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Old 02-26-20, 09:04 AM   #3
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Join Date: Feb 2011
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The ground will still be frozen for a few months yet, but I'm going to start with the inside work. First on the list are the heat exchanger coils in my 100 gal. tank. I already have a 60' 1" copper coil for the DHW preheat. That leaves about 24" diameter circle by 25" height inside the coil to work with. Since I potentially have a lot of collector area and want to be able to work around say a 10F delta T, I want to maximize surface area and keep a pressure drop low as possible. I picked up 4 coils of 50' x 1/2" OD refrigeration copper to accomplish this. I think 4 coils in parallel should leave a similar area as the 1" pex pipe. 1/2" cu should be easier to bend in the confines space. Values to calculate the heat transfer are hard to find. Engineering toolbox gives anywhere from 50-200btu per sqft of pipe surface area per degree f... hmmm....
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