Bridging the Gap Between Earth Sciences and Mechanical Engineering: A Systematic Approach to Model Ground Source Heat Pumps with Deep Boreholes

Modelling of geothermal heat pump systems rarely integrates detailed surface and subsurface components. Simplifications such as neglecting the geothermal gradient, the different geological units intersected by the systems, and/or variable building loads, are common across current modeling approaches. These simplifications are particularly problematic for deep systems (e.g., >1 km). A new approach is presented to model a well doublet or a deep borehole heat exchanger (DBHE) with several heat pumps, which combines a comprehensive subsurface numerical model with codes capable of handling variable heat demand throughout the year. Groundwater flow and heat transfer are simulated with the subsurface model. Operating flow rates and number of activated heat pumps are adjusted during the simulation according to their efficiency and demand at a given time. Simulated heat production is constrained by technical and safety criteria to reflect realistic building conditions. The codes allow the simulation of cases in which the geothermal system is designed to partly meet demand, while maximizing its contribution. The thermal power production and electric consumption of the system are calculated. An illustrative example is provided for a sedimentary basin with a low geothermal gradient (~23.5 °C/km) using the Bécancour area in eastern Canada.