Geoheatpump

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Geothermal Heat PumpsFor School Applications

John A. ShonderOak Ridge National Laboratory

Rebuild America Geothermal Workshop

March 5, 2002

Concord, NH


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Mission of the U.S. Department of

Energy's Federal Energy

Management Program (FEMP)

y Reduce the cost of government byadvancing energy efficiency, water

conservation, and the use of renewableenergy sources, and by helping agenciesmanage their utility costs.

y FEMP relies on ORNL and other national

labs to carry out its programs and provideexpert assistance to federal agenciesworking to reduce their energy use andcosts.


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Executive Order 13123

y Through life-cycle cost-effective measures, eachagency shall reduce energy consumption per

gross square foot of its facilities, excludingfacilities covered in section 203 of this order, by30 percent by 2005 and 35 percent by 2010relative to 1985.

y GHP is one technology being used to meet these

goals


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ORNL is the home of FEMPs GHP

Core Team

y Mission: Provide support and technicalassistance to Federal agencies developing

and implementing GHP projectsy Also, to develop "tools of the trade" to

make GHP technology just as easy forFederal facilities to procure and install as

more conventional equipment.


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Presentation outline

y Why GHPs are popular for schoolapplications

y Basics of GHP operation and performance

y GHP system configurations

y Site characterization

y Design of GHP systems


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Presentation outline

y Construction costs

y Maintenance costs

y Advantages and disadvantages of GHPs

y Case study of the Maxey ElementarySchool in Lincoln, Nebraska


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Some reasons why GHPs are

popular for schools

y Reduced energy use and energy costs

One of the most efficient HVAC technologies

availabley Reduced maintenance costs

Modular, residential-sized units

No complicated controls required

y Lower life cycle cost

Saves money for school district


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Some other reasonsy No outdoor equipment

Improved aesthetics

Reduced vandalism

y Quiet operation

y Reduced mechanical room space

y Individual room control

y Low source energy use and low airpollutant emissions green technology


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y According to EPA, in 2000, geothermal

heat pumps were installed in 450 schoolsin 30 states (undoubtedly more by now)

http://www.epa.gov/globalwarming/publications/outreach/technology/geothermalheatpumps.pdf


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The technology goes by many

different names

y Ground source heat pumps (GSHP)

y Ground coupled heat pumps (GCHP)

y Geothermal heat pumps (GHP)

y GeoExchange (GX?)

y Earth energy systems


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Why GHPs are more efficient

than other HVAC equipment

y GHPs exchange heat with the earth, ratherthan with ambient air

y Earth provides a much better heatexchange medium

Stable temperature year-round

Generally cooler than ambient air when

cooling is needed, and warmer than ambientair when heating is needed


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Deep earth (and groundwater)

temperatures in the U.S.


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Capacity of a typical 4-ton

geothermal heat pump vs. EWT

0

10

20

30

40

50

60

20 30 40 50 60 70 80 90 100

Enterng watertemperature (F)

apacity(kB

tu/hr)

Heating capacity

ooling capacity


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Efficiency of a typical 4 ton GHP as

a function of EWT

0

1

2

3

4

5

6

20 30 40 50 60 70 80 90 100

ter atertem erat re ( )

Heat

OP

0

5

10

15

20

25

C


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Basics of GHP operation

Compressor

Water-to-refrigerantcoil

Air-to-refrigerantcoil

Expansion

valve

FanAir filter

Air inlet

(Return +OA)

Conditioned air(Supply)

Heat recovery coil

Reversingvalve


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GHP System options


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200 Ft.

20 Ft.

25 Ft.

4 Ft.

One heat pump on its own

ground loop


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Ground loops can be vertical or

horizontalGenerally requires1500-3000 ft2 landarea per ton


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HeatPump

HeatPump

HeatPump

HeatPump

DP

Signal Wire to DriveTransducer

Variable Speed DrivePump

PurgeValves

Aux.Pump

Interior PipeHeaders

HeatPump

Commercial system: multiple

GHPs on a common loop


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AA

HDPE u-tubes invertical bores.

Common loop conditioned by

vertical ground heat exchanger

Generally requires250-300 ft2 of landarea per ton


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Productionwell pump

River or

other surfacebody

Optionalinjection

well

Plate heat exchanger


groundwater

Generally requireswells with flow of2-3 gpm/ton


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L k

E CUL B


surface water (closed loop)Typ y 15 /( p 15-20 f ) g85 / f

f p k


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surface water (open loop)

Plate heat

exchanger

Water intake

Water dischargePump

More suited towarm climates, orcooling-onlyapplications


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Single or common loop conditioned by

standing column well

submersiblepump

perforatedintake

discharge

sleeve

formation

soil

A Aoptionalbleed


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Other methods of conditioning a

single or common loop

y Wastewater streams

y Community loop

y Potable water supplies (where allowed)

y Hybrid systems:

condition with 2 or more of above

condition with 1 or more of above andoutdoor air


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Many ways to configure indoor

equipment as well

y Each room has its own air-to-water heatpump

y One heat pump serving several roomsy Water-to-water heat pumps provide hot

and/or chilled water to coils (2-pipe or 4-pipe systems) or console units

y Outdoor air pretreatment (see below)


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Site Characterization: evaluation of

sites geology, hydrogeology, and

other characteristics

y Presence or absence of water

Determines whether groundwater or surface

water heat pumps can be usedy Depth to water

Affects drilling costs for open loop GWHP

y Water (or soil/rock) temperature

Affects required flow rate (open loop GWHP) orheat exchanger length (closed loop systems)


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Site Characterization (continued)

y Depth to rock Influences drilling cost, borefield layout

(closed loop)

y Rock type Affects thermal conductivity

Affects drilling costs

Influences feasibility of certain system types

y Nature and thickness of unconsolidatedmaterials overlying the rock. Affects drilling costs


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Other important site characteristics

y Land area available

y Planned or current land use (e.g. parking

lot, playground, tennis court, etc.)y Location of underground utilities

y State regulatory climate

Can impact every aspect of the design


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Sources of information for site

characterization

y State water regulatory agency

y State geology department

y Well completion reports from nearby waterwells

y Geologic and hydrologic maps

y U.S. Geological Surveyy Local experience


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Once the system type is decided,

further tests are often required

y Vertical loop: Thermal Conductivity Test

Measures deep earth temperature as well

Important for loop field designy Open loop: Well Test

Water flow

Water quality (including chemistry)


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Design of GHP Systems (inside the

building)

y Outdoor air treatment is a primary aspectof design

Schools have high ventilation air requirements During peak heating conditions, unheated OA

mixed with RA results in low (


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Several ways of treating outdoor air

y Dedicated water-to-water heat pumpsupplying OA preheat coil

y Sensible heat recovery unit to absorb heatfrom exhaust air

y Conventional heat source (gas boiler,electric resistance, etc.)

y Each method has advantages anddisadvantages in terms of first costs andoperating costs


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Many aspects of GHP design are

similar to the design of any

conventional HVAC system

y Determine peak heating and peak coolingload for each zone of the building

y Select heat pumps to meet design loads(remember that capacity depends on EWT)

y Heat pumps should be located with dueconsideration for serviceability

y Size ventilation system components:ductwork, fans, preheating coils, etc.


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Retrofits: Existing equipment

influences cost-effectiveness of

various GHP designs

y Central/terminal systems (ductwork or no)

y Water loop for two- or four-pipe system? If

so, potential for re-use as GHP water loopy What space is available in zones for

individual heat pumps?

Above dropped ceiling p horizontal units

Mechanical closets p vertical units

Through-wall PTAC units & perimeterpconsole units


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Three basic configurations of

geothermal heat pumps

vertical

horizontal

console


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Outside the building: borefield

sizing (for vertical bore systems)

y Decide on borehole and u-tube size, grouting

y Determine ground properties from in situ test

y Design borefield layout (rows v columns,spacing)

y Determine whether antifreeze is required

y Select design EWT

y Enter all information (including loads) intoborefield design program iterate if necessary

y Design exterior headers


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A number of programs available

to design ground heat exchanger


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Design packages ORNL has tested

y GchpCalc (www.geokiss.com)

y GlhePro (www.igshpa.org)

y RightLoop (www.wrightsoft.com)

y GS2000 (Caneta Research)


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Design programs have greatly

improved since 1996


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Important considerations for design

of groundwater heat pumps

y Groundwater availability, quality andtemperature

y Required flowy Water disposal method

y Design of plate heat exchanger


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Other system types have their own

idiosyncrasies

y Open and closed loop surface water heatpumps

y Standing column wells


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Pumping/Piping Subsystem is

another key design element

y Follow Kavanaughs grading system forvertical bore systems

Pump hp/100 tons Grade5 A -- Excellent5-7.5 B -- Good7.5-10 C -- Mediocre

10-15 D -- Poor >15 F -- Bad


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Ways of minimizing pumping power

(closed loop systems)

y Water flow rate


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GHPs should also be considered for

domestic water heating

y A heat pump is the most efficienttechnology for water heating

y Can use dedicated water-to-water heatpump, or desuperheaters on selected heatpumps supplementing conventional DHW

y In cooling-dominated applications, can

reduce required bore length and systemcosts


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Resources for GHP Designers

y Ground-Source Heat Pumps: Design of Geothermal

Systems for Commercial and Institutional Buildings,

Kavanaugh and Rafferty (ASHRAE, 1997)

y Commercial/Institutional Ground Source Heat Pump

Engineering Manual. Caneta Research. (ASHRAE, 1995)y Closed Loop/Ground Source Heat Pump Systems:

Installation Guide (IGSHPA)

y Learning from Experiences with Commercial/Institutional

Heat Pump Systems in Cold Climates, Caneta Research.

(CADDET, 2000)y Chapter 31: Geothermal Energy. 1999 HVAC Applications

Handbook (ASHRAE)


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Problem:

Lack of construction-cost-estimating

guide for GHP family

y RS-Means is the industry standard

Referenced by HVAC cost-estimating software

Does not include some GHP family members

y Available GHP cost data are largelyanecdotal important factors areunknown

Type of estimate preliminary, per squarefoot, bidder price, etc.

Scope whether costs for site work, design,electrical, demolition, controls, etc., areincluded


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Solution: HVAC Construction- and

Maintenance-Cost Database


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Installed Cost ofCommercial Vertical Bore GHP Projects(new construction)

$0

$500

$1,000

$1,500

$2,000

$2,500

$3,000

0 50,000 100,000 150,000 200,000

Conditioned area (square feet)

Inst

alledcost(thousands[2001])

mean cost:

$14.61/ft2

( 6%)

Construction Cost Database


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Summary for Vertical Bore:

y Commercial New Construction

$14.61 per square foot ( 6%)

y Commercial Retrofit $11.50 per square foot (wide variation due to

small dataset)

y Large Residential Retrofits

$3,312 per ton (wide variation due to smalldataset)


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Groundwater heat pumps

y $3000-$5000 per ton for well watersystems (open loop and standing column

well)


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Optimizing the Cost/Benefit Ratio of

GHP Projects

y In vertical bore projects, minimize borelength by using industry-standard

borefield design programy Perform thermal conductivity test

y Avoid complex control systems


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Available Maintenance Cost Data

GHP/Conventional HVAC

SourceASHRAE

HandbookCaneta/ASHRAE

MEANS

Arm CERLORNL

Date Reported 1986 1998 mid-70's 1999/2000

HVAC System

Types

80's

conventional,

no GHP

GHP70's

conventional

GHP,

ACC/GHWB,

WCC/GHWB

# of Bldgs 342 25 task-based 20

Bldg Types Commercial

Schools,

Commercial,

Residential

Military Schools

Age of Bldgs or

Systems2-25 years 1-15 years n/a 2-32 years

Avg. Ann.

Maint. Cost per

Sq Ft

32/ft2 9.3 - 10.9/ft2 n/a

9.27/ft2 (GHP),

8.75/ft2

(ACC/GHWB),

18.71 /ft2

(WCC/GHWB)


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Estimating energy use of GHP

systems (as required by LEED,

ASHRAE 90.1)

y DOE-2 (PowerDOE, etc.) Fairly good model, includes ground loops

y Trane Trace Can be used, but no ground loop model

y TRNSYS Contains sophisticated ground loop model, but

somewhat difficult to use

y Trane System Analyzer Includes GHP, but not an hourly program


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Web sites with information on GHPs

y www.ornl.gov/femp

y www.eren.doe.gov/femp/financing/espc/ghpresources.html

y

www.igshpa.okstate.edu/y www.ghpc.org

y http://geoheat.oit.edu/

y www.geokiss.com

y http://www.alliantenergygeothermal.com/y A Google search on the term geothermal heat

pump turns up other interesting links


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Advantages of GHPs

y High efficiency

Lower energy consumption

Lower energy costy Low maintenance cost

y Low life cycle cost

y No outdoor equipment

y Greater occupant comfort


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Disadvantages of GHP

y First cost can be higher than forconventional systems

y Not all system types feasible in alllocations

y Limited pool of designers

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