Download - Geothermal 101
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Introduction toGeothermal
Comfort Systems
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Defining “Geothermal” Energy
• Dictionary definition– Relating to the internal heat of the earth
• The Earth acts as a giant solar collector, absorbing approximately 50% of the energy emitted by the Sun.
• Air temperatures may fluctuate as much as 50F above and below the annual average. However, only a few feet below the surface, the changes in earth temperatures are much less severe.
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Defining “Geothermal” Energy
• “High Temperature” Geothermal– Refers to heat temperatures from
typically hundreds of feet deep within the earth, sometimes exceeding 300F.
– These include geysers and other hydro-geothermal reservoirs.
• “Low Temperature” Geothermal– Refers to shallow earth temperatures
found anywhere, utilizing a mechanical device (geothermal heat pump) to transfer heat to and from the ground.
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Laws of Thermodynamics
• First Law– Conservation of Energy (Basically, you
can’t get more energy out than you put in.)
• Second Law– Heat energy flows from an area of high
heat to a area of low heat. – You cannot stop this process, only
speed it up or slow it down.
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The Basic Ground Source Heat Pump System
• The earth loop is placed in the ground either horizontally or vertically, or it can be placed in a pond.
• Water and anti-freeze is circulated through the pipe, transporting heat to the heat pump during the heating mode and away from the heat pump during the cooling mode.
• The heat transfer takes place inside the heat pump in a water-to-refrigerant heat exchanger.
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Energy Source
• During the heating season, the earth serves as a heat source. (HE - Heat of extraction)
• During the cooling season, the earth serves as a heat sink. (HR - Heat of rejection)
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Equipment Performance Ratings
• Geothermal and ground water heat pumps are tested under ISO Standard 13256-1, which replaces the former standards of ARI-330 (ground loop), ARI-325 (ground water/open loop) and ARI-320 (water loop/boiler-tower).
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Equipment Performance Ratings
• ARI has designated the efficiency ratings for water-to-air heat pumps as:– Energy Efficiency Ratio (EER)
• EER = BTU output divided by power watt input• For cooling operation under steady state test
conditions
– Coefficient of Performance (COP)• COP = BTU output divided by BTU input• For heating operation under steady state test
conditions
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Heat Pump Operation
• Geothermal heat pumps consist of four circuits:– Distribution circuit
• The system that distributes the conditioned air or water solution throughout the home or building and returns it to the unit.
– Refrigerant circuit• A sealed and pressurized circuit of refrigerant
including compressor, expansion valve, water-to-refrigerant heat exchanger(s), air coil, reversing valve. The refrigerant is either R-22 or R-410A.
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Heat Pump Operation
• Geothermal heat pumps consist of four circuits:– Ground loop circuit
• The piping system buried in the ground has fluid that is circulated by pumps to and from the geothermal unit.
– Hot water circuit• Domestic water can be heated in a geothermal
unit with a device called a desuperheater. A piping connection is made from the geothermal unit to the water heater.
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Heat Pump Operation
• Each of these circuits is closed and sealed from the others—there is no direct mixing.
• However, heat energy does transfer from the refrigeration circuit to the other three circuits.
• The refrigerant flow will change direction when the unit changes modes (heating or cooling).
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Heat Pump Operation
• The Four Circuits in a Geothermal Heat PumpDistribution Circuit
Earth Loop Circuit
Refrigeration Circuit
Hot Water Circuit
= Flow of Energy(Heat)
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Heating Mode Operation
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Cooling Mode Operation
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The Basic Refrigeration CycleCompressor
CondenserEvaporator
TXV
High PressureVapor State
High PressureLiquid State
Low PressureLiquid State
Low PressureVapor State
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The Refrigeration Cycle
• Heating Mode Operation
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The Refrigeration Cycle
• Cooling Mode Operation
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Geothermal Loops
• Closed Loops– Horizontal– Vertical– Pond/Lake
• Open Loops– Well water
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Typical Earth Loop FeaturesCircuit Piping
(usually ¾” or 1” IPS)
Multiple Circuits(trenches or bores)
Header Pit
Reverse-Return Header
Supply & Return Piping(usually 1-1/4” or 1-1/2” IPS)
Foundation Penetration
Equipment & Flow Center
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Piping Material
• Geothermal earth loops are constructed using pipe with the following characteristics: – Polyethylene—designated as High Density
PE3408.– SDR-11; IPS sizes ¾” diameter and larger– All connections done using heat fusion at 500F.– Highest rating available for stress crack
resistance. – Carbon black provides UV protection from sun– Elongation of 6 times original length before
failure.
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Horizontal 4 & 6 Pipe Loops
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Horizontal Slinky Loops
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Horizontal Bore Loops
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Horizontal Pond/Lake Loops
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Horizontal Pond/Lake LoopsSlim Jim Lake Plate Heat
Exchanger
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Vertical Loops
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Typical Installation – Closed Loop
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Closed Loop Freeze Protection
• In climates with moderate to dominant heating loads, anti-freeze is used for freeze protection.
• Various types and concentrations of antifreezes are used. – Environol– Methanol– Propylene glycol
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Typical Installation – Open Loop
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Open Loop Systems
• Key Considerations– Adequate water supply (1.5 gpm per ton
in addition to household requirements)– Good quality water (low mineral
content)– Adequate discharge location (drainage
ditch, field tile, pond, etc.)
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Key Benefits of Geothermal Systems
• Energy savings for heating, cooling and DHW
• Quiet operation• No outdoor condensing unit required• Less maintenance• Long life• Safe and clean-- No flames, fumes, flues• Environmentally Friendly• Decreases peak demands for electricity
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Other Applications
• Commercial applications (offices, retail, hotels, apartments/condos, resorts)
• Institutional applications (schools, hospitals, nursing homes)
• Industrial applications (process water heating & cooling, manufacturing plants)
• Pools and spas• Snow melt / ice melt• Radiant floor heating