solar air heating collectors

[Seasoned Oak]

Some of those designs look OK .The foundation where its exposed on the south side would be a good place for solar. Venting could be easy with natural rising of heated air.
Same line of thinking with solar panels. Integrating panels with roof coverings will be more accepted ,like "solar shingles".
I do love solar. It was like spring at my house today and every sunny winter day, despite never rising above freezing just on the other side of those windows. Ill always have a sun room. Mine is only 144SF of floor space,but 150+sq ft of glazing, next one will be 2x as big.

 

[denjohn]

Could a solar air heat collector be used to preheat the inflow of a mini split?

 

[jebatty]

I looked at the window screen and downspout designs for a solar air heater. My available space is about 2.5' x 24', and I think a screen design would be difficult due to the length, but a downspout design would work very well: 2 x 10' sections per run, several runs, cost about $50 for the downspouts. This may be worth a try to see how much heat my install location could produce, and what a dent that might make in my electric consumption for heat.

 

[Circus]

Could a solar air heat collector be used to preheat the inflow of a mini split?

No.
Solar air works when it's collector is warm, isolated when it's cold. Sucking air through when it's cold is counterproductive.

 

[GaryGary]

I looked at the window screen and downspout designs for a solar air heater. My available space is about 2.5' x 24', and I think a screen design would be difficult due to the length, but a downspout design would work very well: 2 x 10' sections per run, several runs, cost about $50 for the downspouts. This may be worth a try to see how much heat my install location could produce, and what a dent that might make in my electric consumption for heat.

The downspout might be a good choice.

There are some comparative tests of downspout and screen collectors here: http://www.builditsolar.com/Experimental/AirColTesting/Index.htm
The results were a bit dissapointing for the downspout, but that may have been in part due to the test -- I could never get the air distribution in the downspouts as even as I would have liked.

There is a test of a horizontal screen collector here: http://www.builditsolar.com/Experimental/HorizontalScreenCol/HorizontalScreenCol.htm
A pretty crude test, just laid collector on its side, but it did do pretty well.
So, maybe a screen collector would work OK in your case?

Scott's site has some nice stuff on downspout collectors and he has one that is similar to what you want to build.
http://www.n3fjp.com/solar/index.htm

Gary

 

[jebatty]

I'll check out the links. Thanks.

The screen collector has the screen laid at a slope from end to end, works over a short length but what about a 20' length? I like the idea of a downspout collector because it keeps moisture out of the collector box, recirculates it, and any condensing moisture stays in the down spouts, to be evaporated out on the next solar run. The flat plate collector I made years ago would collect moisture condensation in the collector box which ultimately rotted out the box.

As to even air flow through the spouts, spout restrictors/dampers could be used with a ribbon (very high tech) one could visually observe the airflow, adjust the damper(s) as needed, and get relatively even flow.

I think I could build a 20' collector for about $200, have some parts lying around I can scavenge. What I really like about solar collectors is the minimal operating and maintenance cost. I have all the stove wood I need, but it all takes work and time to get the btu's. I also have a 30w solar panel that might be incorporated to power a 12v fan.

 

[Where2]

I also have a 30w solar panel that might be incorporated to power a 12v fan.

I've got a 20W 12V panel I keep lying around for experiments. I have noticed that running my 0.5A muffin fan (130cfm) from the 20W panel, I see 18-19V on the fan leads if I don't run a connection to a battery to load down the panel. You might want to consider this when choosing a fan, or designing your setup. The ultimate setup would have a fan controller with a user selectable delta-T and a couple of different resistance loads in series with the fan motor so you could operate the fan at multiple speeds to extract the available heat. Then again, I design complicated control systems for theme parks, and may be thinking too complicated for simple air heating.

 

[jebatty]

Thinking off the cuff now. Most DC motors will operate over a pretty wide voltage range. Might a panel operate to start a12vdc motor when panel voltage rose to, say 8v, fan would speed up as panel voltage rises, max out at about 18-19V and likely not damage the motor?

 

[GaryGary]

I'll check out the links. Thanks.

The screen collector has the screen laid at a slope from end to end, works over a short length but what about a 20' length? I like the idea of a downspout collector because it keeps moisture out of the collector box, recirculates it, and any condensing moisture stays in the down spouts, to be evaporated out on the next solar run. The flat plate collector I made years ago would collect moisture condensation in the collector box which ultimately rotted out the box.

As to even air flow through the spouts, spout restrictors/dampers could be used with a ribbon (very high tech) one could visually observe the airflow, adjust the damper(s) as needed, and get relatively even flow.

I think I could build a 20' collector for about $200, have some parts lying around I can scavenge. What I really like about solar collectors is the minimal operating and maintenance cost. I have all the stove wood I need, but it all takes work and time to get the btu's. I also have a 30w solar panel that might be incorporated to power a 12v fan.

Hi,
Sounds like the downspout collector might work best for you.

Just as a side point, I don't think that the sloping screen is a necessary feature for good performance. The idea of the slope of the screen is that air enters on the glazing side of the screen, and works its way through the screen from front to back as it goes up, so the slope allows for more flow area on the inlet side at the bottom when there is more flow there, and then slopes to allow more flow area behind the screen at the top when most of the flow is on the back side of the screen. Its a nice mental picture of the flow, but no one that I know of has actually verified that this is what really happens inside the collector.

I'm doing some more testing with 2 by 3 ft collectors of various air collector configurations, and I tried one with two layers of screen very quickly and kind of randomly installed -- it was stapled to the sides of the collector box and the only "rule" was to not let the screen touch the glazing or the back of the collector. Itt took less than 5 minutes to cut out and install the absorber. It ended up performing a little better than the carefully sloped screen. So, I think that the important thing is to have the layers of screen that the sun heats up and good airflow around the screen to pick up the heat. The difficult thing with air collectors is getting good heat transfer from the absorber to the air -- air is low density and low specific heat, so the transfer is hard -- lots of absorber area and good flow over the absorber help.

Where you are, the twinwall polycarbonate glazing would be a good choice for higher efficiency.



Gary

 

[Circus]

Collectors with black sheet metal (metal furnace duct metal) hung within, cooled by rising air on both sides are usually only about 2 1/2" deep. As long as one wall duct is higher than the other, any shape works. Removing siding behind the collector and using the house's sheathing as the collector's backside insulation exposes the collector only 1 1/2" beyond the house's siding. Forget baffles, restrictions etc. Twin walled polycarbonate, good stuff

 

[jebatty]

In the early '80's I made a 4 x 8 corrugated metal, painted black, hot air collector. It performed very well, cool basement air in and 110-140F air out, 50 cfm bathroom exhaust fan for the air movement, snap switch. But condensing moisture killed it after a couple of years.

Twin walled polycarbonate looks very good.

 

[arbutus]

I love solar ... where it makes sense. Our previous house had a large air solar collector on it when we bought it. 16' x 16', 2x6 framed vertical wall added onto the south side of the original A Frame ... in Michigan's western lower peninsula, where the sun does not shine more than half a dozen days during the winter.

Those few days that the sun did shine, as well as sunny spring days, it would heat the house all by itself, for about six or seven hours. 9 - 4 or so. There was a simple thermostatic switch set to 90F, a blower ducted into the upper part of the A Frame living room that blew downwards, and two wall inlets near the floor. The panels were single glazed, with an commercial dimpled aluminum collector, and about an inch of airspace behind the collector and plywood, with fiberglass insulation behind that.

It really did help in the spring, but wasn't needed in the summer when it was usually sunny, and there just wasn't enough sunlight to make it worth while for winter.

 

[jebatty]

I really do love wood for the stove and the Tarm, and heating with wood has saved us a ton of money, but wood also is work, and after putting in the solar electric and watching it put out power (sun is shining, will be a little over 33kwh today) and not have to do anything, now that is sweet. Hence, add low cost solar hot air to supplant some of the electric used to heat the basement. Extra free, no work heat in Oct (Nov and Dec usually very cloudy), Jan and into spring will be very welcome.