International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 07 | July -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 514 Comparative Study of Transient Conditions for Continuous Operation and Intermittent Operation of EATHE System Operated in Winter Season: A CFD Approach Abhishek Agarwal 1* , Mohd. Yunus Sheikh 2 , Rohit Misra 3 -----------------------------------------------------------------------------------------***---------------------------------------------------------------------------------------------- Abstract - The objective of the present work is to investigate the transient conditions of Earth Air Tunnel Heat Exchanger under intermittent operation using Computational Fluid Dynamics software FLUENT 6.3. Simulation runs have been carried out for winter heating case using three different soil thermal conductivities. Results obtained for intermittent operation of EATHE system have been compared with those obtained for continuous operation in terms of temperature rise of air and COP of the system. Simulations reveal that the rise in air temperature obtained during intermittent operation is better than that obtained during continuous operation of EATHE. These results shown significant improvement in heating potential during intermittent operation is observed for EATHE buried into soil having low thermal conductivity. 1. Introduction To reduce peak load passive cooling system are recommended such as EATHE system. There are many reported experimental and analytical studies on EAHE. The ground temperature at depths of about 2 m to 3 m is practically independent of seasonal variation. During winter the ground temperature is higher than the ambient temperature and during summer it is lower. This offers great opportunities for coupling a building to the ground to provide favourable protection from adverse outdoor conditions, throughout the year. The indoor air is circulated through small diameter cylindrical ducts that are buried horizontally, at a depth of at least 2 m. Given the large thermal inertia of the ground, it can considered as a considerable heat source or heat sink, depending on the season. As a space cooling technology utilizing natural energy, earth–air–pipe systems have attracted increasing interest for energy conservation [1–5]. Mihalakakou et al. [6–8] and Jacovides et al. [9,10] used earth–air–pipe heat exchangers in cooling agricultural greenhouses. Kumar et al. [11] evaluated the conservation potential of an earth– air–pipe system coupled with a building with no air conditioning. The cooling power for the earth pipe with length of 60 m, diameter of 0.10 m and air flow velocity of 5 m/s was 19 kW, which was adequate to maintain an average temperature of 27.65 °C for a single room in India. To improve the feasibility and comfort for space cooling, coupled a desiccant cooling set-up on the basis of the earth–air–pipe. A specific study on the thermal saturation and recovery of the soil under intermittent and continuous EAHX operation is performed by Mathur et al. [22]. 2. Description of CFD model Computational fluid dynamics (CFD) is used to solve the fluid flow, heat & mass transfer problems by dividing the objects into grid form and applying governing equations on each grid. CFD based model solved these governing equations in the form of partial differential equation. Numerical solution of these equation gives temperature and pressure distribution, flow parameters. CFD helps to reduce long tedious experimental work and enhance the accuracy of work. To examine the air temperature rises in winter season of EATHE system, CFD software, FLUENT 6.3, was used. CFD software, GAMBIT 2.4.6 has been used to design and meshing 60 m long, 0.1 m diameter pipe. The model incorporates the effect of turbulent air flow on the thermal performance. The element type and the grid density were selected to be variable according to the sensitivity of temperature quantity, so that the calculation can adapt to the actual situation and reach a high level of accuracy. Because the temperature changes more sharply around the pipe wall, the grid is designed to be denser in that area, while it is sparser farther away from the pipe wall. In the present study it has been assumed that air is incompressible and the soil is homogeneous and its physical properties are constant. It was also assumed that the property of the pipes and ground materials do not change with temperature and engineering materials used in the CFD model are isotropic and homogeneous.This was validated by experimental results. Figure 1. Four different views of CFD model for EATHE