SL-08-034 -- Long-Term Ground-Temperature Changes inGeo-Exchange Systems ✓ Most Recent

This paper examines thermal interaction among boreholes in geo-exchange systems with vertical ground heat exchangers. Borehole thermal interaction is caused by ground thermal imbalances and results in long-term ground temperature changes that can have a significant impact on borefield sizing and heat pump performance. Long-term temperature changes are quantified in this paper using the concept of temperature penalty, T_p, which represents an effective increase (or decrease) of the undisturbed ground temperature to account for borehole thermal interactions. A comparison is made with current values of T_p found in the ASHRAE Handbook—HVAC Applications (ASHRAE 2003). Finally, a general correlation, adequate for engineering calculations, is
proposed to estimate T_p.

Units: SI