Characteristics of heat fluxes in subsurface shallow depth soil layer as a renewable thermal source for ground coupled heat pumps

Abstract The soil heat fluxes (G) in subsurface shallow depth soil layer (SSDSL) are characterised by dynamics of diurnal, monthly, seasonal and annual behaviour. The soil heat very often is underestimated as a part of heat balance of the pedosphere, because its values are relatively small in comparison with sensible turbulent heat and latent heat fluxes. These fluxes concern mainly with net solar radiation and natural thermal properties of soils and plant cover. The soil heat in SSDSL is jointed with commonly widely available and relatively easy acquiring energy resources. This paper aims to present the thermal regime of heat fluxes in SSDSL and its climatic conditions in central Europe, taking into consideration the agriculture periphery characteristics of Wroclaw (Poland). The measurement results gathered across ten years (August 2007–July 2017) and the conducted thermal analysis aim to evaluate the utilization of SSDSL as a heat source for ground coupled heat pumps (GCHP). The measurements of G (positive soil heat fluxes G > 0 and negative G   0 reached 331,8 MJ∙m−2 (92,2 kWh∙m−2) for the bare soil and 179,0 MJ∙m−2 (49,7 kWh∙m−2) for the grassy area. The similar ten-year values for G