International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 05 Issue: 07 | July 2018 www.irjet.net p-ISSN: 2395-0072 © 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1254 Analysis of working parameters affecting the performance of Earth-air tube heat exchanger (EATHE): A review Bhawna Singh Mechanical engineering student, G.B. Pant Institute of Engineering and Technology, Pauri Garhwal, Uttarakhand, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract – One of the major concerns of an ideal air conditioning system is to provide enough comfort levels within the building. Moreover, the last few years have been an explicit example of the increased per capita energy consumption. This significant plunge has not only added to improved living standards but it also threatens the subsistence of human resources due to heavy reliance on conventional sources of energy to meet the regular energy demands. Hence it becomes crucial to explore and utilize nonconventional energy resources which prove to be clean, inexhaustible, easily exploitable and most importantly sustainable. Thus, several methods of passive air conditioning being developed in the present era such as ground cooling, nocturnal radiative cooling(NRC) prove to be an efficient as well as economic solution to the persisting problem of limited conventional energy resources. Moreover, earth as a heat source and heat sink is a well studied subject and is one of the fastest growing applications of renewable energy in the current worldwide scenario. Hence the aim of this study is to investigate the effect of various working parameters such as pipe length, material, depth of burial, air flow rate and several other factors that contribute to the proper functioning of an earth air tube heat exchanger and to bring in light the further advancements that could be made to enhance the thermal performance of EATHE systems. Key Words: EATHE, conventional energy resources, passive air conditioning, NRC, thermal performance 1. INTRODUCTION With regards to the continuous depletion of nonconventional energy resources and the excessive rate of greenhouse gas emissions, it has become imperative and urgent to look out for alternative sources to mitigate the widespread use of conventional fuel. This diversification of energy resources has captured the attention of many researchers and scholars to contribute towards development of much cleaner and sustainable energy sources. Earth air tube heat exchanger is one such major outcome. Earth air tubes are often a viable and economical alternative or supplement to conventional central heating or air conditioning systems since there are no compressors, chemicals or burners and only blowers are required to move the air. These are used for either partial or full cooling and their use can help building meet passive house standards. In the case of cooling a building, the ground is the heat sink, and the building to be cooled acts as heat source. In the case of heating, these functions are reversed-the ground becomes the heat source and the building heat sink. Heat is extracted from or rejected to the ground by means of buried pipe, through which a fluid flows. This buried pipe is commonly called ground loop heat exchanger [1]. The basic principle behind the functionality of EATHE system is the Dznear constantdz ground temperature which is achieved at certain depth of the earth’s surface. Because of the relatively high thermal inertia of the ground, temperatures in the ground lag those at the surface, and their fluctuations decrease with depth below grade; moreover, soil temperature gets closer to the mean annual ambient air temperature with increasing depth. This raises the possibility of using the ground for heating air when ambient temperatures are lower than the ground temperature and cooling air when they are higher. However, such systems have faced many restrictions, when the consumers reject more heat than they extract over the annual cycle and hence the size of the ground heat exchangers is increased. To avoid the problem of oversized EATHE setup and to increase their efficiency, a hybrid ground-coupled cooling system can also be used. 2. Types of Earth air tube heat exchangers There are two general types of earth air heat exchangers: open and closed. In open systems, ambient air passes through tubes buried in the ground for preheating or pre-cooling and fresh fluid is circulated through the ground loop heat exchanger. This system provides ventilation while hopefully cooling or heating the building’s interior. In closed systems, both the ends of the pipe are kept inside the control environment, which can be a room in case of air and a tank in case of water, the system is said to be closed loop because the same fluid is passed continuously over and over through the loop [1]. The subsections provided below briefly discuss the highlights of both open and closed EATHE systems: 2.1 Open-loop system: This type of system uses wells or surface body water as the heat exchange fluid which circulates directly through the ground heat pump (GHP) system. Once it has circulated through the system, the water returns to the ground through the well, a recharge well, or surface discharge. This option is practical only where there is an adequate supply of relatively