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Old 08-18-12, 11:00 PM   #151
Exeric
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Well, I've been thinking about your saying I might have too much BTUs. I suppose that is possible but it probably won't be a problem if I use a thermostat to control venting it either outside or into the living space. I've got a lot of details to work out yet but too much heat would be a luxury-I might be able to use the excess for other things, like heating water. I actually don't think I'll have too much as it regularly gets down to 20 degrees F here for a low each winter.

BTW, you have a very nice home.

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Old 08-19-12, 04:09 PM   #152
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I have had a further thought that may or may not pan out. These are just pipe (duct?) dreams so far. I will have to monitor temperatures as you suggested after sealing off the ridge vents and installing the sealed radiant barrier. If it does become an overly efficient heat collector, big if, then I could use that big 8" ducted fan to blow the hot air anywhere. It could even be even be to an air/water heat exchanger located elsewhere.

I have never liked the idea of having those solar collectors in the attic or on the roof, or on the side of the house if the south side of the house is viewable to the street. In the first case you would have accessibility problems once the attic is insulated and also the leakage problem. In the second case you would be using up prime space for solar cells. Third case, well, they're ugly. You could locate the heat exchanger anywhere, including a completely out of the way shaded area.

One more big advantage of doing it this way. You can't really store the heat energy in air efficiently over long periods of time. So when it gets cold at night in winter the blown hot air is gone. On the other hand if you have more heat collected from the attic during the day than you need then you one could store that heat in the water tank and release it at night. This really would only work though if you can collect more BTUs during the day than you require. Same big "if".

Last edited by Exeric; 08-19-12 at 04:21 PM..
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Old 08-19-12, 07:24 PM   #153
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A hot air-to-water HX would likely be very lossy.
If it wasn't, there would already be loads of attic-air hotwater systems.
Here's a hot air system that makes a little hot water.
DIY Solar Air Heating Collector with Water Heating

Solar hot air systems can be made cheaply, but they are typically used for space heating during sunny days.
If these systems can be run off-grid, they can be very useful during cold weather power failures.
(Around here a large ice storm can mean no grid power for days. In some cases weeks).


If I could move 10k or 15k BTUh into my basement for 5 hours a day, I think it would help heat the whole house.
It would mean that my air source heat pumps (ASHP) would use less power heating our home during sunny days.
(The sun already helps a lot, due to our south facing windows).



Heating my basement would also help keep the ASHP hotwater heater from
making it too chilly in the basement..

Right now, I don't have a cheap way to heat my basement.
All that hot air in the attic is looking pretty attractive.
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Old 08-19-12, 09:15 PM   #154
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I agree on the hot air system, if I can find suitable glass, I'm looking to do exactly that before it gets too cold and snowy to assemble a wood frame to put one together. Air to water makes less sense, better to heat the water directly since it has higher density. Same with water to air, probably best and cheaper to just pipe the air into the house.

Not sure why you want to heat the basement though, usually there isn't a risk of it freezing if the upstairs is warm and the warm air is likely not going to migrate down much, might as well just pipe the hot air into a room that could use the heat. In my case I'd pipe it into my lower level living room and the bedroom is right above it along with it being open to the rest of the house.
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Old 08-19-12, 10:29 PM   #155
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Quote:
Originally Posted by MN Renovator View Post
I agree on the hot air system, if I can find suitable glass, I'm looking to do exactly that before it gets too cold and snowy to assemble a wood frame to put one together. Air to water makes less sense, better to heat the water directly since it has higher density. Same with water to air, probably best and cheaper to just pipe the air into the house.
I see your point, but you may be ignoring the basis of my reasoning. I so far haven't mentioned that I have an L shaped porch on the east and south side of my house that is very large. It adds a significant amount of roof area to my hip roof that its attached to. It may be that Xringer is correct and I have an abundance of BTUs between that roof and the radiant reflector. Only experimentation will tell for now.

However, if there is much more than I need on the coldest clear winter days, then I should use it, no? The most efficient way would be to blow the air directly during the daylight hours, as you said. But what if every time the house gets too hot and the thermostat turns it off or directs the hot air outside it instead directs that extra hot air to a heat exchanger that heats water for later. That makes sense to me.

Also, I wouldn't necessarily pooh pooh an idea because others aren't doing it. Most people are sheep to some extent. Of course that logic does not make an idea good because no one is doing it. It just says that because no one is doing something is a poor reason for disqualifying an idea.
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Old 08-19-12, 11:33 PM   #156
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"Also, I wouldn't necessarily pooh pooh an idea because others aren't doing it. Most people are sheep to some extent. Of course that logic does not make an idea good because no one is doing it. It just says that because no one is doing something is a poor reason for disqualifying an idea."

It obviously can be done. But, at what cost?
Maybe I'm bias by my past misadventures with solar hot water and all it's standard problems.

If you really want a solar hot water system, it's going to be very difficult to get good output,
without using standard design outdoor panels, placed out where the sun shines.
My idea of an attic/indoor air to anti-freeze HX, looks like a large car radiator driven by a large fan,
connected to a pump and a controller.

My idea of space heating is to use a fan & duct to move attic air into my basement (workshop area).
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Last edited by Xringer; 08-20-12 at 02:01 PM.. Reason: spellchk
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Old 08-20-12, 04:51 AM   #157
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"However, if there is much more than I need on the coldest clear winter days, then I should use it, no? The most efficient way would be to blow the air directly during the daylight hours, as you said. But what if every time the house gets too hot and the thermostat turns it off or directs the hot air outside it instead directs that extra hot air to a heat exchanger that heats water for later. That makes sense to me."

That makes more sense to me now that you've worded it that way. Keep us posted.
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Old 08-25-12, 12:16 AM   #158
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I won't be getting to this in the next month as I have a lot of other projects I have to attend to. It is hard not to get ahead of myself here and end up making plans based on guesses. When i get back to it one of the first things I need to experiment with is simply painting a small portion of the underside of the roof black. Perhaps it will make the roof a more efficient heat radiator. I'll just use the finger test and see if painted and unpainted adjacent areas feel different. Low tech.

After that decision to paint or not to paint the radiant barrier goes up, the vents get sealed temporarily and some temperature measurements finally get done. Major decisions on how to proceed will be made at that point. Sorry to be so slow about getting to this but at the moment life intrudes.
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Old 08-25-12, 12:46 AM   #159
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Sealing the vents, be very careful. What kind of roofing do you have?

I bought my first house at 18 and second at 19. The second house was a shell with 4 walls and a roof. There was no roof vents or gable vents. Needless to say, the three tab roofing started to curl the first summer there. I learned really quick why its important to have the vents.

But, if you are monitoring the temps, and the heat doesn't build up, then sounds like a great idea.
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Old 08-25-12, 02:27 AM   #160
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I have shingles. Blocking vents will just be for a day to get a baseline temp measurement, so no worries there.

Best,

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