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Old 11-04-11, 10:43 AM   #141
MetroMPG
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I wonder if some kind of seasonally adjusted venting would be the way to optimize this setup.

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Old 11-04-11, 11:30 AM   #142
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My old house didn't have enough ventillation. It was over 140F a couple of times when I went up there in the summer.
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Old 11-04-11, 11:48 AM   #143
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Quote:
Originally Posted by MetroMPG View Post
I wonder if some kind of seasonally adjusted venting would be the way to optimize this setup.
In common construction, there needs to be enough venting to prevent ice dams when the roof has a snow load. When there is a snow load that doesn't let the sun hit the roof, there is no light hitting the black surface to heat up the attic. It gets more dangerous when half the snow has melting so you've got a roof exposed to light(and heat) but there is a chunk of snow towards the bottom of the roof where it is cool but will melt enough on the bottom bottom side from attic heat to become an ice chunk. Of course if there are attic air bypasses that heat in many attics may very well not be the 'free heat' from the sun but rather heat that decided to make its way into the house. ...at least that is how I understand it all.

It seems the alternate idea is to create a house to where the attic is all living space and the space between the roof and living attic is fitted with a properly installed radiant barrier and super insulated. ...then you really don't have any attic heat to harvest.

In the summer, extra venting would be beneficial to keeping the attic cool. I asked my energy auditor about adding extra venting to keep the house cool in the winter, he looked at the vents and told me that there were enough vents and vent area but the fact that they were painted over reduced their effective opening to the attic. He suggested that I replace the ones I have or clean them up.
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Old 11-06-11, 10:50 PM   #144
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I was reading about applications for my new controller board,
http://ecorenovator.org/forum/applia...ontroller.html
and I saw a very interesting idea..

A poster was looking for a Smart attic fan for summer use.
Another poster told him about using a cheap controller that could be configured
to monitor both the inside and outdoor air temperature.
Then program it to only turn on the fan when two conditions exist.
1. It was above a certain temperature outdoors (like 75F).
2. AND, when the attic (or garage) inside temperature was greater than, 10F warmer.
(Those numbers could be tweaked for best efficiency).

Then, he said one could also write a winter program, to turn on the fan,
when the attic(or garage) temperature was colder than the outdoor air temperature!
(Like when a warm front moves in during the night)..


That got me thinking about this thread. It's a way of moving some warmer
air into your attic (or garage), if the solar input isn't there yet.

Think about it. If your attic is really cold before sun up, the only heat around,
is your rooms below. A warmer attic means less heat loss from below.


I hate going out in the morning when it's 35 or 40F and finding my car is still at 20 or 30F..
The instant I leave the garage, every square inch of glass fogs, up on the outside!
Sometimes, it actually forms a layer of ice!



Anyways, it seems like this kind of programmable device could be useful,
not only in using your attic fan to bring in warm air, but to use as a controller
to bring down warmed attic air, as needed.

A programmable thermostat (with a real-time-clock) that could help you
hoard warm air in the attic and then bring it down to warm the house, on demand,
when the attic air was warmer than downstairs..?.
(You would likely need 4 DS18B20 temperature sensors and 2 SSRs)..
Cost maybe $60 for the whole rig..
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Old 03-14-12, 04:26 PM   #145
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Well its already that time of year. My attic fans have been kicking in the past few days. It has been unseasonably warm out lately though.
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Old 03-14-12, 06:25 PM   #146
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While you're harvesting free heat from your attic, I'm harvesting... maple sap.
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Old 03-14-12, 06:39 PM   #147
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I just opened the windows today and blew the air in the sunny side and let it flow out the opposite side. It's warm enough to be almost too warm. I'm contemplating testing out the air conditioner to be sure its ready for the season but I think I'll wait on that.
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Old 03-14-12, 08:40 PM   #148
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Quote:
Originally Posted by MetroMPG View Post
While you're harvesting free heat from your attic, I'm harvesting... maple sap.
I have a buddy that's doing that.. He showed me pics of his rig.
I could not believe 'boiling' setup. His wood burner looks like it could heat the local Walmart store!
I guess it takes a LOT of BTUs to get that maple favor on your pancakes!
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Old 08-18-12, 06:36 PM   #149
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Hi all, I'm new here and am interested in this subject of using attic heat. I've been doing some research and have come to some conclusions. The first one is that a well vented roof is not ideal if you want to use attic heated air to warm the house in winter. However, just to draw air down to the house will require some sort of inlet venting to the attic. So good soffit vents are needed low on the roof but any vent at the peak of the roof has to be controlled and managed to try to maintain any heat that accumulates. This is best done with a thermostatic switch.

The second thing I realized is that you want to concentrate the rays of the sun and not dilute them. For instance, a north facing facet of the roof is really not contributing anything to heating the attic, so the space beneath that section of the roof is just diluting the heating effect. You also obviously want a very dark roof. So in the interest of getting the most concentrated effect I came up with this plan which I intend to build over the next few months

The first thing is installing a radiant reflective barrier that will be hung from the bottom of the rafters on the east, west, and south facing part of the roof. Near the peak of the roof it will terminate in a small plenum shape that is fully sealed except for an 8" duct coming out of it. Inside the plenum shaped area a fan will be installed that has the input drawing air that is moving along that boundary layer between the roof and the bottom of the rafters, the 8" duct exiting the plenum goes to the output of the fan. The ducted air will go either directly to a vent cap in the roof or else directly down to the living space.

The reason I'm hoping this idea will work better than the usual implementation is that one only heats the air trapped between the radiant reflector and the dark roof. You will have a continuous laminar flow of air from the soffits vents to either the ridge vent or to the living space. The heating effect will not go to unrecoverable parts of the structure with this method. In theory at least it seems like it might be a very efficient way to recover attic heat in winter.
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Old 08-18-12, 07:30 PM   #150
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We have a small ranch style( 40x20) home. The main solar capture area is where I've edited
the picture to show where solar panels might be installed.
That side is facing south, and does get mighty warm.
This week my attic sensor registered 121 deg F. It wasn't a very hot week.


I once did some calculations of the theoretical solar gain (@100% absorption),
IRRC, it came out to over 150,000 BTUh.

So, if I wanted to send some heat down to my basement, my guesstimate
of available BTHh in the attic (with good sun) will be good for at least 15 to 20k BTUh.
Even with the ridge vent bleeding warm air out the peak..

My ridge vent spacer/filter material looks like coarse hardware cloth. Not very effective in allowing free air flow.
Plus, I have no soffits vents to help with the ventilation. Just the two little square vents on each end of the house.

My point is, you might have way more BTUh in your attic than you need. (for space heating).
So perhaps your system for bringing down that warm air might not need to be very elaborate.?.
Maybe there is some way to rig up a test setup this fall when it starts getting cool?

If you don't have a remote thermometer sensor in your attic, you might want to get one.
Help you find out what kind of heat you are getting up there.

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