Analysis of the convective heat exchange effect on the undisturbed ground temperature

• The undisturbed ground temperature is used for boreholes lengths calculations for geothermal.
• The appropriate correlation for convection gives an accurate ground temperature profile.
• The model is validated with 13 thermocouples inserted inside a 46 m probe at different depths.

The ground temperature is an important parameter for several applications such as ground source heat pumps, agricultural greenhouses and ground energy storage systems. This paper describes a numerical model based on 1D transient heat conduction equation, using the energy balance on the soil surface as a boundary condition. The absorbed solar radiation by the soil, the convection heat transfer between the soil and the ambient air, as well as the long wave radiation exchange between the soil and the sky have been considered. An hourly simulation over a whole year (8760 h) with 1 h time step has been conducted using real meteorological data including global solar radiation, ambient dry bulb and dew point temperatures as well as the wind velocity. The model has been validated against measurements and analytical calculations for a site located in Montreal (Canada). The model is applied to investigate the effect of convective heat flux, calculated using three different correlations on the deep ground temperature for different climates. It has been found that in general, McAdams (1954) and Kusuma (2004) correlations can be used for different climates with relatively good agreement between measurements and calculations.