Cooling and heating potential of earth-air tunnel heat exchanger (EATHE) for non-air-conditioned building

Abstract

A numerical model to predict energy conservation potential of earth-air heat exchanger system and passive thermal performance of building has been developed. This model improves upon previous studies by incorporating effects of ground temperature gradient, surface conditions, moisture content and various design aspects of earth-air-tunnel heat exchanger (EATHE). The model is based on simultaneously coupled heat and mass transfer in the EATHE and is developed within the scope of numerical techniques of finite difference techniques and FFT (Matlab). The model is validated against experimental data of a similar tunnel in Mathura (India), and is then used to predict the tube-extracted temperature for various parameters such as humidity variations of circulating air, airflow rate and ambient air temperature. The model is found to be more accurate in predicting tube extracted temperature variations along the length (error range ±1.6%). The earth-air-tunnel is further coupled to a non-air-conditioned building to study reduction in cooling and heating loads. The cooling potential of an 8m earth tunnel is found adequate (19KW) to maintain an average room temperature 27.65°C. However, an auxiliary energy load of 1.5KW for the winter season is required to achieve comfort conditions with an EATHE system affecting an average room temperature of 24.48°C. The present model can be easily coupled to different greenhouse and building simulation codes.