Opinion

FEASIBILITY THE USE OF GEOTHERMAL HEAT SOURCE/SINK TO PROVIDE COOLING Created by Mirmanto, Mataram University, Mataram, NTB, Indonesia e-mail: [email protected]

Sight Glass

Geothermal energy is a renewable energy that is abundantly available inside the earth. Nowadays, it is becoming popular energy source because it is free to be explored, free pollutant, and is flexible to to be utilized. Geothermal energy (heat source) usually comes out from Volcano or deep well. Volcano and deep well provide heat energy that can be flowed to the surface of earth. After reaching the surface, the heat energy can be utilized as Heat Pump, Heat Process such as drying, cooking etc, and Electrical Power Generation as well as Heat Source of Absorption Cooling system. According to www.earthtoair.com.au, earth's temperature within 15 m of depth is about 19 o C. It means that the earth can be used for absorbing heat as long as heat comes from area that has temperature more than that. Because comfortable condition for people is at temperature of 25-27 oC, so that it is possible to use earth to absorb heat for changing temperature from more than 27 oC to 25-27 oC. Figure 1 shows schematic of refrigeration plant that uses earth as heat sink.

Check Valve Acces Valve

Sight Glass

Evaporator

Ball Valve

Check Valve

Oil Separator

Receiver

Accumulator Compressor

High Pressure Liquid Low Pressure Liquid Low Pressure Vapor High Pressure Vapor

Reversing Valve

Ball Valve

Acces Valve

Cooling room

Ball Valve

Check Valve

Condensor

Ball Valve Ground Source (Heat Sink)

Figure 1. Refrigeration Plant using earth as heat sink In Indonesia, where average temperature in noon is about 30-34 oC, this refrigeration system is feasible to use in practical case as long as this refrigeration system is used on earth. However, may be it needs modifying when it is used in underground room because usually underground room has more complex condition such as more humid, hotter, fresh air inadequacy etc.

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Except earth can absorb heat, which comes from on earth, it can give heat when its distance downward measured from the surface is far more than 15 m as well. Heat from this depth can be used for providing cooling, by means of an absorption refrigeration system. This system uses earth as heat source that can be used for evaporating ammoniac from ammoniac-water solution in the refrigeration machine. By using this system, geothermal heat source is feasible to provide cooling

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(see figure 2). Check Valve Acces Valve

Ball Valve

Reversing Valve

Check Valve

Oil Separator

Receiver

Accumulator

Evaporator

Pump

Ball Valve

Ball Valve Ground Source (Heat Sink)

Mixing Chamber Acces Valve Separator

Condensor

Compressor

High Pressure Liquid Low Pressure Liquid Low Pressure Vapor High Pressure Vapor Low pressure hot water Low pressure cold water

Sight Glass

Cooling room

Ball Valve

Check Valve

Ground Source (Heat Sink)

Ammoniac-water solution Ammoniac vapor-water

Deep Well

Condensor

Figure 2. Absorption Refrigeration Plant using geothermal heat source and heat sink Unfortunately, those both systems require big initial infestation, because condenser that is buried underground must be designed accurately in order to have good performance and high effectiveness. However, when they are run in a long time, those systems can be cheaper than conventional refrigeration system because of their low operating cost. Moreover, to prove this opinion, one has to make an economical analytic for those systems above and conventional refrigeration system in practical study.

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