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The earth-air heat exchanger (EAHE) is a promising technique which can effectively be used to reduce the heating/cooling load of a building by preheating the air in winter and vice versa in summer. In the last two decades, a lot of research has been done to develop analytical and numerical models for the analysis of EAHE systems. Many researchers have developed sophisticated equations and procedures but they cannot be easily recast into design equations and must be used by trial-and-error. In this paper, the author has developed a one-dimensional model of the EAHE systems using a set of simplified design equations. 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 enable designers to calculate heat transfer, convective heat transfer coefficient, pressure drop, and length of pipe of the EAHE system. A longer pipe of smaller diameter buried at a greater depth and having lower air flow velocity results in increase in performance of the EAHE system.

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Modeling is very useful tool in order to predict the effect of the operating parameters like pipe length, radius, depth of burial and air flow rate on the thermal performance and heating/cooling capacity of earth-air heat exchanger (EAHE) systems. Till date many researchers have carried out a number of studies on calculation models for earth-air heat exchanger systems. The analysis of EAHE systems started with the development of one-dimensional models. The two-dimensional models came into practice during the 1990s and were replaced by three-dimensional models in recent years. Latest models are dynamic and technically more advanced which can provide room for all types of grid geometry to produce detailed thermal analysis of EAHE systems. This paper reviews on calculation models of EAHE systems as of the end of March, 2014.

Earth-air heat exchanger system can be used effectively to reduce heat energy demand of buildings in cold and dry winter weather conditions. A quasi-steady state, three-dimensional model based on computational fluid dynamics was developed to evaluate the heating potential of earth-air heat exchanger system. The simulation model of earth-air heat exchanger system is developed in computational fluid dynamics platform CFX 12.0. The simulation results obtained from computational fluid dynamics modeling of earth-air heat exchanger were validated by experimental observations taken on experimental setup installed in Bhopal (Central India). A good agreement was observed between simulation results and experimental observations with maximum values of coefficient of correlation and root mean square of percent deviation 0.999 and 2.1%, respectively. The experimental setup of earth-air heat exchanger with polyvinyl chloride pipe of 19.228 m length and 0.1016 m diameter buried at 2 m depth discussed in this article gives the maximum and minimum rises in air temperature of 8.2°C and 6.8°C for air flow velocities of 2 and 5 m/s, respectively. It was seen that the rise in air temperature is faster for the initial length of the pipe and it became moderate for the remaining length. The total hourly heat energy gain or heating potential obtained from experimental setup of earth-air heat exchanger varied from 0.59 to 1.22 MJ h for air flow velocities of 2-5 m/s. The air flow velocity is found to greatly affect the thermal performance of earth-air heat exchanger system.