How groundwater flow field change affects heat transfer in groundwater heat pumps based on physical experiments

This study presents a simulation of potential changes in groundwater in three wells within a Quaternary gravel aquifer in the city of Ljubljana when groundwater cooled by about 4 °C is reinjected into it. The research focuses on the mass transport of calcite in the vicinity of boreholes. According to our results, the impact of the changes in the geochemical composition of the water is relatively small (around 1%). Although the waters are approximately in equilibrium, calcite may be dissolved and sometimes precipitated within the aquifer when cooled water is reinjected into it. The amounts of precipitated calcite always decrease with decreasing temperatures of the reinjected water, which can lead to calcite dissolution if the temperature difference is large enough and the water is only slightly oversaturated. This novel finding is significant since previously published studies have mostly focused on understanding the scaling (precipitation) of calcite and not its dissolution. The mass transfer of calcite is relatively low, but in a scenario of long-term pumping for several years, such low values could lead to a dissolved or precipitated mass of several hundreds of kilograms of calcite per year (at a pumping rate of 46 L/s).

Section: Introductionmentioning

confidence: 99%

The Influence of Water Temperature on the Hydrogeochemical Composition of Groundwater during Water Extraction and Reinjection with Geothermal Heat

Verbovšek

2023

“…The higher the pumping capacity of the well, the more significant the increase in the thermal conductivity of the BHEs and the better the heat exchange efficiency [29]. Different pumping and recharge well-group layout schemes also have a greater impact on heat exchange efficiency [30]. It has been discovered that the groundwater level has an overall decreasing trend with a longer extraction time, but the temperature remains largely unchanged [31].…”

Section: Introductionmentioning

confidence: 99%

Optimizing the Layout of a Ground Source Heat Pump System with a Groundwater–Thermal Coupling Model

Li,

Liu,

Wang

et al. 2023

The exploitation and utilization of shallow geothermal energy are of great significance to realizing China’s “double carbon” goal and promoting a green economy and social development. However, many projects using ground source heat pumps to exploit shallow geothermal energy have disrupted the thermal balance of the geothermal field due to insufficient preliminary research, affecting the sustainable utilization of shallow geothermal energy. Therefore, a 3D groundwater–thermal coupling model was established in this paper using the geotemperature data of a ground source heat pump system in Xi’an. This study investigated the response characteristics of the groundwater–thermal system to the ground source heat pump system using the numerical simulation method and discussed the optimal layout scheme of the system on this basis. After years of simulation, it was found that long-term operation of the ground source heat pump system under actual operation produces “cold accumulation”. In addition to artificial intervention of the groundwater flow field, the effects of the system operating parameters and layout settings are also investigated to alleviate this cold accumulation. The results show that changing the operating parameters so that the heat transfer is the same in winter and summer, cross-locating the cooling holes with the heating holes, and placing multiple pumping and recharge wells downstream can alleviate the cold accumulation in the heat exchange zone. The results of this numerical simulation study provide an important reference for solutions to mitigate the accumulation of ground cold and heat in developing shallow geothermal energy using borehole heat exchangers and to suppress the downstream geotemperature disturbance via the ground source heat pump system.

“…They discovered that when heating and cooling loads are in close proximity, it increases heat extraction. Li et al [29] carried out an experimental study to examine the influence of groundwater flow variation on heat transfer characteristics. They compared different layouts of abstraction and injection well groups to enhance the efficiency of GWHP.…”

Section: Introductionmentioning

confidence: 99%

Laboratory Investigation of Impact of Injection–Abstraction Rate and Groundwater Flow Velocity on Groundwater Heat Pump Performance

Sezer,

Sani,

Singh

et al. 2023

Using low-temperature (shallow) groundwater as a heat source or heat sink is a common practice to supply space heating or cooling, especially in the United States, Canada, China, and several European countries. The groundwater heat pump (GWHP) system has been extensively studied in recent decades using numerical approaches, which have some limitations in understanding the soil’s thermal behavior. Therefore, a laboratory-scale experimental study involving cooling tests was carried out to investigate the impact of GWHP on system performance and sustainability with varying groundwater flow velocities and injection and abstraction rates. The results demonstrated that groundwater flow velocity, as well as injection and abstraction rates, significantly impact thermal plume development. Higher injection and abstraction rates create a larger thermal plume, thereby decreasing abstraction temperature. However, groundwater flow prevents heat development around the well by dispersing the heat in the groundwater flow direction. Furthermore, the results indicate that the energy gain only increased by 81% and 107%, with a respective increase of 100% and 200% in injection and abstraction rates.