Abstract
In this paper, a novel optimal design method for ground source heat pump (GSHP) system based on hydraulic characteristics of buried pipe network (BPN) is proposed. The influence of BPN hydraulic characteristics and soil thermal balance on the operation efficiency of GSHP system are considered. This paper studies the GSHP system of a building in Changsha in the Central and South China Hilly Region. First, referring to the soil thermal property test, a simple simulation model is built using TRNSYS. Furthermore, the influence extent of various factors on soil thermal balance are studied by orthogonal experimental design method (OED). Then, the BPN model of this system is established and TRNSYS is employed to establish the GSHP system model of the building. A comprehensive coefficient of performance of the whole year transportation system (COPall) is presented as the evaluation index to optimize the borehole depth (Bd), borehole spacing (Bs), buried pipe length (Bl) and buried pipe form. These results indicate that, the resistance of vertical buried pipe accounts for 80% of the total resistance in a BPN partition. Reducing the Bl from machine room to BPN by 80% in the whole BPN, and the total resistance decreases by 31.8%. It is found that there is a power function relationship between the average temperature rises of soil (ΔT) and the BPN resistance (H). Considering comprehensively, Bd of this project should be designed within 60 m-100 m and Bs should be designed 4.0 m-5.0 m. When the Bl is certain, the COPall reaches its maximum when the Bs is 3 m. For any Bs between the two buried pipe forms, the Bl corresponding to the maximum COPall is almost the same. They are 25.2 km for single U- tube and 67.2 km for double U- tube respectively. When the Bl is the same, 24 km is the critical length of two buried pipe forms. Our work can provide theoretical basis and guidance for the optimization design of GSHP in similar areas.
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