This doesn’t look like much (house project)

kmead

kmead

Old enough to know better
One of the projects around the house I have been working through is an attic fan. This is a fairly powerful fan which is thermostatically controlled to remove the overheated air in the attic space of our house. In our house which was an early truss roofed structure, it is rather confined and at the time in 1970 they didn’t allow for much airflow.

The fan I chose has a Bluetooth connection to an app which can be on my phone. There are different programs which can be applied and monitored. The monitoring has been eye opening learning just how hot it has been getting up there, getting well over 130 at times before I completed the install. The air temps when I was doing the install were above 120.

Today I completed the work (aside from paint which will come later). Doesnt’ look like much from here but it involved a fine variety of building systems: electrical, ducting, siding and some minor metal fabrication. It was not a fun job.

The house stays much cooler and the AC runs less. The energy cost is about equal to two or three old style light bulbs on high and about one old incandescent on low.

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2 of the houses (older homes) I've lived in had "whole house" attic fans, with either pressure drawn or manually opened louvered grates located on the top floor interior ceiling. Not a common feature on modern homes. The fans of course evacuated the hot air in the attic, but also created a wonderful breeze through whatever windows or doors were left open. With the exception of "sweltering hot" summer days, I was always impressed with how much cooler and comfortable the houses were, using such a simple device. Nice job Karl. Time and money, well spent!
 
I agree with the others about these fans being a benefit. I've been in friend's homes with such fans - mostly ones like Tom described - and the effect was very noticeable. Just crawl up into any attic on a warm day and feel how much hotter it is. Hot air rises and the heat gets trapped in that enclosed space.

Something that really shocks me is they do not use them in this desert, with the soaring high temperatures. Stick your head just barely into the attic opening on a summer day and you will literally pass out from the severe heat. Are the fans not effective above a certain level of heat? We do have a couple of vents on the roof for the attic space. But they are passive and clearly do not do much good. I'd really like to see what one of those fans like Karl's would do here.

Another thing that has become very clear to me in this extreme climate is the difference between direct and indirect sunlight. By that I mean the effect of being the shade vs in the direct sun. A simple experiment is to set up a small shade (like a EasyUp) in the middle of the yard. Stand just next to it - in the sun - for a few minutes, then step under the shade for a few minutes, then back into the sun. The difference in heat level is significant. Yet the ambient temp of the general air mass in that overall area is no different, especially out in the yard on a breezy day where the air circulates constantly. But the heat level on the body is certainly higher. And this is supported with testing; I've set digital temperature sensors (for a remote scientific thermometer) in various places to compare the temperatures. In the direct sun the temp increases dramatically compared to a few inches over in indirect sunlight. So why not build a large "umbrella" shade over critical things like the air conditioner units (yes, plural, we have three primary AC units on this house). Or better yet, make a huge shade over the entire house structure. Actually there are a few custom homes in the desert that have done exactly that, for that very reason. Although it is costly to do so, it seems the benefit would pay off over time, just like the attic fans do.
 
I've seen other "whole house" attic fans that draw air from inside the house and blow that up into the attic. That helps create a breeze in the house to cool the inside down as well (of course it wouldn't be used if you have the central air on).
 
MikeHynes said:
I've seen other "whole house" attic fans that draw air from inside the house and blow that up into the attic. That helps create a breeze in the house to cool the inside down as well (of course it wouldn't be used if you have the central air on).
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That's the type I've experienced at friends homes. As Tom said, if you open a couple of windows it completely cycles the air through the house. Naturally you would not want to do that in these extreme outside temperatures; you would only be drawing in hotter air. But fans to draw air through the attic - from outside to outside, from one end of the attic to the other - to prevent the buildup of heat up there would seem beneficial.

I even thought it may help to duct a small amount of cool air (i.e. from the central air conditioning system) into the attic, then vent that air outside, just to cool it down a bit up there. That would seem like a waste of cool air, but if the attic were cooled down then the interior of the house would also cool down. Also the air ducts are in the attic. So cooling the surrounding air around those ducts will help prevent cooling loss before the conditioned air reaches the interior. Sort of like some form of insulating effect for both the house and the ducts. As you might imagine, the insulation used here is excellent, like that in extremely cold climates. But there is only so much it can do to separate the wide temperature differential between the two areas (inside and outside).
 
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Nice work! I like the idea of BT / phone app controller - the one I put in years ago just uses a (not very accurate) adjustable thermostat. Definitely drops the temps in the attic. I didn't bother with any external mesh since it's nowhere near a roof line like yours.
 
My last house had about 4,000 sq. ft. of hot attic. I decided to take advantage of the steady breeze on the mountain ridge and installed a pair of large turbine vents that were powered by wind and/or convection. They made a remarkable difference in house temperature. Another cool feature was that if you were up in the attic while they were spinning and stuck your head up inside, you would get a 360 degree view of the outside as the blades turned semi transparent while spinning.
 
We have turbines on the roof. But I'm not convinced they really make a big difference in this extreme climate. But I could be wrong.
 
Dr.Jeff said:
We have turbines on the roof. But I'm not convinced they really make a big difference in this extreme climate. But I could be wrong.
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Depends on if you have a decent amount of wind. No wind, no turbines turning.

The other issue is where is the air coming in from that the turbines are drawing from, on my house there is a decent sized vent on the opposite gable, intermittent (and rather inadequate) eave vents under the soffit and then a ridge vent which was added by the cheating idiots who replaced the roof before I bought the house.

Soffit vents are best as the tend to pull air in from a shaded area elevated above the heated ground, along the underside hot roof surface and then across and out of the roof through the fan or your turbines. Natural air currents can work with soffit to ridge venting due to the thermo siphon process of a inlet bringing cool air in down low and the hotter air rising and venting up high. In our house due to there being vents at both ends, soffits and ridge, the air didn’t move well up unless there was a breeze pushing in the gable vent to the opposite gable and through the ridge.

I will be adding a second one of these in our utility room ceiling to serve as a whole house fan. This is at the far end of the house from our bedrooms so it would allow us to partly open a variety of windows at that end to gain notable air movement through the house when it is cooler in the late evening or early morning. Getting the interior thermal mass of plaster down in temp and closing up during the hours where it heats up above the interior ambient is our normal process when we are home. Adding the interior fan would allow us to get that cooling action before leaving for work, closing up and not being there to monitor the changeover point of exterior temp to interior temp. I appreciate living in a moderate climate where the night time air temps tend to dip to below 70 overnight. Definitely not Los Vegas…
 
kmead said:
Depends on if you have a decent amount of wind. No wind, no turbines turning.

The other issue is where is the air coming in from that the turbines are drawing from, on my house there is a decent sized vent on the opposite gable, intermittent (and rather inadequate) eave vents under the soffit and then a ridge vent which was added by the cheating idiots who replaced the roof before I bought the house.

Soffit vents are best as the tend to pull air in from a shaded area elevated above the heated ground, along the underside hot roof surface and then across and out of the roof through the fan or your turbines. Natural air currents can work with soffit to ridge venting due to the thermo siphon process of a inlet bringing cool air in down low and the hotter air rising and venting up high. In our house due to there being vents at both ends, soffits and ridge, the air didn’t move well up unless there was a breeze pushing in the gable vent to the opposite gable and through the ridge.

I will be adding a second one of these in our utility room ceiling to serve as a whole house fan. This is at the far end of the house from our bedrooms so it would allow us to partly open a variety of windows at that end to gain notable air movement through the house when it is cooler in the late evening or early morning. Getting the interior thermal mass of plaster down in temp and closing up during the hours where it heats up above the interior ambient is our normal process when we are home. Adding the interior fan would allow us to get that cooling action before leaving for work, closing up and not being there to monitor the changeover point of exterior temp to interior temp. I appreciate living in a moderate climate where the night time air temps tend to dip to below 70 overnight. Definitely not Los Vegas…
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Wind certainly isn't lacking here; we constantly see 50-70 MPH gusts. And unfortunately that brings a ton of sand dust with it, so you cannot open any windows regardless of the outside temp. But throughout most of the year it isn't cool enough outside to want them open anyway. There is a period of the year where the overnight lows never get below 100* F.

The roof turbines are interesting. They spin at a very high RPM, but I'm not sure they move much air. For one thing there isn't really a "fan blade" of sorts inside to actually draw air up from under them. So they don't seem to be any better than just a open vent. I've looked at all of the ones sold locally and they are all made the same way, so I assume that is how they all are?

Something you discussed is a bigger issue though. There doesn't appear to be any other vents on the entire roof aside from those turbines. So even if they did draw air up/out, there's no way for more air to come into the attic and replace it. But then again, that would be 115+* air coming in so maybe it doesn't make a huge difference in this climate. It also doesn't help that the sun is beating down on the roof all day; the heat energy soaks into it and you can't touch with your bare hands. Living in a oven.
 
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