(GHP) Geothermal Heat Pump Energy Transfer

The COP of any heat pump system is determined by the source and sink temperatures. As seen in part (a) above the greater the distance between "source" and "sink" the lower the COP. The Nordic heat pump operates like an air conditioner in reverse. Liquid Freon travels to an expansion device which lowers its temperature and pressure until it begins to vaporize inside the groundwater heat exchanger or evaporator. The warmed Freon gas travels to the compressor where it is squeezed into a high pressure hot gas while the chilled water is returned to the earth. The hot gas travels to the air heat exchanger or condenser where it condenses and gives up its heat.

 A Technical Explanation of COP From Carnot's experiments and calculations a theoretical equation was established. 
  
                                 Temp (high) ° Kelvin  
COP (carnot) = -------------------------------------- 
                                Temp (high)-Temp (low)  

All calculations are in Rankine degrees, therefore we must add 460 degrees to every figure we put in the equation. For a room temperature of 72 ° F. on a day when the air temperature was 32 ° F we would have the following equation. 
 
                                   (460° + 72°)K 
COP (max theoretical) = --------------------------------------  
                                            (460° + 72°)K - (460°+32°) K  

                                 532 
COP (max theoretical) = --------------- = 13.3  
                                 40  

As stated above this is the theoretical COP available, however, in actual practice it is found that heat pump efficiency calculations must be based on refrigerant temperature rather than source and sink temperatures. To get heat to transfer from 47 ° F groundwater, the water on the evaporator side (30 ° F ) and approximately 100 ° F or 30° F warmer than room temperature to transfer heat to the air in the home.

Therefore in the actual equation we must use 30 ° F and 100 ° F as the T (high) and T (low) in equation (1).  
(2) COP (less mechanical inefficiencies) = 560°K / (560-490) °K = 560 / 70 = 8

A COP of 8 would be terrific if we could get it, however, due to inefficiencies in the electric motors, compressors, well pumps, etc, we generally end up with a COP corresponding to the bottom line of the graph.