Modelling and Simulation of Earth Air Tunnel Heat Exchanger

Abstract

The Earth Air Tunnel Heat Exchanger (EATHE) is an efficient technique used to reduce the cooling load of a building. In the past years, many researchers had developed analytical and numerical models for the analysis of EATHE systems, but were unable to recast into design equations, and had used the trial-and-error method for the analysis. This paper focuses on modelling and simulation of the EATHE system for geographical conditions, with average day temperature ranging from maximum 45°C for Nagpur [21.14° N, 79. 08° E}. The method to calculate the Earth's Undisturbed Temperature (EUT), and more recently developed correlations for friction factor and Nusselt number, are used to ensure higher accuracy in the calculation of heat transfer. The developed equations can be utilized to calculate heat transfer, convective heat transfer coefficient, and length of pipe of the EATHE system. A longer pipe of smaller diameter buried at a greater depth with lower air flow velocity results in increase in peiformance of EATHE. In this paper a simple Excel based mathematical model has been developed in order to design the EATHE. This model helps in determining characteristic dimensions, air flow rate, selection of blower and economic investments in an EATHE system.