Accurate design of BHE fields for geothermal heat pump systems: The ASHRAE-Tp8 method compared to non aggregated schemes applied to different European test cases

Abstract

The European targets addressed to greenhouse gas emissions reduction require a series of actions, including the role to be played by heat pumps and ground-coupled (GCHP) high performance ones. The correct design of the Borehole Heat Exchangers (BHE) field is the core of any GCHP project. The building heating and cooling demand is one of the inputs that shape the problem, to be associated with the use of precalculated temperature response factors describing the ground thermal response to different BHE field arrangements. Commercial codes (e.g. EED, GLHEPRO) can address such a complex computing task by referring to the monthly step thermal loads. In this paper, the monthly approach is compared with the three thermal pulses approach (modified ASHRAE-Tp8 method) by investigating a series of typical building structures in Europe (Tabula webtool database). Hourly heat load profiles for different European countries (Italy, France, Sweden, Germany, Spain) are calculated by EnergyPlus simulations. The present analysis, based on a representative set of building heat demands in Europe, demonstrates that the simple three-pulses approach with the Tp8 formulas is able to provide the correct BHE field overall length with 5% accuracy (average error 2.22%) with respect to the reference monthly calculations performed with commercial codes.