Problem 4.14 - The BSU Geothermal Heat Pump System (Wintertime)

Recall Problem 4:13 in which we evaluated the summertime operation of a geothermal heat pump system modeled after the system currently under construction at Ball State University in Indiana. It's purpose is to provide hot water at 65°C year round together with air-conditioning during summer and space heating during winter.

In this exercise we wish to evaluate the system for wintertime operation, in which we wish to provide hot water at 65°C as well as space heating at above 20°C, while the outdoor air temperature could be as low as -10°C. In this operation we introduce two double-port control valves as shown below, to switch between summertime and wintertime operation, in which the geothermal heat source now becomes the evaporating section of the heat pump, and the refrigerant subcooler now heats the water system used for space heating.

 

Note again that this system was devised by us for purposes of this exercise only, and no data about the system was obtained from BSU. We have used the Refrigerant R134a, since this is the only refrigerant for which we have tables available. In fact we had to add new data to our tables, since with a limit of 1.6 MPa we could not reach the required temperature of 65°C. Note that the mass flow and actual power required is not specified, thus this model will represent a system suitable for any size. All energy results will be in units of kJ/kg.

Using the conditions shown on the diagram do the following