Space Heating Panel

[ChrisOlson]

My first serious attempt at solar heating - I built a forced air heating panel for my new shop.  It's a 4 x 8 foot panel insulated to R15 on the back and sides and a sheet of 1/4" tempered low-E glass on the front.  I'm using two 80 CFM duct fans to force air into the bottom corners of the panel with a single outlet in the top center.  I got a DuctStat mounted on the top duct where it comes thru the shop wall and it turns the fans on at 80 degrees F.

Yesterday it was cloudy and raining most of the day and I had to run the fans on manual to get any heat out of it.  The air temp in the shop was 65 degrees and it put out 75 degree air for most of the day, raising the temp in the shop to 70 degrees by late afternoon.

Today we had bright sunshine and the panel put out 140 degree air until it got up to 75 degrees in the shop, and then I shut it off.

With the air temp in the shop at 65 with 140 out, my calculations indicate it can develop roughly 13,000 BTU in direct sunshine.



--
Chris

[Dave B]

 Chris,

  Wait till the sun gets even lower in the sky on those bright Winter Days and with your panels mounted vertical, you think you have heat now ? Like I said before, since I built and installed mine I still chuckle everytime they kick on the star heat. I'm at about 42 degrees lat. and in the snow belt, these help reduce my propane usage for heat 9 months of the year. Very nice job, you will love that project.  Dave B.

[artv]

Hi Chris,...I've been thinking of making acouple of these, since its so easy...You said "i've got a DuctStat mounted on the top duct"
I assume that's some type of thermostat??.......
Also when the sun goes down ,do you lose heat back out through or is there some form of shut-off??
Nice and simple ....suits me to a T.........artv

[ChrisOlson]

Hi Chris,...I've been thinking of making acouple of these, since its so easy...You said "i've got a DuctStat mounted on the top duct"
I assume that's some type of thermostat??.......
Also when the sun goes down ,do you lose heat back out through or is there some form of shut-off??
Nice and simple ....suits me to a T.........artv

Hi Art,

This is a photo of the DuctStat:



It has a switch for Off, On, Activate in Cool Mode (as temperature rises), Activate in Heat Mode (as temperature falls).  It has another switch to set the temperature spread for on/off, and a knob you can adjust for the temperature set point.  I got it at Menards for $25.

There is no need for a shutoff.  It would be no different than a window in your house and most people don't have shutoffs for their windows.
--
Chris

[ChrisOlson]

  Wait till the sun gets even lower in the sky on those bright Winter Days and with your panels mounted vertical, you think you have heat now ? Like I said before, since I built and installed mine I still chuckle everytime they kick on the star heat. I'm at about 42 degrees lat. and in the snow belt, these help reduce my propane usage for heat 9 months of the year. Very nice job, you will love that project.  Dave B.

Hi Dave,

I have wanted one of these for a long time, as I think you know.  I finally decided to build one and try it, and I'm pleased with it.  I've tried various things because I didn't know how many CFM I should put thru it.  I had a bathroom fan on it first, and that didn't move enough air and it ran way too hot - the glass was warm (actually hot) to the touch.

I found these duct fans at Menards for $19 each and they seem to work really good.  They move enough air to keep the glass on the panel cool, the exhaust air is cooler, but much better airflow thru the panel.  I think I'm extracting more heat with the dual duct fans than I was with the bathroom fan, even though the heat coming out is lower temperature.
--
Chris

[Dave B]

Right on Chris, I experimented the same way here and found the same to be true. Mine kick on at 110 deg. and off at 90 and run a constant 120-140 in direct sun with the front of the glass just warm. I saw 180 deg. out with less CFM but lost a lot of flow and therefore heat off the glass. I'm filling up my house with heat from these as we speak, no propane again tonight even though probably in the 40's again. I'm laughing and always do when ever they kick on with 2000 watts of star heat.  Dave B.

  Wait till the sun gets even lower in the sky on those bright Winter Days and with your panels mounted vertical, you think you have heat now ? Like I said before, since I built and installed mine I still chuckle everytime they kick on the star heat. I'm at about 42 degrees lat. and in the snow belt, these help reduce my propane usage for heat 9 months of the year. Very nice job, you will love that project.  Dave B.

Hi Dave,

I have wanted one of these for a long time, as I think you know.  I finally decided to build one and try it, and I'm pleased with it.  I've tried various things because I didn't know how many CFM I should put thru it.  I had a bathroom fan on it first, and that didn't move enough air and it ran way too hot - the glass was warm (actually hot) to the touch.

I found these duct fans at Menards for $19 each and they seem to work really good.  They move enough air to keep the glass on the panel cool, the exhaust air is cooler, but much better airflow thru the panel.  I think I'm extracting more heat with the dual duct fans than I was with the bathroom fan, even though the heat coming out is lower temperature.
--
Chris

[drew4justice]

Chris--looks great.

It appears that you used the siding that your shop is covered with and then painted black, correct?  If so, how does the air route through the box?  Does it simply skim over the metal, or does is snake through a channel of some sort? 

[ChrisOlson]

The heat collector is corrugated 28 gauge building steel pained flat black.  It's insulated behind and on the sides.  As the panel warms up the heated air rises and comes out the top duct without the fans running.  It triggers a DuctStat that turns the fans on when the air temp in the panel gets to 80 degrees.  The twin duct fans force air in the bottom corners and it comes out the top center of the panel.  This is a photo of the ducts coming thru the wall in the shop - it's still wired temporary with some extension cord.  But hopefully this weekend I can get time to wire it permanent.





Cloudy day today and 50-55 degrees outside and that panel put out 80-85 degree heat for about six hours.
--
Chris

[drew4justice]

Makes sense, and adheres to your photos... to answer my own question, it appears that the air simply rises across the collector, rather than funnels through ductwork or snakes through tubes, such as the aluminum can designs seen abroad.  I would conclude that this proves a simpler design is effective.

[ChrisOlson]

Yes, the air is just heated as it passes thru the panel.  There's about a 1/2" of room between the top of the bumps in the steel and the glass, and that probably causes the air to tumble a bit as it goes thru the panel.  But I don't know that that makes much difference.  When I first built it I used a bathroom fan on it and that didn't move enough air thru it.  The glass was running way too hot.  I increased the airflow to about double with the duct fans, and now the glass runs cooler and I get more BTU out of it.

There is no zig-zag airflow pattern or anything.  Just air forced in the bottom, it comes out the top, and it works really good.  I've heard of some guys using plexi-glass on these things.  I know for a fact that plexiglass would melt, or at least warp really bad, if I would've used it on this panel.

Like I said, this is my first attempt at solar heating.  I didn't really look at any plans, or copy anybody else's design.  I just went "seat of the pants" and built the thing.  Not much science or design involved in it.  Just a sun heated piece of steel with air blowing over it. 
--
Chris