Attic Cooling and Solar Performance

[Volusiano]

I have a whole house fan installed already. The “idea” would be to connect an exterior air intake to the duct work and use the fan for house cooling. The fan is in the ceiling of an open foyer. Flip on the switch and louvers open up and the fan sucks air out of the living spaces and pushes it into the attic area. From there it escapes out the attic vents (soffit and ridge). It’s mainly used when the smoke alarm goes off due to something being in the oven too long.

I follow everything except the part in bold above. I thought the flow intake is from the wide open space inside the house in the open foyer into the attic. So what would changing this flow by connecting an exterior air intake to the duct work (what duct work?) accomplish anything? Where is this duct work located? What goes into this duct work and what comes out of it? I don't understand the description/explanation/logic at all.

[OvertheSun]

I follow everything except the part in bold above. I thought the flow intake is from the wide open space inside the house in the open foyer into the attic. So what would changing this flow by connecting an exterior air intake to the duct work (what duct work?) accomplish anything? Where is this duct work located? What goes into this duct work and what comes out of it? I don't understand thedescription/explanation/logic at all.

I can sort of see this. Some energy recovery ventilators can be installed to bring fresh outside air directly into your existing HVAC ductwork. An advantage is that the entire house is ventilated instead of just one room, using the existing distribution system of HVAC ductwork.

Another advantage is that if you install it in the return side, the outdoor air can be directed to pass through whole house air filters, humidifiers and/or dehumidifiers. In Southern California, the air is very dusty and can get very dry if the wind is blowing off the desert. Bringing all that dust into the house was a big downside for me of the typical whole house fans that rely on opening first floor windows. Plus anything that requires that i do something twice a day, like opening and closing windows at just the right time, isn't going to happen.

So it sounds like DavidT wants to do the same thing except use the whole house fan to draw outdoor air into and then though the HVAC ductwork rather than blow it in with a ventilator. I would think you would need some sort of damper to close off the outdoor air intake when the HVAC is being used rather than the fan. But it begs the question of why would you want to ventilate your whole house just to cool your attic, which is what is sounds like he wants to do. Why not just use an attic fan? Whole house fan uses less electricity than AC, but not less than an attic fan.

[Volusiano]

But it begs the question of why would you want to ventilate your whole house just to cool your attic, which is what is sounds like he wants to do. Why not just use an attic fan? Whole house fan uses less electricity than AC, but not less than an attic fan.

Exactly! That's why I was confused. I thought he was just talking about cooling the attic. But instead of using an attic fan, he said he already has a whole house fan installed already, venting out into the attic, which is fine. I thought he was talking about redirecting the air flow through THAT whole-house fan which he already has, which is why it didn't make sense.

Instead, now with your explanation, it sounds like maybe he's talking about ADDING ANOTHER whole-house fan, which draws outside air and blows it into his main duct work. Now he can keep his windows closed, run BOTH whole-house fans, so that outside air is drawn in by the NEW fan, out into the main duct work into all rooms the house, then maybe also turn the OLD fan on so that it will suck the inside-the-house air out into the attic.

If the intent is to just cool the attic, and attic fan would have suffice.

The only sensible reason to add another new whole-house fan to blow outside air into the duct work is so that he doesn't have to open up the windows but still able to get fresh air in, then push it back out into the attic with the old fan. I can't imagine the kind of noise 2 whole-house fans would make together running at the same time... But oh well, if it's already noisy running 1 fan, how much noisier can another fan add to it anyway?

[SunEagle]

Understood. You want nice, you pay nice and it sure does feel good. Depending on season/location you can reduce a lot of A/C use. I'm north of San Diego and inland some from the coast. Summers are quite toasty but not brutal. My A/C operates about 120-150 hrs./yr. depending on weather. Night time ventilation does the rest along w/ 78 deg. F. daytime thermostat setting. Cooling degree days on a 60 deg. F. base is about 1800 or so. 3,000 ft.^2 conditioned space.

I believe I have seen your house from satellite imaging and it looks like a very nice home and location. The picture doesn't show any pv panels so it must be before you installed them.

[J.P.M.]

I can sort of see this. Some energy recovery ventilators can be installed to bring fresh outside air directly into your existing HVAC ductwork. An advantage is that the entire house is ventilated instead of just one room, using the existing distribution system of HVAC ductwork.

Another advantage is that if you install it in the return side, the outdoor air can be directed to pass through whole house air filters, humidifiers and/or dehumidifiers. In Southern California, the air is very dusty and can get very dry if the wind is blowing off the desert. Bringing all that dust into the house was a big downside for me of the typical whole house fans that rely on opening first floor windows. Plus anything that requires that i do something twice a day, like opening and closing windows at just the right time, isn't going to happen.

So it sounds like DavidT wants to do the same thing except use the whole house fan to draw outdoor air into and then though the HVAC ductwork rather than blow it in with a ventilator. I would think you would need some sort of damper to close off the outdoor air intake when the HVAC is being used rather than the fan. But it begs the question of why would you want to ventilate your whole house just to cool your attic, which is what is sounds like he wants to do. Why not just use an attic fan? Whole house fan uses less electricity than AC, but not less than an attic fan.

Energy recovery units are a very different animal, primarily heat exchangers of some form, often w/some filtering. Whole house ventilators are vent fans on steroids. I've designed a few heat recovery/make up air units for industrial/commercial applications and some clean room applications back in the day. There are some residential units available and they work, but until you seal off air leaks, other measures are probably more cost effective, and in the meantime, the house will be less dusty by virtue of the tightening up. Different subject and off message.

Like others , I'm not sure what the OP is describing. However, as O.T.S. and V. point out, if outside air is brought into the dwelling by any path when it is warmer outside than inside, the A/C load is going to increase. That doesn't sound like a good outcome. If what the poster is describing is to add an inlet to the whole house fan OUTSIDE the conditioned space, damper off the inside fan inlet, and then exhaust through the attic - that may work, but I'd bet on ducting/damper complications, more noise, more air leaks, more maintenance and more failure points.

Respectfully, it sounds to me like the OP is confused about the original purposes of a whole house fan. All this seems like a lot of work for an uncertain outcome. If it was me, I wouldn't like the odds, but it's a free country.

I'm w/ O.T.S. on the attic fan - I'd get a properly sized, dedicated attic fan that slightly pressurizes the attic (blows IN) and call it done. As far as cooling the panels, as one of the moderators suggested, get a fan, go up on the roof and experiment - although w/out some instrumentation, I'd be dubious of obtaining decipherable much less meaningful data.

[J.P.M.]

I believe I have seen your house from satellite imaging and it looks like a very nice home and location. The picture doesn't show any pv panels so it must be before you installed them.

Thank you. We like it. Million $$ 200 deg. view from WNW to SE, past L.A. and Big Bear w/ Palomar mts. on the east. 1500 ft. el., quiet all the time & dark at night. A bit sunnier and warmer than San Diego. Electric panels installed 10/14/2013. Marker: House directly north has 14 Sunpower 215's on a mission tile roof scattered east and above a skylite. I'm the off white house to the south w/ 2 slightly off kilter 4 X 8 Sunearth water heating panels installed 04/2007. My electric array is 6 ft. to the east, 16 panels, 4 X 4 in landscape, high point 2" below the ridge line w/ 8" clearance roof deck to bottom of panels. Davis weather station 3 ft. to the north on array C.L. Stink vents were moved. Google hasn't caught up yet and shows naked, brown concrete tile roof in need of work. SD - CSI - 17646, FWIW.

[DavidT]

Let me see if I can erase any confusion on the intent of my original idea… Apologies for the long post.

I already have a whole house fan installed. Rarely used. On very hot days AC would be a must, otherwise the second floor bedrooms would bake. But there are plenty of days and even more nights where simply passing air through the house would work for us to cool it off. If I turn on the whole house fan, which pulls air from the living area and blows it into the attic, I obviously need to replenish the air in the living space with air from the outside. So I was thinking that if I installed an air intake and plumbed it to my HVAC duct work, when I turn on the fan it would pull air coming in via the intake through my duct work and out my vents, then exhausted into the attic via the fan. So this would use the HVAC duct work to keep air circulating in every room.

The reason for posting here on the solar forum is that if I’m pushing that much air through my attic, it would have to cool the attic some in the summer since the heat caused by the baking roof wouldn’t simply accumulate in the attic. The fan would push it out. So the question was… would the byproduct of cooling the attic actually increase my solar panel production. I could see this potentially happening since there would be less radiant heat coming through the roof and hitting the underside of the solar panels. There seems to be some differing opinions as to whether or not there would be any effect on solar production, but most people are leaning towards the answer being no. My panels do sit between 4-6 inches off the roof, so there is airflow underneath them.

Reducing my energy consumption has sort of become a hobby for me. When I talked to the HVAC guy he did mention ERV systems. But we both agreed that anything involving duct work plumbing on system installation (which an ERV would be) would not be cost effective. My AC unit is fairly efficient and since we set it at 80 degrees in the summer it’s not cranking away to the extent it would be for some other folks. It sounds like I need to bag the idea of using the whole house fan for cooling the house on a part time basis, but I’d still like to experiment with using it a couple days this summer to see if it has an effect on my solar panel performance.

I should point out again that I live in Maryland and it gets pretty humid here in the summer. So a big draw back with using the fan to draw air through the house is that I’d be bringing in all that humid air. Aside from the concerns about mold (which would be a significant concern), the AC unit would have to work harder each time it was turned on to re-condition this now more humid air. For anyone thinking mold isn’t much of a concern… we just spent $2,400 having the chimney relined on a rental property since the moisture inside the chimney was leaching through the bricks and causing mold in a second floor bedroom.

[J.P.M.]

Let me see if I can erase any confusion on the intent of my original idea… Apologies for the long post.

I already have a whole house fan installed. Rarely used. On very hot days AC would be a must, otherwise the second floor bedrooms would bake. But there are plenty of days and even more nights where simply passing air through the house would work for us to cool it off. If I turn on the whole house fan, which pulls air from the living area and blows it into the attic, I obviously need to replenish the air in the living space with air from the outside. So I was thinking that if I installed an air intake and plumbed it to my HVAC duct work, when I turn on the fan it would pull air coming in via the intake through my duct work and out my vents, then exhausted into the attic via the fan. So this would use the HVAC duct work to keep air circulating in every room.

The reason for posting here on the solar forum is that if I’m pushing that much air through my attic, it would have to cool the attic some in the summer since the heat caused by the baking roof wouldn’t simply accumulate in the attic. The fan would push it out. So the question was… would the byproduct of cooling the attic actually increase my solar panel production. I could see this potentially happening since there would be less radiant heat coming through the roof and hitting the underside of the solar panels. There seems to be some differing opinions as to whether or not there would be any effect on solar production, but most people are leaning towards the answer being no. My panels do sit between 4-6 inches off the roof, so there is airflow underneath them.

Reducing my energy consumption has sort of become a hobby for me. When I talked to the HVAC guy he did mention ERV systems. But we both agreed that anything involving duct work plumbing on system installation (which an ERV would be) would not be cost effective. My AC unit is fairly efficient and since we set it at 80 degrees in the summer it’s not cranking away to the extent it would be for some other folks. It sounds like I need to bag the idea of using the whole house fan for cooling the house on a part time basis, but I’d still like to experiment with using it a couple days this summer to see if it has an effect on my solar panel performance.

I should point out again that I live in Maryland and it gets pretty humid here in the summer. So a big draw back with using the fan to draw air through the house is that I’d be bringing in all that humid air. Aside from the concerns about mold (which would be a significant concern), the AC unit would have to work harder each time it was turned on to re-condition this now more humid air. For anyone thinking mold isn’t much of a concern… we just spent $2,400 having the chimney relined on a rental property since the moisture inside the chimney was leaching through the bricks and causing mold in a second floor bedroom.

I'm assuming you intend to operate the whole house fan ONLY when it is cooler outside than inside ? Otherwise, bringing warm high dew point air into a cooler dwelling can cause moisture problems.

The air intake you install will take OUTSIDE air and feed that air to the existing HVAC ducting ? Why not just crank a window or two on the 1st floor or basement and see how that goes for a start ? Distribution is often less of a prob. w/ whole house fans due to the volume of air usually involved provided doors between conditioned spaces are left open or cracked a bit.

Cooling the house via fans can be a great idea if done right. It's been done for going on 100 years now. Some A/C will always be necessary when the outside temp. is greater than the thermostat set point , night or day. Usually the house will be buttoned up at such times and the fan off. The latent A/C load from venting w/ the fan will usually be relatively small and probably not much more than it would have been w/out the fans, but hard to quantify.

[Volusiano]

First of all, if you want to implement an outside inlet into your existing duct work, you'll need to have a way to remotely open and close this outside inlet when you turn on and off your whole-house fan. And not just remotely open and close, but this louver or damper should probably also have some kind of insulation property as well. I assume that the louver between your whole-house fan and the attic right now probably doesn't have insulation property. But that's probably OK because the attic acts as a buffer zone to help insulate somewhat against the direct outdoors. But this new outside inlet feeding into the duct work doesn't have a buffer zone, so it needs to be insulated.

Also, the louver for your existing whole-house fan probably is very simple and closes by gravity and opens by forced air going upward -> very little cost. On the hand, a remote controlled insulated inlet sounds like beaucoup $.

Having said that, J.P.M's suggestion to just open up a door or window (or more) would serve the same purpose, without having to go through the trouble of doing all the above. This also gives you a lot more options for entry points. Opening a window in a remote bedroom ensures that fresh air goes into that room right away. With the "feed-the-duct-work" approach, where you're now pulling and not pushing the air, the flow of the fresh air may take the path of least resistance and draws most of the fresh air out of the nearby vents already, and that remote room may never see enough fresh air reaching that room's vent.

Secondly, I assume that you would never run the AC and whole-house fan together at the same time because otherwise the conditioned air will end up going into the attic -> wasteful.

The concern about making the AC working harder to dehumidify as well as cool the house is not a valid concern in my opinion. The dehumidification is just a beneficial byproduct of the cooling. But the AC doesn't know or care about the humidity. It only cares about the temperature. If you keep cycling the AC long enough, the humidity get incrementally reduced to a point where it feels nice and dry. But if you keep introducing more humidity into the house every night, the AC is not going to work harder the next morning to remove this extra humidity. The AC is going to work just the same as before to lower the temperature just like before. So you'll end up with a cool but more humid house at least for a good part of the morning until that humidity is eventually taken away (as a byproduct of the cooling) by the afternoon. That's why people say not to oversize your AC to your house because your house may get cool too quickly before it has a chance to get dry as well.

[DavidT]

I'm assuming you intend to operate the whole house fan ONLY when it is cooler outside than inside ? Otherwise, bringing warm high dew point air into a cooler dwelling can cause moisture problems.

The air intake you install will take OUTSIDE air and feed that air to the existing HVAC ducting ? Why not just crank a window or two on the 1st floor or basement and see how that goes for a start ? Distribution is often less of a prob. w/ whole house fans due to the volume of air usually involved provided doors between conditioned spaces are left open or cracked a bit.....

Setting costs aside, moisture does appear to be the true Achilles Heel here. I do intend to experiment with opening a few windows, but it’s not a practical long term solution. Ironically, just like I have 33 panels on the roof, I also have 33 windows in the house (not counting the two in the attic). Opening and closing even a quarter of those each day, or having to get up to shut them in the middle of the night when it rains… just not practical.

Another issue is that if I did decide to use the fan for the long term I’d need to swap out the current motor with a two speed motor. The thing is a beast when it’s on – moves a lot of air (noise). That would be more expense to recoup. Plus I would think it would need a thermostatic control.

Since my solar panels over-produce, there’s not a lot of incentive financially for me to lower my electric consumption, but it’s still a bit fun trying.

[DavidT]

..... Also, the louver for your existing whole-house fan probably is very simple and closes by gravity and opens by forced air going upward -> very little cost. On the hand, a remote controlled insulated inlet sounds like beaucoup $.

Having said that, J.P.M's suggestion to just open up a door or window (or more) would serve the same purpose, without having to go through the trouble of doing all the above. This also gives you a lot more options for entry points. Opening a window in a remote bedroom ensures that fresh air goes into that room right away. With the "feed-the-duct-work" approach, where you're now pulling and not pushing the air, the flow of the fresh air may take the path of least resistance and draws most of the fresh air out of the nearby vents already, and that remote room may never see enough fresh air reaching that room's vent......

Not sure if the louver is insulated or not, but we never get a cold draft from it- even when I forget to put some insulation back over it during the winter.

I had considered the pulling vs. pushing air issue. I figured vent settings might have to be tinkered with. But that would be very problematic when going back and forth between the fan and the AC unit.

You'd think this would be a simple thing, but so many issues arise making it seem very impractical.