Advanced Hybrid Model for Borefield Heat Exchanger Performance Evaluation, an Implementation in Modelica

Abstract

Accurate and computationally efficient borefield mod-els are important components in building energy sim-ulation programs. They have not been implemented in Modelica so far. This paper describes the imple-mentation of an innovative approach to model bore-fields with arbitrary configuration having both short-term (minutes) and long-term accuracy (decades) into Modelica. A step response is calculated using a com-bination of a short-term response model which takes into account the transient heat transfer in the heat car-rier fluid, the grout and the immediately surrounding ground, and a long-term response model which calcu-lates the boreholes interactions. Moreover, an aggre-gation method is implemented to speed up the calcu-lations. Validation shows good results and very high computational efficiency.