Geothermal Systems

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Geothermal Systems
GEOTHERMAL SYSTEMS UMF EDUCATION CENTER GORHAM
MIDDLE SCHOOL Presented by Richard A.Nadeau,
PE, RCDD, LEED AP Alan G. Kuniholm, AIA, LEED
AP Katherine M. Everett, PE
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What is Geothermal?

• Ground source heat pump system
• Earth used as a heat exchanger
• Drilled wells are pathways
• Earth temperature is relatively constant at
  approx. 50?F
• Earth is used to bank or store energy for the
  opposite season

Satellite Photo at Night Showing Electric Light
Usage and Light Pollution
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Why Geothermal?

• Reduction of local greenhouse gas emissions
• Reduction of carbon footprint
• No stack
• No boiler or chiller
• Attractive payback and return on investment of
  first costs
• Stabilize utility costs

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Where to Use Geothermal?

• Combined heat and cooling applications
• Good building envelope
• Low temperature (water) systems cannot
  accommodate large temperature swings
• Site considerations - bore fields

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Types of Systems

• Open loop
• Standing column
• Supply and return well
• Closed loop
• Vertical
• Horizontal

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Open Loop
Standing Column Well
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Open Loop
Supply and Return Well
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Open Loop Systems

• Ground water is pumped directly into the system
  and returned to the open source.
• Pumps are sized to deal with an increased pump
  head.
• Ground water contains minerals and other
  contaminants that negatively affect equipment and
  increase maintenance costs.
• May require filtration equipment or secondary
  heat exchangers to deal with contaminants.
• Require large amounts of water to meet
  heating/cooling needs.
• Lower initial cost,
• fewer wells, deeper wells approx. 1,500 feet
• More prone to failure from
• Dry wells
• Collapsed wells
• Salt, grit or other contaminants
• Higher pumping costs

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Closed Vertical Loop
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Closed Loop Systems

• Utilize a dedicated fluid loop that is circulated
  through the ground or pond in order to exchange
  energy.
• Ground or pond water does not mix with loop
  water.
• Grout protected aquifer
• There are more options for closed loop systems.
• Higher costs
• Many more wells, piping and grout
• More efficient
• Many more successful installations

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Operating Concept Closed Loop

• Water in primary loop is circulated through well
  and emerges at 50?F
• Secondary loop circulates 50?F water through heat
  pumps
• Water-to-water heat pump
• Water-to-air heat pump
• Water-to-water heat pumps raise water temperature
  to 120?F for radiant slabs, cabinet unit heaters
  and preheat coils
• Water-to-air heat pumps, heat and cool spaces

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Closed Horizontal
Loop (Slinky)
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Slinky Field
Horizontal Field
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Considerations

• Design
• Geothermal Consultant
• Cost of Construction
• Cost per well
• Cost per sq. ft.
• Construction Options and Issues
• Manifold location
• Vault or building
• Location of bore fields
• Expansion possibilities
• Access
• Bore hole waste
• Scheduling
• Test bore before budget completion
• Construction sequencing
• Required Area
• 1 well 1,000 sq. ft. x 15 20 feet apart

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Geothermal Feasibility Analysis

• Test well
• Water quality/quantity
• Flux
• Temperature
• Geology
• Design
• Energy modeling, payback and ROI

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Mechanical Systems Used with Geothermal

• Water-to-water heat pumps
• Radiant slabs
• Cabinet unit heaters
• Air handler heat exchanger pre-heat coil
• Water-to-air heat pump
• In rooms
• In corridors

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Heat Pumps

• Thermo-dynamic refrigeration process
• Refrigeration gas is compressed and expanded with
  compressor and evaporator coil
• As the refrigeration gas is compressed or
  expanded heat is absorbed or released depending
  on which coil the air or water passes through.
• Refrigerant valve in unit can be reversed to
  change heat pump cycle so the space can be heated
  and cooled in the same day.
• Similar operation as refrigerator, window A/C
  unit, or dehumidifier

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How does a heat pump work ?

• Normally, the heat pump reverses the refrigerant
  in the refrigeration loop

COMPRESSOR
COMPRESSOR
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Traditional heat pump systems
TRADITIONAL DISTRIBUTED HEAT PUMP SYSTEM
CENTRAL HEAT PUMP SYSTEM
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Ground source heat pump systems
GROUND SOUCE DISTRIBUTED HEAT PUMP SYSTEM

• We use ground as a heat source and a heat sink
  (ground replaces the boiler and the cooling tower)

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Heat pumps use Refrigeration Cycle

• We use refrigeration cycle to defy nature

EVAPORATOR
CONDENSER
COMPRESSOR
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Advantages of Heat Pump System

• Can heat and cool same building simultaneously
• Modular 1,000 sq. ft. per pump
• Energy efficient, decentralized, cycles as
  required
• Heat or cool energy is injected or extracted from
  building secondary water loop as required by each
  pump.
• Good for large solar exposures in cold climates
• Water-to-air heat pump 15 more efficient than
  water-to-water heat pump

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Disadvantages to Heat Pump Systems

• Typically need dedicated outside air system
• Limited ventilation air control
• Cycles on and off, does not modulate
• not very good at part load conditions, i.e. not
  as comfortable as VAV system
• Hi efficiency filters not available
• Decentralized maintenance
• Large electrical system

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Recommendations

• Specify with multi-speed fan and size to avoid
  coil frosting, maintain air velocities
• Locate in halls or corridors
• Reduce noise
• Increased access
• Allow adequate room for pump replacement and
  filter pull
• Many small units
• lt 5 ton better than larger units

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UNIVERSITY OF MAINEAT FARMINGTON

• College of Education,
• Health, Rehabilitation
• USGBC
• LEED - GOLD

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SW Perspective
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Geo Section Winter
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UMF Education Center

• Solar orientation to maximize daylight
  infiltration.
• Warm or cool energy is stored in the earth bank
  of the geothermal well field to be drawn during
  the next season. (Warm energy stored during
  the summer is drawn in the winter for heating,
  and cool energy stored during the winter is drawn
  in the summer for cooling.)
• 40 geothermal wells spaced 20 feet apart.
• Wells approximately 357 foot in depth.
• 2 HDPE high density polyethylene pipe treaded to
  the bottom of each well and grouted in place with
  a special grout to optimize thermal transfer.

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UMF Ground Loop Riser
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UMF Education Center

• Each well is piped to supply and return manifolds
  in the basement mechanical room.

• Insulated Manifold

Manifold
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• Water-to-water pumps generate 120-degree water,
  which is pumped via a secondary loop to the heat
  recovery preheat coils, cabinet unit heaters, and
  radiant slab heating system.

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UMF Education Center

• Utilize water-to-air heat pumps

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• Loop water pumps operate with variable frequency
  drives, controlled by loop pressure

• Ventilation air heat recovery unit on roof

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Thermal Well Drilling
Geothermal Well Drilling
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Piping From Wells
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Piping at Top of Wells
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Energy Modeling Analysis 1 - 2004
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Energy Modeling Analysis 2 - 2006
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Energy Comparison Roberts 75 Building vs.
Education Center
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Roberts 75 Building vs. Education Center
Savings/Month
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GORHAM MIDDLE SCHOOL
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• Aerial view of the site. The geothermal bore
  field lies below the field hockey field (outlined
  in red, below), and the pipe trench follows the
  red line into the building.

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Drill rig drills 116 354-foot bore holes
and line them with temporary steel
casings.
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• The bore field showing the exposed steel casings.

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• Two lengths of well pipe are inserted
• into each steel casing.

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• Notice the elbow that joins the two lengths of
  pipe (supply and return) near the
  bottom of each well.

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• A typical well pipe and steel casing. The casings
  are removed and thermal grout poured around the
  pipe.

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• The well pipe is connected to a web of trench
  pipe.

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• The trench approaches the building below the rear
  parking lot.

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• The supply and return piping enters the building
  in two large culverts through the foundation wall.

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• The trench pipe is sorted into two bundles
  supply and return.

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• The piping is protected from frost with layers of
  rigid insulation and then carefully back-filled.

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• The supply and return piping is sleeved through
  precast concrete panels near the mechanical room.

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• Well supply and return pipes feed into
  headers
• that distribute water to heat pumps

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• The water is circulated by four large electric
  pumps,
• two for the building and two for the field.

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• Ductwork carries the heated or cooled air from
• heat recovery preheat coils.

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Thank You