# Window screen solar heater



## wy_white_wolf (Oct 14, 2004)

Been building a window screen air heater following Gary's design at builditsolar.com. Finished size is 6' by 16'. Hopefully this will take the chill off in the garage this winter.

Vents cut shown from the outside.
View attachment 30726


Inside framing around the vents. The top will extend in to become a shelf and the bottom will be just under my workbench
View attachment 30727


View attachment 30728


Top outside before screen
View attachment 30729


Bottom outside before screen
View attachment 30730


2 layers of aluminum screen in the first one
View attachment 30731


View attachment 30732


All painted black
View attachment 30733


Polycarbinate and trim installed.
View attachment 30734


WWW


----------



## Roadking (Oct 8, 2009)

Looks good. Unfortunately for me, I don't have southern exposure on the garage...Hope it works for you.

Matt
PS...I visit Gary's site quite often.


----------



## Harry Chickpea (Dec 19, 2008)

Unless there is a check valve for the air at the bottom, whenever the sun isn't shining on it, it will work to COOL your garage. Hot air will enter at the top, get cooled and sink, and exit out of the bottom. Thermosyphoning doesn't care about the intent of the builder.


----------



## SolarGary (Sep 8, 2005)

Very nice job!

I'm guessing you are going to put in the poly film backdraft dampers on the top vents?

Gary


----------



## wy_white_wolf (Oct 14, 2004)

SolarGary said:


> Very nice job!
> 
> I'm guessing you are going to put in the poly film backdraft dampers on the top vents?
> 
> Gary


I was thinking about getting a couple of the automatic openers that are used on greenhouses. I think I can adapt something like this. 

Maybe also add the poly vents on the bottom if it cools off to quickly in the evening.

WWW


----------



## Harry Chickpea (Dec 19, 2008)

Bottom would be more effective.


----------



## SolarGary (Sep 8, 2005)

wy_white_wolf said:


> I was thinking about getting a couple of the automatic openers that are used on greenhouses. I think I can adapt something like this.
> 
> Maybe also add the poly vents on the bottom if it cools off to quickly in the evening.
> 
> WWW


Just as an experiment, I'd first try the poly vents on the top for one of the collector bays and see what you think.

I've always been very impressed with how well they work. Even when the sun is weak enough that it only warms the air a few degrees going through the collector they open just a bit to accommodate this -- then as the sun gets more intense they keep opening further to accommodate the increased flow. When the sun goes off the collector, and the reverse flow starts, they immediately get sucked up against the hardware cloth backing screen to stop the flow.

Vents on the bottom are a little bit more effective, but harder to do with the poly film because they have to blow into the wall. 

One "feature" of most control systems for solar collectors is that they never turn on (or off) at exactly the right time. The sensors that run them do their best to sense when there is just enough solar to make collection work, but they never get it quite right. The nice thing about the poly dampers is that they work directly off the collector airflow -- as soon as the absorber starts heating and warms the air it starts moving up, and that starts to push the poly open.

If you try the greenhouse vents, I'd really like to hear how that works out.

Gary


----------



## wy_white_wolf (Oct 14, 2004)

For the bottom vents I'm thinking about hanging some poly over them that is slightly smaller than the openings. Then using trim boards that would reduce the size slightly. Vents are 5.5" x 19.5" so I can sacrifice a little for the poly to fall against.

Gotta get it sided, wired, insulated and sheetrocked before I do much more worring about that.

WWW


----------



## watcher (Sep 4, 2006)

How many layers of screening did you use? I remember reading an article on the efficiency of different types, metal and plastic, and different number of layers of screen for solar thermal use. IIRC, they discovered three layers of black plastic gave the best results.


----------



## wy_white_wolf (Oct 14, 2004)

watcher said:


> How many layers of screening did you use? I remember reading an article on the efficiency of different types, metal and plastic, and different number of layers of screen for solar thermal use. IIRC, they discovered three layers of black plastic gave the best results.


2 layers aluminum.

WWW


----------



## fishhead (Jul 19, 2006)

Good job! I've often wondered why more people don't cover their entire south walls with collectors.

It looks like they would even be good on ice fishing shelters.

Why is screen more effective than just painting the background black? Is it because the screen fibers are round and provide a flat surface for the sun's rays no matter the angle of the sun?


----------



## SolarGary (Sep 8, 2005)

fishhead said:


> Good job! I've often wondered why more people don't cover their entire south walls with collectors.
> 
> It looks like they would even be good on ice fishing shelters.
> 
> Why is screen more effective than just painting the background black? Is it because the screen fibers are round and provide a flat surface for the sun's rays no matter the angle of the sun?



Hi,
The flow through absorber collectors (like screen) are more efficient because on air heating collectors the big challenge is getting the heat transferred from the absorber to the air, and the flow through collectors have both good airflow over the absorber and lots of heat transfer surface area.

This is side by side test of screen (and others) vs empty black box:

http://www.builditsolar.com/Experimental/AirColTesting/Index.htm

"So, the heat output from the reference collector is about 1.67 times that for the empty box collector" (where the reference collector is a 2 screen absorber collector.


Bob's amazing solar heated ice fishing shack: http://www.builditsolar.com/Projects/SpaceHeating/SolarIceShack/SolarIceShack.htm
Gary


----------



## fishhead (Jul 19, 2006)

Thanks Gary.


----------



## Ky-Jeeper (Sep 5, 2010)

Very good job.http://simplysolar.supporttopics.com/ Here you go if have you have not visited. I have pretty much the same heater 12'x8'.


----------



## fishhead (Jul 19, 2006)

How many btu's does this put out? 

I wonder if anyone has a map that shows btu output based on location, solar radiation, expected cloud cover and collector size and type. If the data exists I'll bet the map could be made using GIS.


----------



## light rain (Jan 14, 2013)

Thank you all for posting this. While I don't understand a lot of it maybe the more I read will advance my comprehension. Being in zone 4 it could be very helpful to counter our energy costs.


----------



## wy_white_wolf (Oct 14, 2004)

fishhead said:


> How many btu's does this put out?
> 
> I wonder if anyone has a map that shows btu output based on location, solar radiation, expected cloud cover and collector size and type. If the data exists I'll bet the map could be made using GIS.


Won't know for sure until I do some testing this winter. I'm hoping it will have the winter chill taken out of the shop so I can tinker after getting home from work.

WWW


----------

