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Earth air tunnel heat exchanger (EATHE) systems are inadequate to meet the thermal comfort requirements in semi-arid regions as they require large pipe lengths. The effectiveness and performance of such system can be increased by increasing soil moisture content, making as wet soil configuration. In the present work, the thermal performance of the EATHE system with dry and wet soil has been evaluated during the peak summer season. Further, the thermal behavior of these two EATHE systems has been compared on the basis of temperature of air flowing through buried pipes at different sections along the length. For the same a theoretical model is developed and validated with experimental results and found in good agreement with an error ranging from 2.44% to 10.85%. Moreover, the exergetic analysis has been carried outto investigate the work potential and scope of maximum utilization of energy. Results reveal that thepipe length can be reduced by 12–14 m with wet EATHE system as compared to dry EATHE system for the same cooling performance. The second law analysis shows that the maximum exergetic efficiency is 52.25% and 53.18% for dry and wet soil EATHE systems respectively. [ABSTRACT FROM AUTHOR]

In the present research thermal performance of earth air tunnel heat exchanger (EATHE) coupled with a solar air heating duct has been experimentally evaluated for arid climate of Ajmer city of northwestern India, during winter season. An attempt has been made to enhance the heating capacity of EATHE system by coupling it with a solar air heating duct at the exit end. Results show that the air which comes out of coupled EATHE system is relatively hotter than the air supplied by the stand alone EATHE system. It was found that the heating capacity of EATHE system got increased by 1217.625–1280.753 kWh when it was coupled with solar air heating duct with a substantial increase in room temperature by 1.1–3.5 °C. The COP of the system also increased up to 4.57 when assisted with solar air heating duct. Therefore, the heating capacity of EATHE can be significantly increased by coupling it with solar air heating duct. [ABSTRACT FROM AUTHOR]

Abstract: Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and Computational Fluid Dynamics modeling. Effects of time duration of continuous operation, thermal conductivity of soil pipe diameter and flow velocity on thermal performance of EATHE under transient conditions have been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of EATHE. Study reveals that the effect of pipe diameter due to prolonged use of EATHE system on its thermal performance is least in case of soil with higher value of thermal conductivity. Results show that the increase in flow velocity leads to deterioration in thermal performance of EATHE system. Under steady state condition, drop of 18.8°C in air temperature is obtained, whereas, under transient conditions cooling of air reduces from 18.7°C to 16.6°C for soil thermal conductivity of 0.52Wm−1 K−1, after 24h of continuous operation. [Copyright &y& Elsevier]

Abstract: Effect of soil thermal conductivity and time period of continuous operation of EATHE on thermal performance has been carried out for different pipe length of EATHE using experimentally validated CFD simulation. In this paper, the authors aim to study the underground temperature characteristics of the soil surrounding the EATHE pipe and the effect of duration of operation of EATHE on its thermal performance. Maximum air temperature drop of 15.6, 17.0 and 17.3K are observed for soil thermal conductivities of 0.52, 2 and 4Wm−1 K−1 respectively. Maximum deterioration in the performance in terms of temperature drop obtained during continuous operation of 24h is recorded as 2.9K for soil with thermal conductivity of 0.52Wm−1 K−1. Thickness of soil annulus surrounding the pipe up to which the thermal influence is observed depends on the thermal conductivity of the soil and period of continuous running of EATHE system. The thickness of the soil annulus beyond which no significant rise in temperature of soil is observed is equal to the pipe diameter. [Copyright &y& Elsevier]

Abstract: Thermal performance of earth air tunnel heat exchanger (EATHE) under transient operating conditions has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and computational fluid dynamics modeling. Effect of time duration of continuous operation and thermal conductivity of soil on thermal performance of EATHE under transient conditions has been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. Under steady state condition, a drop of 18.8°C is obtained in air passing through EATHE having 0.1m diameter and 60m length, at 5ms−1 flow velocity, whereas, the transient analysis shows that for soil having thermal conductivity of 0.52Wm−1 K−1, the cooling of air reduces from 18.7°C to 16.6°C, after 24h of continuous operation. Change in cooling effect after 24h of operation for soil thermal conductivity of 2.0Wm−1 K−1 and 4.0Wm−1 K−1, reduced from 18.8°C to 18.5°C and 18.8°C to 18.7°C respectively. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of earth air heat exchangers. [Copyright &y& Elsevier]

Abstract: Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions in winter season has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and Computational Fluid Dynamics (CFD) modeling. Effect of time duration of continuous operation and thermal conductivity of soil on thermal performance of EATHE under transient conditions has been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. Under steady state condition, a rise of 19.6°C is obtained in air passing through EATHE having 0.1m diameter and 60m length, at 5m/s flow velocity, whereas, the transient analysis shows that for soil having thermal conductivity of 0.52Wm−1 K−1, the heating of air reduces from 19.4°C to 17.2°C, after 24h of continuous operation. Heating effect after 24h of operation for soil thermal conductivity of 2.0Wm−1 K−1 and 4.0Wm−1 K−1, reduced from 19.6°C to 19.2°C and 19.6°C to 19.5°C, respectively. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of earth air heat exchangers. [Copyright &y& Elsevier]

Abstract: A new term ‘Derating Factor’ is devised for evaluating deterioration in thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions in predominantly hot and dry climate of Ajmer (India) using experimental and computational fluid dynamics modeling with FLUENT software. Maximum air temperature drop obtained using steady state approach for EATHE of pipe length 100m, pipe diameter 0.2m and at air velocity of 5ms−1 is 18.4°C, 18.7°C and 18.4°C for soil thermal conductivity of 0.52, 2.0 and 4.0Wm−1 K−1 respectively. However, the maximum air temperature drop obtained using transient approach during 24h of operation vary between 18.3°C and 14.0°C, 18.3°C and 17.2°C and 18.6°C and 18.0°C for soil thermal conductivity of 0.52, 2.0 and 4.0Wm−1 K−1 respectively. The derating factor is found to be a function of thermal conductivity of soil, duration of continuous operation of EATHE and length of pipe. The analyzed cases have shown the range of derating to be as minimal as 0.2% to as high as 68%, which if ignored while designing may lead to poor performance of earth air heat exchangers. Maximum value of derating factor is observed after continuous operation of EATHE for 24h. [Copyright &y& Elsevier]

Abstract: Increasing the coefficient of performance of air-conditioner with air-cooled condenser is a challenging task especially in areas where weather conditions are quite hot. The performance of conventional vapour compression system based air-conditioners can substantially be improved by coupling these active cooling systems with less energy intense passive cooling systems. In the present research, an attempt has been made to enhance the performance of active cooling system by coupling it with EATHE in four different hybrid modes and thermal performance of the developed hybrid cooling system has been investigated experimentally. The power consumption of conventional 1.5 TR window type air conditioner is found to be reduced by 18.1% when cold air from EATHE is completely used for condenser cooling of the air-conditioner. [Copyright &y& Elsevier]