Proposal of Technical Guidelines for Optimal Design of Ground-Source Heat Pump Systems

An innovative design methodology for ground-source heat pump (GSHP) systems has been developed, based on the evaluation of energy exchange and performance during the entire operational life. This novel procedure takes into account design solutions in which GSHPs are coupled with other heating and cooling technologies and finds the reciprocal optimal shares of thermal loads in terms of cost-benefit indicators. The proposed method is holistic; in other words, it incorporates in a single set of equations all the interactions among the three macro-systems governing the energy balance of GSHPs: building thermal energy loads, efficiencies of generators (heat pump and back-up systems), and thermal response of the ground (taking into account the sustainability of the source). The optimal design parameters and energetic and economic outputs of the procedure are: - thermal capacities of the heat pump and back-up generators; - size, number and position of ground heat exchangers; - flow rate in the ground-coupled loop; - load shares between GSHP and back-up systems (control strategy); - required energy input during multi-year operation; - energy savings with respect to the exclusive use of conventional back-up systems or, conversely, to the use of the sole geothermal system; - installation and operational costs; - key investment indicators. Guidelines to be followed by professionals for an effective design procedure in the case of ground-coupled vertical borehole heat exchangers (BHEs) are illustrated step-by step.