Development and Validation of Numerical Models of Borehole Heat Exchnager for Gshp (double U-tube Type and Concentric Tube Type)

Since a GSHP (Ground source heat pump) system uses thermal heat of the ground as a stable source of heat, its high system efficiency is expected to help save energy and reduce CO2 emissions, as well as alleviate the heat island effect because it does not release heat to the atmosphere. In Japan, the concept of GSHP systems began to attract interest from around 1980 as an energy-efficient technology, and the use of such systems has increased in recent years as concerns about environmental conservation have heightened. To promote the use of GSHP systems in Japan, it is essential to prepare sufficient engineering data and tools for predicting and evaluating system performance, while reducing the initial cost. The performance of a GSHP system depends largely not only on the heat exchanger’s heat extraction and injection of efficiencies, but also on the heat pump’s operating performance characteristics and the load profile of the building. To predict and evaluate the system’s operating performance, it is necessary to consider the interrelated actions of three factors: the ground heat exchanger’s performance characteristics, the heat pump’s performance characteristics and the building’s load profile. However, many of the engineering support tools for GSHP systems do not consider the temporal aspect of the building’s load profile and the heat pump’s operating performance (Nagano et at., 2006), making it difficult to quantitatively predict the performance and effectiveness of the installed system. Our ongoing study on GSHP systems aims to quantitatively predict the performance and effectiveness of the installed system, and thereby to provide guidance on appropriate operation and control schemes. To do this, we require an analysis model that can simulate the thermal behavior of a ground heat exchanger in consideration of the building’s load profile and the heat pump’s performance profile. This paper reports on our development of transient analysis models that simulate the performance of ground heat exchangers (Borehole type, hereafter referred to as BHE) and our validation of these models through a comparison with the operation records of a system installed in a building.