Geothermal Heating / Cooling Systems – Overview of Application in New Hampshire David G. Lamothe Senior Project Manager GZA GeoEnvironmental, Inc.
Geothermal Heating/Cooling Systems – Overview of Application in New Hampshire
Presented To: EBC New Hampshire Chapter Program Renewable Thermal Energy in New Hampshire
January 8, 2013 David Lamothe, P.E., IGSHPA AI Senior Project Manager GZA GeoEnvironmental, Inc. Manchester, New Hampshire 603-232-8716
[email protected] 2
What is “Geothermal”?
Ground Source Heat Pumps (GSHPs) (not power generation) Low temperature thermal exchange (~40-90°F)
Uses renewable energy stored in the earth to heat and cool 3
Why Geothermal?
Mean earth temperature
CONSISTENTLY ~55°F 4
How Does It Work?
Furnace and AC replaced by GSHP
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Energy Efficiency
Earth Coupling (3 to 5 kW)
Heating and Cooling (4 to 6 kW)
Grid (1 kW)
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Geothermal Operation – SUMMER
GEOEXCHANGE SYSTEM (REJECTS HEAT BTUs) Heat is Absorbed by Soil/Rock from Fluid
Earth = HEAT SINK
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Geothermal Operation – WINTER
GEOEXCHANGE SYSTEM (EXTRACTS BTUs) Heat is Absorbed by Fluid from Soil /Rock
Earth = HEAT SOURCE
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Single Building
District system graphic Supply and Return Headers Vault/manifold
Wells drilled and connected in circuits 9
District System Serves multiple buildings
District system graphic Vault/manifold Central Well Field
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Hybrid System
• Economic and/or design decision to optimize performance and limit capital costs • Combine geothermal wells and heat pumps with: – Chillers or cooling towers to boost cooling – Solar thermal collectors to boost heating – Supplemental fossil fuel for heating
To serve peak demand that occurs only a portion of total operating time
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Distribution Systems (Building Side)
Geothermal Heat Pump • Transfers heat from the ground loop to water or air distributed to the building Media: – Water-to-water (hydronic systems) – Water-to-air
Distribution System • Ducted forced air system • Hydronic/Chilled Beams • Radiant floor (hydronic) heating with ducted cooling 12
Ground Heat Exchanger (Ground Loop)
Exchanges heat with the ground – Open to Diffusion Wells (ODW) – Standing Column Wells (SCW) SCW and CL – Closed Loops (CL) Vertical Wells • Vertical • Horizontal
Dominant Ground Loops in NH
Also - Pond Loops • Direct • Indirect 13
Standing Column Well
• Combine extraction and injection well • Typically 1,500 feet deep • In-well pump 20’ (min.) into rock
• Efficiency comes from advective heat transfer • Performance is dependent upon quality and quantity of water encountered and ability to bleed
(Credit: Water Energy)
Typ. 6.5 in. diam. in rock, uncased 14
What is “Bleed?” Drywell, water body
10 gpm 90 gpm 100 gpm
Issues:
Induces Flow to Well
Responsibly discharged to same aquifer Subject to permitting requirements Environmental Concerns?
Foundation Settlement? 15
Closed Loop Vertical Wells •Closed pipe loop
•Indirect heat exchange with ground •Typ. 300 - 500 feet deep
•Ground temperature, thermal conductivity and diffusivity important •Lower maintenance than open systems
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Closed Loop Vertical Wells 1.25-inch HDPE pipe
Soil / Rock
Thermally enhanced grout
Factory fused U-bend
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Additional Loop Options
Open to Diffusion Wells (ODW) (extraction/reinjection wells)
Advantages Lower Horizontal Slinky Closed Loops Installation Cost Vertical Slinky Closed Loops
Surface Water: Closed or Open Systems Disadvantages • Lower Thermal Capacity • Significant Site Disruption 18
Selection of Ground Loop
Logistics
Permitting
Recommended Ground Loop Risk Tolerance (O&M, Cost)
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Selection of Ground Loop
Logistics – Phasing/sequencing Physical restrictions – available space for well field Closed loop - closer spacing but more wells typ. required
Geology Soil, bedrock, and groundwater conditions Depth to rock, water quantity and quality Unstable rock – CL recommended Environmental conditions Soil or groundwater contamination in vicinity? AUR/AUL? 20
Selection of Ground Loop Permitting requirements More rigorous for open systems
Client’s risk tolerance Permitting
O&M / Cost (Estimated payback period) Water quality issues - Poor water quality (i.e. high Fe, Mn or hard water, low pH) – CL recommended to avoid scaling and fouling issues
(Risk tolerance is often primary factor in selection)
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Permit Considerations - NH
NHDES State UIC registration (Underground Injection Control)
More rigorous permitting for Open Loop vs. Closed Loop UIC registration for CL Open systems (Open, SCW): UIC registration Water Use Registration and Reporting for > 20,000 gpd (~14 gpm) – report monthly use on a quarterly basis Groundwater Withdrawal Program (>57,600 gpd = 40 gpm) needs large groundwater withdrawal permit
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Permit Considerations – NH
(Continued)
Open Loop For Commercial/Industrial/Institutional Residential is Exempt
Raw Water Quality Testing Required for VOCs Primary inorganics (As, nitrate/nitrite) Radiological (Gross Alpha/Beta, Radium, Uranium) Secondary inorganics (Na, Cl, Fe, Mn) pH, temperature, TDS Bacteria (total coliform [fecal and E. coli]) for discharge water
If bleed used – must return to same aquifer 23
Permit Considerations – NH
(Continued)
Closed Loop Allowed antifreeze (DRAFT) Propylene glycol Ethanol Also Methanol, Potassium Acetate, Calcium Magnesium Acetate (CMA)
Pipe Materials HDPE
Fiberglass
Grout: Bentonite slurry, Bentonite and sand, Cement & Sand
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Financial Incentives for Geothermal 20 to 40% heating/cooling energy savings
Federal Tax Credits (sunset 2013 comm/2016 res) State Tax Credits in some states
Utility Rebates / Rate Reductions Renewable Energy Credits (RECs) Where to Start? Database of State Incentives for Renewables & Efficiency (“DSIRE”, www.dsireusa.org) http://energy.gov/savings 25
Geothermal Payback Period
Depends on the situation New construction? Replacing an old system?
Condition of existing system? 7 to 15 years typical