Solar air over water

GaryGary · 01-09-20, 01:12 PM

Hi,

Here is an interesting solar air to water heater that goes a long ways back, but is very simple.
https://www.builditsolar.com/Project...aterHeater.pdf

The air to water heat exchanger they build by just attaching fins to the outside of the hot water storage tank makes it really simple, but probably not as efficient as a radiator style heat exchanger.

I think one challenge you face is that solar air heating collectors tend to be less efficient than solar water heating collectors. You can see this in the test results that the SRCC gets for air vs water heating collectors -- http://solar-rating.org/
Maybe this has to do with low specific heat and low density of air making it hard to get really efficient heat transfer from the absorber to the air flow?

For a drain-back copper collector, I like this one:
https://www.builditsolar.com/Experim...perAlumCol.htm
Its easy to build, uses only half inch copper pipe with no expensive fittings.
I think that for a single glazed collector with a steep tilt, it can be left in the summer stagnated without hurting the collector. About $6 per sqft.

This is the one I use mounted on the side of my house for water and space heating, and even with double glazing (which makes the collector run warmer when stagnated), it has been just fine for about 10 years.
https://www.builditsolar.com/Project...Space/Main.htm

But, if you go with the air to water design, it will be very interesting to see what you learn.

Gary

01-09-20, 01:12 PM	#11
GaryGary Apprentice EcoRenovator Join Date: Nov 2008 Location: SW Montana Posts: 139 Thanks: 1 Thanked 21 Times in 15 Posts	Hi, Here is an interesting solar air to water heater that goes a long ways back, but is very simple. https://www.builditsolar.com/Project...aterHeater.pdf The air to water heat exchanger they build by just attaching fins to the outside of the hot water storage tank makes it really simple, but probably not as efficient as a radiator style heat exchanger. I think one challenge you face is that solar air heating collectors tend to be less efficient than solar water heating collectors. You can see this in the test results that the SRCC gets for air vs water heating collectors -- http://solar-rating.org/ Maybe this has to do with low specific heat and low density of air making it hard to get really efficient heat transfer from the absorber to the air flow? For a drain-back copper collector, I like this one: https://www.builditsolar.com/Experim...perAlumCol.htm Its easy to build, uses only half inch copper pipe with no expensive fittings. I think that for a single glazed collector with a steep tilt, it can be left in the summer stagnated without hurting the collector. About $6 per sqft. This is the one I use mounted on the side of my house for water and space heating, and even with double glazing (which makes the collector run warmer when stagnated), it has been just fine for about 10 years. https://www.builditsolar.com/Project...Space/Main.htm But, if you go with the air to water design, it will be very interesting to see what you learn. Gary