Search

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: Earth–air–tunnel heat exchanger (EATHE) systems are insufficient to meet the thermal comfort requirements in summer conditions. Therefore, evaporating cooling has been integrated with EATHE to enhance the thermal comfort hours. Economics of integrated EATHE–evaporative cooling system to reduce/avoid the use of air-conditioner and electric heater is analyzed by evaluating simple Internal Rate of Return (IRR) on investment. For this analysis a transient and implicit model based on computational fluid dynamics has been used for evaluating the energy saving obtained by the use of EATHE system integrated with evaporative cooling. Four base cases of existing systems, i.e. air-conditioner and electric heater have been considered for carrying out the economic analysis. Moreover, three different types of blower (i.e. energy efficient blower, standard blower and inefficient blower) have been considered for evaluating the energy saving and financial viability of the proposed system. These results of IRR calculation shows that wherever, the existing air conditioner and heaters are efficient, their replacement with proposed EATHE system is not a technically and economically viable option. It is observed that the IRR value is greatly dependent on the electric tariff and the energy efficiency of the blower used in the proposed EATHE system. [Copyright &y& Elsevier]

Abstract: Performance of simple earth–air-tunnel heat exchanger (EATHE) is enhanced by integrating an evaporative cooler at the outlet. Year round hourly analysis of the integrated system has been carried out for predominantly hot and dry climatic conditions using multiphase computational fluid dynamics (CFD) modeling with FLUENT software (version 6.3). The analysis has been carried out individually for all 8760h of the year for the city of Ajmer (India), considering the temperature and humidity of ambient air as condition of inlet air. Results show that a simple EATHE system provides 4500MJ of cooling effect during summer months, whereas 3109MJ of additional cooling effect can be achieved by integrating evaporative cooler with the EATHE. Although the winter season in most of the cities in hot and dry climatic zones is very short, analysis of the 8760h show that the EATHE system is capable of providing 4856MJ equivalent of heating effect at such locations. For every hour, the condition of the outlet air has also been matched with the thermal comfort zone specified ay ASHRAE-55. Results show significant improvement in usefulness of the EATHE system when integrated with evaporative cooler in hot and dry climatic conditions. [Copyright &y& Elsevier]

Abstract: Earth–pipe–air heat exchanger (EPAHE) systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth–air–pipe heat exchanger systems. The model was developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth–air–pipe heat exchanger systems are studied. The 23.42m long EPAHE system discussed in this paper gives cooling in the range of 8.0–12.7°C for the flow velocities 2–5m/s. Investigations on steel and PVC pipes have shown that the performance of the EPAHE system is not significantly affected by the material of the buried pipe (pipe). Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. The COP of the EPAHE system discussed in this paper varies from 1.9 to 2.9 for increase in velocity from 2.0 to 5.0m/s. [Copyright &y& Elsevier]

Abstract: Earth–pipe–air heat exchanger (EPAHE) systems can be used to reduce the heating load of buildings in winter. A transient and implicit model based on computational fluid dynamics is developed to predict the thermal performance and heating capacity of earth–air–pipe heat exchanger systems. The model is developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth–air–pipe heat exchanger systems are studied. The 23.42m long EPAHE system discussed in this paper gives heating in the range of 4.1–4.8°C for the flow velocities 2–5m/s. Investigations on steel and PVC pipes have shown that performance of the EPAHE system is not significantly affected by the material of the buried pipe. Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. [Copyright &y& Elsevier]

In the present study, CFD-based parametric analysis is carried out to optimise the parameters affecting the temperature drop and heat transfer rate achieved from earth air tunnel heat exchanger (EATHE) system. ANSYS FLUENT 15.0 is used for CFD analysis, and k-ε model and energy equation were considered to define the turbulence and heat transfer phenomena. For a straight EATHE system configuration, four design and operating parameters, i.e., diameter of the pipe (A), length of pipe (B), inlet air velocity (C), and inlet air temperature (D), are considered at four different levels in Taguchi method. The Taguchi method is used to obtain maximum air temperature drop and heat transfer rate. The best combination of parameters for achieving a maximum drop in air temperature is A1B4C1D4 and that for obtaining maximum total heat transfer rate is A4B4C4D4. Statistical analysis reveals the percentage contribution of different factors for air temperature drop in the following order: inlet air temperature (57.80%), diameter of pipe (20.66%), length of pipe (12.03%), and air velocity (9.51%), while, for heat transfer rate, pipe diameter (53.28%), inlet air temperature (30.87%), air velocity (9.40%), and length of pipe (6.45%). [ABSTRACT FROM AUTHOR]