Quote:
Originally Posted by AC_Hacker
I was reading over the paper, and here is a screen shot of the beginning of the conclusion:
Your comment?
-AC |
Strange
Obviously contrary to the pictures in the same paper:
Same paper, page 22:
"For coil-type GHEs, when the pipe size increases, the
piping cost slightly increases. However, the increasing
pipe size means the lower head loss, and thus, the lower
annual operation cost of the circulating pump. This is
the reason for the decreasing trend of LCC as the pipe
size increases"
Anyway, there always is a sweet spot for pipe diameter and trench size.
I am not sure if the flow needs to be turbulent, as the exchanger is large and the heat exchange speed is limited by soil, not fluid... That is my personal opinion, and I am no specialist
As far as I know the ground exchangers are always sized for ground conductivity, not piping.
You can always take all the heat offered by the ground, the problem is that one should not collect more heat than is allowed for the given conductivity, otherwise the pipe may freeze or the ground around the pipe will take long time to recover constant temperature. That sometimes renders the exchanger useless.
There are cases the ground freezes around coils. I've talked with one heat pump technician that told me he once was on a service call to repair installation that was 'broken', as the owner described it. He dug to the pipe, it was in June, and the pipe with the surroundig ground was frozen since winter.
More cases of decreasing temperature and freezing are described in the Internet.
In other words: you can size the coil ground exchanger for 100W/tube meter, but that will only work for a short period, because the temperature of the ground will decrease rapidly or even the ground will simply freeze around the coil.