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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)

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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.


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)

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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.


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)

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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.


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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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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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

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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

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

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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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