steven pinette geothermal

1Maine Section ASCE2008 Technical SeminarLewiston, MaineMarch 20, 2008

ENERGY AND INFRASTRUCTURE

MAINE GOETHERMAL ENERGYMAINE GOETHERMAL ENERGYWAITING TO BE TAPPEDWAITING TO BE TAPPED

AN OVERVIEWAN OVERVIEW

Steve PinetteSenior [email protected]

Tremendous resource energy consumption greenhouse gases

Maine and New England

US Military, GSA, Midwestern/Northwestern US and Canada

2Heat generated Heat generated from: from:

1) cooling in the 1) cooling in the earthearths core, and s core, and

2) radioactive 2) radioactive mineral decaymineral decay

Heat Heat dissipated dissipated out through out through the mantle the mantle & crust& crust

to 3,000 oC

+3,000 to

7,000 oC

45-70+ oC

Big GHigh Temp. Geothermal in areas

associated with thin crust, volcanoes, rift areas .

3High Temperatures Generated at Plate Boundaries

4Geothermal Heatflow Map of North America, 2004Adapted from Southern Methodist University Geothermal Laboratory

BIG GLittle g

How Do We Tap this Heat?How Do We Tap this Heat?

1. Closed1. Closed--loop systemsloop systems

2. Standing column wells2. Standing column wells

3. Slinky systems in soil trenches3. Slinky systems in soil trenches

4. Open loops, pond loops, 4. Open loops, pond loops, ..

MOST COMMON

5Closed loop systemClosed loop system no contact between no contact between the water in the pipes and groundwater the water in the pipes and groundwater

No drawdown of water table No drawdown of water table

extracts heat onlyextracts heat only

Typically 300 400 ft. deep; borings 4 5 inches diameter; geo-loop is 1.25 inches diameter HDPE

200 Ft.

20 Ft.

25 Ft.

4 Ft.

One heat pump on its own ground loop

Source: Oak Ridge National Laboratory

6AA

HDPE geo-loop

u-tubes in vertical bores.

Common loop conditioned by vertical ground heat exchanger


HDPE loop

Tremie pipe

Closed-loop boreholes typically 25 ft. apart; geo-loop being grouted

7DPE Geo-loop pipe generally guaranteed or 50 years)

DPE lines running from headers to building; several bore holes per header

8Geo-loop entry via pre-fabholes in foundation

Standing Column Well(typically up to 1500 deep; used mainly in Northeast)

submersible pump

perforated intake

discharge

sleeve

Rock formation

soil

A Aoptional bleed

to heat pumps

***Groundwater quality is critical to run these systems!!

9Below a depth of about 800, need auxiliary compressor or two rigs running in tandem to provide compressor air capacity to lift drill cuttings up the borehole

- Without extra compressor, some cuttings remain in the borehole to damage well pumps and other equipment

pproviding auxiliary air

10

Ground loops can be vertical or horizontal

Generally requires 1500-3000 ft2 land area per ton


Lake

HDPE Coils withUV Protection inLoose Bundles

A

A

Common loop conditioned by surface water (Closed loop)

Typically, 15 tons/acre (depth15-20 ft) or as high as 85 tons/acre for well stratified deep lakes


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Productionwell pump

River orother surface

body

Optionalinjection

well

Plate heat exchangerA

A

Open-loop conditioned by groundwaterSpent Water can be discharged to injection well or to

surface water body no recirculation

Generally requires wells with flow of 2-3 gpm/ton


Open-loop conditioned by surface water

AA

Plate heat exchanger

Water intake

Water dischargePump

More suited to warm climates, or cooling-only applications


***Not appropriate for State regulated water bodies in Northeast No-discharge farm ponds generally okay

12

GHP System Options


Other methods of conditioning a single or common loop:

Wastewater streams Community loop Potable water supplies (where allowed) Hybrid systems (e.g., partial cooling with a

chiller during peak periods)


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HeatPump

HeatPump

HeatPump

HeatPump

DPSignal Wire to Drive Transducer

Variable Speed DrivePump

PurgeValves

Aux.Pump

Interior PipeHeaders

A

A

HeatPump

Commercial system: multiple GHPs on a common loop


Heat pumps atGorham Middle School

Closed loop

140,000 sf

~200 tons

119 boreholes,

375 ft. depths

4.5 dia.

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In New England, most of the systems will be closed-loop or standing-column well systems installed in bedrock

Primary ConcernRock Type and its Thermal Properties

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Amount of Heat supplied to boreholesAmount of Heat supplied to boreholes

FourierFouriers Law s Law

Q = Q = --kA kA dT/dxdT/dxRate of heat

Production

Coefficient of Thermal Conductivity

Temperature gradient

Area

BTU BTU (Q)/hour(Q)/hour

Thickness = Thickness = 1 inch (dl)1 inch (dl)Differential Differential

temperature temperature = 1 degree = 1 degree

(dT)(dT)

1 foot1 foot

1 foot1 foot

Q = k Q = k A A dT/dldT/dl

Calculate K (thermal conductivity)

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Measuring Thermal Conductivity Closed-Loop Borehole

Q We know how much heat (BTUs) the building will need

A ?? The area that we need to supply this heat (borehole area how many borings and to what depth?)

K We can estimate this based on rock type, but there are broad ranges in the same rock type better to better to testtest

dT/dx (temp. gradient) We can guess, but better to better to testtest

***If you use general values, usually end up with conservative design. In one case, testing allowed designer to reduce number of proposed boreholes by 50%.

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Required by the system design softwareRequired by the system design software

Source: GRTI, 2006

Also need to know Heat Capacity

The quantity of heat required to raise the temperature of a system by one degree (can obtain standard values for this)

Need to know this plus the thermal conductivity to calculate diffusivity

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Thermal Diffusivity

Thermal conductivity of a substance divided by the product of its density and heat capacity

For Standing Column Wells with bleedwe also need to know

Sustainable Well YieldWell Yield

***This is one key reason for system problems***

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Broad Range of Thermal Conductivities in Similar/Same Rock Types

Source: Montan Universitt (www.uniloben.ac.at)

ThermalThermal Coefficients for Common MaterialsCoefficients for Common MaterialsKK CpCp Diff (Diff ())

BTU/hrBTU/hr--ftft--ooFF Btu/lbBtu/lbooFF ftft22/day/day

GraniteGranite 1.51.5--2.12.1 0.210.21 1.01.0--1.41.4MarbleMarble 1.21.2--1.91.9 0.220.22 0.80.8--1.21.2GneissGneiss 1.31.3--2.02.0 0.220.22 0.90.9--1.21.2QuartziteQuartzite 3.03.0--4.04.0 0.200.20 2.22.2--3.03.0SlateSlate 0.90.9--1.51.5 0.220.22 0.60.6--0.90.9SandstoneSandstone 1.21.2--2.02.0 0.240.24 0.70.7--1.21.2LimestoneLimestone 1.41.4--2.22.2 0.220.22 1.01.0--1.41.4Moist SandMoist Sand 1.41.4--1.71.7 ---- 0.80.8--1.0 1.0 Dry SandDry Sand 0.80.8--1.41.4 ---- 0.80.8--1.31.3

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Other features that affect heat transfer

Fractures Fractures Voids in the rock Voids in the rock Water saturationWater saturation

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Higher Thermal Conductivity if saturated

with groundwater

Entering Water Temperature Affects System Efficiency

0

1

2

3

4

5

6

20 30 40 50 60 70 80 90 100

Entering water temperature (F)

Hea

ting

CO

P

0

5

10

15

20

25

Coo

ling

EER


Its not a parameter that we can control, butHigher Temp more efficient for heatingLower Temp more efficient for cooling

heating cooling

IncreasingEfficiency

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Deep earth (and groundwater) temperatures in the U.S.

46 (400)

50.1 (190)

50.5 (400)47.5(115-135)

52.9(115-1500)

64

Maximum Temperatures (oF)

48.1 (450)

48.1 (420)

48.0 (405)49.8 (400)

Explanation?

Off-shore Seamount??

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Test Groundwater for Chemical Parameters***Critical for Standing Column Well Systems!!!

Dissolved Oxygen, Specific Conductivity, pH, TurbidityField Parameters

Radon, Uranium, Hardness, Alkalinity, Ammonia-N, Ortho-Phosphorous, Dissolved Organic Carbon, Cyanide, Total Dissolved Solids, Total Dissolved Solids, Total Suspended Solids, Total Coliform Bacteria, Color, Odor, Iron Bacteria

Other Parameters

Volatile Organic Compounds (VOCs), Semi-volatile Organic Compounds (SVOCs)

Synthetic Organic Compounds

Br, Cl, F, NH3-N, NO2-N, NO3-N, PO4, SO4Other Ions

Ag, Al, As, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Pb, Ni, Sb, Se, Si, Sr, Tl, Ti, V, ZnMetals

Water Quality and Standing Column Well System

submersible pump

perforated intake

discharge

sleeve

Rock formation

soil

A ABleed must be clean

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COROSION INDICESfor Standing Column Wells only

Chloride concentration (road salt, paleoseawater, marine environment)

Calcium Carbonate Saturated pH Langelier Index Aggressive Index Rynzar Stability Index

Advantages of GHPs

High efficiency Lower energy consumption & CO2 footprint Lower energy cost

Low maintenance cost Low life cycle cost No outdoor equipment Greater occupant comfort

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***Less Greenhouse Gas Emissions***

Note: This takes into account emissions from electric power plant (non-renewables)

Source: Whitney Engineering, 2008

So Lower energy consumption Smaller Carbon Footprint

what about $ Payback period??

27

CLOSED LOOP (Source: Whitney Engineering)

PROBABLE CONSTRUCTION COSTS GORHAM MIDDLE SCHOOLSq. Ft. 140,000 Heating ~3,000,000 Btu/hr. Feb.

Cooling ~292 tons cooling in JulyA. Data:

Cost $/Sq. Ft.Total New Building $11,800,000 84.29Total Mechanical $ 2,419,000 17.28Base HVAC Systems $ 1,831,300 13.08

Geothermal Field $ 653,900 4.67Boilers, Cooling Tower $ 540,000 3.86

B. Cost Comparison: Geothermal vs. Conventional HVAC

Base HVAC Systems $ 1,831,300 $ 1,831,300Geothermal Bid Price $ 653,900 -Conventional Bid Price - $ 540,000Total $ 2,485,200 $ 2,371,300

C. Extra Cost for Geothermal: $ 113,900 ($0.81/SF)

ECONOMIC EVALUATION (Source: Whitney Engineering)

Project: Gorham Middle SchoolSq. Ft. 140,000

BOREHOLES STANDING(Closed Loop) COLUMN

WELLS1. Extra Cost for Geothermal $ 113,900 $ 293,0002. Energy Savings $ 40,000 $ 40,000

3. SIMPLE PAYBACK 2.85 Years 7.3 Years

Note: Energy savings based on Middle School with conventional Water Source Heat Pump (WSHP)system and Gorham Middle School with geothermal HVAC

system

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Bowdoin College Dorms Standing-Column Well Example

(Source: Harriman Associates)

66,000 sf with 180 beds

Heated/cooled with Standing-Column Well system

Uses

seven 1500-foot wells with

seven 30-ton heat pumps

2,500 gallon cistern to collect bleed water; this water is used to flush toilets had no place to discharge heat recovery ventilation

Compared to 2M BTU gas boiler & 150-ton chiller Geothermal system was $515,000 more

Design Payback 9.6 years Actual Payback 6.2 years

Closed-Loop vs. Standing-Column Wells

Closed-Loop Pro In-ground system is robust and durable; little attention after

installation Pro Existing or future groundwater quality is not a major concern,

except during drilling Pro - Less/little need for regulatory oversight and permitting Con Higher front costs ($2,600 - $3,000 per ton installed [Harriman]) Con Requires a larger area for bore field

Standing-Column Wells Pro Lower front costs ($2,400 -$2,800 per ton installed [Harriman]) Pro Can be sited around existing buildings and requires smaller

footprint Con - Groundwater quality and sand/grit create major problems for

equipment Con - Requires more DEP oversight and permitting

steven pinette geothermal

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