A novel TRNSYS type for short-term borehole heat exchanger simulation: B2G model

Abstract

Theoretical approach for model parameters calculation is described.The short-term model is validated against experimental data of a real GSHP. AbstractModels of ground source heat pump (GSHP) systems are used as an aid for the correct design and optimization of the system. For this purpose, it is necessary to develop models which correctly reproduce the dynamic thermal behavior of each component in a short-term basis. Since the borehole heat exchanger (BHE) is one of the main components, special attention should be paid to ensuring a good accuracy on the prediction of the short-term response of the boreholes. The BHE models found in literature which are suitable for short-term simulations usually present high computational costs. In this work, a novel TRNSYS type implementing a borehole-to-ground (B2G) model, developed for modeling the short-term dynamic performance of a BHE with low computational cost, is presented. The model has been validated against experimental data from a GSHP system located at Universitat Politècnica de València, Spain. Validation results show the ability of the model to reproduce the short-term behavior of the borehole, both for a step-test and under normal operating conditions.

Coupling short-term (B2G model) and long-term (g-function) models for ground source heat exchanger simulation in TRNSYS. Application in a real installation

“…The B2G model has been previously validated in [30] and [31]. In both works, the validation was performed on a short-term basis, only with the B2G model predicting the evolution of the fluid temperature for a period of 10-15 hours.…”

“…B2G model was firstly presented and validated against different experimental data in [30] and [31]. In the present section, a brief description of the model is provided as an introduction to the further development presented in the current paper.…”

“…In the present section, a brief description of the model is provided as an introduction to the further development presented in the current paper. More information about the B2G shortterm model can be found in [30,31].…”

“…These parameters can be determined taking into account the borehole geometrical characteristics and thermo-physical properties. The full procedure to determine the values of all the parameters in the thermal network is described in [30,31] and is not reported in the present paper. Despite that, the importance of the ground thermal capacitance calculation needs to be highlighted as it depends on the portion of the ground perturbed by the heat injection and it affects the time horizon of the short-term model.…”

“…For the short-time model, a novel model based on the thermal network approach has been developed, called B2G model. The B2G model has been previously validated against experimental data corresponding to BHEs located at Stockholm [30] and Valencia [31]. This model has proven to be able to correctly predict the behaviour of the fluid temperatures exiting the borehole for heat injection/extraction times up to 10 hours, while keeping a very accurate prediction of the instantaneous response as well.…”