Application of Hourly Simulation in Designing Vertical U-Pipe Underground Heat Exchanger of Ground Source Heat Pump System

Design of underground heat exchanger is crucial to application of ground source heat pump system. This paper presents the method and self-developed program for designing vertical U-pipe underground heat exchanger using numerical simulation. The program´s accuracy was validated by comparison of outlet temperature between field test and simulation: the biases are not more than 1 centi-degree in most cases. This paper conducted a 30-years dynamic simulation using annual hourly loads as inputs and recommended a scheme of underground heat exchanger. This scheme ensures that the hours during which heat pump inlet temperature exceeds 32 centi-degree is not more than 18 in summer. And also the inlet temperature in winter is higher than 5 centi-degree. The authors indicate that heat rate per meter of borehole is insufficient for designing underground heat exchanger, and hourly simulation is essential.