Influence of ground surface boundary conditions on horizontal ground source heat pump systems

Abstract

In this paper, the effects of ground surface boundary conditions, especially diurnal shading, on performance of horizontal ground source heat pump (GSHP) systems were studied. Firstly, a GSHP system model, which consists of the heat transfer of horizontal ground heat exchangers (GHEs) and the integration of the heat pump, and the ground surface boundary model are introduced. The diurnal shading model for canyon streets is also introduced. Then, effects of ground surface boundary conditions and shading on horizontal GSHP systems are studied. Results show that different assumptions on ground surface boundary conditions have significant impact on outcomes and should carefully be considered during analysing. The outlet fluid temperature and fluctuation in North-South (N-S) streets are higher than those of East-West (E-W) streets. The increase in street aspect ratios and latitudes could decrease sunshine exposure time of the streets. Daily variations of solar radiation and shading influence the outlet temperatures of horizontal GHEs up to buried depth of 2.5 m. Therefore, the effects of solar radiation and shading should be considered when studying shallow horizontal GHEs.