Upgrade of the B2G dynamic geothermal heat exchanger model: optimal location of the ground nodes

Abstract

In order to optimize the design and operation of a ground source heat pump system, the modeling of the Borehole Heat Exchanger (BHE) and its coupling to the heat pump operation becomes crucial. This becomes key for those systems with on/off operation, where it is important to model the short-term response of the BHE accurately. Furthermore, the modeling of the local variation of the ground temperature near the BHE will be highly influenced by ground thermal properties and the operation of the system. In this context, the novel B2G dynamic model was developed and experimentally validated in previous works for a single U BHE and adapted to a novel coaxial spiral configuration. In order to consider the influence of the soil surrounding the BHE, two ground nodes were initially defined and their position (penetration radii) was calculated for a specific type of soil and operating conditions. This paper presents an upgrade of the B2G model, with a descripton of penetration radii calculation. For this purpose, a comparison between the B2G model and the Infinite Cylindrical Source model was carried out to find the penetration radii that reproduce the ground thermal response with a higher accuracy under the corresponding soil thermal properties and operating conditions.