a bit" with respect to the ceiling under the radiant barrier. Could you quantify "quite a bit"?

Do you think that home in Figure 3 had air conditioning running?

I get the impression when you took 'high school physics' that you used to cheat on your lab reports so that your results perfectly matched whatever the theory said.

You have finally grasped the concept that the ceiling temperature depends on the air temperature below it as well. You owe me one. :)

Perhaps you can return the favour some day and give me some tips on how to match paint colours when I rennovate. :)

Now all you have to do is realize that you will not have the exact same temperature in each room of a house and you are all the way there.

I would say that rich pickering is one of a hand full of posters on this site who has experienced weather colder than I have in the past. I thought I was ahead of things when I moved south. Not freezing my a$$ off anymore, but dealing with named storms.