Importance of Groundwater Flow on Life Cycle Costs of a Household Ground Heat Pump System in Japan

抄録

This paper analyzed life cycle costs of a ground source heat pump system used in a residence of Japan considering an advection effect of groundwater flow of eight different Darcy velocity. The required length of a single borehole heat exchanger was determined in each seven area of different heating/cooling loads to minimize the life cycle cost during 20 years through heat pump simulations. This study revealed that the effect of groundwater flow appeared when the velocity was more than 10 m/y and was almost converged when the velocity reached at 200 m/y. The cost decreased almost linearly according to the logarithms of the velocity. The velocity range was possible in steep valleys and alluvial fans of Japan. This study also showed that the costs were related mainly to the total loads, and secondarily to the groundwater flow conditions for the household system. Among seven areas, the household system was economically suitable relative to conventional air source heat pump systems in the cold areas 1 and 2 without initial cost reduction. The moderately warm areas 3 to 5 also became suitable when the initial costs would be reduced by 20 % as a common target of current R&D projects.