Generation of gridded temperature map of constant-temperature layer based on meteorological data for shallow geothermal applications

The energy exchange between the subsurface and the infrastructure may serve as an effective way to reduce energy consumption in space heating. In China, the concepts of climate battery and shallow geothermal have obtained growing attentions. The depth and the temperature of the constant-temperature layer (CTL), also called neutral zone, in the ground are significant factors during the design modeling. Unfortunately, the lack of knowledge in these site-dependent variables often leads to conservative design of ground heat exchangers and thus limits their implementations due to the high upfront cost. This study presents an improved analytical model based on the subsurface energy balance equation, which can be used to estimate the temperature and depth of CTL based on the meteorological and geological datasets. The model was first validated against the temperature records from 77 shallow geothermal case studies in China. With the development of remote sensing technology and agricultural dataset, the spatial mapping of CTL was then generated based on the variability of the geological and meteorological parameters. Finally, the simplifications were made to the proposed model when there is no available meteorological data and proven as sufficiently robust in results delivery. By performing this model at the initial stage of the engineering practice, the long-term heat exchange potential of the geology can be anticipated with higher fidelity, and the suitability of a certain region to be treated as a climate battery may be determined without costly drilling efforts.