Abstract
Evaluation of appropriate areas to introduce a closed-loop ground-source heat pump (GSHP) system in the case of a standard detached residence was conducted in Akita Plain, Japan. Depth of borehole heat exchanger (BHE) required to use a GSHP system was taken as the suitability index, which is simpler for the general public to understand and to promote the system. Heating and cooling loads of the standard size detached residence were calculated based on the 2013 Energy Conservation Standard. To estimate BHE depths and estimate a suitable area, identical 3D BHE models were constructed at 30 points in the plain. Required BHE depths were determined by performing heat exchange simulations at each location using the calculated loads and heat exchange rates. A suitability map showing distribution of the required BHE depths was prepared. BHE depths were shorter in the north-western area compared to the other parts, implying that the coastal lowlands in this area are more suitable for closed-loop system in the standard detached residences in terms of heat exchange performance as well as the cost reduction. Thickly distributed Quaternary System with higher thermal conductivity is contributing to shorter BHE depths. The suitability map is effective to adopt potential areas for the system installation in the standard detached Japanese residences.
Highlights
In ground source heat pump (GSHP) system, heat energy of low enthalpy is exchanged with that of shallow underground
As underground temperature is relatively stable throughout the year, a GSHP system is considered to be good for energy saving and eradication of heat island phenomena in urban areas [1,2]
Depth of borehole heat exchanger (BHE) required to satisfy heating and cooling loads of the detached residence was taken as a suitability index
Summary
In ground source heat pump (GSHP) system, heat energy of low enthalpy is exchanged with that of shallow underground. This eventually results in higher initial cost In this situation, the optimum depth of BHE required for efficient heating and cooling. Shrestha et al [9,10] prepared suitability maps depicting the distribution of effective thermal conductivity and coefficient of performance of a particular GSHP system with its operating costs in Tsugaru Plain of northern Japan. The optimum required depth of BHE should be assessed which can result in higher performance and lower cost, in order to promote GSHP system in Japan. The required depth of BHE that satisfies these heating and cooling loads were computed incorporating the results of regional groundwater flow and heat transport analysis, which is a novel approach to assess possible areas to introduce a closed-loop system. Areas with shorter BHE depths are appropriate to install closed-loop system in terms of heat exchange efficiency and cost reduction
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