Thermal Conductivity and Using Thermally Enhanced Grouts to Maximize Borefield Performance

Thermal Conductivity Intro - Slide 1.1 - 1 Copyright © 2011

Thermal Conductivity and Using ThermallyThermal Conductivity and Using ThermallyEnhanced Grouts to Maximize Borefield PerformanceEnhanced Grouts to Maximize Borefield Performance

Daniel Bernstein -PresidentDaniel Bernstein -President

Gaia Geothermal, LLC

www.gaiageo.comwww.precisiongeothermal.com


About Gaia Geothermal, LLCAbout Gaia Geothermal, LLC

• USA-based software firm that develops geothermal loopfield design and TC/TRT analysis tools: “GLD” Software

• In business for over a decade• Customers in approx. 60 countries• www.gaiageo.com


Class OutlineClass Outline

• First things first: Is a geo system justified?• Is a TC test necessary?• What does a TC test look like in the field?• TC test data analysis and report generation• Typical errors and bad data sets• Grouts and Borefield Performance


Learning ObjectivesLearning Objectives

In today’s presentation you will learn:• A step-by-step process for determining if geo

is a good fit for a project• A step-by-step process for determining when

it is important to conduct a TC test• What a field TC test looks/feels like• What good/bad TC test data look like


Is a Geo System Justified?Is a Geo System Justified?

• Before you conduct a TC test it is important to first determine if a geothermal system is the right technology for the project

• If a geo system is a good solution a TC test is not always necessary

• There is a logical, analytic framework for determining:– is a geo system justified?– is a TC test warranted?


Is a Geo System Justified: An ExampleIs a Geo System Justified: An Example


Client desires GeoExchange system

Determine energy needs•Monthly peak loads•Monthly energy loads•Annual energy balance

Determine site capability•Area available for GHX•Geological constraints•Regulations

Estimate energy cost of various system options

Design conventional system because capital cost and/or site not suitable for installation of Geo-Exchange system

Vertical GHX if site area is limited

Horizontal GHX if space available

Pond/lake GHX if appropriate

Hybrid options - boiler, fluid cooler, waste heat recovery, thermal energy storage, etc.

Design of ground heat exchanger (GHX)

Work with owner, architect, system designer to adjust loads, energy balance

Specifications and drawings

Construction, quality control, commissioning, operator training

Feasibility

Design

Implementation

Open well system if appropriate

Determine system impact•Equipment efficiency•Distribution design temp•Fresh air system

Design of mechanical system

Standing column if appropriate

Estimate construction cost of system options

Confirm geology of site for GHX performance (TC test)

Confirmation

Thanks to Terry Proffer of Major Geothermal
















Feasibility

Design

Implementation







Confirmation




Is a Geo System Justified: EnergyIs a Geo System Justified: Energy

Monthly Energy Output* Daylight contours Climate Understanding















Feasibility

Design

Implementation







Confirmation

















Feasibility

Design

Implementation






Confirm geology of site for GHX performance (TC or pump test if warranted)

Confirmation




Is a Geo System Justified: The SiteIs a Geo System Justified: The Site















Feasibility

Design

Implementation







Confirmation


Is A Geo System Justified?Is A Geo System Justified?


Is a Geo System Justified: Payback?Is a Geo System Justified: Payback?

Using GLD, we can conduct a quick and comprehensive lifecycle analysis.

The Geo system payback looks good and the client decides to move forward with geo. Now, it is time to determine whether or not to conduct a TC test.















Feasibility

Design

Implementation







Confirmation


Is a TC Test Justified?Is a TC Test Justified?


Is a TC Test Justified?Is a TC Test Justified?

• Before you conduct a TC test it is important to first determine if it is necessary

• First estimate the conductivity• Second, conduct a best case/worst case

sensitivity analysis• Third, compare the best case/worst case

installation costs• Determine whether or not to perform a TC

test


Is a TC Test Justified: TC EstimatesIs a TC Test Justified: TC Estimates

17

Estimate the TC values from drill logs, data tables, geological data, etc.


Is a TC Test Justified: Best Case/Worst CaseIs a TC Test Justified: Best Case/Worst Case

Enter the best case/worst case TC values into design software and calculate drilling requirements.



16465.5 14087.2Total Length (ft) Total Length (ft)


Is a TC Test Justified: Best Case/Worst CaseIs a TC Test Justified: Best Case/Worst Case$296,379 - $253,569.60 = $42809.40



Maximum loopfield cost difference: $42,809TC Test Cost: $10,000Difference: $32,809

Perform a TC test? Absolutely!Why? You might save your clients $32,000!


What a Field Test Looks LikeWhat a Field Test Looks Like


What a Field Test Looks Like: ToolsWhat a Field Test Looks Like: Tools








Native Ground Temperature: An AsideNative Ground Temperature: An Aside

• Direct measurement– Insert temperature measuring device into loop and

record temperature every X meters and calculate mean

• Circulating temperature measurement– Set logging interval to two seconds and record circulating

data for about ten minutes– Watch for pump heat






Purging Air From The System: An AsidePurging Air From The System: An Aside

• Use bypass valve assembly• Critical to test operation• Critical to stable data collection• Improper purging can cause damage to test

equipment



• Verify all sensors are connected and communicating with the logger

• Start circulating pump and engage the heating elements– You want to obtain ~ 15- 25 Watts per vertical ft of

bore

• Verify proper readings• Secure and lock unit










Data AnalysisData Analysis



• Check that all data are consistent before shutting down test

• Transfer data from logger into GLD or other software tool

• Analyze data set














TC: 0.98 Btu/hr•ft•⁰F TD: 0.62 ft²/dayT: 55.5° F

Clean, consistent power

44

Good DataGood Data


TC: 1.11 Btu/hr•ft•⁰F TD: 0.82 ft²/dayT: 61.0° F

Irregular, inconsistent power

45

Bad DataBad Data


TC: 0.89 Btu/hr•ft•⁰F TD: 0.65 ft²/dayT: 54.0°- 57.0° F

Irregular, inconsistent

power

46

Ugly DataUgly Data


Ugly Data?Ugly Data?


0

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Learn MoreLearn More

Field Training Course:www.geotrainers.com


Grout

BoreholeWall

Heat ExchangerPipes

Soil

Grout Conductivity and Borefield PerformanceGrout Conductivity and Borefield Performance

• How does Grout Conductivity Influence Borefield Performance?



• Borefield Performance?Definition: Long term average equipment COP/EER

Equipment COP/EER based on entering fluid temperaturesLong term average system COP/EER

System COP/EER includes circulation pumps


Example 1


• Borefield Performance?



• How does Grout Conductivity Influence Borefield Performance?

1) Grout conductivity influences borehole thermal resistance (BTR)2) Higher grout conductivity = lower BTR = less drilling for a certain level of performance (defined as COP/EER)

EXAMPLE:Case 1 Case 2

Target EER/COP 17.7/4.2 17.7/4.2

BTR 0.21 0.24

Drilling 16250 ft 17985 ft


• Definition:Ability of grout to transport heat

• Range: varies

• Impacthigher conductivity = more efficient heat transfer = less drilling

Example 1

Grout ConductivityGrout Conductivity


Example 1

100 borehole system Grout Conductivity Bore length Total length Cost ($12/ft)

0.00 6039ft 603900ft $7,246,800

0.45 369ft 36900ft $442,800

0.57 350.3ft 35030ft $420.360

0.69 341ft 34100ft $409,200

0.79 335ft 33500ft $402,000

0.88 329ft 32900ft $394,800



Example 1



Example 1

1 bag bentonite: $10/ 1 bag of sand: $31:1 ratio costs $13 for 25 ft of grouting with ~ 0.45 conductivity4:1 ratio costs $22 for 25 ft of grouting with ~ 0.88 conductivity

$3300 to drill$290 to grout


$3890 $3590


$3670

$220 $90




• Take Home Message:

1) You can design a geothermal borefield to give you a wide range of performance values (COP/EER)2) By adjusting the grout conductivity, you can possibly save on the

drilling necessary to provide the performance you require3) There is an optimal tradeoff point between the grout conductivity

and drilling savings. For cost effective design, you can calculate it for your project


Daniel Bernstein –PresidentDaniel Bernstein –[email protected]@gaiageo.com

Gaia Geothermal, LLC

www.gaiageo.comwww.precisiongeothermal.com


Heat Rate

TrtnTsup

Flow Rate

Cold TempHot Temp

GroundLoop

Test EquipmentTest Equipment

Thermal Conductivity and Using Thermally Enhanced Grouts to Maximize Borefield Performance

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