Study on the Long-Term Performance and Efficiency of Single-Well Circulation Coupled Groundwater Heat Pump System Based on Field Test

Although buildings are often heated and cooled by single-well circulation coupled groundwater heat pump systems, few studies have evaluated the long-term performance of these systems. Therefore, the present study investigated the performance of these systems by analyzing the efficiency and energy consumption using 4 years of operating data. The results indicate that the coefficient of performance (COP) of the system gradually decreases because of thermal breakthrough or an accumulation of cold. In addition, the sealing clapboards could effectively slow down thermal breakthrough. In addition, compared with the heating period, the COP of the heat pump unit (HPU) and system increases, and its energy consumption decreases in the cooling period. It was also found that partial heat loss occurs when water from the single-well circulation outlet penetrates the main pipeline. Moreover, the heat-exchange efficiency of a single HPU exceeds that of multiple HPUs, and the COP of a HPU decreases during operation with increasing indoor temperature. Accordingly, we improved the performance of system by increasing the underground heat storage. Herein, we focus on optimizing the system design during long-term operation, which includes taking steps such as lengthening the sealing clapboards, using insulated pipes, discharging the remaining water and adding intelligent control devices.

Evaluation of measures to improve the performance of an open loop ground source heat pump system in the chalk aquifer: a case study

A case study documenting the development of a groundwater-fed district heat network in Colchester, UK, is presented. The performance of an open loop groundwater heating and cooling system (also known as a ground source heat pump (GSHP)) is a function of the performance of individual boreholes and interactions between the boreholes. When performance does not meet its design capacity or decreases with time, various measures can be undertaken to improve either the performance of individual wells or the performance of the system as a whole.Output from the first exploration borehole was less than expected, placing the business case for the development in jeopardy. Consequently, refinements to the remainder of the drilling programme were implemented including three to improve the performance of individual wells and two to improve performance of the system in its entirety. Results of these refinements are presented and may be used to inform the design of new open loop groundwater heat pump systems (GSHPs) and/or the rehabilitation of existing systems that have experienced diminished performance.Yields from three wells drilled using the reverse circulation method were more than double those drilled with the direct water flush method. A significant improvement in the performance of abstraction wells due to reinjection was observed. Specific capacity in abstraction wells increased by c. 40% due to reinjection, where the distance between abstraction and reinjection locations was 535–717 m. Allowing an excess pressure of up to 0.2 MPa in the reinjection boreholes meant that reinjection could be achieved with fewer wells.Outputs from abstraction wells were not increased by extending the depth of boreholes from 135 to 200 m or implementing additional acid treatments.

Semi-analytical model for dynamical modeling thermal recycling in a doublet well of open-loop groundwater heat pump with variable heat extraction

<p>The performance of a GroundWater Heat Pump (GWHP) is critically influenced by the thermal recycling between wells, i.e. the proportion of thermally affected injected water that is pumped back by the extraction well. The use of the complex potential theory, assuming a homogeneous aquifer and a uniform regional flow, to assess the evolution of the extraction temperature from a doublet is presented. One major limitation in the available models in the literature is that they assume a constant extraction flow rate and constant heat extraction. This is unrealistic since buildings energy loads vary naturally with time during the day, the month and the year. To overcome this, the present paper develops a semi-analytical model to dynamically determine the extraction temperature of a doublet GWHP taking into account a variable extraction heat flow. Results obtained are benchmarked to a finite-element Comsol Multiphysics numerical model under different conditions, which enlightens the limitations of the proposed model. The developed model can be easily used to assess the technical potential of a GWHP.</p>

Numerical Modelling of a District Scale Groundwater Heat Pump Operation: Case Study from Colchester, UK

<p>Groundwater heat pumps (GWHP) are an environmentally friendly and highly efficient low carbon heating technology that can benefit from low-temperature groundwater sources lying in the shallow depths to provide heating and cooling to buildings. However, the utilisation of groundwater for heating and cooling, especially in large scale (district level), can create a thermal plume around injection wells. If a plume reaches the production well this may result in a decrease in the system performance or even failure in the long-term operation. This research aims to investigate the impact of GWHP usage in district-level heating by using a numerical approach and considering a GWHP system being constructed in Colchester, UK as a case study, which will be the largest GWHP system in the UK. Transient 3D simulations have been performed pre-construction to investigate the long-term effect of injecting water at 5°C, into a chalk bedrock aquifer. Modelling suggests a thermal plume develops but does not reach the production wells after 10 years of operation. The model result can be attributed to the low hydraulic gradient, assumed lack of interconnecting fractures, and large (>500m) spacing between the production and injection wells. Model validation may be possible after a period operational monitoring.</p>

Exergy Analysis of Building Heating with a Groundwater Source Heat Pump

The paper presents an exergy analysis of the groundwater heat pump operation for theneeds of building heat-ing. The analysis was conducted on a monthly basis, given the dependence of exergy on the changing state of the envi-ronment. Changes inheating coefficient and exergy efficiencyof thegeothermal heat pumpheating systemdepending onthe influentialparameters wereanalyzed: groundwater temperature fromthe pumping well, changes in the ground-water temperature on the heat pump evaporatorand water temperature inthe heating system.The obtained results provide insight into thermodynamic indicators of heat pump operation depending on the groundwater temperature and the operation mode of the building heating system. The conducted analysis provides guidelines for the design and opti-mization of heat pumps that work with groundwater as a heat source.