Abstract
Although ground source heat pump (GSHP) systems are more efficient than conventional air source heat pump (ASHP) systems, their high initial investment cost makes it difficult to introduce them into small buildings. Therefore, the development of a method for reducing the installation costs of GSHPs for small buildings is essential. This study proposes a modular ground heat exchanger (GHX) for cost reduction and an improved workability of GSHPs. In addition, a numerical model was constructed for the analysis of the performance of the modular GHX. However, to easily introduce the new GHX at the building design stage, the development of a performance prediction method for the introduction of modular GHXs to small buildings is necessary. Therefore, the entering water temperature (EWT) equation was derived from the calculation methods in the heat transfer process, and the ground temperature model was developed in consideration of the operation condition. The numerical results showed that the average values of EWT and ground temperature were 8.11 °C and 8.00 °C, respectively under an average ambient temperature of 0.42 °C. In addition, the performance prediction model was compared with the numerical results. The results showed that the coefficient of variation of the root mean square error (RMSE) of the ground temperature and EWT model were 5.20% and 1.33%, respectively.
Highlights
The performance of ground source heat pump (GSHP) systems is more stable than that of other heat source systems because the former use heat from the ground, which maintains a constant temperature throughout the year
In a GSHP system, entering water temperature (EWT) is an important element that affects the performance of the heat pump and ground heat exchanger (GHX), and the performance prediction equation can be used to calculate EWT using the ground temperature and LWT
Because the heat source temperature was always higher than the set-point (4 ◦ C), the results showed that the system on/off depended on the load temperature
Summary
The performance of ground source heat pump (GSHP) systems is more stable than that of other heat source systems because the former use heat from the ground, which maintains a constant temperature throughout the year. GSHP systems exhibit higher efficiency in energy use compared to conventional air source heat pump (ASHP) systems, their high investment cost, which includes the drilling cost and the difficulty in securing sites for system introduction, makes their introduction into small buildings difficult. For a typical closed-loop GSHP system, earthwork and boring account for approximately 40% of the total construction cost (Figure 1). For the introduction of GSHP systems into small buildings, ground heat exchangers (GHXs) that can efficiently use the installation area and reduce the initial investment cost are required. As the modular GHX is installed at a depth of 2 to 4 m, it can significantly reduce drilling and installation costs compared to the closed-loop type, which is installed at a depth of 100 m or more
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