I have been doing some research on heat exchangers (vertical and horizontal) and was wondering why is it that HDPE is the most commonly used piping. Wouldn't copper piping offer better conductivity and in turn better heat transfer allowing for a reduced heat exchanger size? I have seen some examples of copper being used in horizontal configurations but have not seen copper piping being used in any vertical config's yet. Does anyone know why this is so?
The short answer is: HDPE is still a better conductor than dirt so having a better conductor pipe like copper will not extract any more heat from the ground.
Agreed To brief further - the rate-limiting step is the soil thermodiffusivity and/or thermoconductivity. hdpe is extremely durable. Look at the DX refrigeration systems. They use copper.
Copper pipe In many soils copper will degrade very rapidly. It is a great heat exchange material but very suseptable to corrosion. Typical guarentee on HDPE is 50 years. Cary
Lest we forget; $$$$. Plastic is cheaper. DX which also was pointed out for using copper was described by a midwest earthlinked (direct exchange) distributor as creating ground freeze which can radially cut ground loops. Therefore they design systems to off cycle much more than water source systems. They boast higher COPs when running but use larger systems with larger 1 stage compressors.....losing ground gained. In other words conducting heat too quickly for soil to recover offers no advantage. j
