Undisturbed ground temperature in Melbourne

The ground surface temperature changes with the diurnal cycle of solar radiation and ambient air temperature. However, the amplitude of the ground temperature variation diminishes with the increase of the depth of the ground and after a certain depth of the ground, it becomes almost constant, where is termed "undisturbed ground temperature (UGT)". At this depth, the seasonal changes of solar radiation and ambient air temperature changes will no longer affect onground temperature. It is one of the important parameters for designing of the ground heat exchangers and building energy analyses. In this study ground temperatures at various depths in Melbourne were investigated using a 40 m deep borehole instrumented with thermistors. The ground temperatures at various depths (0 m to 40 m) in Melbourne were also simulated by using three methods: Kasuda formula method, simulation (TRNSYS, Type 77), and simplified correlation (developed by Ouzzane et al. in 2015) and the results were compared with the measured data. Root mean square error (RMSE) and mean bias error (MBE)were used to validate and verify the methods. It was found that the estimated ground temperatures at 2, 21, and 40 m depths by Kasuda formula method and simulation (TRNSYS)have the same trends as that of the measured data. The measured annual temperatures of ground at 2 m depth were between 14.7°C and 19.8°C, while the temperature at 21 m and 40 m depths remained almost constant. RMSE and MBE of the simulation (TRNSYS, Type 77) were found to be 1.39°C, and -1.39°C respectively compared to measured data at 21 m depth. Based on these values, we conclude that simulation (TRNSYS, Type 77) can reliably predict the ground temperature for the selected site in Melbourne