Using attic heat for the house

[Daox]

Yup, the roof is my big 'ol solar collector.

I'd like to reverse the fans in summer. But, it kind of gets complex since I can't just reverse the fans. I'd have to come up with some duct work in order to reroute the fan's blow direction.

[AC_Hacker]

Originally Posted by Daox

Yup, the roof is my big 'ol solar collector.

It's likely that some percentage of the heat you're recycling is coming from your house... either way this is a great project.

It reminded me, in certain respects, of some exergy analysis reports I have come across for some commercial European buildings, wherein the heat decay through a building was followed and utilized appropriately at various stages of decay... a whole new way to think about heat.

I'm curious if the heat build up in the attic that is added to your room heat, ever gets excessive, enough to cause you to over-ride the fan from the attic.

If that ever gets to be the case, it would suggest some heat storage for later use... like maybe an air-to-water exchanger in the attic, and a large water heater tank in the basement, to ease you through the chilly evenings.

Or maybe storing heat all the time for DHW preheat.

...anyway, great project!

-AC_Hacker

[Daox]

Good point, I could tell in my test that the fans weren't able to move the heat as quickly as I had hoped for. 2 degree F increase an hour isn't horrible, but there is a lot more heat up there. However, I like the simplicity of the system. Its cheap and easy. I'm quite open to ideas on how to improve it though.

As we move into summer, and heat is no longer needed for the house, DHW heating is a great alternative for using attic heat. I was thinking of running some PEX tubing up there as a simple preheater, and drain it for winter. If you wanted to get fancier, you could add a pump and thermostat to heat up a tank. With my acquisition of the solar hot water panels, it will not be needed. However, I'd love to see someone else do it.

[Daox]

Well, I got my new sensor the other day and soldered up the one I needed in the kitchen this morning. I also made a temporary mount for the sensor under the cabinet next to my fridge. This keeps the sensor out of the path of the warm air blowing in and should give an accurate 'room' temperature.

Now, I just need a sunny day where my attic gets up to temp to try it out. Its been so gloomy lately. Today is very sunny so far, but its really windy. We'll see if it gets up to temp or not.

[solar1]

Do you have those Heat Recovery ventilation systems that pump warm air from your roof space or attic , as we have them here in New Zealand ?? They have a differential and max and min settings so you are not blowing cool air down when its too cold up there???

[Daox]

I'm not sure what heat recovery ventilations systems you're talking about. This thread tells what I'm doing. Yep, it has a thermal differential controller controlling the fans.

[Daox]

I did make a few more tweaks to the differential controller the other day. Mainly, I was getting some noise over the long run of the wire going to the kitchen sensor. So, I added a 10 uF capacitor near the controller to act as a buffer. This smoothed out the signal and everything seems to be working great. See the thermal differential controller thread for more info.

I still need a nice sunny day to see if it kicks on though. The other day was nice and sunny, but it must have been too windy. As I saw, the attic only got up to about 65F yesterday.

[solar1]

Have a look at this link psl-heat transfer systems and this photo explains it .

[solar1]

how do you insert photos in this ??

[Daox]

When I came home today I saw the fan was running. Unfortunately, I have no idea how much it helped. I think I'm going to connect my laptop to the arduino to do some data logging just to get an idea of how its working.