A Ground Resistance for Vertical Bore Heat Exchangers With Groundwater Flow

Abstract

A new ground resistance was developed for use in existing vertical bore heat exchanger VBHEx design algorithms. The new ground resistance accounts for the added heat transfer mode of convection due to groundwater flow by using as its foundation the solution for a moving line heat source. The combined ground resistance is presented in terms of the dimensionless Fourier and Peclet parameters. Results show that significant convection heat transfer may occur within a variety of hydrogeological regimes, particularly when the Peclet number is larger than 0.01. Since the new model captures the influence of groundwater flow, the resulting ground resistance differs markedly from the conduction-only ground resistance currently used in many vertical borehole heat exchanger design algorithms.

A Review of the Modelling of Thermally Interacting Multiple Boreholes

“…Due to the difficulties encountered both in modeling and computing the convective heat transfer and in learning about the actual groundwater flow in engineering practice, each of the methods presented in the previous sections is based on Fourier"s law of heat conduction and neglect the effects of groundwater flow in carrying away heat. Where groundwater is present, flow will occur in response to hydraulic gradients, and the physical process affecting heat transfer in the ground is inherently a coupled one of heat diffusion (conduction) and heat advection by moving groundwater [63]. Similar to the models discussed in the previous sections, here as well, the objective is to evaluate the temperature response in the soil surrounding GHEs.…”

“…Similar to the models discussed in the previous sections, here as well, the objective is to evaluate the temperature response in the soil surrounding GHEs. The effect of ground water is analyzed using numerical [26,[64][65][66] and analytical approaches [63,67].…”

Heat Transfer Modeling of the Ground Heat Exchangers for the Ground-Coupled Heat Pump Systems

“…Although a GHE is composed of a buried pipe that commonly is surrounded by grouting material, approximation by a line source is commonly accepted in heat transport models of GCHP systems (Diao et al, 2004;Eskilson, 1987;Sutton et al, 2003). The underground is assumed to be homogeneous with respect to the thermal and hydraulic parameters.…”

“…The solution of equation (15) for an infinite porous medium with a uniform initial temperature was given by Sutton et al (2003) and Diao et al (2004) …”

Experimental setup to measure the heat-exchange processes by controlling thermal and hydraulic conditions

“…The design of a BHE to be used in a shallow geothermal system is based on the evaluation of the thermal exchange capacity of the whole system constituted by the BHE itself and the surrounding ground. The energy performance of the system mainly depends on the thermal properties of the sediments and on possible groundwater flow (Sutton 2003). Moreover, the continuous heat exchange with the subsoil modifies the thermal status of the subsoil itself which, in turn, affects the thermal gradient in the BHE surroundings.…”