Abstract
Heat pumps become more and more popular heat source. They can be an alternative choice for obsolete coal fired boilers which are emissive and not ecological. During heat pump installation designing process, especially for heat pumps with higher heating capacity (for example those suppling larger buildings), a simulation of heat balance of ground heat source must be provided. A 3D heat transport model and groundwater flow in the geothermal heat source for heat pump (GSHP) installation was developed in FEFLOW according to Finite Element Modelling Method. The model consists of 25 borehole heat exchangers, arranged with spacing recommended by heat pump branch guidelines. The model consists of both a homogeneous, non-layered domain and a layered domain, which reflected differences in thermal properties of the ground and hydrogeological factors. The initial temperature distribution in the ground was simulating according to conditions typical for Europe in steady state heat flow. Optimal mesh refinement for nodes around borehole heat exchangers were calculated according to Nillert method. The aim of this work is to present influence of geological, hydrogeological factors and borehole arrangement in the energy balance and long term sustainability of the ground source. The thermal changes in the subsurface have been determined for a long term operation (30 years of operation period). Some thermal energy storage applications have also been considered.
Highlights
Geothermal source heat pumps are more and more popular these days
In order to compare different operating regimes different scenarios were taken into consideration: 1) parameters homogeneous, not balanced energy load 2) parameters homogeneous, balanced energy load 3) parameters according to different layers of the model, not balanced energy The changes of the ground temperature were simulated over 30 years
The borehole heat exchangers (BHE) system was operating according to assessed monthly load as shown in Tab. 2
Summary
When borehole heat exchangers are installed, especially in close proximity, they can interfere each other and decrease efficiency of heat pump. Their operating regime is very important for sustainable long term operation. 20 years, while the heat sources (heat exchangers in the ground) are considered to have operational period of even 50 years. In the area 25 borehole heat exchangers (BHE), each of 100 m length were set 10 m from each other. In the vicinity of wells grid points were refined, to obtain better accuracy (Fig. 1). Parameters of borehole heat exchangers are given in Tab. 1. The fixed power of BHEs were connected with time regime to obtain assumed energy (Tab. 2)
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