KSCE Journal of Civil Engineering (0000) 00(0):1-4

Copyright 2014 Korean Society of Civil Engineers

DOI 10.1007/s12205-013-0597-1

Environmental Engineering

pISSN 1226-7988, eISSN 1976-3808

www.springer.com/12205

TECHNICAL NOTE

Design and Performance Evaluation of Low Cost Earth to Air Heat Exchanger
Model Suitable for Small Buildings in Arid and Semi Arid Regions
Anil Kumar Misra*, Mayank Gupta**, Manish Lather***, and Himanshu Garg****
Received September 23, 2013/Revised February 22, 2014/Accepted May 19, 2014/Published Online December 1, 2014

Abstract
An experimental study was performed on a prototype model of Earth to Air Heat Exchanger System (EAHE) equipped with low
cost material like PVC pipes and exhaust fans made on temporary platform. Emphasis was given on the design of the duct system
suitable for small houses without any space in urban and rural areas. Tests were performed to predict the cooling potential and impact
of the material on the performance of EAHE system. Experiment was performed continuously for more than three weeks and the
result shows that irrespective to the inlet air temperature (ranges from 34oC to 44oC), outlet air temperature was recorded between
20oC to 22oC, which shows the effectiveness of the system. No significant affect of the material used for making the underground air
pipe system was recorded on the performance of the model. The Minimum EER (W/W) ratio calculated for the prototype model was
around 3.78, which is equivalent to a Energy Star 5 rating, the most efficient system. The weekly energy saving potential of the model
before and after integration of EAHE was analyzed i.e., around 5 kWh/week and 20 kWh/week respectively. This considerable
increase in weekly energy savings potential of model due to EAHE leads to mitigation of CO2 emissions if implemented in the
residential, commercial and industrial buildings and the corresponding annual carbon credit of these buildings can be decreased
manifold. The Life Cycle Cost (LCC) analysis of model also shows that the payback period is around 3 to 4 years for the investment
on EAHE system. After a series of experimental analysis the study also reveals that EAHE system is easily and economically feasible
technique which can drastically reduce the consumption of energy in future and eliminate the need for conventional compressor
based cooling systems.
Keywords: earth to air heat exchanger, duct system, open loop system, energy consumption, environmental management

1. Introduction
Worldwide researchers making climate mitigation policies to
regulate activities that produce changes of the concentration of
the atmospheric carbon, like the production of electricity used in
buildings, as large amount of energy is consumed by the
buildings cooling and heating systems (Diaz et al., 2013). Air
conditioning systems has been widely used for cooling and
warming of all types of buildings but due to global warming by
Chlorofluorocarbons (CFCs) and continuous depletion of the
ozone layer it is imperatively needed to reduce high grade energy
consumption and explore alternative techniques. Engineers,
researchers and scientist are working and developing new
technologies of cooling and heating of the buildings consumed
low electricity. One of such technologies is Earth-to-Air Heat
Exchanger (EAHE) system that uses the ground for heating or
cooling of buildings (Lee and Strand, 2008). EAHE system can
be constructed in all types of the building and regions. Several

studies have been carried out to investigate different components

of EAHE system, like computational simulations (Misra et al.,
2012), numerical studies (Su et al., 2012), improvements and
optimizations (Ghosal et al., 2005), real applications (Xiaa et al.,
2012), economic and physic analysis (Ozgener, 2010). The
EAHE system increases the building internal temperature during
the winter and reduces it during the summer due to this cooling
system consume lower electrical energy to reach the thermal
comfort of the building.
Within the subsurface temperature varies with depth and this
variation in temperature depends on numerous factors (Papiel et
al., 2001) like (a) Structure and physical property of the ground
(b) ground surface cover (c) climate interaction determined by
air temperature, wind, solar radiation, air humidity and rainfall.
The thermal inertia of the soil is high and the temperature
fluctuations at the ground surface are attenuated deeper in the
ground. A time lag also occurs between the temperature
fluctuations at the surface and in the ground. Due to this, at a

*Associate Professor, Dept. of Civil and Environmental Engineering, ITM University, Gurgaon, Haryana 122017, India (Corresponding Author, Email:
anilgeology@gmail.com)
**B. Tech Degree Student, Dept. of Civil and Environmental Engineering, ITM University, Gurgaon, Haryana 122017, India (E-mail: mayank1673@gmail.com)
***B. Tech Degree Student, Dept. of Civil and Environmental Engineering, ITM University, Gurgaon, Haryana 122017, India (E-mail: manishlather@sify.com)
****B. Tech Degree Student, Dept. of Civil and Environmental Engineering, ITM University, Gurgaon, Haryana 122017, India (E-mail: Himanshu0907@gmail.com)
1

Anil Kumar Misra, Mayank Gupta, Manish Lather, and Himanshu Garg

sufficient depth, the ground temperature is lower than the outside

temperature in summer and higher in winter (Hepbasli, 2003;
Bansal et al., 2009).
In EAHE system variations in subsurface temperature is
utilized for the cooling of the buildings, cold storages, offices,
laboratories etc and will be helpful in minimizing the impact of
climate change through reducing the energy demand and
consumption. The study carried out by Eckert in 1976 showed by
very simplistic calculations, the potential of the earth to be used
as an energy source i.e., a heat sink or a heat store. The earth
temperature for light dry soil at a depth of approximately 10
feets varies by 3oC from the mean soil temperature, which is
approximately equal to the mean annual air temperature and has
a phase lag of about 75 days behind the ambient air temperature
(Krarti and Kreider, 1996).
The present study deals with modelling, analyzing the affect of
materials and assessing the performance of EAHE system
suitable for small residential houses without open space in urban
as well as rural areas with earth-pipe-air heat exchangers in open
loop mode. This experiment is suitable for design calculation and
feasibility studies. Throughout the investigation tenure i.e., more
than three weeks, daily variations in indoor and outdoor
temperatures were recorded. The entire experiment has proved
the suitability of EAHE system for reducing the energy consumption
in the buildings.

2. Design of EAHE System

EAHE systems are considered suitable for residential, commercial
and industrial buildings having some open area for the
construction of earth-pipe-air heat exchanger tunnel system. In
the present study EAHE prototype model was constructed to
proof that it can be built within small houses without any open
area. There are two major types of EAHE system (Ozgener,
2011; Chaudhary and Misra, 2013) open loop EAHE system and
closed loop EAHE system. Like any other civil engineering
structure in the formation of EAHE system study of the site and
lithology are essential. These include study of subsurface geology,
depth of the vadose zone and zone of saturation, availability of
the major aquifers at the construction site, depth to the bed rock
and study of the hydraulic and thermal properties of the soil and
rock at the site. These informations play an important role in the
design and selection of the type of EAHE system to be used
(Ozgener and Ozgener, 2010; Ozgener et al., 2011).

3. Factor Affecting Performance of EAHE System

Depth of underground air tunnel: Any depth between two to

four meters is most suitable, because at these depths earth
temperature is usually constant throughout the year.
Air velocity and air temperature: Air velocity has significant
impact on the performance of the EAHE system. Experiments
based on the prototype model shows that at higher velocity the
indoor temperature decrease is less as compare to slow velocity.
This is because at slow velocity air would be in contact with soil
for longer period of time and the heat exchange between soil and
air will be more.
Temperature and tube diameter: The diameter of the underground
air tunnel significantly affects the performance of the EAHE
system. Studies carried out (Krarti and Kreider, 1996) on
relationship between temperature variation with tube diameter
and distance from the entry point indicates that the outlet
temperature depends significantly upon the pipe diameter. An
increase in the tube diameter results higher outlet air temperature.
Heat exchanged between the air and the soil is proportional to the
diameter of the tube. Therefore, as the pipe diameter increases,
less heat is exchanged between a unit mass of air and the
surrounding soil, resulting in a smaller decrease of the outlet air
temperature.
3.1 Experimental Setup
The entire experimental setup of the EAHE systems was
developed to generate real experimental data through which the
effectiveness of this system can be analyzed and proved. While
forming the experimental setup especial attention was given on
the area and cost of the construction materials. Table 1 shows the
cost analysis of different tunnel construction materials. While
selecting the appropriate construction material for the EAHE
system emphasis was given on the (a) Locally available materials
(b) procedures of construction (c) life of the material (d)
moisture content of the material.
For the construction of the prototype model a metal tray was
used as the base of the system. The tray used was rectangular
with dimensions, length 99 cm, width 99 cm, and height 10.5
cm. PVC pipes were used for making loop having the diameter
of 25 mm having a total length of 25 m (Fig. 1). The entire loop
system was filled with hard, compact and clay rich soil taken
from a depth of 3 m and inlet and out let points of the loop
system were located (Fig. 2). For measuring the temperature of
the air at inlet and outlet points of the loops two PT-100 sensors

Table 1. Cost Analysis of Suitable Tunnel Material for EAHE System (Chaudhary and Misra, 2014)

There are several factors that directly or indirectly affect the

performance of the EAHE system. Some of the most important
factors are as follows:
Soil Type: Although in all types of soils EAHE system can
perform, but in sandy soil its performance is much better as
compare to other soil types because sandy soil can capture heat
and dissipate heat more efficiently as compare to other soil types.
2

Type of construction material

10 cm Brick wall with 1.5 cm cement
plaster
10 cm PCC wall
1 cm bamboo mesh with 1.5 cm soil
cement plaster

Cost
(Rs/ m)

Heat Transfer
Coefficient
(W/m2-oC )

850

2.8

1050

4.00

200

3.40

KSCE Journal of Civil Engineering

Design and Performance Evaluation of Low Cost Earth to Air Heat Exchanger Model Suitable for Small Buildings in Arid and Semi Arid Regions

with the range of 0-199oC, with least count of 0.1oC was used.
Measurement of humidity was carried out using humidity
sensors (thermo hygrometer). A 1000 rpm fan was used to throw
the air inside the pipe and its speed was controlled with the aid of
an electronic regulator. Using anemometer, the inlet air velocity
was measured and the speed of the fan was adjusted at that value
for which the EAHE system gives the lowest temperature for a
particular ambient temperature. The rate of fall in the temperature
at higher speed is more but the final temperature at slow speed
was less as compared to that at high speed (Fig. 3). This indicates

Fig. 1. Arrangement of the PVC Pipe Loops within the Prototype

Model

that the performance of the EAHE system depends upon the air
velocity and is not affected by the material of the buried pipe,
therefore a cheaper material pipe can be used for making the duct
system. This finding is also supported by the study conducted in
this are by Bansal et al., 2010.

4. Discussions
The findings of the experimental set up of the EAHE system
has proved the utility and effectiveness of the system for reducing
the energy consumption and minimising the impact of climate
change. Experiment was performed continuously for seventeen
days and the result shows that irrespective to the inlet air
temperature (ranges from 34oC to 44oC), outlet air temperature
was recorded between 20oC to 22oC. Fig. 4 shows the performance
of the prototype model. Usually the efficiency of air conditioning
system is measured by the Energy Efficiency Ratio (EER). The
EER is the ratio of the cooling capacity to the power input in the
system and the higher EER rating of the system shows that the
system is more efficient. In India, energy labeling is carried out by
Bureau of Energy Efficiency (BEE) an autonomous body, Ministry
of Power. Most of electrical appliances are given the rating on the
basis of Energy Efficiency Ratio (EER). The Minimum EER (W/
W) ratio calculated for the prototype model was around 3.78, which
is equivalent to a Energy Star 5 rating, the most efficient system.
To determine the energy savings the mass flow rate that is
specific heat of air was calculated with the following relationship:
Specific Heat of the air = (Temperature inside
Temperature outside) = power released to the soil
Power released to the soil =
Thermal power extracted from the air-flow
The Energy Efficiency Ratio (EER) of the system was calculated:
Energy Efficiency Ratio (EER) =
(thermal power extracted from the air flow)/
(electric power required by the fan)

Fig. 2. Arrangement of the Inlet and the Outlet Ducts

The results show that weekly energy saving potential of the

model before and after integration of EAHE were 5 kWh/week
and 20 kWh/year respectively. Through these savings the Life

Fig. 3. Variation in the Rate of Cooling at Low and Fast Air Flow
Velocity

Fig. 4. Performance of the Prototype Model from May 1, 2013 to

May 17, 2013

Vol. 00, No. 0 / 000 0000

Anil Kumar Misra, Mayank Gupta, Manish Lather, and Himanshu Garg

Cycle Cost (LCC) analysis of the system was estimated which

shows that the investment made on the construction of EAHE
system could be reimbursed in terms of energy saving cost
within 3 to 4 years. Further the air velocity experiments shows
that the performance of the EAHE system is not affected by the
material of the buried pipe, therefore a low cost material pipe can
be used for making the underground tunnel system.
Thus depending on the ambient temperature of the location, the
Earth Air Tunnel system can be used to provide both cooling during
the summer and heating during winter to buildings, offices, cold
storages, labs etc. EAHE system is capable of reducing the energy
consumption consumed by cooling (air conditioning) and warming
systems. Directly or indirectly EAHE system is capable of helping
in environmental management and minimizing the impact of
climate change by reducing the consumption of coal, hydrocarbons
and other bio fuels used in generating power in thermal power plants
and in houses for cooking and heating purposes.

5. Conclusions
The conclusions based on thermal performance and energy
saving of the prototype model equipped with EAHE system is as
follows:
1. The prototype model demonstrates that EAHE systems can
be constructed easily in small houses, even without open space.
The model shows that the room air temperature was lower than
outside temperature 10-15C during summer and this leads to
considerable energy saving potential of the model.
2. The model also demonstrates that in Indian climatic conditions, if the houses constructed with EAHE systems can
save energy and with simple design of the ducts houses can
be easily constructed at all locations, especially in hot and
dry climatic regions of semi-urban and rural areas all over
the India for achieving thermal comfort.
3. The minimum energy efficiency ratio for cooling using the
EAHE system was determined as 3.78 which is equivalent
to an energy star 5 rating; it indicates that if the EAHE system designed following model specification can be more
energy efficient.
4. Air temperature drop was more with low air flow velocity as
compare to high air flow velocity. Therefore it can be concluded from this that the performance of the EAHE system
is not affected by the material of the buried pipe, therefore a
cheaper material pipe can be used for making the underground tunnel system.
5. The present study should be extended for experimental validation with real time condition by constructing with a small
urban house without any open area with open loop system
and accordingly EER should be determined.

Acknowledgements
We thank all the faculty members of the Department of Civil

and Environmental Engineering, ITM University, for providing

working facilities and also for continuous encouragement.

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