Comparison between simplified and detailed models for vertical ground-coupled heat exchangers

Geothermal energy is a promising technique for solving greenhouse gases emissions. One of the most interesting application is the use of heat pumps coupled with earth, by the use of close circuits with water flowing inside vertical boreholes. Many installations are addressed to small applications for residential issues, mainly for heating purposes, but many plants can also be applied to commercial users. For both applications the use of suitable tools is required for properly sizing the ground heat exchangers. In this paper two models are investigated and compared: ASHRAE method, a simplified calculation based on simple inputs and a specific model developed by authors, namely CARM (CApacity, Resistance Model). This last tool is presented and a tuning of the model is presented against measured values in a building equipped with ground source heat pump