I was in a debate with a local contractor regarding the COP's of an open loop system vs. a closed loop system. His argument was defending the higher efficiency of the open loop vs. the closed loop. This is obvious if you have every study a submittal on any manufacturers unit. The system demand formula (DMD) is reliant on the utility voltage as well as the amp draw of the compressor. Once DMD is formulated and subsequently plugged into the HE formula to obtain our COP. My question is this: Since we are reliant on compressor operating current do develop this number, wouldn't it be important to also figure in the operating current of the well pump to deliver this water? I realize that the well pump current is not entirely directly effecting the DMD, but I can't help but agru that is needs to be taken in to account in some capacity to get an accurate COP. As we all know, a correctly sized closed loop will be very efficient. I am not an open loop fan for many reasons, and I will leave it at that. Any thoughts? Scott
You are right, the heatpump COP depends partially on the entering water temperature (EWT) which is higher with open systems, thus a higher COP. In our area they run about 20% more efficient that way. But you must subtract for total system efficiency the increased energy consumption of a well pump versus a small circulation pump.
The cost of moving the water must be included or you are leaving out a cost of operation. There is a straight forward annalysis of this on our website and shines a bright light on the myths surrounding which exchange is more efficient. Eric
