Modelling earth-to-air heat exchanger behaviour with the convolutive response factors method

This paper shows a new numerical model of earth-to-air heat exchanger. The system is discretized into “n” sections perpendicular to the exchanger pipe. In each section, the problem of conduction is solved using response factors method in order to reduce computational time. Each response factor is calculated using a finite elements program that solves 2D conduction problems. The particularity of this problem is that the time-constants are very high, making it impossible to use conventional properties of response factors to reduce the number of calculations. We will set out a new approach to solve this particular problem. Heat flux entering the pipe is then expressed as a function of the temperature of the air crossing the pipe and the external solicitations. A heat balance is then applied for each layer to find the resulting outlet air temperature. The model is then compared to an analytical model and a 3D model based on the dynamic finite volume approach. Finally an example of coupling between an earth-to-air heat exchanger and a low-consumption building is presented.