Experimental study on heat transfer of soil with different moisture contents and seepage for ground source heat pump

Abstract

Geothermal energy is a renewable energy source for heating, ventilating and air-conditioning (HVAC) systems, and is leveraged by ground heat exchanger (GHE) which is a key element of ground source heat pump (GSHP). The performance of GHE is significantly affected by soil thermal properties. To explore the heat transfer characteristics of soils with different moisture contents (MC) and seepage, a well-controlled sandbox was established and a series of experiments were performed. The results demonstrated that the soil with higher MC had stronger heat dissipation capacity, especially when seepage occurred. The temperature sensor 25 cm from the sandbox-centre detected temperature changes at the 452nd, 206th and 297th min under dry, unsaturated and saturated conditions, respectively. Moreover, the dominant mode of heat transfer in soils with different MCs was conduction, and the elevated heat-releasing rate enhanced heat propagation by moisture transfer. Furthermore, the size of the thermally affected zone was proportional to the thermal diffusivity, which was 2.14 × 10−7, 5.18 × 10−7 and 4.74 × 10−7 m2/s under dry, unsaturated and saturated conditions, respectively. Overall, these results indicate that the MC is a critical factor in characterizing soil heat transfer. This study provides guidance in choosing the installation environment for GHE and confirms the importance of matching soil characteristics with the GHE load.

Seepage Velocity: Large Scale Mapping and the Evaluation of Two Different Aquifer Conditions (Silty Clayey and Sandy)

“…Two additional important sustainable applications related to groundwater flow are geothermal systems and underground thermal energy storage (UTES) systems [48][49][50][51][52][53][54][55][56][57][58][59]. These systems were first used due to the oil crisis of the 1970s to identify alternative sources of energy [60,61], and have subsequently been proven to be successful in solving various challenges.…”

An Overview of Sandbox Experiment on Ground Heat Exchangers

“…Wang et al [72] performed sandbox experiments encompassing dry, unsaturated, saturated, and seepage sand conditions. Figure 16 presents the heating temperature and capacity of the electric heating rod under dry, unsaturated, saturated, and seepage sand Different from the approach adopted by Li et al [71], which involved using a U-shaped tube as the heat exchanger and constant-temperature water tanks on both sides of the sandbox to facilitate horizontal seepage flow, Wang et al [72] developed a 1.5 × 1.5 × 1.0 m cuboid adiabatic sandbox with horizontal seepage, with the schematic diagram shown in Figure 15. To facilitate water seepage, two water chambers with a width of 0.15 m were constructed on opposite sides of the sandbox.…”

The Bin Method to Investigate the Effect of Climate Conditions on the SCOP of Air Source Heat Pumps: the Italian Case

“…Duicu's study [4] reported the advantages of using heat pumps as a renewable source of energy. Different studies are also related to the employment of ground sources heat pumps [5]; in those applications, the performance of the entire heating and cooling system is significantly affected by soil thermal properties [6] and the circuit arrangement of the ground heat exchanger [7]. Regarding ASHP, in the recent literature, the effects of climate conditions are investigated by Mouzeviris and Papakostas [8] with reference to Greece.…”