Thermal resistance capacity model for transient simulation of Earth-Air Heat Exchangers

In the present paper, a new hybrid model for transient heat transfer in Earth-Air Heat Exchangers (EAHE) based on thermal resistance capacity circuit is developed. To evaluate the performance of the EAHE, part of the solution field (soil around the pipe) is analytically solved. To assess the heat transfer in pipe and within the fluid inside the pipe, the solution field is divided into different layers. Using a capacity resistance network, the governing equations in the form of Ordinary Differential Equations (ODE) are derived and then coupled with analytical portion are solved by numerical discretization. In the current model, the effect of the thermal capacity of the soil around the pipe is taken into account in the simulation. Thus, using the proposed model, the thermal saturation of the soil is captured. Moreover, the effect of the variation of ambient temperature is considered on the heat exchanger performance. Ultimately, the results of the presented model are compared with experimental and numerical ones, and acceptable agreement is observed. Using the model, then, the effect of buried depth, fluid velocity, and the operation strategies of the system (continuous or intermittent) is investigated on the performance of the EAHEs.