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A STUDY ON THE FEASIBILITY OF USING
GEOTHERMAL COOLING AS AN ALTERNATIVE
TO CONVENTIONAL AIR CONDITIONING
An Investigatory and Exploratory Project
Presented to the Faculty of
Westfield Science-Oriented School and Colleges
Las Pias City
In Partial Fulfilment of the
Requirements in General Science
Danielle Alison B. Black
HS1- Consunji
December 2011
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Chapter I. INTRODUCTION
Background of the Study
The world is currently experiencing problems involving our energy resources.
The problem is the rate that the worlds energy demands are increasing is faster than
the rate at which renewable sources are being developed.
So until the time that both renewable and fossil fuelled energy resources can be
stabilized to meet demand, the only real solution is to look for ways to reduce our
energy consumption.
Looking at how much electricity we use, you will see that air conditioning
contributes the largest share of our total energy consumption. This is particularly true in
summer, where the use of air conditioning can contribute to more than 50% of
household electrical consumption. Of course we can just stop using our aircons, but that
would only work on cool days, like around Christmas time, but it would also make our
homes very uncomfortable during summer. So the better solution would be to look at
how to make an aircons use less electricity.
The reason why aircons use so much electricity is because of the compressor.
This is the most important part of the aircon because it compresses the heat that is
taken from inside the room and transfers that heat outside where the heat is radiated
into the atmosphere. The compressor makes sure that the temperature of the aircons
condenser is always hotter than the outside ambient air temperature, so that the heat
will transfer from the condenser to the outside air. When the heat is transferred (or
exchanged) to the outside air, the now cool air is brought back into the room. That is
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why aircons are also called heat exchangers. If there was a way to construct a heat
exchanger that does not use a compressor, then it would be possible to have a very
energy efficient air conditioner.
For a compressor-less heat exchanger to work, it has to be able to radiate its
heat into a place that is cooler than the room being cooled. One possible place is the
earth itself. In the Philippines, the ground temperature beyond 5m below the surface is
constant at 25C, regardless of what the outside temperature is. This can be as low as
20 C if ground water is present, usually around 30m below the surface.
This project aims to explore the feasibility of building a compressor-less heat
exchanger as an alternative to conventional aircons. The heat exchanger will take the
heat from a room (the same way as a regular aircon) and then use the earth as a heat
sink to absorb that heat. Since the ground temperature will always be lower than the
temperature of the room being cooled, then there is no need for a compressor. It should
be possible to get the room to cool down to the same temperature as the ground.
Because this type of heat exchanger will only use a radiator, a blower fan and a
small water pump, its energy consumption can be much lower than what an aircon uses
but it will still be able to provide the same cooling as a regular aircon.
The researcher chose to conduct this study because the world needs to find a
way to prevent the abatement of our non-renewable resources by making use of our
renewable energy resources for a better future.
If this experiment is successful, it will prove that it is possible to make an energy
efficient air conditioner.
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Objectives of the Study
The researcher considers the following objective of the study:
1. The study aims to determine if ground source geothermal cooling can be
used as an alternative for conventional air-conditioning
2. The study also aims to determine if a ground source geothermal cooling
system will use less electricity than a conventional air conditioner.
Statement of the Problem
This study seeks to answer the following questions:
1. Can ground source geothermal cooling be an alternative of air-conditioning?
2. Will a ground source geothermal cooling system use less electricity than a
conventional air conditioner?
Hypothesis
1. The ground source geothermal cooling is a possible alternative for
conventional air-conditioning.
2. The ground source geothermal cooling system will be more energy efficient
than a conventional air conditioner.
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Scope and Delimitation
This study will focus on proving the concept of ground source geothermal
cooling. The output of this project will be a scaled down ground source geothermal
cooling system using a miniature room mock up with a heat exchanger and a heat sink
in a simulated ground cooling system.
As a proof of concept, this project will not be done in full scale, but it will identify
possible issues to be considered for building a full-scale version.
Significance of the Study
To the students, this study shows that they can help the environment at a young
age. And in the future, they can use this study as a guide for a better living.
To the researchers, this study will provide the basis for further study on how to
build a full-scale ground source geothermal cooling system that can potentially replace
the use of conventional aircons.
To the businessmen, this study will help them in finding new ways in saving
money because this study promotes less use of electricity. Therefore, less money is
spent.
To the country, this study is significant because of the amount of electricity that
can be saved by this system can result in not only lower electricity bills, but also lessen
our countrys use of fossil fuels and reduce our CO2 emissions.
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Definition of Terms
Fossil fuels. Fuels that are formed by natural processes such as anaerobic
decomposition of buried dead organisms. The age of the organisms and their resulting
fossil fuels is typically millions of years, and sometimes exceeds 650 million years.
Ground source geothermal cooling. A central cooling system that pumps heat to or
from the ground. It uses the earth as a heat sink. This design takes advantage of the
moderate temperatures in the ground to boost efficiency and reduce the operational
costs of heating and cooling systems
Heat Exchanger. A device for transferring heat from one medium to another.
Heat Sink.A device or substance for absorbing excessive or unwanted heat
Renewable energy.Renewable energy is energy which comes from natural resources
such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally
replenished).
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Chapter II. REVIEW OF RELATED LITERATURE
Throughout the history of man, people have been taking advantage of the
insulating properties of the earth as protection from the weather. From the time that
Stone Age man started moving out of caves and into man-made dwellings during the
Middle Paleolithic Age 50,000 years ago, fully or semi-underground man-made shelters
were the primary means used by man to protect himself from extreme heat or cold.
(Clark, J. Desmond, 1982. The Culture of the Middle Paleolithic/Middle Stone Age)
This use of underground shelters as well as above ground earthen structures
continued throughout the ancient and modern times, because earthen structures
provide constant year-round indoor temperatures, regardless of the outdoor
temperature. (Roy, Robert, 2006. Earth Sheltered Houses).
Modern geologists have since determined that underground temperature for any
specific location on the planet remains constant throughout the year and is equal to the
average annual temperature for that specific region (California Energy Commission,
2009. Geothermal or Ground Source Heat Pumps). In the Philippines, the underground
temperature has been determined to be 25.8 degC above the water table or when there
is no ground water present, and 20.3 degC when ground water is present (Philippine
Atmospheric, Geophysical and Astronomical Services Administration, 2001. Climate of
the Philippines).
In the United States and Europe, the use of coolant piped into the ground is
called ground source geothermal cooling. This is primarily used to reduce energy
consumption during the winter months where the ground temperatures are higher than
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the ambient air temperature. It has also been used secondarily for cooling in summer,
when the ground is cooler than the ambient air. However, the low average humidity
makes evaporative coolers cheaper and more efficient, therefore, the use of ground
source geothermal as a replacement for conventional airconditioning is limited. Several
non-commercial and experimental ground source geothermal air conditioning systems
are being used and tested in some southern US states where the high summer humidity
prevents the efficient use of evaporative coolers (Gannon, Robert, 1978, Ground-Water
Heat Pumps - Home Heating and Cooling from Your Own Well).
In the Philippines, there is a potential to use ground source cooling because the
ground temperature can be as much as 15 degC cooler than the ambient air
temperature at the peak of summer. Air conditioning manufacturers recommend that for
maximum comfort and efficiency, conventional airconditioners should be set to a
temperature exactly 10 degC lower than the outside temperature (Jan F. Kreider. 1996.
Handbook of heating, ventilation, and air conditioning). Since the ground temperature
can be as much as 15 degC cooler than the outside air, then a compressor-less ground
source cooling air conditioner can potentially provide the same cooling as a standard air
conditioner.
Also, with a 15 degC temperature difference between the ground and the inside
of a house or building will allow the use of a simple heat exchanger using water pump
and a heat sink buried underground below the water table to take the hot indoor air from
a house or building and transfer that heat into the ground (Winnick, J,1996. Chemical
engineering thermodynamics).
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Chapter III. Methodology
Materials
This study used a small scale mock-up of a ground source cooling system. The
following materials were used to construct the mock-up:
1. Cardboard box (1m x 1m x 1m)
2. Foam roofing insulation
3. Heat sink / radiator
4. Electric blower fan (computer fan)
5. Aquarium water pump
6. Ducting (3" diameter)
7. Rubber hoses
8. Ice cooler
9. Coiled aluminium tubing
10. Digital thermometers
11. Timer
To construct the mock-up of a house, the cardboard box was first lined with foam
insulation. Then Two 3-inch holes were cut into the box, one on each side and ducting
was attached to each hole. A digital thermometer was put inside the house to observe
the changes in air temperature during the experiment.
To simulate the ground, the ice cooler was filled with water and ice added to
attain a temperature of 20.3 degC measured with a thermometer. Ice was then added
as needed during the experiment to keep the temperature constant.
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For the heat exchanger, the tubing from the box was connected to an electric
blower fan. The radiator was them attached to the other end of the fan. The other end of
the duct was then attached to the opposite side of the radiator.
To simulate the underground heat sink, coiled aluminium tubing was put into the
ice cooler. Rubber hoses were then attached to both ends of the aluminium tubing. To
circulate the water between the radiator and the heat sink, an aquarium water pump
was used and connected to both the radiator and the heat sink so that water could
circulate between the heat sink and the radiator.
Procedures
Before starting the experiment, the temperature of the box was measured and
noted. Then the blower fan and water pump were turned on to circulate the coolant and
the timer was started.
With the fan and the pump running, the temperature of the box was constantly
monitored and any changes in temperature over time were noted. Simultaneously, the
temperature of the ice box was also monitored to make sure that the temperature
remained constant. If the temperature of the ice box increased, then additional ice was
added as needed to maintain a constant 20.3 degC temperature.
The heat exchanger was kept running until the time that the temperature of the
box became constant. The ending temperature and the elapsed time were then noted.
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Chapter IV. RESULTS AND DISCUSSIONS
A. Presentation of Data
Four tests were conducted using the mock-up in order to examine how the mock
up performs under daytime and night time temperature conditions. A description of
each test and the results are discussed below.
As this is a test of a cooling system, the temperatures both inside and outside of
the test box were measured before and during the test. Likewise the temperature of the
coolant box was measured and maintained at 21C to simulate the constant ground
temperature.
In the following discussions, "outdoor temperature" shall refer to the ambient
temperature outside the box, "indoor temperature" shall refer to the measured
temperatures inside the box, while "ground temperature" shall refer to the temperature
of the coolant box.
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Test No. 1 : Daytime test. Starting indoor temperature SAME as outdoor
temperature
This test was conducted in the daytime with the mock-up set outdoors in a
shaded location. The indoor temperature inside the mock-up was equalized with the
outdoor temperature prior to the test. At the time of the test, the outdoor temperature
was measured to be 32C with the ground temperature kept constant at 21C.
The results are shown in Table 1 below.
Table 1 : Test No. 1 Measured Temperature Over Time
Time
(Minutes)
Outdoor
Temperature (C)
Ground
Temperature (C)
Indoor
Temperature (C)
Temp DifferenceIndoor vs
Outdoor (C)
Temp DifferenceIndoor vs
Ground (C)
0 32 21 32 0 +11
1 32 21 32 0 +11
2 32 21 32 0 +11
3 32 21 31 -1 +10
4 32 21 29 -3 +8
5 32 21 28 -4 +7
6 32 21 28 -4 +7
7 32 21 27 -5 +6
8 32 21 27 -5 +6
9 32 21 27 -5 +6
10 32 21 26 -6 +5
11 32 21 26 -6 +5
12 32 21 26 -6 +5
13 32 21 25 -7 +4
14 32 21 25 -7 +4
15 32 21 25 -7 +4
16 32 21 25 -7 +4
17 32 21 24 -8 +3
18 32 21 24 -8 +3
19 32 21 24 -8 +3
20 32 21 24 -8 +3
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As seen in Table 1 (above), for the first two minutes of the test, there was no
recorded change in the indoor temperature. Beginning the 3rd minute, the indoor
temperatures began to fall at a relatively constant rate until 17 minutes into the test,
where the indoor temperature remained constant until the end of the test.
By the end of the test period, the mock-up was able to achieve a constant indoor
temperature of 24C, which was 8C cooler than the outside temperature, and only 3C
warmer than the ground temperature. This is illustrated in Graph 1 (below).
Graph 1: Results of Test No. 1 (Daytime, Indoor and Outdoor Temperature Sameat Start)
19
21
23
25
27
29
31
33
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature(C)
Time (Minutes)
Outdoor Temp
Indoor Temp
Ground Temp
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Test No. 2 : Daytime test. Starting indoor temperature HIGHER than outdoor
temperature
This test was done in the daytime with the mock-up set outdoors in the shade.
The indoor temperature was raised by 5C above the outdoor temperature. This was
done to simulate a real world scenario where the inside of a house may be warmer than
the outside temperature because of internal heat sources such as stoves, appliances,
and body heat from people. At the time of the test, the outdoor temperature was
measured to be 32C with the ground temperature kept constant at 21C and the indoor
temperature was raised to 37C. The results are shown in Table 2 below.
Table 2 : Test No. 2 Measured Temperature Over Time
Time
(Minutes)
Outdoor
Temperature (C)
Ground
Temperature (C)
Indoor
Temperature (C)
Temp Difference
Indoor vs
Outdoor (C)
Temp Difference
Indoor vs
Ground (C)
0 32 21 37 +5 +16
1 32 21 35 +5 +16
2 32 21 34 +4 +15
3 32 21 33 +3 +144 32 21 32 +2 +13
5 32 21 32 +1 +12
6 32 21 32 0 +11
7 32 21 31 0 +11
8 32 21 30 -2 +9
9 32 21 30 -3 +8
10 32 21 28 -4 +7
11 32 21 28 -4 +7
12 32 21 27 -5 +6
13 32 21 26 -5 +6
14 32 21 26 -6 +5
15 32 21 25 -7 +4
16 32 21 25 -7 +4
17 32 21 25 -7 +4
18 32 21 24 -8 +3
19 32 21 24 -8 +3
20 32 21 24 -8 +3
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As seen in Table 2 (above), the temperature immediately began to drop from the
very beginning of the test until the indoor temperature reached the same as the outdoor
temperature of 32C after four minutes. and then the temperature remained steady for
three minutes before continuing to drop until it reached a minimum of 24C after 18
minutes.
Although the starting indoor temperature was higher by 5C than on Test No.1,
then ending temperature was of 24C was the same for both Test No.1 and Test No.2.
This is illustrated in Graph 2 (below).
Graph 2: Results of Test No. 2 (Daytime, Indoor and Outdoor TemperatureHigher at Start)
19
21
23
25
27
29
31
33
35
37
39
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature(C)
Time (Minutes)
Outdoor Temp
Indoor Temp
Ground Temp
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Test No. 3 : Night time test. Starting indoor temperature SAME as outdoor
temperature
This test was done at night time with the mock-up set outdoors in the shade. Just
as with Test No.1, the indoor temperature was first equalized with the outdoor
temperature before starting the test. At the time of the test, the outdoor temperature
was measured to be 28C with the ground temperature kept constant at 21C. The
results are shown in Table 3 below.
Table 3 : Test No. 3 Measured Temperature Over Time
Time
(Minutes)
Outdoor
Temperature (C)
Ground
Temperature (C)
Indoor
Temperature (C)
Temp Difference
Indoor vsOutdoor (C)
Temp Difference
Indoor vsGround (C)
0 28 21 28 0 +7
1 28 21 27 -1 +6
2 28 21 27 -1 +6
3 28 21 26 -2 +5
4 28 21 26 -2 +5
5 28 21 25 -3 +4
6 28 21 25 -3 +4
7 28 21 24 -4 +3
8 28 21 24 -4 +3
9 28 21 23 -5 +2
10 28 21 23 -5 +2
11 28 21 23 -5 +2
12 28 21 23 -5 +2
13 28 21 22 -6 +1
14 28 21 22 -6 +1
15 28 21 22 -6 +1
16 28 21 22 -6 +1
17 28 21 22 -6 +1
18 28 21 22 -6 +1
19 28 21 22 -6 +1
20 28 21 22 -6 +1
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As seen in Table 3 (above), after one minute, the indoor temperature began to
fall at a constant rate until 13 minutes into the test, afterwhich the indoor temperature
stayed constant until the end of the test.
By the end of the test period, the mock-up was able to achieve a constant indoor
temperature of 22C, which was 6C cooler than the outside temperature, and only 1C
warmer than the ground temperature. This is illustrated in Graph 3 (below).
Graph 3: Results of Test No. 3 (Night time, Indoor and Outdoor TemperatureSame at Start)
19
20
21
22
23
24
25
26
27
28
29
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature
(C)
Time (Minutes)
Outdoor Temp
Indoor Temp
Ground Temp
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Test No. 4 : Night time test. Starting indoor temperature HIGHER than outdoor
temperature
This test was done at night time with the mock-up set outdoors in the shade. Just
as with Test No.2, the indoor temperature was raised by 5C above the outdoor
temperature to simulate indoor heat sources. At the time of the test, the outdoor
temperature was measured at 28C with the ground temperature kept constant at 21C
and the indoor temperature was raised to 33C. The results are shown in Table 4 below.
Table 4 : Test No. 4 Measured Temperature Over Time
Time
(Minutes)
Outdoor
Temperature (C)
Ground
Temperature (C)
Indoor
Temperature (C)
Temp Difference
Indoor vsOutdoor (C)
Temp Difference
Indoor vsGround (C)
0 28 21 33 +5 +12
1 28 21 32 +4 +11
2 28 21 32 +4 +11
3 28 21 31 +3 +10
4 28 21 30 +2 +9
5 28 21 29 +1 +8
6 28 21 28 0 +7
7 28 21 28 0 +7
8 28 21 28 0 +7
9 28 21 27 -1 +6
10 28 21 26 -2 +5
11 28 21 25 -3 +4
12 28 21 25 -3 +4
13 28 21 24 -4 +3
14 28 21 24 -4 +3
15 28 21 23 -5 +2
16 28 21 23 -5 +2
17 28 21 22 -6 +1
18 28 21 22 -6 +1
19 28 21 22 -6 +1
20 28 21 22 -6 +1
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As seen in Table 4 (above), the temperature immediately began to drop from the
very beginning of the test until the indoor temperature reached the same as the outdoor
temperature of 28C after six minutes. and then the temperature remained steady for
three minutes before continuing to drop until it reached a minimum of 22C after 17
minutes.
This drop in temperature over time is illustrated in Graph 4 (below).
Graph 4: Results of Test No. 4 (Daytime, Indoor and Outdoor TemperatureHigher at Start)
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21
23
25
27
29
31
33
35
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature
(C)
Time (Minutes)
Outdoor Temp
Indoor Temp
Ground Temp
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B. Analysis of Data
Based on the data collected, the experiment was able to achieve a decrease in
the indoor temperatures in all of the four tests. This can clearly be seen in Graph 5
below.
These results show that it is possible for a simple heat exchanger using the earth
as a heat sink to cool an enclosed space.
Graph 5: Comparative Temperature Drop for Tests 1,2,3 & 4
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21
23
25
27
29
31
33
35
37
39
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Tem
perature(C)
Time (Minutes)
Test No.1
Test No.2
Test No.3
TestNo.4
DayOutdoor Tem
NightOutdoor Te
Ground Temp
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It was also noted that in both the daytime and nigh time tests, the coolest
temperatures attained were the same, even when the beginning temperatures were
increased above that of the outside temperature.
For the daytime tests (Tests No.1 and No.2), even if they had different starting
indoor temperatures, 32C for Test No.1 and 37C for Test No.2, both were able to
reach the same ending temperature of 24C. The only difference was the length of time
it took for the tests to reach their minimum temperature, 17 minutes for Test No.1, and
18 minutes for Test No.2. This can be seen in Graph 6 below.
Graph 6: Comparative Temperature Drop for Daytime Test No.1 and No.2
19
21
23
25
27
29
31
33
35
37
39
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature(C)
Time (Minutes)
Test No.1
Test No.2
Outdoor Temp
Ground Temp
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Similarly, for the night time tests (Tests No.3 and No.4), even if they had
different starting indoor temperatures, 28C for Test No.1 and 33C for Test No.2, both
were able to reach the same ending temperature of 22C. The only difference was the
length of time it took for the tests to reach their minimum temperature, 15 minutes for
Test No.3, and 17 minutes for Test No.2. This can be seen in Graph 7 below.
Graph 7: Comparative Temperature Drop for Night Time Test No.3 and No.4
It was also observed that both the daytime and night time tests were able to
achieve significant cooling compared to the outside temperature, with the daytime tests
achieving indoor temperatures that were 8C cooler than the outside air. Likewise, the
night time tests achieved temperatures -8C cooler than the outside air. However,
19
21
23
25
27
29
31
33
35
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Temperature(C)
Time (Minutes)
Test No.3
Test No.4
Outdoor Temp
Ground Temp
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the neither the daytime nor the night time tests were able to achieve the same
temperatures as the ground, with the lowest daytime test temperatures ending at +3C
warmer than the ground temperature. Likewise, the night time test temperatures ended
at +1C warmer than the ground temperature. These results be seen in Table 1 below.
Table 1: Comparative Temperature Difference for Day and Night Tests
Maximum Temp Difference
vs Outdoor Temperature
Minimum Temp Difference
vs Ground Temperature
Day Time Test No.1 & 2 -8C +3C
Night Time Test No. 3 & 4 -6C +1C
Since the process of heat exchange slows down as the temperature difference
becomes smaller, this may explain why the night time temperature difference is not as
large as the day time temperature difference.
Also, it was noted that the minimum temperature difference vs the ground
temperature was lower for the night test at +1C compared to the day test at +2C.This
may be because heat was still entering the mock-up box and the coolant hoses, thus
preventing the system from achieving equal temperature with the ground.
However, even with external heat entering the system, the indoor temperatures
of 24C in the daytime and 21C at night attained by the geothermal cooling system
were still comparable to that of a conventional air conditioner.
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Chapter V. CONCLUSIONS AND RECOMMENDATIONS
Conclusions
Based on the study investigated, the following conclusions were drawn:
1. It was possible to use a ground-source geothermal cooling system as an alternative
to conventional air-conditioning. Therefore, hypothesis Number 1 is accepted.
2. Since the ground source geothermal system only used a water pump and a fan and
no air compressor, then the system uses less electricity and is more energy efficient
than an air-conditioner. Therefore, hypothesis Number 2 is accepted.
Recommendations
Based on the study done, the following recommendations were made:
1. Try to use better insulation on the system to see if it is possible to attain indoor
temperatures equal to the ground temperature.
2. Try to test on a larger scale and with higher heat loads (ie test in direct sunlight) to
further explore the system's efficiency.
3. Repeat the tests and measure humidity along with temperature to test if the system
can also control humidity similar to an air-conditioner.
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BIBLIOGRAPHY
I. Books
Clark, J. Desmond, 1982. The Culture of the Middle Paleolithic/Middle Stone Age
Cambridge University Press
Roy, Robert, 2006. Earth Sheltered Houses
New Society Publishers
Winnick, Jack, 1996. Chemical engineering thermodynamics
Wiley
Jan F. Kreider. 1996. Handbook of heating, ventilation and air conditioning
CRC Press
Gannon, Robert. 1978. Ground-Water Heat Pumps Home Heating and Cooling
from Your Own Well
Times Mirror Magazines, Inc.
II. Internet
Climate of the Philippines.Retrieved 2001 from
http://kidlat.pagasa.dost.gov.ph/cab/statfram.htm
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