Abstract
Intermittent operation can improve the coefficient of performance (COP) of a ground source heat pump (GSHP) system. In this paper, an analytical solution to analyze the geo-temperature restoration performance under intermittent operation of borehole heat exchanger (BHE) fields is established. For this purpose, the moving finite line source model is combined with the g-function and the superposition principle. The model takes into account the heat transfer along the borehole, thermal interference between BHEs, and the influence of groundwater flow. The accuracy of the model is validated through comparison with an experiment carried out under intermittent operation. The model makes it possible to analyze the geo-temperature restoration performance and its influencing factors, such as BHE spacing, heat flow rate, operation mode, and groundwater flow. The main conclusions of this work are as follows. The heat transfer along the borehole should be considered when analyzing the geo-temperature restoration performance. When the BHE spacing increases, the soil temperature change decreases and the heat recovery improves. Therefore, adequate borehole separation distance is essential in the case of a multiple BHE system with unbalanced load. The presence of groundwater flow is associated with interference between the BHEs, which should not be ignored. In the case of long-term operation, the groundwater flow is beneficial to the geo-temperature recovery process, even for downstream BHEs. Finally, a greater groundwater flux leads to a better geo-temperature recovery.
Highlights
The use of geothermal energy in space conditioning of buildings has increased rapidly during the past several decades
The ASHRAE manual [9] was the first to discuss the advantages of a hybrid ground source heat pump (HGSHP) system, which uses a cooling tower as a supplemental heat rejecter
Studies show that intermittent operation of the ground source heat pumps (GSHP) can reduce the heat accumulation in the vicinity of borehole heat exchanger (BHE) [13], which can improve to some degree the coefficient of performance (COP) of the pump
Summary
The use of geothermal energy in space conditioning of buildings has increased rapidly during the past several decades. In order to investigate the intermittent operation performance of a GSHP system, Cui et al [20] developed a finite element numerical model for the GHEs in alternative operation modes They found that the discontinuous operation mode and the alternative cooling/heating modes can effectively alleviate heat accumulation in the soil around BHEs, improving the performance of the system. The main objective of this paper was to obtain an analytical solution to be used in the analysis of the performance of an intermittently operating BHE field, in terms of geo-temperature restoration, and with the consideration of the groundwater flow. This solution is obtained by combining the moving finite line source model with a g-function, while observing the superposition principle. This paper provides a reference for the rational utilization in underground projects of intermittently operating GSHP systems
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
