Ground Source Heat Pumps: An Introduction

1
Ground Source Heat Pumps An Introduction

• David Peterson
• National Renewable Energy Laboratory
• Golden, CO

2
Presentation Outline

• Introduction
• State of industry
• System components
• Design and installation
• Economics
• Performance case studies
• Federal, State, and utility incentives
• Recommendations
• Resources

3
Introduction
4
Terminology

• Ground source heat pumps (GSHP)
• Geothermal heat pumps (GHP)
• Ground coupled heat pumps (GCHP)
• GeoExchange systems
• Earth energy systems

5
What is a Ground Source Heat Pump (GSHP)?

• GSHP is a electrically powered system that
  utilizes the earths relatively constant ground
  or groundwater temperature to provide heating,
  cooling, and hot water
• Instead of burning fossil fuels to create heat
  like conventional systems, GSHPs move heat that
  already exists
• In heating mode, a GSHP moves heat from the
  ground or groundwater into the building
• In cooling mode, a GSHP moves heat from the
  building and deposits it into the ground or
  groundwater.

6
Common Comments on GSHPs

• Advantages
• High efficiency results in lower energy
  consumption cost
• Lower maintenance cost
• Lower life cycle cost
• No outdoor equipment
• Greater occupant comfort
• All electric - can be powered by renewable energy

• Disadvantages
• First cost can be significantly higher than
  conventional systems
• Not all system types feasible in all locations
• Limited pool of qualified designers and
  installers in many locations

7
State of Industry
8
Ground Source Heat Pump Domestic Shipments,
2002-2006
Source EIA, Survey of Geothermal Heat Pump
Shipments, 2006
9
Ground Source Heat Pump Domestic Shipments, 2006
Source EIA, Survey of Geothermal Heat Pump
Shipments, 2006
10
Barriers to wider GSHP Implementation

• Tend to have significantly higher first costs
  compared with conventional systems
• Generally longer paybacks when replacing natural
  gas heating systems
• Lack of awareness
• Lack of uniform standards design and
  installation accreditation has yet to receive
  nationally standardized accreditation
• Shortage of qualified designers and installers.

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System Components
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GSHP System

• Ground or groundwater heat exchanger
• Heat pump
• Interior heating/cooling distribution system
• Domestic hot water heating (optional)

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Ground or Groundwater Heat Exchangers

• Ground Coupled Heat Pump (closed loop)
• Groundwater Heat Pump
• Surface Water Heat Pump

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Vertical Ground Coupled Heat Pump
Piping is inserted to deep vertical
boreholes. Boreholes are grouted to improve heat
transfer and protect groundwater.

• Advantages
• Requires less land than other closed loop systems
• Requires smaller amounts of pipe and pumping
  energy
• Likely to yield the most efficient performance of
  closed loop systems

• Disadvantages
• Higher initial cost due to the drilling of
  boreholes
• Problems in some geological formations (an issue
  in parts of MA)
• Limited availability of experienced drillers and
  installers

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Horizontal Ground Coupled Heat Pump
Placement of straight or slinky piping in
shallow (6-8ft) horizontal trenches.

• Advantages
• Likely less expensive to install vertical closed
  loop
• Requires less specialized skill and equipment to
  install, so contractors are more widely available

• Disadvantages
• Need more space
• Ground temperature and thermal properties
  fluctuate with season, rainfall, and burial depth
• Lower efficiency
• Problems in some geological formations (an issue
  in parts of MA)

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Surface Water Heat Pump
The piping is anchored to the bottom of a nearby
body of water

• Advantages
• Low cost due to reduced excavation costs
• Low maintenance
• Low operating costs

• Disadvantages
• Possible damage to piping in public lakes
• Significant temperature variation if lake is
  small/shallow

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Groundwater Heat Pump System
Uses groundwater as heat sink and source. Water
is pumped through the system, then discharged.

• Advantages
• Have the lowest installed cost, especially in
  larger applications
• Uses less space
• Well water contractors are widely available
• Long track record in large commercial applications

• Disadvantages
• Local water and enviro. regulations may restrict
  use
• Limited water availability
• May need fouling precautions
• High pumping energy required if system poorly
  designed or water pulled from deep aquifer

Source 2003 ASHAE Applications Handbook
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Groundwater Heat PumpStanding Column Well
Water is pumped from bottom of well and
re-injected at the top

• Heat exchange rate is enhanced by the pumping
  action
• Often utilized where little land is available or
  the bedrock is close to the surface
• During peak heating and cooling, the system can
  use a bleed cycle to control the column
  temperature

Source Orio, 2005. A Survey of Standing Column
Well Installations in North America, ASHRAE
Transactions. Information for Evaluating
Geoexchange Applications, prepared for NYSERDA by
the Geothermal Heat Pump Consortium.
19
Hybrid Systems

• Use several different geothermal resources, or a
  combination of a geothermal resource with outdoor
  air (most often, a cooling tower)
• Particularly effective where cooling needs are
  significantly larger than heating needs.
• Cooling tower used to reject excess heat
• Main benefits
• Reduces loop field size, and thus costs, by
  allowing for the ground loop to be undersized for
  the cool load, but sized for the smaller heating
  load
• Avoid increase in ground temperature due to load
  imbalances

Source Federal Energy Management Program,
Assessment of hybrid geothermal heat pump
systems, 2001
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Heat Pump
21
Heat Pump Performance Standards

• EER (Energy Efficiency Ratio)
• Cooling capacity (in Btu/hour) of the unit
  divided by its electrical input (in watts) at
  standard (ARI/ISO 13256-1) conditions of 77F
  entering water for closed loop models and 59F
  entering water for open loop systems.
• COP (Coefficient of Performance)
• Heating capacity (in Btu/hour) of the unit
  divided by its electrical input (also in Btu/h)
  at standard (ARI/ISO 13256-1) conditions of 32F
  entering water for closed loop models and 50F
  entering water for open loop equipment.

Ratings are only used as a measure to compare one
GSHP to another, and do not reflect actual
performance
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Selecting the Most Energy-Efficient GSHP

• Choose models that qualify for the Energy Star
  label
• Open Loop gt3.6 COP (H) gt16.2 EER (C)
• Closed Loop gt3.3 COP (H) gt14.1 EER (C)
• Direct Exchange (DX) gt3.5 COP (H) gt15 EER (C)
• Most efficient models have dual-speed compressor
  systems and increased heat exchange area, and
  thus cost significantly more

23
Heat Pump Efficiency and Entering Water
Temperature
Source Shonder, ORNL
24
Heat Pump COP vs System COP
Source Ground Source Heat Pumps - Design for
Performance, Shapiro, 2008, http//www.efficiencyv
ermont.com/pages/BBBD2008/Ground20Source20Heat2
0Pumps_Shapiro.pdf
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Design and Installation
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Outside the Building Site Evaluation

• Presence or absence of water
• Determines whether groundwater or surface water
  heat pumps can be used
• Depth to water
• Affects drilling costs for groundwater coupled
  systems
• Water (or soil/rock) temperature
• Affects required flow rate (open loop GWHP) or
  heat exchanger length (closed loop systems)
• Depth to rock
• Influences drilling cost, borefield layout
  (closed loop)

• Rock type
• Affects thermal conductivity
• Affects drilling costs
• Influences feasibility of certain system types
• Nature and thickness of unconsolidated materials
  overlying the rock.
• Affects drilling costs
• Land area available
• Planned or current land use (e.g. parking lot,
  playground, tennis court, etc.)
• Location of underground utilities

Source Shonder, 2002
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Outside the Building Tests are Required for
Commercial-Sized Systems

• Vertical Ground Coupled Thermal Conductivity
  Test
• Measures deep earth temperature as well
• Important for loop field design
• Groundwater Well Test
• Water flow
• Water quality (including chemistry)

Using rules of thumb are not recommended
Source Shonder, ORNL
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Inside the Building Design similar to any
conventional HVAC system

• Determine peak heating and peak cooling load for
  the building
• Select heat pumps to meet design loads (remember
  that capacity depends on entering water
  temperature)
• Heat pumps should be located with due
  consideration for serviceability
• Size ventilation system components ductwork,
  fans, preheating coils, etc.

For retrofits, existing equipment (ductwork)
greatly influences cost-effectiveness of GSHP
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Residential Design Considerations

• Reduce house loads significantly!
• Lower pump energy by reducing friction
• Lower other electric parasitic energy
• Use realistic COPs in design
• Simpler more reliable!

Source Shapiro, 2008
30
IGSHPAs Guidelines for Evaluating Residential
Contractors

• Contractor should follow the installation
  procedures established by IGSHPA (only available
  for closed loop systems)
• Installers should be accredited by IGSHPA or
  another recognized institution that trains and
  certifies contractors (such as a manufacturer).
• Ask for and check references
• Get several estimates in writing
• Get a warranty that guarantees performance that
  covers the installed systemnot just the heat
  pump itself.
• Insist on a written contract that includes all
  terms, including costs and start-stop dates.

Under-qualified contractors are one of the most
common sources of performance problems
31
Commercial GSHP Considerations

• Seasonal cooling loads for commercial buildings,
  which are dominated by internal heat loads, are
  much higher than seasonal heating loads even in
  cold climates.
• This causes a thermal mismatch between seasonal
  cooling and heating loads seasonal cooling loads
  can be many times larger than heating loads and
  presents a challenge for sizing the ground loop
  or groundwater heat exchanger.

Source Geothermal Heat Pump Systems
Applications and Technology Development, EPRI,
2003
32
Choosing a Commercial GSHP Designer

• If they cannot be found, seek experienced
  designers and installers from outside the local
  area
• Seek designers who are familiar with the most
  recent guidance (ASHRAE 1997, 2003)
• Training is essential, but experience is also
  crucial

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Economics of Residential Systems
34
Residential Installation Costs
Source An Information Survival Kit For the
Prospective Geothermal Heat Pump Owner,
Rafferty, for Heat Spring Energy, 2008,
http//www.heatspring.com/downloads/ intro/Geothe
rmalSurvivalKit.pdf
35
Residential Installation Cost from Indiana Study
Note Indiana has a mature GSHP industry.
Source Indiana Residential Geothermal Heat Pump
Rebate Program Review, 2008, http//www.in.gov/o
ed/files/GHPProgramreport.pdf
36
Residential GSHP Costs in MA

• Installation costs
• 20K to 30K for a 3-4 ton system
• Viewed as the primary barrier
• Much higher than the new generation of high
  efficiency air source heat pumps and gas furnaces
• Energy cost savings
• Most significant when replacing electric
  resistance or heating oil
• Marginal to no savings when compared high
  efficiency air source heat pumps and gas
  furnaces/AC systems
• Highly dependant on the price of electricity vs
  natural gas/heating oil

37
Residential Heating Cost Comparison
Based on the annual energy consumption for
space-heating in a single-family household
61.3 Million Btus/Year in 1997.
Calculator http//www.energyexperts.org/ fuelcalc
/default.asp
38
Residential Case Study (1997) Hartford, CT

• New Construction (well-insulated, tightly sealed
  building envelop)
• Heating Load 49,614 Btu/hr
• Cooling Load 30,568 Btu/hr
• Closed loop vertical 2x250ft bores
• 4.2 ton heat pump
• Total cost - 19,283 (includes ductwork)
• Northeast Utilities Rebate - 2,971 (713/ton)
• Oil-fired furnace/electric AC cost estimate -
  16,200
• Simple payback period was less than one year

Source Geothermal Heat Pump Consortium
39
Economics of Commercial Size Systems
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Commercial System Cost Comparisons
Source How to buy an energy-efficient ground
source heat pump, Federal Energy Management
Program, 2001, http//www.ornl.gov/sci/femp/pdfs/g
shp-pro-chal.pdf
41
Nebraska School Analysis
GSHP had lowest LCC and lower first cost than
widely-used HVAC systems
Source Geothermal Heat Pumps in K-12 Schools,
ORNL, 2000, http//www.ornl.gov/sci/femp/pdfs/ghps
inschools.pdf
42
ASHRAE Case Studies(vertical, closed-loop
systems)
Source Operating Experiences with Commercial
Ground-Source Heat Pump Systems, ASHRAE, 1998
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Performance Case Studies
44
Standing Column Well GSHPs at Harvard
Source Ground Source Heat Pumps at Harvard
Lessons Learned, 2007 http//www.uos.harvard.edu/f
mo/building_maintenance/GSHP_Sharable.pdf
45
Standing Column Well at MA School

• Standing column well system replaced an existing
  electric heating system in 1997.
• Graph shows schools annual electricity
  consumption for heating in kWh

Source Standing Column Wells Ten Years in a New
England School, Orio, 2006
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Programs and Incentives
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Government Tax Incentives

• Federal
• Tax credit of up to 2,000 per household for GSHP
  costs
• 10 investment tax credit, not limit
• Until 2016

• State Examples
• IN - 1,500 for residential systems
• MD - 1,000/ton with 3K max for residential and
  10K max for others

Source DSIRE, http//www.dsireusa.org/index.cfm?
CurrentPageID2EE1RE1
48
Utility Strategies for Reducing the First-Cost
Barrier

• Provide design assistance, drill test boring,
  life-cycle cost analysis
• Loop leases or financing where payments are
  charged to customers monthly electric bill
• Pay for the loop
• Low interest loans
• Rebates
• Special GSHP electricity rates

Source Geothermal Heat Pump Report, Johnson,
2007
49
Nurturing Contractor Development

• Offer training for installers, as well as for
  design engineers and architects
• Invest in new tools to assist in the GSHP
  installation process
• Develop a contractor referral network to support
  a partnership of local drillers, installers, and
  dealers

Source Johnson, Geothermal Heat Pump Report,
2007
50
Recommendations
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ACEEE GSHP Assessment

• Commercial
• In some markets, a commercial GSHP systems first
  costs may be less than competing systems
• GSPH are competitive with 4-pipe chilled water
  systems, less expensive than chiller-VAV systems,
  but more expensive than simple roof-top systems
• For systems over 100 tons, assume competitive
  costs

• Residential
• Costs savings vary widely from 20 to 60, with
  higher savings based on houses with resistance
  heat
• Without a developed infrastructure, ground loop
  installation cost are substantial
• In most regions, residential installations will
  be much more expensive.

Recommendation Focus on commercial sector
Source Emerging Energy-Saving Technologies and
Practices for the Buildings Sector as of 2004,
ACEEE
52
Residential GSHP in New England

• Economics are generally less favorable than in
  other areas of the country mostly due to lower
  cooling requirements.
• Economics are also hampered by the relative cost
  effectiveness of fossil fuels for space heating
  as opposed to electric based GSHP technology.
• With high electricity rates, the Northeast is at
  a comparative disadvantage for electric based
  technologies.
• However, there has been some shift in the
  relative cost of electricity due to the rapid
  price escalation of fossil fuels in the past few
  years.
• Residential applications may be worthy of
  consideration.

Source Report to Congress Ground-Source Heat
Pumps at Department of Defense Facilities,
Shonder, 2007
53
Commercial GSHP in New England

• Due primarily to cooling requirements, commercial
  scale applications possess more favorable
  economics.
• Site-specific factors determine applicability.
• Standing column well systems have the widest
  application of any system type in commercial
  scale applications in the Northeast.
• Vertical ground coupled systems are often cost
  prohibitive due to the high costs of shallow
  bedrock drilling.
• Horizontal ground coupled systems, when land area
  requirements can be met, are generally hindered
  by unfavorable soil and topography conditions.
• Surface water systems, they are essentially
  unfeasible due to low water temperatures during
  the heating season.

Source Report to Congress Ground-Source Heat
Pumps at Department of Defense Facilities, 2007
54
Recommendations

• Generate a state-specific document similar to the
  Geothermal Heat Pump Manual commissioned by the
  New York City Department of Design and
  Construction (http//home2.nyc.gov/html/ddc/downlo
  ads/pdf/geotherm.pdf)
• Encourage system owners to monitor GSHP
  performance and publicize the results.

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Resources
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Publications for GSHP Designers

• Ground-Source Heat Pumps Design of Geothermal
  Systems for Commercial and Institutional
  Buildings, Kavanaugh and Rafferty (ASHRAE, 1997)
• Chapter 32 Geothermal Energy, 2003 HVAC
  Applications Handbook (ASHRAE, 2003)
• Commercial/Institutional Ground Source Heat Pump
  Engineering Manual, Caneta Research (ASHRAE,
  1995)
• Closed Loop/Ground Source Heat Pump Systems
  Installation Guide (IGSHPA)
• Learning from Experiences with Commercial/Institut
  ional Heat Pump Systems in Cold Climates, Caneta
  Research (CADDET, 2000)

57
Geothermal Design Software

• Building Life Cycle Cost Program (BLCC)
• Elite Software (HVAC design)
• Ground heat exchanger design tool for Residential
  (GlhePro, IGSHPA)
• Wrightsoft (GHP system design software)
• Software Advice (site that reviews and compares
  construction software)
• GchpCalc (www.geokiss.com)
• GS2000 (Caneta Research)

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GSHP On-line Resources

• EPRI Electrical Power Research Institute
  (http//my.epri.com/portal/server.pt)
• Oak Ridge National Laboratory (www.ornl.gov/femp)
• IGSHPA - International Ground Source Heat Pump
  Association (www.igshpa.okstate.edu/)
• ASHRAE (www.ashrae.org)
• Geothermal Heat Pump Consortium (www.ghpc.org)
• Geo-Heat Center (http//geoheat.oit.edu/)

59
Contact Information

• David Peterson
• National Renewable Energy Laboratory
• david_peterson_at_nrel.gov
• 303-275-3615