I ( and the internets) recommend black aluminum screen. It's a much more efficient conductor of heat, and seems to hold up better over time. Mine still looks like the day I built it.
I ( and the internets) recommend black aluminum screen. It's a much more efficient conductor of heat, and seems to hold up better over time. Mine still looks like the day I built it.
In reply to DrBoost :
Interesting - I will have to see how my screen works out. It was cheap - $50 or so for 4ftx100ft roll - and according to this the fiberglass screen absorbs more light than the al.
https://www.builditsolar.com/Experimental/ScreenAbsorber/ScreenAbsorber.htm
Is absorbing more light the only meaningful parameter? not really, but this site says after all the testing that the fiberglass screen absorber is the one to beat.
http://www.n3fjp.com/solar/comparisonhotair/comparisonhotair.htm
All in all, I bet the difference between al and fiberglass screen is very small regardless of which is better.
Last weekend I painted:
Then today I got to making holes in my nice walls...
Used aluminum tape to make ducts. This took forever. I'm thinking of a better way to do this.
Went outside, stapled up the screen, and screwed on the poly.
And finally I redid the little bit of siding on that side of the collector array.
I didn't get it done till late in the day but I did have a small amount of hot air already flowing. Very encouraging so far!
Now I can just work my way across. Cutting the holes is definitely the time consuming part of this project, but I sort of expected that.
Is that screen going straight up and down, parallel to the wall, or at an angle?
DrBoost said:Is that screen going straight up and down, parallel to the wall, or at an angle?
It's at a slight angle (further out at top). This is a suggestion by the author of the original article, who posted as a follow up about 10 years after original install. Although it probably doesn't make a huge difference either way, the idea is to increase screen surface area slightly and help promote airflow.
Since airflow is the main limiting factor of these collectors, I'm trying to help promote as much as possible.
Why white paint instead of black?
Dr. Hess said:Why white paint instead of black?
Mostly because the rest of the garage is white. However, the part that needs to absorb the sun's energy is the screen, which is already black. In fact, I'd be ok if the sun reflected off the building and had another shot at hitting the screen.
I said the aluminum tape wasn't a great solution so I grabbed some metal I had laying around and some tools:
Better, warmer, gooder:
Two strategic slices and voila!
These will be much nicer. Still not fast to make. But I made as many as I had material for while sitting in front of the bears game tonight (what a heartbrake) so they are multitaskable.
Got the second set of holes cut and second screen and glazing up today. Here's how it currently looks with lots of rain forecast tomorrow.
Looks great! Keep up the good work.
Robbie said:DrBoost said:Is that screen going straight up and down, parallel to the wall, or at an angle?
It's at a slight angle (further out at top). This is a suggestion by the author of the original article, who posted as a follow up about 10 years after original install. Although it probably doesn't make a huge difference either way, the idea is to increase screen surface area slightly and help promote airflow.
Since airflow is the main limiting factor of these collectors, I'm trying to help promote as much as possible.
That's what I was hoping. We're planning on a move to a sunnier climate in the next 18 months. I will build another one for sure.
Some encouraging pictures from my ir camera.
Don't have as much temp gain or as much airflow as I'd hoped yet however. I haven't caulked the panels on from the outside yet though, and since today was really windy I think I was probably loosing most of my air out the sides of the collector.
IR pics are fantastic!
You may want to think about some sort of flap over the hot-air duct. These panels will run in "reverse" all night and will suck hot air out of the room and cool it off thru the panels.
I've seen simple flaps added. I've seen the air-flow equivalent of a p-trap. Never seen it done, but I think a green-house opener would be a neat way of handling this.
Yeah, I will be adding flaps. Right now I'm just focused on cutting all these darn holes.
Whew! Outside done. And all holes are cut.
I didn't finish before the snow however, and it was darn cold outside today (10-15). At least it wasn't windy and the sun was out. Digging my siding out of the snow was fun. Haha.
Then after an hour or so I went to get the ir camera.
Highest surface temp I could find was about 26 degrees. So the double wall polycarbonate is insulating at least a bit! It is supposed to have r value of about 1.6.
Here is inside.
Keep in mind this is the surface temp of the vent. The air coming out is much warmer. But you can see how the heated air is warming the walls and ceiling.
Now I just need to bend up a ton of metal pieces to finish the duct holes and then do my flaps. But at least the outside work is done.
That is pretty awesome. My backyard is so shaded I don't think there would be much benefit for me doing this but it is interesting to read about. Could you put the flaps on a motorized actuator with a light sensor so they automatically close when the sun goes down?
In reply to EvanB :
The vents are actually much simpler than that! Basically you cover the hole with chicken wire or hardware cloth, then attach light plastic sheet (like a trash bag) above the hole. Air can go one way, but in the other direction the air is stopped. A crude but apparently effective one way valve.
I want to start measuring temperature. I think I want to measure temp at 4 spots simultaneously. (Heater intake, heater out vent, inside ambient, outside ambient)
Something that logs temp every 15 minutes or so would be awesome. I don't mind 4 individual devices.
Anyone know of anything super cheap? I can find loggers for about $20 each but would really rather keep total cost to more like $20. Anyone have something I can borrow? Should I hit eBay? Maybe just get regular thermometers and check them every hour for a couple days?
Why is the wall section to the right of the collectors showing a similar heat signature as the collectors in the IR images? Isn’t that an insulated wall ? Is the surface temperature of the siding comparable to the collectors?
Robbie said:I want to start measuring temperature. I think I want to measure temp at 4 spots simultaneously. (Heater intake, heater out vent, inside ambient, outside ambient)
Something that logs temp every 15 minutes or so would be awesome. I don't mind 4 individual devices.
Anyone know of anything super cheap? I can find loggers for about $20 each but would really rather keep total cost to more like $20. Anyone have something I can borrow? Should I hit eBay? Maybe just get regular thermometers and check them every hour for a couple days?
https://randomnerdtutorials.com/esp32-with-multiple-ds18b20-temperature-sensors/
You could also use a microcontroller like that^^ to algorithmically control flaps. Although there is something to be said for the simplicity of plastic over chicken wire.
TenToeTurbo said:Robbie said:I want to start measuring temperature. I think I want to measure temp at 4 spots simultaneously. (Heater intake, heater out vent, inside ambient, outside ambient)
Something that logs temp every 15 minutes or so would be awesome. I don't mind 4 individual devices.
Anyone know of anything super cheap? I can find loggers for about $20 each but would really rather keep total cost to more like $20. Anyone have something I can borrow? Should I hit eBay? Maybe just get regular thermometers and check them every hour for a couple days?
https://randomnerdtutorials.com/esp32-with-multiple-ds18b20-temperature-sensors/
THANKS! I may actually try that as I already have an arduino and this might be a good initial project for me to get my feet wet with it.
SVreX said:Why is the wall section to the right of the collectors showing a similar heat signature as the collectors in the IR images? Isn’t that an insulated wall ? Is the surface temperature of the siding comparable to the collectors!
I think the surface temp of the siding is absolutely similar to that of the collectors (yes, it is an insulated wall). The sun is shining on it after all... I think the temp of the siding is due to the direct sunlight and not much due to heat coming from inside the building - though there would be some as the building can't be perfectly insulated. But also look at the metal gutter filled with snow. Also hot from just the direct sunlight.
I like the concrete foundation below the siding and collectors. It was warmer than ambient already because the temp dropped significantly from the week or so before. So the concrete was still 'warm' (maybe 25-30 degrees).
One very anecdotal data point is that I was able to work in the garage last night for about an hour wearing only a sweatshirt and I was comfortable. I bet air temp was about 45. it was 15 degree high and sunny both yesterday and the day before. I'll take that any day of the week.
nice work!
In reply to Robbie :
So, the exterior shots aren’t really telling us much...
(But the interior is pretty obvious!)
What’s the temp range in those interior shots? Is the delta 20*, or more like 2*?
SVreX said:In reply to Robbie :
So, the exterior shots aren’t really telling us much...
(But the interior is pretty obvious!)
What’s the temp range in those interior shots? Is the delta 20*, or more like 2*?
The interior shot I posted says the range is 21.6 to 44. I took a few others at the same time that are similar. The exterior ones say -76 to 30 or so. But I don't know how it gets a surface temp when you point at the sky so that is probably what the -76 comes from.
EDIT: also, the aluminum ladder there is what I had been using outside. It had been sitting outside most of the day and I had brought it in only a few minutes before the picture was taken.
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