A study on modeling and performance assessment of a heat pump system for utilizing low temperature geothermal resources in buildings

Low and moderate geothermal resources are found in most areas of the world. A very efficient way to heat and air-condition homes and buildings is the utilization of ground source heat pumps (GSHPs), also known as geothermal heat pump (GHPs), to obtain heat energy from low temperature geothermal resources. The present study deals with the modeling and performance evaluation of a heat pump system utilizing a low temperature geothermal resource, which is approximated to a geothermal reservoir. The system was designed, constructed and tested in Nigde University, Nigde, Turkey and has been successfully operated since 2005. Energy and exergy analysis methods were used to assess the system performance based on the experimental data. Exergy destructions (or irreversibilities) as well as energy and exergy efficiency relations were presented for each component of the heat pump unit and the whole system, while some thermodynamic parameters, such as fuel depletion ratio, relative irreversibility, productivity lack, exergetic factor and improvement potential, were investigated for the system. Energy and exergy efficiency values on a product/fuel basis were found to range from 73.9% to 73.3% and 63.3% to 51.7% at dead (reference) state temperatures varying from 0 to 25 °C for the heat pump unit and entire system, respectively. It is expected that the model presented here would be beneficial to the researchers, government administration, and engineers working in the area of heat pump systems for residential applications.