Designing the Ultimate Solar Hot Air Collector!

[gaiatechnician]

Extremely good video, Scott. We should post it around as the entry to simply solar. You can add new input as captions near the end to indicate if the downspout collector became super or so so. Google did nearly a perfect job close captioning what you said so the video can be internationally very useful too.

Brian

[GScottVideos]

@gaiatechnician Thanks for your kind words and good suggestions Brian!

[josephdupont]

How about double glazing on the top section?

[GScottVideos]

@josephdupont Hi, there are lots of things remaing to try and compare, including double glazing and single glazing on an otherwise identical collector. Double glazing provides more insulation, but reduces the amount of heat reaching the collector interior, so there is a school of through that single glazing is okay unless your climate is really cold.

[johnlvs2run]

What is the purpose of the insulation? The insulation does not reflect the heat, but absorbs the heat, then gradually loses the heat through the back and the sides. Radiant barrier foil would reflect the heat, basically doubling the heat that passes through the absorber.

Yes, the black will get hot. But you could probably not stand in front of radiant barrier foil in that same position, because the heat coming off would be like standing in front of an oven.

[GScottVideos]

@johnlvs2run Hi, Insultion behind the aborber adds R value between the absorber and the back wall of the collector (which also adds a little R value) to slow the heat escaping through the back. Heat is going to do one of two things - either be picked up by the air we are passing through the collector, or escape in some other way. By insulating the back, we are limiting the unwanted escape routes and ensuring as much heat is in our airflow that is returned to the house as possible.

[johnlvs2run]

@GScottVideos Thank you for your quick response. The same as an attic, RBF does not get as hot as insulation as it reflects 95-97% of the heat, and does not allow the heat to get in the attic. Insulation absorbs the heat, after it is already in the attic, and thereby keeps heating the house through the day, AND the night, by gradually releasing the heat it's absorbs, also keeping the attic very hot.

[johnlvs2run]

@johnlvs2run I just now did a basic experiment on concrete, 66F in the shade, 74 in the sun, and the RBF was only 66 degrees! However, sunscreen a few inches above the RBF went to 108F, and 98 above the concrete in the sun. I should also try black roofing paper and do a more formal test. However I think this shows the backing temperature is not a good guide as to the absorber temperature that is above the backing.

[GScottVideos]

@johnlvs2run Hi, the insulation significantly reduces the heat loss through the back and side of the collector.

[thestonemaster81]

Thank you for all your information. Is it better the have double pain glass or just a single glass. Or does plastic work better. I was thinking the double pain glass would hole the heat in better but does it take longer to heat up?

[GScottVideos]

@thestonemaster81 Hi, Double pain glass has a higher R value (good), but lower light transmittance (bad). They tend to balance out. Use what you have most accessible!

[SurferTomRI]

Great video Scott. Can you share some videos or URLs with plans for building a Screen Collector?

[GScottVideos]

@SurferTomRI You Bet! I did a video specifically on building the screen heat absorber for a screen hot air collector. The whole process literally only takes 10 minutes. YouTube won't let me post links here (they edit links out of replies), but I can share that and plenty others when you join our SimplySolar e-mail group.

Thanks for your kind words on the video!

Take care,

Scott

[GNDxero]

Scott, This is a great video, I really appreciate you putting this together. I'm building a garage currently and hope to install these on the lower section of my gambrel roof. I'm wondering, will i have to cover these in the summertime to keep from melting themselves? I was thinking about coming up with a design that lets it flop down off the roof in the summer and faces the glazing towards the house so they wouldn't heat up. Keep up the great work!

[GScottVideos]

@GNDxero Hi, thanks for your kind words! If you use any materials that might melt, consider covering the collectors with black plastic (rolls are available at HD for a few bucks) for the summer. That said, if you build vertically or at a high tilt angle, you will probably be fine as the high summer sun won't be as intense on the collector. I have not covered my vertical downspout collector, it has a little PVC in it and it has been fine for three summers now.

[MrPapaMichael]

Great video! I built two pop can collecters and have been playing with different fans with different cfm ratings. What you say in this video is right on. My pop can collecters work very well but were a lot of work to build. Once again great work and I'm looking forward to more studies.

[TheBillythekid2010]

The video was so good and the info is so helpful. Thanx_Billy

[JANDLWOODWORKING]

This Video was Awesome!!! Thank you so much for all your hard work!!!

[RimstarOrg]

Great video, Scott! See you on SimplySolar. -Steve

[GScottVideos]

@RimstarOrg Thanks Steve!

[my2cents0]

Great video! When i built my can solar heater i thought about downspouts but did not like how thick the aluminum is,i needed fast heat transfer.I will be watching you to see what designs you think are the best,thanks for doing this;you can see mine on my channel,i have another in the works now. (\O

[GScottVideos]

@my2cents0 Thanks for your kind words! Our "arm chair" theory on cans is that while they have good turbulence, the aluminum is so thin it won't conduct heat all the way around the back efficiently. Also, we have had reports that the can collectors have a high pressure drop. That said, we have been surprised many times when our actual tests proved our theories wrong. If you could build a double layer screen and compare it to your can collector, that would be great!