Renewable Energy

GEOTHERMAL ENERGY

Sommario

GEOTHERMAL ENERGY ................................................................................................................. 1

Part 1 INTRODUCTION .................................................................................................................. 3

Part 2 CLOSED-LOOP SHALLOW GEOTHERMAL SYSTEMS ................................................. 6

Geothermal piles .............................................................................................................................. 7

Shallow horizontal collectors ........................................................................................................... 7

Borehole heat exchangers ................................................................................................................ 7

Part 3 HEAT PUMPS ....................................................................................................................... 8

Heating .........................................................................................................................................

9Cooling

9P-h curve

9COP/EER

10Evaporators and condensers

11Shell and tubes

11Compressor types

11Expansion valve

12Refrigerant

12Catalogue data

12ADSORPTION HEAT PUMP

12Component of a heat pump system

–PART 4 SIZING OF BOREHOLE HEAT EXCHANGERS

13BHE sizing methods

Sizing tables

14Numerical simulation software (FEFLOW)

151ASHRAE method ....................................................................................................................... 15

Eskilson method ......................................................................................................................... 17

–PART 5 OPEN LOOP SHALLOW GEOTHERMAL SYSTEM ................................................... 18

Water well components .................................................................................................................. 18

Drilling techniques ......................................................................................................................... 19

PERCUSSION DRILLING ....................................................................................................... 19

ROTARY DRILLING ............................................................................................................... 19

Roto percussion or Downhole hammer ..........................................................................................

20 Casing and screen

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20 Well sealing

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20 Well development and purge

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PART 6 DESIGN OF GROUNDWATER HEAT PUMPS (GWHPs)

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Thermal recycling

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Thermal impact assessment

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WATER WELL SIZING

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The screen

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23The gravel pack

23–PART 7 ELECTRICITY PRODUCTION FROM GEOTHERMAL RESOURCES

Earth structure

Geothermal flux

Geothermal reservoir

Vapour dominated reservoir

Liquid dominated reservoir

Hot dry rock reservoir

25Power plant

25Dry steam power plant

252Flash power plant

26Binary cycle power plant

26Characterization of geothermal reservoir

–PART 8 ENVIRONMENTAL AND ECONOMIC ASPECT OF HEAT PUMPS AND GEOTHERMAL ENERGY

27Energy end environmental benefits of heat pumps

1. Dry steam: saturated vapour used directly in a vapour turbine (exploit this resources with Rankine cycle)
2. Wet steam: partially saturated water used in a vapour turbine after separation of the liquid phase (flash plants)
3. Binary plants:

Heat drawn from the geothermal fluid can be used with an Organic Rankine Cycle turbine, which uses a volatile fluid that can reach high pressure and is then sent to a turbine. This technology can be used for various applications such as beer production, greenhouses, aquaculture, and the cheese industry.

Ground source heat pumps are heat pumps that utilize the shallow underground as a heat source or sink. There are two different techniques for this:

1. Closed-loop heat exchangers: This involves using pipes in a horizontal loop under the ground.
2. Heat exchange with groundwater: This is an open loop system that includes an abstraction well and an injection well.

A heat pump is a machine that transfers heat from a "cold source" to a "hot sink" through the provision of mechanical work (in the case of a vapor compression heat pump) or heat (in the case of an absorption heat pump). The flow of heat goes against the natural transfer, as heat is transferred from a hotter zone to a colder zone. Heat pumps induce this flow of heat.

The cold sources that can be used with heat pumps include air, surface water, groundwater, and the ground. The energy efficiency of a heat pump is measured by its coefficient of performance (COP).

Coefficient of Performance) which depends on “cold source” and the “hot sink”. The temperature difference between the The smaller is this different the higher is COP, so more efficient. The ground temperature is almost constant through the year; warmer than air during winter and it is → cooler than air during summer therefore a higher COP is achieved. The temperature of the ground is more or less constant due to the temperature oscillations in the shallow underground. The amplitude of the temperature oscillation through the year diminishes as depth from the ground surface increases. The evolution of the ground temperature is the result of heat balance in the underground (a part of heat is reflected a part is adsorb). At low depths: - Absorbed solar radiation - Sensible heat - Lent heat (condensation or evaporation) - Wind - Precipitations At large depths: - Radioactive decay - Geothermal heat flux 4 There are three main heat transport mechanisms: • → Conduction (red)