Ground possesses high heat capacity as well as its insulation potential so, at a sufficient depth, the ground temperature is constant. It is found that throughout the year the temperature of earth remains almost constant at a depth of 4m. This temperature is found to be higher than that of the outside air in winter and vice versa in summer. This paper focuses on the various designing parameters of Earth air tunnel heat exchanger for room conditioning thereby utilizing the clean energy. This paper reviews the work done till date about the various design factors one should consider while designing the EATHE system, viz. velocity and mass flow rate of the air through tunnel, soil nature & material of the pipe, cross-section of the pipe.

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
118
ANALYSIS OF VARIOUS DESIGNING PARAMETERS
FOR EARTH AIR TUNNEL HEAT EXCHANGER SYSTEM
AKSHAY KHOT
Department of Mechanical Engineering, Sinhgad College of Engineering,
Pune, Maharashtra, India
ABSTRACT
Ground possesses high heat capacity as well as its insulation potential so, at a sufficient
depth, the ground temperature is constant. It is found that throughout the year the temperature of
earth remains almost constant at a depth of 4m. This temperature is found to be higher than that of
the outside air in winter and vice versa in summer. This paper focuses on the various designing
parameters of Earth air tunnel heat exchanger for room conditioning thereby utilizing the clean
energy. This paper reviews the work done till date about the various design factors one should
consider while designing the EATHE system, viz. velocity and mass flow rate of the air through
tunnel, soil nature & material of the pipe, cross-section of the pipe.
Keywords: Clean Energy, Earth Air Tunnel Heat Exchanger (EATHE), Heat Transfer, Room
Conditioning
1. INTRODUCTION
The EATHEs are considered as an effective substitute for heating/cooling of buildings. This
is basically a series of metallic, plastic or concrete pipes buried underground at a particular depth.
Through pipes the fresh atmospheric air flows. According to the temperature difference the heat
transfer takes place between soil and air in pipes. The efficient design of the system is necessary as
the system will ensure good performance. In that accordance the cross section area & type of cross
section of pipe, velocity of air & nature of soil plays key role in efficiency of system. This uses green
and clean energy in order to minimize pollution and to minimize conventional energy consumption.
Also there are two major types of EATHE system exist: ‘open-loop’ (i.e., drawing outside air
through the pipes to ventilate the house) or ‘closed-loop’ (i.e., re-circulating the air from the building
through the earth tubes).
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND
TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 12, December (2014), pp. 118-125
© IAEME: www.iaeme.com/IJMET.asp
Journal Impact Factor (2014): 7.5377 (Calculated by GISI)
www.jifactor.com
IJMET
© I A E M E

2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp.
Fig. 1: Layout of EATHE showing its operation in winter
The second kind seems to have fallen out of favor, probably because it is insufficient to
provide heating to the building by itself, and because it does not help meet the b
requirements.
1.1 Work in India
A large earth-air tunnel system meant to provide thermal comfort inside the whole building
complex at one of the hospitals in India has been evaluated
model is developed to validate the e
cross-sectional area 0.528 m2
and with an air velocity of 4.89 m
of approx. 512 KWh and a heating capacity of 269
inadequate for providing the necessary comfort conditions.
2. DESIGN PARAMETERS
One of the important aspects in concern of EAHEs is categorization of the site in terms of
geology availability. The knowledge of soil thermal and physi
density, diffusivity etc.), depth of bedrock, depth to water and the nature of soil is required. This
information guides the designer in the selection of the type of EAHE system to be used and in the
design of the system. Ghosal and Tiwari
with a greenhouse. Ghosal and Tiwari
and cooling with EAHE in New Delhi, India. It was found on average 7
5–6°C lower in the summer than those of the same greenhouse without EAHE. They showed that
greenhouse air temperature increased in the winter and decreased in the summer with increasing pipe
length, decreasing pipe diameter, decreasing m
increasing depth of ground up to 4m.
Using the following equation heat transferred can be calculated:
Psbl = Spipe. h. (Tair-Tpipe)
Where,
Psbl = sensible heat transfer rate (W)
h= heat exchange coefficient (W/m^2
Tpipe =pipe surface temperature (˚C)
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
119
Layout of EATHE showing its operation in winter
The second kind seems to have fallen out of favor, probably because it is insufficient to
provide heating to the building by itself, and because it does not help meet the b
air tunnel system meant to provide thermal comfort inside the whole building
complex at one of the hospitals in India has been evaluated by Bansal [4]
developed to validate the experimental measurements. An 80m length of the tunnel with a
and with an air velocity of 4.89 m/s is found to have a cooling capacity
h and a heating capacity of 269 KWh. The heating capacity was found to be
inadequate for providing the necessary comfort conditions.
DESIGN PARAMETERS
One of the important aspects in concern of EAHEs is categorization of the site in terms of
geology availability. The knowledge of soil thermal and physical properties (thermal conductivity,
density, diffusivity etc.), depth of bedrock, depth to water and the nature of soil is required. This
information guides the designer in the selection of the type of EAHE system to be used and in the
Ghosal and Tiwari [6] reported the modeling of an earth to air heat exchanger
with a greenhouse. Ghosal and Tiwari [6] developed a new thermal model for green
and cooling with EAHE in New Delhi, India. It was found on average 7–8°C higher
C lower in the summer than those of the same greenhouse without EAHE. They showed that
air temperature increased in the winter and decreased in the summer with increasing pipe
length, decreasing pipe diameter, decreasing mass flow rate of flowing air inside buried pipe and
increasing depth of ground up to 4m.
Using the following equation heat transferred can be calculated:
)
r rate (W) Spipe = pipe surface area (m^2)
= heat exchange coefficient (W/m^2-K) Tair =air temperature (˚C)
˚C)
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
© IAEME
Layout of EATHE showing its operation in winter
The second kind seems to have fallen out of favor, probably because it is insufficient to
provide heating to the building by itself, and because it does not help meet the building’s fresh air
air tunnel system meant to provide thermal comfort inside the whole building
by Bansal [4]. A simple theoretical
m length of the tunnel with a
is found to have a cooling capacity
capacity was found to be
One of the important aspects in concern of EAHEs is categorization of the site in terms of
cal properties (thermal conductivity,
density, diffusivity etc.), depth of bedrock, depth to water and the nature of soil is required. This
information guides the designer in the selection of the type of EAHE system to be used and in the
reported the modeling of an earth to air heat exchanger
developed a new thermal model for green-house heating
C higher in the winter and
C lower in the summer than those of the same greenhouse without EAHE. They showed that
air temperature increased in the winter and decreased in the summer with increasing pipe
ass flow rate of flowing air inside buried pipe and
= pipe surface area (m^2)

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
120
2.1 Material of pipe & Velocity limit
Bansal [10] carried out the experiment on the pipe of 23.42m length and 0.15m diameter,
temperature rise of 4.1–4.8 1C has been observed for the flow velocity ranging from 2to5m/s. The
hourly heat gain through the system is found to be in the range of 423.36–846.72kWh. Fig. 2
represents the comparison of the results of the simulation and experiments for air velocity of 2.0m/s
at the outlet of the steel and PVC pipes, respectively. Fig. 2 and Fig. 3 also depict that as the velocity
of air is increased, the temperature of the air at the outlet of the pipe gets reduced. The reduction in
temperature of the air at the exit of pipe due to increment in air velocity occurs because when the air
velocity is increased from 2.0 to5.0m/s, the convective heat transfer coefficient is increased by
2.3times, while the duration to which the air remains in contact with the ground is reduced by a
factor of 2.5.Thus the later effect is dominant and therefore, lesser rise in temperature is obtained at
higher air velocities. At higher velocities though the rise in temperature of air is less yet the total
heating effect achieved per unit time is much more.
Bansal [7] concluded the experiment with the statement it’s the velocity of air through the
pipe which affects the system performance greatly and not the material of buried pipe. Also stated
that velocity 2m/s is most suitable & economical to achieve desire effect.
Fig. 2: Temperature distribution along the length of the pipe for exit velocity 2.0 m/s for (a) steel
pipe and (b) PVC pipe.

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
121
Fig. 3: Simulated temperatures along the length of the pipe for various exit velocities for (a) steel
pipe and (b) PVC pipe.
2.2 Soil Nature and operation period
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 by Bansal [9]. CFD System designed to validate EATHE model comprises
of horizontal cylindrical PVC pipe of 0.10 m inner diameter with buried length of 60 m and buried at
a depth of 3.7 m in a flat land with dry soil. Globe valves are fitted in pipe assembly for flow control
of air. At the inlet, the open end of this single pipe was connected through a vertical pipe to a 0.75
kW, single phase variable speed blower having maximum speed 2800 RPM and maximum flow rate
of 0.093 m3
/s. Ambient air is forced through the EATHE system with the help of blower. Velocity of
air through the pipe can be varied by changing the RPM of the blower with the help of an auto
transformer (0 – 270 V, 2 A. max., type: 2D-1Phase with a least count of 1 V). Energy consumption
of the blower at 5 m/s is measured as 0.2 KW. Effect of thermal conductivity of soil on the thermal
performance of EATHE system has also been studied by using three different types of soil namely
S1, S2 and S3 in this study having thermal conductivity 0.52, 2.0 and 4.0Wm_1 K_1.
Following color figures represents the temperature variations along pipe length after certain
interval of time for different types of soil.

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
122
Table 1: Effect on soil temperature along the length of pipe at different period of time
Length of Pipe
(m)
Air Temperature at different section for soil S1,S2,S3 after different time
interval (Kelvin)
10
After 1hr After 12hr
S1 S2 S3 S1 S2 S3
312.9 312.9 312.9 316.8 316.8 316.8
30 305.8 304.6 304.3 310.9 308.1 306.8
Fig.5: Temperature contour of air and soil at 10 m section from for pipe inlet after 12 h for three
soils (a) 0.52Wm/ K, (b) 2.00Wm/ K and (c) 4.00Wm/ K.

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
123
Fig. 6- Temperature contour of air and soil at 30 m section from for pipe inlet after 12 h for three
soils (a) 0.52Wm_1 K_1, (b) 2.00Wm_1 K_1 and (c) 4.00Wm_1 K_1.

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
124
Maximum deterioration in the performance in terms of temperature drop obtained during
continuous operation of 24 hr is recorded as 2.9 K for soil with thermal conductivity of 0.52Wm/ K.
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.
3. CONCLUSIONS
1. EATHE can be used as substitute for the conventional air conditioning systems
2. EATHE-evaporating cooling hybrid systems can be used in summer for better results.
3. More the thermal conductivity of soil better is the thermal performance of EATHE
4. With increasing pipe length, decreasing pipe diameter, decreasing mass flow rate of flowing
air inside buried pipe and increasing depth of ground up to 4 m performance of EATHE
becomes better.
4. REFERENCES
1. V. Bansal, R. Misra, G.D. Agrawal, J. Mathur, Performance analysis of earth pipe-air heat
exchanger for summer cooling, Energy and Buildings 42 (2010), 645–648.
2. Bansal Vikas, Misra Rohit, Agrawal Ghanshyam Das, Mathur Jyotirmay. Performance
analysis of earth–pipe air heat exchanger for winter heating. Energy and Buildings 2009;
41:1151–4.
3. Bharadwaj SS, Bansal NK. Temperature distribution inside ground for various surface
conditions. Building and Environment 1983; 16(3):183–92.
4. N.K. Bansal, M.S. Sodha, S.P. Singh, A.K. Sharma, A. Kumar, Evaluation of an earth–air-
tunnel system for cooling/heating of a hospital complex, Building and Environment 20 (2)
(1985) 115–122.
5. Bansal Vikas, Misra Rohit, Agarwal Ghanshyam Das, Mathur Jyotirmay. ‘Derating Factor’
new concept for evaluating thermal performance of earth air tunnel heat exchanger: a
transient CFD analysis. Applied Energy 2012, in press.
6. Ghosal MK, Tiwari GN. Modeling and parametric studies for thermal performance of an
earth to air heat exchanger integrated with a greenhouse. Energy Conversion and
Management 2006; 47(13–14):1779–98.
7. Bansal Vikas, Misra Rohit, Agrawal Ghanshyam Das, Mathur Jyotirmay. Performance
analysis of earth–pipe air heat exchanger for winter heating. Energy and Buildings 2009; 41:
1151–4.
8. Bansal Vikas, Misra Rohit, Agrawal Ghanshyam Das, Mathur Jyotirmay. Performance
evaluation and economic analysisof integrated earth –air tunnel heat exchanger-evaporative
cooling system Energy and Buildings 55 (2012) 102–108.
9. Bansal Vikas, Misra Rohit, Agrawal Ghanshyam Das, Mathur Jyotirmay. Transient effect of
soil thermal conductivity and duration of operation on performance of earth air tunnel heat
exchanger. Applied Energy 103 (2013) 1–11.
10. Trilok singh Bisoniya, Anil Kumar, Prashant Baredar. Experimental and analytical studies of
earth-air heat exchanger system in India: a review. Renewable and sustainable Energy
Reviews 19 (2013) 238-246.
11. Ozgener O, Ozgener L. Exergetic assessment of EAHEs for building heating in Turkey: a
greenhouse case study. Energy Pol 2010; 38:5141.

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 12, December (2014), pp. 118-125 © IAEME
125
12. Ozgener L, Ozgener O. An experimental study of the exergetic performance of an
underground air tunnel system for greenhouse cooling. Renew Energy 2010; 35:2804-11.
13. Ozgener O, Ozgener L. Determining the optimal design of a closed loop earth to air heat
exchanger for greenhouse heating by using exergoeconomics. Energy Build 2011; 43(4):960–
5.
14. Ozgener O, Ozgener L, Goswami DY. Experimental prediction of total thermal resistance of
a closed loop EAHE for greenhouse cooling system. Int Commun Heat Mass Transfer 2011;
38 (6):711–6.
15. Lee CK. Effects of multiple ground layers on thermal response test analysis and ground-
source heat pump simulation. Appl Energy 2011; 88(12):4405.
16. Omar Mohammed Ismael, Dr. Ajeet Kumar Rai, Hasanfalah Mahdi and Vivek Sachan, “An
Experimental Study of Heat Transfer In A Plate Heat Exchanger” International Journal of
Mechanical Engineering & Technology (IJMET), Volume 5, Issue 4, 2014, pp. 31 - 37, ISSN
Print: 0976 – 6340, ISSN Online: 0976 – 6359.
17. V. N. Palaskar, S. P. Deshmukh, A.B. Pandit and S.V. Panse, Hasanfalah Mahdi and Vivek
Sachan, “Performance Analysis of An Oscilatory Flow Design Heat Exchanger Used In Solar
Hybrid Water System” International Journal of Mechanical Engineering & Technology
(IJMET), Volume 4, Issue 6, 2013, pp. 91 - 99, ISSN Print: 0976 – 6340, ISSN Online: 0976
– 6359.
18. S. Bhanuteja and D.Azad, “Thermal Performance and Flow Analysis of Nanofluids in A
Shell and Tube Heat ExcHANGER” International Journal of Mechanical Engineering &
Technology (IJMET), Volume 4, Issue 5, 2013, pp. 164 - 172, ISSN Print: 0976 – 6340,
ISSN Online: 0976 – 6359.