Cheap Fast Solar Air Heater

[CmeBREW]

Hello Friends,

     I have been meaning to make one of these Solar Air heaters for a year, but never got the time. But after seeing DaveB's Nice development of his Solar Heaters, I just had to finally MAKE the time to put a simple wood design solar heater together and see how it does before summer gets here.

Of course mine is not as nice as Dave's, but it works really good from preliminary testing. So far, it has only taken me 6 hours of work and about $25!

I already had most of the materials.

I used 4 old 6" decking boards, extra Piece of metal roofing (from my brother's cabin), paint I had on hand, and a sheet of 1" insulation board I had bought 2 years ago for this purpose. (I finally got to USE it before it got broke)

Here it is 'Rigged up' for testing thru my window. Today was sunny and a nice 40F degrees outside. I simply allowed cool air to flow in the inlet from outside. (Until I get the return inlet pipe installed soon)

The outside dimensions are nearly 6.5' long by almost 3' wide. It is not mounted to the wall yet.

Here is the frame all painted. It is painted flat black latex on the inside walls. There are 3/4" cleats to screw the steel roofing piece to and for the insulation to screw to the back side of the cleats. So there is 3/4" space inbetween the metal sheet and the insulation. Hope that will be OK. I used two cans of flat spray paint to paint the steel collector.  It has only SINGLE pane glass that slides into a groove I made with my table saw. I have always been worried about condensation and then possible mold developing from these Solar air heaters. But so far (today), I do not see any condensation on the glass or water vapor anywhere, which is good.

There are two pine baffles painted flat black to help circulate the airflow better as Dave showed on his. Thanks Dave.  

 






The inlet and outlet holes come out the sides. Later this year, I plan on making a second collector the same size as this one and hooking it to the side. That is why there is an extra hole in the top right side with a rag in the hole.

The outlet hole in the upper left corner is 2" and the lower right hole is only 1.5". PVC pipe will be epoxied in the holes.

 Funny story as to how I got the nice Tempered 1/8" thick glass.

A neihbor guy saw my spinning windmill and stopped by last year to talk about it. Nice guy. He said he would sell me 8 of these tempered glass panels as he didn't really need them. They went to sliding doors. Anyway I only took 4 (Wish now I got all 8!!) and they were practically free.  They are nice, since they can bend quite a lot and not break. Goes to show ya, a spinning windmill can get you a lot of other nice stuff!

Today, I just got it done and was a nice day to try it out for the first time. Be aware that I do not heat my big living room whatsoever to save on the electric bill.  So the temp is always cold.(about 45F degrees)

Today , it started out at 48F degrees in the room. The concrete slab is very cold under the carpet. Its like a giant air conditioner on all the time.

I temporarily rigged the collector with some 1.5" pvc pipe thru my window. For now, it will go thru my window , but I will replace it with 3" pipe for better flow.

Most of the day today, I let just let the 1.5" pipe stick up thru the window but with NO fan attached.  It did have some good hot air slowly coming out of it.  After a few hours of direct sun it took the temp up about 5 degrees in my big (vawted ceiling) living room. It took the room up to 54 degrees.

Then I decided to try this nice 12V  4 watt 70cmf (4") fan I got from 'Surplus Center' last year.

It is also rigged up with duct tape temporarily. The photo is here:

And WOW what a difference this fan makes!!  Most of the best sun was already past , but in just an hour it took the room temp up to 70 degrees! I was amazed.  If I had had the fan hooked up from the beginning, I bet it would have got to 80F degrees in my big living room and bathroom!  I can't wait for tomorrow. Hope it is sunny.

It has actually exceeded my expectations while using the fan. There was more sun this winter. I wish I had made this before winter started. Oh well, I got one more month to make use of this one and learn and plan for the second collector for this fall.  Now-- on to making a better Hot Water heater for this summer with more of that nice tempered glass. I gotta use it, it is behind my couch in the living room.(Safest place I could find to store them)

Any comments, concerns, pointers, or questions appreciated.

[spinningmagnets]

This is really great! I like your window adapter.

Soon, you will experience a day when the room gets too hot, and you shut it off. Then later when you have a cloudy day or a cold night you will begin thinking about how to store all the extra heat from a sunny day for later.

Based on stuff I've read on builditsolar.com, I'm thinking about a very large insulated box in the attic. It would have to be over a load-bearing wall that was strong enough to carry the weight, and would be filled with a dry stack with masonry cinder-blocks.

I might start with these hot-air panels configured on the south facing wall of the garage. I may have to use steel-reinforcements to hold the weight of the storage.

If it works well in the garage, and it doesn't look too goofy to the wife, I may do this to the house. Also I can store the panels in the garage when its not wintertime.

Thanks for posting!

[wooferhound]

I that one pane of glass or is it a double pane ?

Looks like Harbor Freight Solar Panels on the ground, a stake in the ground with string tied to it and running across the front of the panels shadowing them. This is a solar panel NoNo. Never shade any part of any panel.

[Dave B]

 Great to see this and I know how you feel about how much heat is produced. I have settled now on a 4" fan rated at 90 CFM blowing warm air into my room from the top vent. Originally I experimented with blowing air into the panel inlet at the bottom and with a 65 CFM 4" fan.

 It now runs much more efficient averaging about 110-120 degrees F in bright sun measured when it has been 20-30 degrees F during the day. The snap disk thermostat is a 110 Degree F "on at rise" and off at 90. With the lesser fan the temp would continue to rise to over 140 degrees F in bright sun after initially turning on at 110. Less air flow at higher temps was much less efficient than now with lower temps and more airflow.

 You might wnat to experiment with CFM and thermostat settings also. Of all I have read so far it seems that suggested differential temperature between inlet and outlet of around 40-50 degrees is considered quite efficient.

 Super job, make another one or more. I have a 3rd dual pane glass available yet too and with these equivlent to about 1200-1500 watts each I can't wait to make even more use of the sun as my plans move forward.  Dave B.  

[halfcrazy]

Good catch Wooferhound that sure does look like a rope running across all those panels?

[ghurd]

Cool!

What about the intake?

Is that sucking 20F air in to be heated?

Could it be run over to the other side of the window?

G-

[electrondady1]

i was given two thermo pane glass patio doors last fall and i was thinking of using them for a similar devise .

would they get too hot and crack the glass?

[CmeBREW]

Thanks Woof and Halfcrazy,

 Yes, that is some of the rope I use to hold down the panels during these horribly 60-70mph winds.  They get the full wind gusts on this side of the house. It makes me a nervous wreck at nighttime. Weather is wicked these days. During the cold windy winter I just leave the ropes on-- tired of freezing my fingers off tiing them in sub-zero temps.  Now that warmer weather is here I need to make a better securing frame with no ropes as you point out.  

Thanks.

[CmeBREW]

Thanks Ghurd,

Yes, I don't have the return 'closed loop' intake (Thru the wall) done yet. So it was taking in probably around 40F air from outside.  There is only one window on this side of the house. I am going to cut a hole in the wall for the return today and then it will be even better I'm sure.

Unfortunetly, today has been mostly cloudy sorta like 'half sun' sometimes on and off. It is not doing as well today.  It's been running since 11am and in a few hours only taken the room up 4 degrees from 48F degree cold start.

If I had the second panel done I am sure I could get a LOT more from these 'Half sunny' 'mostly/partially cloudy' days.

-Thanks.

[CmeBREW]

Hello Electrondady,

    I allowed extra room (1/8"- 3/16") in the groove to move and expand in all directions. I have yet to put a bead of silicon caulk around it.  As long as you don't Lock the glass in tightly, I don't see any problem with it.  

[CmeBREW]

Thanks SpinningMagnets,

Yes I've been thinking about those things too. Thats when things start getting more difficult. (storing heat, etc)

I have always wondered about running 10-15 runs of 2" pvc pipe under the cement slab (before pouring the slab//too late for me now) and pumping the warm/hot air thru and using the slab and gravel/ground underneath as a 'capacitor' of sorts. I suppose PEX tubing would be better even though it costs a bit more. It probably has too many losses.

It is very interesting to think about such things.

I too like 'Builditsolar.com' website. Many, Many intresting things to try.  

The idea of the blocks sounds interesting.

-Thanks.  

[CmeBREW]

Thanks for the comment Dave,

Sounds very good. I have a attic fan thermostat switch to experiment with-- I think it will work good.  Would be nice to have it more automatic like yours.

It is a lot of fun and challenging to capture the suns power and use it.

I appreciate the incentive and pointers.  I will keep tweeking this and learn more.

-Thanks.

[Shadow]

Very nice!, I've been following you guys building these,and I wonder if installing them horizontal as opposed to vertical would make a difference? It would seem it would see more sun move across it for a longer period.Or what do you think?

[BigBreaker]

By weight phase change materials like calcium chloride hydrate are much better and probably cheaper than the cinder blocks.  It will "hold" 29C extremely well as that is it's melting point.  You can hang bags of it in your attic to avoid leaks from a large reservoir and to increase the heat conducting surface area.

[spinningmagnets]

Thanks, I will look into that.

[CmeBREW]

Its been a couple of weeks and I wanted to give an UPDATE and one correction.

The correction is when I said it got 72 degrees in the room -- that was inaccurate because I did not realize that the sun at a steep 6 o'clock wide angle was hitting half my white thermometer in the room and made the reading go higher than It should read.

After observing many full sun days the correct (room max temp) reading is anywhere from 60F-65F degrees which is still very good in my opinion.  If it weren't for the cold 50F degree concrete slab floor, it WOULD get the room even warmer easy though.  I also hooked up the return cool air return line to the collector from my bedroom closet. The pipe comes out the side of the wall. Doing so helped to make it a little warmer in both room by closing the loop. As I stated before, I live sorta like an Amish person (no heating) in my living room to save on the electric bill.

So it takes a few hours to slowly warm up the rooms and over-come the cold 50F degree temps of the concrete slab, so that by the end of the (sun shining) hours (about 5-6pm), the room had warmed up from 50F all the way up to 60F-65F.  Not bad for only one heater I think. I love this thing-- wish I had done it sooner.

 But the really neat thing is, the big concrete slab in fact does act like a big 'thermal storage capacitor' to some degree and the solar heater slowly raises the temp of the concrete slab floor over the day and then in the evening long after the sun goes down, the temp in the room SLOWLY goes down over many hours.  THat was the first surprising thing I noticed.

Even at 1am in the night it is still decently warm in the room (about 58F) , even though it is 32F outside!  So I can see a lot of potential there.  I just need to make a second or third solar collector and I can really heat up the concrete slab much better and it will remain quite warm all night long I think.

I wish I knew these things before I poured this concrete floor years ago. I would do many things differently now. The concrete slab can have hard insulation underneath it and piping to better use it as a very effective thermal storage capacitor. I'm still not sure exactly how to do it though.

I forgot to mention that the paint fumes in my room were strong the first day.  The next day was not so bad-- in about a week they are almost undetectable.

This fall I will make at least one more collector and hook it to this one.  I even have extra vynl siding to put on the sides of these to make them look more like part of the house.  Should look much better.

-Thanks.  

-Shadow :  Thanks for the comment.  I'm sorry I don't really know the answer to your question, but I would think that it might avoid 'dead spots' better with a vertical collector instead of going long horizontal directions.  Not sure-I could be wrong-- I am just learning myself.