Numerical heat transfer comparison study of hybrid and non-hybrid ground source heat pump systems

Abstract

Ground Source Heat Pump (GSHP) systems, if improperly designed may lead to overheating or overcooling of the ground. Good designs ensure properly balanced energy storage through adequately sizing ground-loops. Hybrid systems combine conventional Heating, Ventilating, and Air Conditioning (HVAC) with GSHPs in order to significantly reduce the high installation costs of GSHPs. The hybrid systems are designed in such a way that GSHPs provide the base building energy demands while the conventional HVAC is used only during the peak hours. In general, all buildings can be divided into two main categories: cooling dominant and heating dominant. If a building is cooling dominant, ground temperature increases with time and in heating dominant cases it decreases. A severe ground temperature increase/decrease is referred to as 'ground fouling' because it can render the GSHP inoperable, as temperature differences are required to maintain controlled heat flow. This paper compares long-term operation of hybrid and nonhybrid GSHP systems in order to investigate the effectiveness of hybridization at alleviating 'ground fouling'. A homespun 2D finite-volume model is proposed to study heat transfer in ground coupled heat pump systems and is verified against an analytical solution as well as experimental data. Through simulation of different building types, it is demonstrated that hybridization has potential to reduce 'ground fouling' but only in limited cases for which a large portion of the energy demands is being met by the conventional HVAC.

Characterization of the Effects of Borehole Layouts in Geo-exchange

“…The finite element model was validated against the analytical results presented in [42]. The analytical results were generated using a finite line-source model.…”

“…Using the same validation procedure as in Kuzmic et al, [42] the finite element model was validated against analytical and experimental results. Finite element models were created using the same parameters and boundary conditions as in [42].…”

Numerical and analytical study of a geo‐exchange borehole using conventional grout and bentonite‐based backfilling material

“…Similarly, Law and Dworkin 36 found that the recommended distance of 6 m between boreholes does not always prevent thermal interactions between the boreholes of GSHPs. Building on that study, Kuzmic et al 37 developed a 2-D model to study the performance of a hybrid system involving a GSHP and a conventional HVAC (Heating, ventilation, and air conditioning) system as a function of borehole separation. They observed that the hybridization has a potential effect on the ground temperature stability, and could reduce the need for borehole spacing.…”

Experimental analysis of a continuous operating ground source heat pump system in Wuhan, China

“…In the recent researches, most studies have concentrated on improving the performance of the GSHP system by experimental and numerical method. Some papers concentrate on the experiment and simulation on the thermal performance of ground heat exchanger (GHE) for the GSHP system [6][7][8]. Cao et al [6] used the experiment and CFD simulation to make research on the thermal performance for a new type of ground heat exchanger, and also analyzed the entire thermal resistance of the GHE and the soil temperature distribution.…”