Experimental Investigation of Groundwater Heat Pump Usage for District Heating and Cooling

Nearly half of Europe’s total energy consumption is dedicated to buildings. Heating and cooling consist of a significant part of this consumption. Groundwater heat pumps (GWHPs) are highly efficient, environmentally friendly and low-carbon technology that can supply heating and cooling to buildings on small to large scale. Northern Gateway Heat Network is an ongoing project based on GWHP, located in Colchester, UK. The planned project will probably be the largest GWHP system using the confined chalk aquifer to date. It will provide district heating and domestic hot water to healthcare buildings, around 300 dwellings, and offices. The system is designed as part-load to cover 75% of the annual heating demand of the planned development with an 800 kW output heat pump which will benefit from the open-loop groundwater extracted at around 12.5°C.

A laboratory-scale sandbox model having external dimensions of 1.178 m × 0.721 m × 0.715 m (L × W × H) with two acrylic tubes acting as injection and abstraction wells was built to investigate the impact of GWHP operation on the system performance and sustainability. The setup was designed to perform different groundwater flow rates by changing the water levels in the hydraulic head tanks on the left and right sides of the sandbox. Several experiments were conducted considering different scenarios: heating, cooling, heating and cooling, and thermal energy storage to examine their impact on thermal plume development and system performance. The study also aims at investigating the effects of groundwater flow velocity, injection and abstraction rates on thermal plume development.

The experimental results show that the thermal plume reaches the abstraction well in each scenario, causing a change in the abstraction temperature. This phenomenon, called thermal recycling, reduces the thermal energy abstraction from the groundwater. The results also illustrate that groundwater flow velocity, injection, and abstraction rates significantly impact thermal plume development. Higher injection and abstraction rates create a larger thermal plume. However, groundwater flow prevents heat development around the well by dispersing the heat in the groundwater flow direction. The results show that it is important to consider groundwater flow velocity, injection and abstraction rate when designing a GWHP system. The distance between injection and abstraction wells is another significant parameter that should be carefully considered. However, it could not be investigated in the current study as the sandbox model was not suitable for changing the distance between injection and abstraction well. Further studies need to be carried out using large-scale field test and/or numerical simulations.