Earth–air heat exchanger; Soil temperature; Cooling/heating capacity; Auxiliary energy load; ACH (air change rate); Space cooling
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 (EAT). The model is based on simultaneously coupled heat and mass transfer in the EAT and is developed within the scope of numerical techniques of Finite Difference 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%).
These results are further used to study the thermal performance of a non-air-conditioned building. Cooling potential of 80-m earth tunnel is found adequate (19 kW) to maintain an average room temperature 27.65°C. However, auxiliary energy load of 1.5 kW for winter season is required in achieving comfort conditions with EAT system affecting an average room temperature of 24.48°C. The present model can be easily coupled to different greenhouse and building simulation codes.