Proceedings of the

International Conference on Mechanical Engineering and Renewable Energy 2019

(ICMERE2019) 11 – 13 December, 2019, Chittagong, Bangladesh

ICMERE2019-PI-000

IMPLEMENTATION OF AN ECO-FRIENDLY EARTH-TO-AIR HEAT EXCHANGER

FOR COOLING EFFECT USING RENEWABLE ENERGY SOURCES
S M Islam1, Md. Tanvir Khan2* and Z U Ahmed3

Department of Mechanical Engineering

Khulna University of Engineering & Technology, Khulna-9203, BANGLADESH
smislamsakib@gmail.com1, tanvir.anik2196@gmail.com2*, zuahmed@me.kuet.ac.bd3

Abstract- Nowadays the use of air coolers is rapidly increasing with human comfort level, however, majority
of these release harmful gases that have a severe impact on the environment. Most of these gases contain
greenhouse gases that trap heat and lead to depletion of the ozone layer. The purpose of this study is to
design and implement an eco- friendly and cost-effective air cooler. So, a preliminary and improved design
of open-loop earth-to-air heat exchanger is proposed and experimentally implemented in summer. The basic
differences between the preliminary and the improved design are the construction materials, depth from the
earth surface and utilization of Peltier devices. The underground soil temperature is measured in the project
area and the whole system is powered by geothermal and solar energy. The results show that, about 3°C
temperature is reduced for preliminary design and 6-8.5°C for improved design. The improved design is
found to be more effective.

Keywords: Air cooler, Earth-to-air heat exchangers, Eco-friendly, Geothermal and Temperature

1.INTRODUCTION promising solution.

Cooling process is a physical operation in which heat Existing air coolers are mostly commercially
is removed from process fluids or solids using various available for well-off people, particularly living in
methods which are implemented via a cooling system. electricity grid-connected area. Such commercially
Various cooling systems are currently available available systems cannot be an alternative to the remote
worldwide but majority of them uses fossil fuel based area or low-income people. Other non-commercial
energy and has a detrimental effect on the environment. devices either primarily requires a pre-cooling medium
Despite energy acts as a primary catalyst in developing or other sources of energy. Again, these devices cannot
the technological, industrial, economic sectors within the replace the existing commercial systems. Moreover, very
society, rapid developments of industry and population little academic lab-based research projects had recently
growth have led to a surge in the demand in our country. been conducted for a possible alternative to the remote
So it is imperative and urgent to find out the alternative areas. Such conceptual projects had neither any physical
and clean sources of energy to replace the conventional testing or sample data nor performance evaluation of the
fuels which has a limited source and adverse effect on the system, thus making these attempts ineffective. As such,
environment. this project aims to introduce an improved air cooling
Sustainable development is not possible without system for rural and remote places, without any grid-
sustainable energy and renewable Energy is a key to connected electricity by using natural resources only. To
sustainable development. Geothermal energy is a clean, this end, this eco-friendly system will be designed,
environment friendly, sustainable and reliable source of manufactured as prototype, and tested performance with
energy and its supply is independent of season and global for its effectiveness.
energy market dynamics. So, the wise implementation Several researches have been carried out in this field.
and use of geothermal energy could meet our increasing Minichiello et al. [1] found that best energy performances
energy demand and play a vital role in mitigating the can be obtained for wet soil and cold climate. Bojic et al.
adverse effect on the environment. [2] investigated the influence of the season, soil thermal
Geothermal energy can be an interesting alternative conductivity and pipe spacing on energy transfer from the
concerning the production of energy for air conditioning soil to the two pipe earth to air heat exchanger. Singh et
for both industrial and domestic use. Typical vapor al. [3] focused on air conditioning with open loop, zigzag
compression machine uses more energy and emits pattern, and rectangular earth to air tunnel system buried
harmful substances, which is detrimental to the at a depth of 10 feet. Their result showed a 13°C
environment. So, it is necessary to find an eco-friendly reduction from ambient temperature in summer and 5°C
substitute, and here, geothermal energy could be a reduction in winter. Patil et al. [4] conducted a
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comprehensive study on a geothermal earth-to-air system allowed to drop significantly through the phase transition
and showed the effect of different parameters on its of liquid water to water vapor (evaporation). The
performance. They also showed that the velocity range of advantage of it is that the system can cool air using much
2-5 m/s and soil depth of 1.5 to 2 meters are favorable for less energy than refrigeration. In extremely dry climates,
a better performance. Sharan et al. [5] investigated the evaporative cooling of air has the added benefit of
performance of a closed loop, circular pipe earth to air conditioning the air with more moisture for the comfort
heat exchanger buried 3.5m beneath the ground. This of building occupants. [13].
system yields a 7°C reduction from ambient temperature Geothermal systems, one of the most recent
during summer. Bellos et al. [6] in their study proposed innovations in eco-friendly heating and cooling systems,
an eco-friendly refrigerant, R152a for conventional air are growing in popularity in both businesses and homes.
conditioning. Bisoniya et al. [7] done an analytical and Since the earth absorbs nearly half of the sun’s energy, a
experimental study on earth to air heat exchanger. Their geothermal system puts that unused energy to use,
study focuses on the potential of geothermal energy as a making it one of the most efficient and cost-effective
green, clean and unlimited source of energy. Kaushal [8] ways to heat and cool a home. The geothermal energy
did a comprehensive experimental study on an earth-to- system uses loop pipes, which are installed below the
air heat exchanger and showed the effect of different ground. The pipes carry a water solution that absorbs the
parameters in both Summer and Winter. He found out that earth’s heat, which is then released where you need it
air velocity has a crucial effect on its performance, but most. During cold winter months, the absorbed heat is
the effect of pipe material is negligible. transferred through the geothermal system into your
Beside these experimental investigations some home. The heated water solution condenses, circulating
numerical studies are also available. Sardana et al. [9] the heated air to provide the whole house with warmth.
numerically studied the effects of construction material, For cool air during the summer, the process is reversed.
depth, air velocity, pipe length on the performance of The unwanted heat from within your house is absorbed
earth-to-air heat exchanger using Finite Volume Method. through the water solution and taken back underground,
They found that depth from earth, air velocity, pipe length leaving you with a comfortable living space [14].
have significant effects, whereas the effect of pipe
material is negligible. Madane et al. [10] carried out a 2.2 EARTH-TO-AIR HEAT EXCHANGER
CFD analysis of an earth to air heat exchanger and In this current era, there is a strong need to consider alternate and
analyzed its performance. eco-friendly ways for thermal comfort in dwellings and commercial
Off closer relevance to the current project is buildings, and to minimize hazardous effects on the environment.
WindChill Fridge [11], which was a very preliminary An earth air pipe heat exchanger would be one of the many alternate
student project tested in Canadian cool environment. solutions. An earth air pipe heat exchanger is a long metal
They, however, did not present any physical data in or plastic pipe, which is buried a few meters deep that
support of the effectiveness of the system, including utilizes the ground as a heat sink for cooling or heating
ambient temperature. Later, Ahmed [12] showed that the purposes. As the temperature few feet below the ground
original Windchill design is not effective for warm is nearly constant, it substantially reduces ambient air
environment, such as Asia and almost no temperature temperature fluctuations. Therefore, it provides space
variation was observed from the original design. He then conditioning throughout the year, with the incoming air
modified the system and was able to lower the ambient being heated in the winter and cooled in the summer. It is
temperature (30-35°C) by about 3°C. Modifications best suited to mechanically ventilated buildings with a
include: use of two dc fan (one in the evaporation moderate cooling demand, located in climates with a
chamber and the other in refrigeration chamber) to ensure large temperature differential between summer and
constant air flow, use of filter in the air inlets to ensure winter and between day and night. It can either be an
clean air and reduction of pipe diameters similar to open or closed-loop system.
expansion valve in a refrigerator. It appears that further
testing and modifications may be required for better 3. RESEARCH METHODOLOGY
effectiveness of the system.
3.1 Experimental Setup
2. THEORITICAL ASPECTS In order to achieve the above objectives following
methodology is systematically performed.
2.1 Ecofriendly Cooling System
Eco-friendly cooling systems may be seen in various 3.1.1 Preliminary Design
ways, but following two are most common in heating or Two setups are designed for implementing prototypes
cooling applications: so as to study improvements of the previously modified
i. Evaporative Air Cooler cooler design by Ahmed [12]. The copper tubes are
ii. Geothermal System placed at about 1 ft. below the soil surface, similar to the
An evaporative cooler is a device that cools air distance adopted by Ahmed [12]. The prototypes (as
through the evaporation of water. Evaporative cooling shown below) will help to take physical data to assess
differs from typical air conditioning systems, which use their effectiveness. Both setups are different in the sense
vapor-compression or absorption refrigeration cycles. that the first setup has no evaporation chamber whereas
Evaporative cooling works by exploiting water's large tube dimensions are constant in both cases. This test will
enthalpy of vaporization. The temperature of dry air is ensure the effectiveness of the evaporation chamber.

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Setup-1 (Without Evaporation Chamber) cooler fan are attached to the system similarly to the
In this setup (Fig. 1), four different diameter copper Setup-1.
pipes are used, namely 5/8, 3/8, 5/16 and 1/4 in. 5/8 in
pipe is bended as a U-shaped, which is joined with U-
shaped 3/8 in pipe. After that, it is joined with U-shaped
5/16 in pipe which is connected to the cooling unit via U-
shaped 1/4 in pipe. A 4 ft. long PVC pipe is attached with
the 5/8 in in front of the setup, and a funnel is attached
with the PVC pipe to draw air into the pipe. In the cooling
unit, a CPU Cooler fan run by power from solar panel is
attached with body to ensure air flow.

Fig.3: Pipe dimensions and relative positions of the

components for the Setup-2

Fig.1: Pipe dimensions and relative positions of the

components for the Setup-1

Fig.4: Implementation of setup-2 at the KUET premises

3.1.2 Improved Design

This system consists of 22m long 1 inch PVC pipes
joined in U shapes [Fig. 5(a)] and with five horizontal
loops at a depth of 1m with dry soil. One end of the pipe
arrangement is connected with the air inlet unit and
another end is connected with the cooling unit. Air is
Fig.2: Implementation of setup-1 at the KUET premises supplied in the pipes at a rate of 2.3m/s using a dc blower
in the air inlet unit. The cooling unit [Fig. 5(b)] consists
Setup-2 (With Evaporation Chamber) of a cooling chamber, a Peltier module, two cooling fan,
Similar to the Setup-1, four different diameters copper a water block, two heatsinks, a dc pump and a water
pipes are used, namely, 5/8, 3/8, 1/2 and 1/4 in, that is reservoir. The Peltier module is introduced to further cool
shown in Fig. 3. U-shaped 5/8 in pipe is joined with U- the conditioned air.
shaped 1/2 in pipe and the pipe is allowed to rise then First, air is forced into the pipes using the blower. The
above the ground to connect with the evaporation soil temperature lies below the atmospheric temperature
chamber where U-shaped 3/8 in copper pipe is immersed in Summer. So, air travels through the pipe arrangement
in the water. It is then joined with 1/4 in coil which acts and gives up heat to the soil. Then, the air temperature
as expansion device, before joining with 3/8 in again and almost reaches the soil temperature. Now this air travels
goes to the cooling unit. PVC pipe, funnel and CPU through the cooling chamber. Then the air comes into

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contact with the cold face of the Peltier module before 4. RESULTS AND DISCUSSION
leaving the cooling chamber. A water block, heat sink and This chapter is dedicated to the results presentation
a fan is used to cool the hot face of the Peltier module. from the experimental analysis. The results include
The pump circulates water through the water block to variation of velocities for a range of copper pipe
carry off heat from the hot surface of the Peltier module. dimensions, temperature reductions for different setups
presented in Section 3 and underground soil temperature
distributions normal to the surface.

4.1 Preliminary Design of Ecofriendly Cooling

System
Figure 6 shows the temperature calibration curve for
the used temperature measuring device with the standard
available at KUET. The result shows the newly purchased
temperature measuring device fairly agrees with our
standard thermometer and the instrument is found to be
(a) reliable.

43
42

Temperature in oC
41
40
39
(b) 38
Analog Thermometer Reading
37
Used Temperature Measuring
36
Fig.5: (a) Schematic view of improved design. (b) Device Reading
35
Magnified view of the Peltier module unit (inside 0 2 4 6 8 10
cooling unit) Time (minutes)

3.1.3 Underground Soil Temperature Fig.6: Data comparison of the used thermometer with a
Measurement standard.
There was no temperature data under the ground
available on the premises where the prototypes were The cooling effectiveness of the system is now
implemented. In fact, such data is scarce even in the analyzed via temperature measurement in the
country. The temperature distribution of soil under the environment and inside the cooling unit. The reading for
ground is essential. In this regard, the soil is dug 10 ft. different times of a day over three-day period is shown in
down the ground, and 10 thermocouples are placed at Table 1. It appears that about 3°C temperature reduction
each ft. down to track the soil temperature. was found from the system.
3.2 Required Raw Materials and Machining Table 1: Temperature measurements at the cooling unit
Operations of the eco-friendly cooling system
Although a range of raw materials were used in this
project, major components are: Obs Time T0°C TE °C TC °C
i. Different sized copper pipe (3/4, 5/8, 1/2, 3/8,
5/16 and 1/4-inch diameter) No.
ii. Plexi glass 1 10:30 am 34.1 30.9 31.0
iii. CPU cooling fan 17/10/2017
iv. PVC pipe
2 04:30 pm 33.6 29.8 30.0
v. Solar panel 17/10/2017
vi. Copper wire
3 10:30 am 32.9 30.2 30.3
vii. Thermoelectric cooler
18/10/2017
viii. CPU cooler with heat sink
4 04:30 pm 33.0 30.0 30.3
ix. Temperature controller
18/10/2017
x. Thermocouple
xi. 12v dc pump 5 12:20 pm 30.1 27.8 28.3
19/10/2017
After purchasing raw materials, few manufacturing or
machining operations were needed. These operations
were performed both commercial workshops and KUET The effect of varying tube diameter on the air velocity
workshop, where appropriate. and flow rate is presented in Table 2. It is seen that air
velocity increases with the decrease of tube diameters, as
expected. However, the increase of velocity is not the

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same rate as the decrease of tube diameter, and in fact, Table 3: Temperature data for Setup-1, T1
much lower than the theoretical velocity. This and Setup-2, T2 (inside cooling unit)
discrepancy is attributed to the significant losses in tubes
and tube joints, where larger diameter tubes are joined Date T0 °C T1 °C T2 °C
together with sequentially smaller diameter tubes. So, the
tube loss enhances from increased tube length and 22/11/18 28.5 27.0 27.5
number of joints. Additionally, providing uniform flow 25/11/18 29.0 26.5 27.5
rates at tube inlet through a fan was also challenging and 26/11/18 29.0 25.0 26.0
partly contributes to this discrepancy. In contrast, air flow 27/11/18 29.0 25.5 26.0
rates are found to be higher for larger diameter tubes
regardless of the fan position. This reduction in flow rates 4.2 Improved Design of an Ecofriendly Cooling
for smaller diameter tubes are due to the increasing System (Earth-To-Air Heat Exchanger)
blockages associated with tube joints, which inhibits the Despite the designs discussed in sections 3.1.1 are
air flow. Temperatures at the tube outlets are almost ecofriendly, but temperature reduction was found to be
similar to the ambient. minimal i.e. within 3°C. In order to have a better cooling
effectiveness, a new design is proposed in the section
Table 2: Data for air velocity and flow rate through 3.1.2. The result of this new proposed design is presented
varying diameter tubes in Table 4. The data is collected at different times to test
its effectiveness. It is clear that this design is able to
Tube Velocity Distance of Flow rate reduce the air temperature by 6-8.5°C. The cooling unit
temperature is nearly equal to the soil temperature 1m
Diameter (m/s) funnel X 10-4 below the ground surface, which is encouraging.
from the Fan (m3/s)
Table 4: Experimental data for an ecofriendly cooling
3.50 1’ 9.975 system discussed in 3.1.2
(3/4)” 3.30 2’ 9.406
3.18 3’ 9.064 Date Time T0 0C TC 0C TS 0C ΔT
2.56 1’ 5.379 a.m. 0
C
(5/8)” 2.33 2’ 5.264
2.21 3’ 5.056 19/06/19 10.00 37.00 31 29 6.00
2.89 1’ 1.789 23/06/19 09.35 38.00 30 29 8.00
(3/8)” 2.76 2’ 1.717 23/06/19 10.25 41.00 34 33 7.00
2.69 3’ 1.689 25/06/19 10.00 40.50 32 31 8.50
3.34 1’ 1.559 25/06/19 11.00 42.00 34 33 8.00
(5/16)” 3.54 2’ 1.524
3.67 3’ 1.494 4.3 Underground Soil Temperature Distribution
4.26 1’ 1.816 Finally, underground soil temperature distribution
(1/4)” 4.17 2’ 1.772 across soil depth is depicted in Fig. 8. The data presented
4.06 3’ 1.707 here are averaged over the month, as a representative in
a particular month. It is clearly seen that soil temperature
Table 3 shows the temperature data for two setups is nearly constant (within 1°C variation) up to 4 feet
discussed in the section 3.1.1. It appears that the use of down. In winter, the temperature then slightly increases
evaporation chamber might be useful in cold countries in the next 3 feet, and in summer, the temperature
like Canada for WindChill Fridge [11], but for warm decreases slightly for the same height down. From 8 feet,
countries it has no impact at all in terms of temperature the soil temperature goes down, regardless of the season.
reduction. Moreover, temperature increase is observed As expected, the soil temperature is higher in summer
for the addition of evaporation chamber (Setup-2). As and lower in winter, and this tendency up to the 5 feet.
such, it can be concluded that evaporation chamber in this The variations become minimal as the distance down the
kind of eco-friendly cooler is not necessary as it ground increases and at 10 feet the temperature becomes
associates temperature rise and additional cost. almost same, irrespective of the month.
Temperature reduction is not found to be significant for
the Setup-1 reasonably expected, since the primary
objective of this test was the check the adequacy of the
use of evaporation chamber.

© ICMERE2019
 35
[3] Arshdeep Singh and Ranjit Singh, “Performance
Analysis of Rectangular Earth-Air Tunnel
Soil Temperature (in °C) Systemused for Air-Conditioning of the College
30 Classroom.”Journal of Energy Technologies and
Policy, Vol.5, No.4, 2015.
25 [4] Mr. Nilesh S. Shelar. Prof. S. B. Patil, and Prof. N.
C. Ghuge, “A Review on Earth-Air Heat Exchanger.”
International Journal of Engineering Research &
20 Technology, 2016, ISSN: 2278-0181.
Feb Mar Apr [5] G. Sharan, H. Prakash, and R. Jadhav, “Performance
May Jun
15 of Greenhouse Coupled toEarth-Tube-Heat-
1 2 3 4 5 6 7 8 9 10 Exchanger in Closed-Loop Mode,” Researchgate,
Depth (in feet) April 2004.
[6] EvangelosBellos and Christos Tzivanidis,”
Fig.7: Underground soil temperature distribution against Investigation of the Environmentally-Friendly
depth. Refrigerant R152a for Air Conditioning Purposes,”
National Technical University of Athen 30
5. CONCLUSION December 2018.
In this project, improvements of an ecofriendly air [7] Trilok Singh Bisoniya, Anil Kumar,and Prashant
cooler and two other variations are experimentally Baredar,” Experimental and analytical studies of
investigated. In this regard, an improved open loop earth- earth–air heat exchanger (EAHE)systems in India:
to-air heat exchanger is also examined for its A review,” Renewable and Sustainable Energy
effectiveness over others. Underground soil temperature Reviews 19 (2013) 238–246.
distribution was also sought in this project. The results [8] Maneesh Kaushal, “Geothermal Cooling/Heating
are summarized as follows: Using Ground Heat Exchanger for Various
i. WindChill Fridge [11] is not effective at all in Experimentaland Analytical Studies:
warm countries, such as Bangladesh. Moreover, Comprehensive Review,”
evaporation process of the ecofriendly cooler is [9] DheerajSardana, Rishi kumar, Snehal S Patel, and
found to be unnecessary. Gaurav Saini, “Effects of Parameters on
ii. Earth-to-air heat exchanger that uses Peltier Performance of Earth Air Heat Exchanger System
module is found to be significantly effective and (EAHE): A Review.” International Journal of
is found to reduce ambient temperature by 6- Advanced Technology in Engineering and Science,
8.5°C. The increased heat transfer rate of hot Volume No.03, Special Issue No. 02, February 2015.
side of Peltier module would yield better result. [10] VaibhavMadane, MeetaVedpathak, and M. D. Nadar,
iii. Soil temperature is found to be nearly constant “Thermal Analysis of Earth Air Heat Exchanger
(within 1°C variation) up to 4 feet down. In using CFD.” International Journal of Engineering
winter, the temperature then slightly increases in Sciences & Research, May, 2015.
the next 3 feet, and in summer, the temperature [11] Jorge Zapote, Mitchell Weber, Xi Cheng, Michelle
decreases slightly for the same height down. Zhou, WindChill Food Preservation Unit, Student
The variations become minimal as the distance Project, University of Calgary, Canada, 2015.
down the ground increases and at 10 feet the [12] Zahir U. Ahmed, “Design and implementation of a
temperature becomes almost same, irrespective food preservation system without Electricity”,
of the month. Alumni Innovation Challenge, Australia Awards
South and West Asia, 2017.
6. ACKNOWLEDGEMENTS [13] https://en.wikipedia.org/wiki/Evaporative_cooler
The authors would like to thank University Grants [14] http://www.longrefrigeration.com/eco-friendly-
Commission for funding provided via Khulna University heating-and-cooling-systems/
of Engineering & Technology (KUET) for this research
project. Government of Australia is also acknowledged 8. NOMENCLATURE
for setting up the base of the project via Alumni
Innovation Challenge of Australia Awards South and Symbol Meaning Unit
West Asia. The last author sincerely thanks Dr. Chandra T0 Ambient Temperature 0
C
Nath, Hitachi America Ltd., USA for his valuable advice TC Cooling unit (Box)
during the challenge program. temperature
TS Soil temperature,
7. REFERENCES ΔT T0 - Tc
[1] F. Ascione, L. Bellia, and F. Minichiello, “Earth-to- TE Exhaust temperature
air heat exchangers for Italian climates”, Renewable
Energy, 36, pp. 2177-2188, 2011.
[2] M. Bojic, G. Papadakis, and S. Kyritsis, “Energy
from a two-pipe, earth-to-air heat exchanger”,
Energy, 24, pp. 519–523, 1999.

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