Experimental validation of a short-term Borehole-to-Ground (B2G) dynamic model

Abstract

ElsevierRuiz Calvo, F.; Rosa, MD.; Acuña, J.; Corberán Salvador, JM.; Montagud Montalvá, CI. (2015). Experimental validation of a short-term AbstractThe design and optimization of ground source heat pump systems require the ability to accurately reproduce the dynamic thermal behavior of the system on a short-term basis, specially in a system control perspective.In this context, modelling borehole heat exchangers (BHEs) is one of the most relevant and difficult tasks. Developing a model that is able to accurately reproduce the instantaneous response of a BHE while keeping a good agreement on a long-term basis is not straightforward. Thus, decoupling the short-term and long-term behavior will ease the design of a fast shortterm focused model. This work presents a short-term BHE dynamic model, called Borehole-to-Ground (B2G), which is based on the thermal network approach, combined with a vertical discretization of the borehole.The proposed model has been validated against experimental data from a real borehole located in Stockholm, Sweden. Validation results prove the ability of the model to reproduce the short-term behavior of the borehole with an accurate prediction of the outlet fluid temperature, as well as the internal temperature profile along the U-tube.

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

“…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].…”

“…Then, it is possible to solve the heat conduction equation (Fourier diffusion law) taking into account the ground thermo-physical properties. It is important to state that, using the penetration depth for simulation times longer than 18 hours, may produce a losing of accuracy in the instantaneous response, as observed in [30].…”

“…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.…”