Author Topic: Solar air heating panels (Read 11224 times)

Dave B · « **on:** December 15, 2008, 10:28:10 AM »

After saving 3 dual pane 8' sliding door panels from my brother's new window and door relacements I have started on making 2 hot air solar panels. The photo is poor but shows my box framing and 1" insulation on the backs installed. I will be insulating the interior sides the same 1" also. I have routered for a flush glazing install which will be about the last part of the project before installation on the South side of my home.

The glazing is 46" x 76" x 5/8" dual pane making for a convenient use of 48" wide plywood backing and very straight select 2x4's all assembled with deck screws and urethane construction adhesive. These will have flat plate front surface absorbers painted with high temp. flat black with an air gap of approximately 1 7/8" between the absorber and back of the dual pane glazing. I don't think I'll have baffles but rather use this as possibly assisted convection panels using variable speed fans and thermostat if necessary.

There are so many does and dont's out there but it's like building anything, get the basics together and just do it. Tweak it later if need be but DO IT. More progress updates to follow. Dave B

Fixed the photo. TW

tecker · « **Reply #1 on:** December 15, 2008, 04:56:44 AM »

Cold is a good motivator to get something up .You got a good start with the glazing and it should work fine .I started similar with a shipping box , some shower doors and a cheapo solar panel fan combo that provides some positive pressure . I 'm thinking of setting up some reflctive sides to raise and lower to track a bit .Kind of like heliostats one each side .

Dave B · « **Reply #2 on:** December 15, 2008, 11:59:06 AM »

Thanks TW for fixing the photo, I had spaces in the file name the first time. Tecker, you say you used a solar fan combo. Do you have a few more specs on that ? Cost, wattage etc. and how well this seemed to work for you as apposed to maybe an AC driven muffin fan and snap disk or similar thermostat ? Thank you for your reply, I am interested in hearing from others who have solar air heating. Dave B.

GaryGary · « **Reply #3 on:** December 15, 2008, 11:59:27 AM »

Hi,

Building something is good!

How are you going to do the inlet and exit vents? And, how large are the vents?

Baffles can make a big difference depending on the collector:

http://www.builditsolar.com/Experimental/AirCollectors/AirCollectors.htm

It would be nice if you could figure out or include some way of determining if you have large dead areas with little flow -- this would let you know if you need some baffling (or not).

Gary

Dave B · « **Reply #4 on:** December 15, 2008, 12:23:57 PM »

Hello Gary,

Thank you for your reply and link to the finned absorber info. I can't really see the detail of the fins and from the explanation of how they are attached it really is not clear to me the details of the absorber plates tested. I am at that point now where this is interesting to me for sure as I will soon be figuring for the absorber and had thought just a flat plate for simplicity.

Are these fins extending all the way to the glazing face acting as true baffles or are they just extra absorbing material attached to the plate ? It almost looks like these are punched and folded up but then the insulation would be exposed so again I am not completely clear of what is being explained. If you could fill me in I sure would appreciate it.

Right now I was thinking 4" round inlet and outlets with a computer fan blowing air from the outlet with a snap disk arrangement. I realize how baffles and now this fin arrangement can affect the pressure and flow etc. and it is interesting indeed. A reostat on the fan to vary the speed would help to dial it in too I am sure. Hearing from others who have been there done that with the tweaking of the design is very helpful not to have to re-invent the wheel. We see this with the wind generators all the time.

I sure would appreciate any other information on solar hot air that might relate to my project. Thank you again, Dave B.

Jon Miller · « **Reply #5 on:** December 15, 2008, 01:00:15 PM »

Hello Dave and all,

I have just finished building one of these but using red bull aluminum cans.

My panel has 25.4mm of insulation offcuts stuck together with aluminum tape.

The cans are sprayed with standard mat black car paint.

I am using standard rectangular ducting as manifolds, available from large DIY stores, I also used rectangular to circular adapters for the inlet and outlet.

I have used a standard in line extractor fan, 15 watts, I have also used a standard room thermostat to turn the fan on and off.

Single piece of 3mm glass as glazing.

As of today, my panel is currently installed at my sisters house on a south facing wall.

I have got logging temperature sensors installed at the inlet, outlet and a third one for ambient air temperature.

I will be logging data for 5 weeks and then doing a bit of analysis, watch this space.

Today was a very sunny day, I believe the temperature was being lifted about 30 deg C.

Once the fan was on, it wouldn't turn off and the temperature did not go down.

Below are some pictures:

hope these are of some help.

tecker · « **Reply #6 on:** December 15, 2008, 03:17:33 PM »

It's a 5 watt amorphus panel and a power supply fan . Just enough to keep the air moving thru the maze bottom to top . It's bit small and any more would just blow cold .I'll post some pics the helios are about finished and I'll take it down instead working on the roof .

GaryGary · « **Reply #7 on:** December 15, 2008, 07:44:20 PM »

Hi,

On the fins, I was referring mostly to the pdf paper that there is a link to on that page. They tested a range of fins and no fins -- if I am remembering right, the fins make a big difference. I have another paper that covers some additional test work on fins, and also shows a big benefit for fins -- email me if you (or anyone) want a copy of the paper.

Neither paper does a really good job of spelling out exactly what kind of fin design works the best, but the message to me was that fins avoid big dead air spaces and definitely pay their way.

Gary

taget · « **Reply #8 on:** December 15, 2008, 09:12:41 PM »

Cant wait to see how it turns out, thinking of doing something like this on my own home, but im not sure if it is worth it. Good luck

Ungrounded Lightning Rod · « **Reply #9 on:** December 16, 2008, 11:44:38 AM »

I don't know about fins. But a piece of metal fan-folded and expanded so it has deep V-shaped valleys (maybe 4 or more times as deep as wide) will trap pretty much the last bit of light. (The cans do this too in the valleys where the sides meet, but not near their middles.)

Even with a good flat black paint some light, especially long wavelengths, bounces specularly. With a V-grove it bounces further into the groove, and several more times before it gets turned around to come back out, with the pain absorbing most of it on each bounce.

The fan-folding also gives you more area in contact with the air to transfer the heat, so your airflow can be slower. And it also directs the air much like the cans. Let it get near (but not touching - even with thermal expansion) the glass, leave a gap near the top and bottom (with a lower collector: flat, with lower ridges running horizontally, or a single panel sloped so the first bounce tends to go under the main collector). In and out vents on diagonal corners. Then the collector fins also distribute the air evenly across the panel.

MattM · « **Reply #10 on:** December 19, 2008, 05:08:00 PM »

You are going to be losing a lot of material with deep v-corrugations like that. Perhaps with a median like aluminum foil you could get it down in price to where it would be practical. But trying to form it out of metal could be a real bear. You'd be flipping the piece end for end with each bend. Lets say for 1" wide opening by 4" deep v's you are going to be flipping a 48" piece of stock 12 times for a mere 8" of coverage. The typical 48" material in 8' to 10' long stock is going to be impractical. A 26 gauge sheet is already 30 pounds of material for a 4' x 10' sheet and 24 pounds for a 4' x 8' sheet. Remember, this is for but 8 inches of coverage at that rate.

laskey · « **Reply #11 on:** December 19, 2008, 11:04:25 PM »

I did something like that in mine. I used standard wood to create a zigzag air channel. My absorber plate was aluminum flashing that I painted flat black. To disturb the air in the channel, I took some more of my aluminum flashing and cut it into strips that were as deep as the channel (but much longer, and then bent V's in the strip. Leave a short flat space, and staple or screw it to the side of the air channel, bend a V, then leave a flat, then screw, bend a V, and keep going until you've made it all the way around each side of the channel. Then paint black.

I have a Furnace booster fan that forces air into mine when the panel reaches about 90F.

The interior pane of my dual pane window cracked and then broke when we moved it from my basement, but it still reaches 90F and turns on on a sunny day even when it's -25C out (it just doesn't do it as often when it's that cold)

Cya,

Chris

Dave B · « **Reply #12 on:** December 19, 2008, 11:22:00 PM »

Hi Matt,

Actually the corragated approach for the absorber will not be losing or a waste of material. Actually it is designed to increase the surface area which increases the amount of absorbtion. You can't get someting for nothing.

My gap between the insulation and back of the double pane glazing is about 1 7/8". There are many different designs for hot air panels and it appears to me that just like wind power the most efficient designs don't always seem to make sense at first glance. This is why there is no substitute for "hands on experience" with these projects. That's exactly what I plan to do and I'm excited about moving closer to my installation.

Thanks again for your comments, I will probably hit some kind of compromise between a flat plate with fins or baffles. Dave B.

MattM · « **Reply #13 on:** December 21, 2008, 10:19:12 AM »

I would suggest if you want to trap the light in then you use a one-way film on the glass and worry less about the actual surface you are using to absorb. The greenhouse effect is what you are basically after. Materials wise it is cheaper than sheet stock of metal.

Dave B · « **Reply #14 on:** December 21, 2008, 12:19:00 PM »

Hi Matt,

If you have built and or tested any hot air panels with results that could be beneficial to an improved design I would welcome hearing of your results. So far my design is based on the flat panel front faced plate absorber that there is much posted and written information on with regards to the design. There are many schools of thought on active vs. passive and their related designs etc. I like simple and can't wait to get these up and take advantage of some sun as well as my current 16' axial heating water. Dave B.

MattM · « **Reply #15 on:** December 21, 2008, 10:41:55 PM »

I've only experimented with panels two ways, one with a saw tooth shaped back plate out of aluminum and one with a flat back plate out of 24 gauge steel. Both are approximately 4' x 7' with a single pane of glass. The fanciness of the saw tooth back plate didn't add anything to the final product except a lot more work to make and less space in the box for running duct work. My opinion is that the light transparency of the window is probably more so the real limitation here. Not sure how your double pane windows are but if they are treated to block UV light then you might try to find out how to remove it.

I did find that using a matte black was better than a glossy black. In hindsight it is probably a sensible conclusion I should have predicted before the test.

MattM · « **Reply #16 on:** December 21, 2008, 10:46:43 PM »

Addendum - I have seen people online repeatedly recommend metal framework on these flat plate collectors. Wood apparently is prone to weathering effects caused by the heat gradient. Any time you mix hot and cold temperatures like that you will get condensation. That is why mine are all metal construction not including the 3/4" foil-backed closed cell insulation sandwiched between the back plate and outer 26 gauge skin. I reckon each 4' x 7' panel is around 100 pounds assembled.

ghurd · « **Reply #17 on:** December 22, 2008, 11:20:54 AM »

Fans are not all the same. They are designed to move more air at lower pressure, vice versa, or in between. Less air way restrictions make moving the air take less power.

DC fans take less power than AC. Most little AC fans are shaded pole. DC muffin fans with bushings tend to take less power than similar fans with ball bearings.

Comair Rotron has a detailed breakdown of their models.

About 6CF of air in one panel.

CFM changes the air almost 10x per minute. Can do that direct drive with a 1.5W 12V PV and WD12H3.
CFM changes the air 18x per minute. Can do that with a 12W 12V PV and GL12H4V.

Less sun = less CFM. They keep slowly running long after I expected they would stop.

Most muffin fans lower than about 60 or 80CFM use about the same power. Hard to find one that uses less than 100ma and still moves much air.

Run DC fan(s) through a thermostat off the battery bank. Cheaper and headaches.

G-

Dave B · « **Reply #18 on:** December 22, 2008, 11:36:17 AM »

Hi Ghurd,

Thank you for the helpful information on solar. There is so much out there and different ways to do things it makes my head spin. DC fans sound like the way to go and it would be great to run PV automatically but at a cost for sure. I don't have my battery bank yet but that's looking more like a Spring project now. I have the Trace 3624 and now plan to run my axial all winter heating water. It sure has had a work out the past couple days and it will be interesting when I drop it early this Spring to check it over. That will be a year up and running through some serious winds up over 65 MPH and peaks well over 6 KW in turbulant winds when the furling needed to catch up. More updates to follow, the weather is not co-operating for a solar install right now but sure has been good for the wind. Thanks again, Dave B.

ghurd · « **Reply #19 on:** December 22, 2008, 12:59:30 PM »

Make that "Cheaper, more efficient and no headaches".

Ugly weather here too. Bright enough to run a fan from a PV, but it would be blowing cold air. Great windmill weather, but not a single one outside and NO plans to go out there to test anything today!

It was 0F (-18C) when I started the wife's car this morning. Brrr.

solartech · « **Reply #20 on:** January 04, 2009, 02:10:31 PM »

In 1980, my solar design class was challenge to build the most efficient air type solar collector, within a 4ft x 8ft frame. The collectors were tested for efficiency using the schools certified collector test facility. The winner used "lathe shavings" from a metal shop and painted them with a solar grade selective paint. This gave excellent surface area and caused turbulence that increased the heat transfer. While this gave the best immediate results, the absorber plate material compacted and became contaminated on the sunny side of the material. By the end of the school year, the flat plate collector held the top spot.

I have built several steel framed collectors with 2 inch Polyisocyanurate (foil-faced) back and side insulation. A 26 guage paintloc steel absorber plate, coated with a silicon-based heat-resistant selective paint with an absorbtivity of .96 and emissivity of .42. Absorber plate spacers maintained consistent spacing and flow diversion between the insulation and back of the plate. The glazing is 1/8" low iron, patterned glass with a Solar transmittance of 90%. It is sealed with an epdm gasket and held in place with steel battens that will integrate with roof or wall mount flashings. These collectors have lightweight, flexible backdraft dampers and have been used with fans and natural convection.

Most of these collectors have been is constant service since 1983. The actual performance, if measured over the life of the collector, seems to fall in favor of good materials and basic flat plate concepts. During our journey to this conclusion, we encountered failures with: wood frames, standard replacement patio glass, outgassing absorber coatings, fasteners and adhesives.

We could have gone with extruded aluminum frames and would have needed to, if these were a free standing collector. We also considered selectively coated, patterned aluminum absorber plates, but this nearly doubled the cost of each collector. The glazing and insulation were simply the best available and could not be compromised. In 1983, we built these 34" x 76" units for about $140 each. Many of the products and suppliers went out of business after the Regan administration took office and solar tax credits were eliminated. I fear that without a new approach to renewable energy policies, what is green now will turn brown.

Catch66 · « **Reply #21 on:** January 04, 2009, 04:41:36 PM »

Hello Dave B.

I completed this Summer/fall a dual system, having glycol water on top, with aluminum .022 sheets under, water side is attached to sheeting, with absorber bent to fit 3/4 inch copper tubing. Panel measures 3'9 inch x 11'6 inch . I installed 4 x 4 1/2 inch Dc computer fans 2 on each line of 4 inch flex ducting,one goes into bottom and the other at top as it lays Horizontal on roof returning thru center channel to a 6 inch flex duct into attic,into living rooms ceiling. My system's fans are located in basement and pull air through a high grade furnace filter. Where the 2 4 inch lines enter solar panel where I installed 4 inch dryer ducts vertically with flapper closing to eliminate any cycling,back thru at night. Before Christmas we had -20 below was a very clear day, temperature on Air side

at 10:30 A m was up to 63 degrees not enough heat to claim on air side but incoming water from city was 58 degrees. so system used 12 volt pv pump to raise my 50 gal pre heater tank 9 degrees. My location is such that I did not set the desired tilt for panel as I wanted it to stay on roof LOL (We are in a High wind area).Ck. my diary for a look. I only have a total of 50 watt pv but it keeps battery up and will run each system fine.

My next air system I'm going with aluminum screening. I purchased 2 rolls for this project but went a different way.Glazing consisted of 3 dbl. pane glass from daughter's

remodel. I believe I will try the twin wall polycarbonate on next system. Has a nice R rating and very lite.will not break like glass.

<BR><img src="http://www.otherpower.com/images/scimages/4969/Solar_Panel__20_below_With_20_watt__Pv_driver.JPG" width=80%><BR>

bazz · « **Reply #22 on:** January 05, 2009, 07:55:54 AM »

I'm just wondering.....has anyone tried any alternative set ups? Most heaters I have seen use for the most part the same materials.

Has anyone ever tried things like roof shingles, aluminium siding, things like that? Maybe a thin layer of sand?

One of the other things I have read/noticed on two different design is it seems that on one design the heaters with the tubes that go from top to bottom and into little boxes like over here http://www.atlanticenergy.ca/projects/WayneLangilleSolarAirCollectors/tabid/72/Default.aspx seem to have air flow problems.

On the other design like over here (these are just examples) http://h1.ripway.com/glensolar/GlensSolarHeater.htm seem to have very good air flow. (remember I'm talking about design, not the size of the fan)

I'm thinking...and please correct me if I'm wrong (I have not even made one myself yet, but gonna soon) The second design might be better because there is more surface space, and the air get heated continuously....no large gaps to heat.

On a side note....has anyone ever tried to build one of these with a Fresnes lens? I have a crazy idea and was wondering if anyone has ever tried. In theory...(I think)...You could build a box about a 1/4 the size and possibly have more heat output if it is designed correctly. Once again...I could be (and probably am) wrong.

zeusmorg · « **Reply #23 on:** January 05, 2009, 09:56:19 AM »

With a fresnel lens, you're just concentrating the area of solar gain to a minimal spot, a fresnel lens will not increase the solar gain vs a piece of glass the same size, it just focuses it to a smaller area within the collector, and increases the heat there, it does not increase the overall solar gain.

bazz · « **Reply #24 on:** January 05, 2009, 01:34:39 PM »

This is true, but it would generate a lot of heat in that one spot...correct? I'm kinda thinking CPU heat-sink with heat pipes. My thought...once again I could be wrong...You concentrate the energy onto a oversized heat-sink that has heat pipes. The heat pipes run up with radiated heat pipe. Blow a fan through the radiator and it should give off a good amount of heat. So in theory, you would not need a large box....its kinda like Orange juice concentrate, but different...lol

Once again..I have no idea what I'm talking about, just tossing my thought out there.

ghurd · « **Reply #25 on:** January 05, 2009, 02:22:13 PM »

The heat generated in 1 spot is the same amount of heat in the big spot.

The heat sink, pipes, fan, etc. mean almost nothing. It takes the heat from a larger area, concentrates it, then spreads it back out in the large area.

Orange juice concentrate.

You have an orange tree and you make 1 gallon of orange juice. ('spread out heat')

You concentrate the orange juice. ('dense heat'? 'higher temperature'?)

You dilute the concentrate so it is again 1 gallon of orage juice. ('spread out heat')

You start with 1 gallon of orange juice, and end up with 1 gallon of orange juice.

No gain.

The temperature will rise. Because of the power used in the fan (same as the calories your body burned making the orange juice into a concentrate, then back into juice).

Simpler to light a light bulb and do some push-ups.

G-

bazz · « **Reply #26 on:** January 05, 2009, 05:59:20 PM »

That was the best reply to anything I have ever written!! You are Awesome! Thanks!

That also explains it very well, thanks you.

No sarcasm...you rock!

Dave B · « **Reply #27 on:** January 07, 2009, 01:34:16 AM »

Hey everyone,

This is great to see several more replies on solar heating, thank you for the information and ideas. I finally got back to work on my panels and have just completed staining the wooden frames with Sashko Transformation. Plenty left over from my Log Home stain job this past Summer so they will match my back wall very nice. I hope to drop in the absorber plates tomorrow and secure these with silicone caulk and then do some measuring for the vents as well as figuring a couple baffles.

I read about the outgassing of regular high temp flat black paint and wonder if it's worth the extra money for the select coating paints ? It looks as if my absorbers are going to be flat plates of sheet steel. If anyone has any comments or ideas on the select paint for the absorber I'd like to hear about your experiences.

I hope to have some updated photos posted soon. Dave B.

bazz · « **Reply #28 on:** January 07, 2009, 10:32:19 AM »

How about this for a crazy idea?

Cut aluminum cans. Paint them black (Inside and out). (I dont know how practical this part is) You know how overhead projectors have magnifying lenses. (or if you can obtain a lot of magnifying lenses the size of the aluminum cans cheap) You could mount the lens to a focal point on the cut aluminum cans.

That be a lot of cans, a lot of magnifying lenses, and I would think if this is possible it would be a load of heat.

Just tossing ideas out there.

Any thoughts?

spinningmagnets · « **Reply #29 on:** January 07, 2009, 02:16:14 PM »

On Gary's solar collection shed (featured project at www.builditsolar.com), its built with one of the long walls facing south for maximum winter heat collection.

The entire south wall is trickle-water heat collectors, and he mentions that on the coldest days, it does help performance when theres white snow on the ground as a reflector. Effectively and cheaply doubling light hitting collectors.

I'm told infrared light hitting anything black converts to heat (non-visible light, even on a cloudy day), plus direct solar heat is collected too. Adding to collection area is always good for solar hot-air/hot-water during a cold winter.

Solar PV is expensive, so I often read newbies asking about cheap reflectors and concentrating lenses for doubling output. In summer it causes too much heat and damage, but on a cold winter day, perhaps even PV could have a surface-mount temp sensor that actuates a movable reflector to add "just enough" without going over-temp?

ghurd · « **Reply #30 on:** January 07, 2009, 03:11:57 PM »

It still take the heat in a large area (lenses area), concentrates it (focal point), the spreads it back out (hot can surface area).

2 major problems.

The focal point must be accurate.

The aiming point must be insulated.

Any percieved gain would be related to how well the focal point is concentrated.

The sun moves.

The aiming point is fixed, and the lenses are somehow rotating.

As I understand what you are thinking, this means an additional layer of glass is required between the lenses and cans.

The extra glass results in a 15% loss.

"Heat". Define heat. Convert it into watts.

The watts in one square meter equals 1KW of solar energy under perfect conditions.

Subtract the extra reflection, and do not forget to include support structures for the lenses.

"Thoughts". I think what you are thinking is overunity.

Concentrate it enough, and there will be more power than there actually is.

Add enough gears, and eventually the power output will be more than what was inputed.

Adding water to orange juice makes diluted orage juice.

Spinningmagnets understood it different than I did.

Snow (cold) reflects light to PVs, and cold PVs work better. They work even better if the light is brighter.

G-

bazz · « **Reply #31 on:** January 07, 2009, 04:21:29 PM »

So I guess I would have to say that sticking with simplicity would be the best option....There really isn't an efficient way to overclock these things.

Well it was just a few thoughts, and ideas. I just noticed that the boxes builds for the most part are all the same. I was just try to figure out other possibilities.

Lots of good info!

Thanks guys!

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Author Topic: Solar air heating panels (Read 11224 times)