Modelling and Simulation of the Earth-to-Air Heat Exchanger in Laminar Air Flow Regime for the Passive Cooling of Buildings

Abstract

The earth-to-air heat exchanger is a very energy efficient system for preheating and cooling premises, which consists of circulating air through a tube buried at a certain depth in the ground. The temperature of the ground is less variable than that of the outside air, so that the air leaving the exchanger is more temperate. In the warm periods of the year, the air is cooled while it is warmed during the cold periods. The present work is devoted to the modelling and numerical simulation of the mixed convection earth-to-air heat exchanger in laminar regime. The mixed convection equations governing the heat transfers in the earth-to-air heat exchanger and in the building as well as the boundary and initial conditions have been presented and discretized using the finite difference method with an Alternate Direction Implicit (ADI) scheme. The linear algebraic equations obtained are solved using the Thomas algorithm combined with an iterative Gauss-Seidel procedure. The results show that the flow is dominated by forced convection. The analysis of the effect of Reynolds number indicated that the temperature, average Nusselt number and earth-to-air heat exchanger efficiency increase with Reynolds number.