A geothermal resource outputs saturated (liquid) water at 250 C (as in Example 32.5). Consider two
Question:
A geothermal resource outputs saturated (liquid) water at 250 ◦C (as in Example 32.5). Consider two alternative ways to use this resource to deliver space heating at T = 20 ◦C. First, the hot water is circulated through a heat exchanger that transfers its thermal energy with 90% (1st law) efficiency to the space to be heated. Second, the geothermal resource is used to generate electric power at 13% (1st law) efficiency. The electric power in turn runs a heat pump with a 2nd law efficiency of 33% that operates between T and an outside temperature T0. Further, the waste heat from the geothermal power plant in the form of saturated water at 50 ◦C is circulated through a heat exchanger at 90%(1st law) efficiency to provide additional space heating. What is the minimum ambient temperature T0 for which the second system outperforms the first? You will need to look up the specific enthalpy of saturated (liquid) water at various temperatures.
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