Dynamic modeling of intermediate depth geothermal systems

A code was developed to couple numerical models of geothermal doublets and deep borehole heat exchangers (DBHE) with a simple model for heat pumps, responding to a monthly demand for heating and cooling a building. The objective was to compare the performance of systems repurposing one or two idle gas wells to install a DBHE or a doublet to heat a greenhouse. Both systems incorporate several heat pumps, activated or deactivated according to the building energy demand, with the fluid flow rate varied to adapt production to demand. The results suggest that, theoretically, the doublet could supply more heat than the DBHE. Specifically, the doublet could heat a 6950 m2 greenhouse and provide ~70% of the peak demand, while the DBHE would only heat a 2560 m2 greenhouse with the same coverage of peak demand. However, a preliminary cost analysis indicates that installing and operating a doublet over 30 years would cost almost twice as much as a DBHE, which should be considered in the decision-making process.