Abstract
Model simulation allows to present the time-varying temperature distribution of the ground source for heat pumps. A system of 25 double U-shape borehole heat exchangers (BHEs) in long-term operation and three scenarios were created. In these scenarios, the difference between balanced and non-balanced energy load was considered as well as the influence of the hydrogeological factors on the temperature of the ground source. The aim of the study was to compare different thermal regimes of BHEs operation and examine the influence of small-scale and short-time thermal energy storage on ground source thermal balance. To present the performance of the system according to geological and hydrogeological factors, a Feflow® software (MIKE Powered by DHI Software) was used. The temperature for the scenarios was visualized after 10 and 30 years of the system’s operation. In this paper, a case is presented in which waste thermal energy from space cooling applications during summer months was used to upgrade thermal performance of the ground (geothermal) source of a heat pump. The study shows differences in the temperature in the ground around different Borehole Heat Exchangers. The cold plume from the not-balanced energy scenario is the most developed and might influence the future installations in the vicinity. Moreover, seasonal storage can partially overcome the negative influence of the travel of a cold plume. The most exposed to freezing were BHEs located in the core of the cold plumes. Moreover, the influence of the groundwater flow on the thermal recovery of the several BHEs is visible. The proper energy load of the geothermal source heat pump installation is crucial and it can benefit from small-scale storage. After 30 years of operation, the minimum average temperature at 50 m depth in the system with waste heat from space cooling was 2.1 °C higher than in the system without storage and 1.6 °C higher than in the layered model in which storage was not applied.
Highlights
Increasing climate change awareness and the popularity of renewable energy sources are connected with the increasing attention to geothermal energy and devices such as heat pumps
The drop of temperature was most visible in the centre between borehole heat exchangers (BHEs)
The difference in beginning stage, the drop of temperature was most visible in the centre between BHEs
Summary
Increasing climate change awareness and the popularity of renewable energy sources are connected with the increasing attention to geothermal energy and devices such as heat pumps. According to [1], in 2050, electric heat pumps will become more common in most parts of the world. 10,572,395 heat pumps units in operation in Europe [2]. Ground source heat pumps (GSHP) are a popular solution, especially for bigger installations. Several regional studies of the shallow geothermal potential of heat pumps in different geological conditions have been conducted, for example, in Japan [3], Energies 2020, 13, 1341; doi:10.3390/en13061341 www.mdpi.com/journal/energies
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