The Thermal Performance of Earth Air Heat Exchanger

 

Dr. B. Vishali1, J. Venkatesu Naik2

1Asst. Prof. Dept. of Mathematics, School of Engg. and Technology, SPMVV, Tirupati, India

2Asst. Prof. Dept. of Mechanical Engg., School of Engg. and Technology, SPMVV, Tirupati, India

*Corresponding Author E-mail: vishali.batyala@gmail.com, jatrothurahul@gmail.com

 

ABSTRACT:

This paper investigates the Experimental study on the thermal performance of earth air heat exchanger. The temperature of the ground depth of 2m and above remains nearly constant throughout the year .this undisturbed temperature which remains constant is lower than the outside temperature in winter, higher than the outside temperature in winter. In summer the hot atmospheric air is drawn through buried pipes with help of blower and is cooled and during winter the cool air is heated before used for ventilation. A temperature difference of 8oC to 10oC is observed during the summer.

 

KEYWORD: Earth air heat exchanger, Passive cooling, Air conditioning.

 


 

INTRODUCTION:

The innovative approaches of usage of renewable energy resources for space heating/cooling has significantly increased in order to reduce the emissions of chlorofluorocarbons that cause the depletion of ozone layer. The energy consumption in buildings for heating /cooling purpose has significantly increased during the last 3-4 decades. It is noted that about 40% of the total world energy consumption is used by building sector and out of which for space heating/cooling in buildings about 32-33% is utilised[1]. Hence in the context of today’s diminishing fossil fuel reserves, increasing electrical cost, air pollution and global warming, properly designed earth cooling tubes offer a sustainable alternative to reduce or eliminate the need for convectional compressor based air conditioning systems. The utilisation of geothermal energy to reduce heating and cooling needs in buildings has received increasing attention during the last years. The performance analysis of EAHE for summer cooling in Jaipur, India was investigated by Bansal et.al[2]. They investigated that the nature of the material of the buried pipe does not effect the performance of the system instead it is greatly effected by the velocity of the air fluid.

 

To check the performance of the EAHEs installed at different depths a one dimensional numerical model was proposed by Abdelkrim Sehli et.al.[3]  It is found that EAHE system alone do not provide thermal comfort but when combined with convectional air conditioning systems could reduce energy demand in buildings. To study the year around effectiveness of EAHE coupled green house located in New Delhi, a simplified analytical model was developed by Ghosal et.al[4]. When compared with the green house without EAHE it was found that the temperature of the greenhouse with EAHE was more in winter and less in summer. Different combinations of inner thermal curtain, earth air heat exchanger and geothermal heating a thermal model was developed by Shukla et.al [5] for heating green house. The impact of different ground surface boundary conditions on the efficiency of single and multiple parallel EAHE system was investigated by Santamouris et.al.[6] Thus EAHE system has great importance as it is environmental friendly, has low running cost, uses renewable energy. This is suitable for zoo, dairy farms and agricultural purposes where convectional air conditioners use could be uneconomic. The EAHE system is most suitable for summer and winter. There are open and closed ground heat exchangers. In open system the ambient air passes through the pipes that are buried inside the earth’s surface for heating/cooling and the heated/cooled air enters the building. In closed systems the heat exchangers are located underground either in oblique, vertical or horizontal position. The heat from the ground is transferred to a heat pump or vice versa by the heat carrier medium circulated within the heat exchanger. This paper experimentally investigates the use of EAHE system for summer cooling requirements at Tirupati under the climatic conditions of high summer temperatures.

 

WORKING PRINCIPLE OF EARTH AIR HEAT EXCHANGER:

An earth tube is long, underground metal or plastic pipe through which air is drawn. The ambient air travels through the pipe and as it moves it gives up/receives some of its heat to/from the surrounding soil and enters the room as conditioned air. The system consists of a matrix of buried pipes through which air is transported by a fan. In summer the ambient temperature is higher than the ground temperature around the heat exchanger and thus the supply air to the building is cooled. Several simplifying assumptions were made due to the complex mechanisms occurring around the earth tube.


 

Fig.1.Schematic Diagram Of Earth Air Heat Exchanger System

 

PERFORMANCE EVALUATION OF EARTH AIR HEAT EXCHANGER:

The evaluation was done for two continues days. The temperature change for those two days is as shown in fig. 2. The temperature on 17, May slightly increased when compared with that of 18 May, 2017. The evaluation days were fixed having the identical ambient conditions. The atmospheric air temperature is shown in fig.2. The measurement of the temperature is taken as from morning 5-30 AM to 23-30 PM, of the continuous days. It is observed from fig 2 that deviation in atmospheric air temperature during the two continuous days i.e 17th and 18th May 2017 was ± 1.0°C. The temperature ranges from 32°C to 42°C.

 

Fig.2. Deviation in ambient air temperature

 

Fig 3 shows the temperature of air at inlet of earth air heat exchanger system. The temperature of the air at the inlet of earth air heat exchanger setup is same for two days from 5.30AM to17.30PM and slightly variation of  ±1.0°C from 17.30PM to 23.30PM. The temperature range from the 33°C to 42°C.

 

Fig.3.Air temperature at inlet of earth air heat exchanger system

 

Fig 4  shows the out let temperature of the earth air heat exchanger.The temperature difference at the outlet of earth air heat exchanger is 8o C to 10o C when compared with the ambient temperature. On 17th May,it is observed that the outlet temperature at 5.30AMis  21o C and then it slowly increases to 24 o C at 7.30AM and is constantly maintained upto 2.30PM and then it gradually decreases and maintains a constant temperature throughout the day. A similar tendancy is observed on 18th May.

 

Fig.4.Variation of outlet  temperature of earth air heat exchanger system

 

In this fig 5. It is observed at the same depth that the temperature of the earth remains constant throughout the year. The ambient temperature is higher than inside of the earth. The temperature decreases  from the upper surface as we move deep inside the earth. The temperature throughout the  year is constant inside the earths surfaceabove 3 m. In summer, winter and rainy seasons the temperature is constant  above 3 m

 

Fig. 5. Variation in earth’s temperature  with depth

FUTURE SCOPE:

·        We can increase heat transfer rate by introducing a water circulation system or water sprinkle system.

·        We can also use compressor to reduce pressure inside the pipe that give us advantage of rapid cooling.

·        A zinc coated pipe will have great advantage on heat transfer. A model is to be designed and tested to check the validity.

 

REFERENCES:

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2.       Bansal V, Misra R, Agrawal GD, Mathur J. Performance analysis of earth-pipe-air heat exchanger for summer cooling. Energy and Buildings 2010; 42:645–8.

3.       Abdelkrim Sehli, Abdelhafid Hasni, Mohammed Tamil. The potential of earth air heat exchangers for low energy cooling of buildings in South Algeria. Energy Procedia 22012; 496-506.

4.       Ghosal MK, Tiwari GN, Das DK, Pandey KP. Modelling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse. Energy and Buildings 2005; 37:613–21.

5.       Shukla Ashish, Tiwari GN, Sodha MS. Thermal modelling for greenhouse heating by using thermal curtain and an earth–air heat exchanger. Building and Environment 2006; 41:843–50.

6.       Mihalakakou G, Lewis J, Santamouris M. On the heating potential of buried pipes techniques application in Ireland. Energy Buildings 1996; 24:19

7.       C. Peretti, A. Zarrella, M.C. Carli, R. Zecchin, The design and environment evaluation of earth-to-air heat exchangers (EAHE): a review, Renew. Sustain. Energy Rev. 28 (2013) 107–116.

 

 

 

 

 

 

Received on 26.09.2017       Modified on 05.11.2017

Accepted on 09.12.2017      ©A&V Publications All right reserved

Research J. Science and Tech. 2017; 9(4): 635-638.

DOI:  10.5958/2349-2988.2017.00108.5