Abstract
In order to take advantage of different forms of heat pumps and to mitigate thermal imbalance underground caused by long-term operation of ground source heat pumps, hybrid ground source heat pump systems have received an increasing attention. In this research, based on the fact that abundant groundwater resources are commonly available in karst regions, a new strategy is introduced for selecting and determining hybrid ground source heat pump capacity. Five scenarios of hybrid ground source heat pump system coupling groundwater source heat pumps with other supplementary heat pumps are proposed in this article to provide appropriate options to eliminate heat buildup under different hydrogeologic conditions. Methodologies for sizing and selection are established. Then, a case study of techno-economic analysis was performed for a project in the karst region in South China. The results showed that these scenarios can effectively mitigate heat buildup, and under the hydrogeologic condition in the case study. Compared to the solo ground-coupled heat pump solution, the optimal solution (Solution 4 in this study) can reduce the annual costs by 16.10% and reduce the capital investment by 60%. Methodologies developed in this study are beneficial for selecting appropriate approaches to mitigate heat buildup and enhance competitiveness of ground source heat pumps.
Highlights
Heat imbalance is one of the most important problems associated with the ground source heat pump (GSHP) and has a significant impact on system performance
The results found that the temperature difference of two adjacent buried ground heat exchangers (GHEs) at a same depth was very different, and this was caused by the existence of groundwater flow in a karst structure where the GHE penetrated through
The groundwater resources in karst structures are abundant, and it is possible to eliminate the problem of heat buildup using groundwater source heat pump (GWHP) and different HyGSHPs instead of solo ground-coupled heat pump (GCHP)
Summary
Heat imbalance is one of the most important problems associated with the ground source heat pump (GSHP) and has a significant impact on system performance. The installed capacity of GCHPs and ASHPs will be calculated subsequently Such an approach is selected based on the consideration that the users’ load is fixed in the reference case, and coefficient of performance (COP) and operation cost of HP are directly affected by the load ratio. The rate of heat rejected by GCHP system to the ground is calculated as follows[13] qre = ðCOPcs + 3:412Þ ð4Þ qc COPcs where qre (W) is the heat rate rejected by the HP system to the ground, qc (W) is the building cooling demand, and COPcs is the coefficient of performance for cooling of HP system. Two subterranean rivers nearby were assumed as the potential water source for GWHPs. According to the pattern of the flow rate of subterranean rivers, the heating (winter) and cooling (summer) periods were divided into 13 cycles (7 days per cycle), respectively. Drilling cost Thermal exchange rate for the borehole heat exchanger per meter Installation cost
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