steven pinette geothermal
DESCRIPTION
geoTRANSCRIPT
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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
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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 .
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3High Temperatures Generated at Plate Boundaries
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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
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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
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6AA
HDPE geo-loop
u-tubes in vertical bores.
Common loop conditioned by vertical ground heat exchanger
Source: Oak Ridge National Laboratory
HDPE loop
Tremie pipe
Closed-loop boreholes typically 25 ft. apart; geo-loop being grouted
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7DPE Geo-loop pipe generally guaranteed or 50 years)
DPE lines running from headers to building; several bore holes per header
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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!!
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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
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Ground loops can be vertical or horizontal
Generally requires 1500-3000 ft2 land area per ton
Source: Oak Ridge National Laboratory
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
Source: Oak Ridge National Laboratory
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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
Source: Oak Ridge National Laboratory
Open-loop conditioned by surface water
AA
Plate heat exchanger
Water intake
Water dischargePump
More suited to warm climates, or cooling-only applications
Source: Oak Ridge National Laboratory
***Not appropriate for State regulated water bodies in Northeast No-discharge farm ponds generally okay
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GHP System Options
Source: Oak Ridge National Laboratory
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)
Source: Oak Ridge National Laboratory
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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
Source: Oak Ridge National Laboratory
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
Source: Oak Ridge National Laboratory
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??
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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