Fundamentals of Commercial Geothermal Wellfield Design

8/10/2019 Fundamentals of Commercial Geothermal Wellfield Design

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APPENDIX

2010 GHP Systems, Inc.NOTICE: THIS DOCUMENT REPORTS ACCURATE AND RELIABLE INFORMATION TO THE BEST OF OUR KNOWLEDGE BUT OUR SUGGESTIONS ANDRECOMMENDATIONS CANNOT BE GUARANTEED BECAUSE THE CONDITIONS OF USE ARE BEYOND OUR CONTROL. THE USER OF SUCH INFORMATIONASSUMES ALL RISK CONNECTED WITH THE USE THEREFORE. THE AUTHOR AND DISTRIBUTOR ASSUMES NO RESPONSIBILITY FOR THE USE OF THEINFORMATION PRESENTED HEREIN AND HEREBY DISCLAIMS ALL LIABILITY IN REGARD TO SUCH USE.

Fundamentals ofCommercial Geothermal

Wellfield Design

Intended for general distribution to:

Geothermal Wellfield Designers, Engineers & Architects

Distributed by:GHP Systems, Inc.

1000 N 32nd

AveBrookings, SD 57006

Prepared by:Kris Charles Jeppesen

About the Author:

Kris Jeppesen is the President of GHP Systems, Inc.,a leading manufacturer and supplier of commercial geothermal wellfieldproducts. Jeppesen has been involved in the geothermal industry

for many years as a contractor, researcher, geothermal training center instructorand design engineer. He is an IGSHPA Certified Trainer and an AEE Certified

GeoExchange Designer. He received his B.S. and M.S. in Mechanical Engineeringfrom South Dakota State University.


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FUNDAMENTALS OF GEOTHERMAL WELLFIELD DESIGN 2010 GHP Systems, Inc.NOTICE:THIS DOCUMENT REPORTS ACCURATE AND RELIAB LE INFORMATION TO THE B EST OF OUR KNOWLEDGE B UT OUR SUGGESTIONS AND RECOMMENDATIONSCANNOT BE GUARANTEED B ECAUSE THE CONDITIONS OF USE ARE BEYOND OUR CONTROL. THE USER OF SUCH INFORMATION A SSUMES ALL RISK CONNECTED WITHTHE USE THEREFORE. THE AUTHOR AND DISTRIBUTOR ASSUMES NO RESPONSIBILITY FOR THE USE OF THE INFORMATION PRESENTED HEREIN AND HEREBY DISCLAIMS

ALL L IABILITY IN REGARD TO SUCH USE. 1

INDEX

INTRODUCTION

Defin it ion ............................................................................................. 2

GROUND CONDITIONS

Land Area Availabi li ty and Drill ing Conditions ................................ 2

Test Bore ............................................................................................. 3

Formation Thermal Conductivity Test .............................................. 4

VERTICAL HEAT EXCHANGER DESIGN LENGTH

Effects of Heating versus Cooling of Wellfield Sizing ..................... 5

Effects of Equipment .......................................................................... 6

Geothermal Borehole Resistance ..................................................... 6

Sensitivity Analysis ............................................................................ 7

SYSTEM PIPING DESIGN

Pipe Sizing .......................................................................................... 9

Header Design Using Mult iple Circuits ............................................. 9

Reverse Return ................................................................................. 10

Reduced Header ............................................................................... 10

Single Supply and Return Mains ..................................................... 11

Multiple Supply and Return Mains .................................................. 11

Manifolds ........................................................................................... 12

MATERIALSPipe .................................................................................................... 13

Grout .................................................................................................. 13

Anti freeze .......................................................................................... 13

APPENDIX

Mean Water Temperature Graph ..................................................... 14

Flow Characteristics of HDPE Pipe ................................................. 15

Example VHE Report ....................................................................... 18

Example Formation Thermal Conductivity Analys is ..................... 19

Detailed Drawings

VHE Borehole Detail ........................................................................ 20Geothermal Wellfield Layout ............................................................ 21Vault Detail ...................................................................................... 22

Example Geothermal Wellfield Specifications ............................... 23


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INTRODUCTION

With the rapidly growing interest in commercial geothermal heat pump systems, thedemand for qualified designers, engineers and architects who can successfully tackle theseprojects has also increased. In many cases, designing the geothermal wellfield causes the

main difficulty for the designer. A poorly designed geothermal wellfield can lead to poorsystem performance, excessive installation costs, and unnecessary liability. The intent ofthis design guide is to outline procedures and design techniques necessary to optimize thegeothermal wellfield design.

DefinitionA closed-loop geothermal wellfieldexchanges energy with the earth bycirculating a water orwater/antifreeze solution throughplastic pipe buried beneath the

earths surface. A vertical closed-loop geothermal wellfield typicallyconsists of multiple vertical heatexchangers (VHEs). VHEs areconstructed by drilling holesgenerally ranging from 50 to 400feet deep in the earth and theninserting two pipes with a fitting

joining the two pipe ends at thebottom (called a u-bend pipeassembly). The remaining openannulus of the drilled borehole is

then backfilled or grouted, therebyencasing the u-bend pipe assembly(see diagram at right).

VERTICAL HEAT EXCHANGER (VHE)

SPECIFIED DEPTH

U-BEND PIPE

GROUT OR BACKFILL

EARTH

GROUND CONDITIONS

Land Area Availability and Drilling Condit ionsA geothermal system can usually be implemented by any heating/cooling application -- providingthat favorable conditions exist to do the geothermal wellfield installation. Available and suitableland area may be a constraint as to the feasibility of installing a geothermal heat pump system.

A rough rule of thumb is that there should be a minimum of 225 sq-ft of land area available per ton(12,000 Btuh) of design load capacity. However, designing longer VHE depths and/or tighter VHEgrid spacing can accommodate land area constraints. Installation areas should be relatively level,dry, free of trees, underground utilities and other obstacles complicating the installation. Once thegeothermal wellfield is installed, this land area can become a parking lot, park, football field or avariety of other applications.


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Another significant factor determining the feasibility of the wellfield is whether or not the drillingconditions are favorable. Drilling logs from wells drilled in the area can usually be obtained from theState and can provide the designer with general expectations of the subsoil formation. Additionalinformation on drilling difficulty can be obtained by contacting local drillers from the area. Obviously,the more difficult the drilling conditions the more expensive the wellfield installation.

Test BoreThe primary unknown factor that changes from one geothermal wellfield project to the next is theVHEs borehole composition. The borehole soil/rock composition plays a significant roledetermining drilling costs and total required VHE lengths. For smaller geothermal wellfield projects(30 ton or less), drilling logs of water wells can provide reasonable assumptions. However, a testbore should be drilled on site to obtain accurate drilling conditions and to increase the designreliability for larger commercial wellfield projects. In addition, it is also recommended to install a u-bend pipe in accordance with the anticipated design length so that a formation thermal conductivitytest can be performed as described in the following section.

Drilling contractors will assume the worst case drilling conditions in their bids if they are unfamiliarwith the drilling conditions and if a drilling log is not provided with the bidding documents. Inflated

drilling costs will significantly increase the bid price for the entire geothermal wellfield project. Adetailed drilling log similar to the one below should be included with bid documents.

TEST BORE DRILLING LOG

DRILLING LOCATIONGHP SYSTEMS, INC.1000 N 32NDAVE.BROOKINGS, SD 57006

PERMIT NO NA

CONTRACTOR JOHN JAMES

DRILLING LICENSE XXXX1234

DEPTH IN FEET

FROM TO DESCRIPTION0 3 TOP SOIL

3 22 BROWN CLAY

22 85 GRAY CLAY

85 153 BROWN CLAY

153 159 SAND & GRAVEL

159 165 SOFT SAND STONE

165 187 GRAY SHALE

187 200 RED SHALE

200 LIMESTONE HARD

STATIC WATER LEVEL 15 FEET

DRILLING METHOD MUD ROTARY

TOTAL DRILLING TIME 1.5 HOURS

U-BEND INSTALLED YES HDPE PIPE

GROUT TYPE Thermally Enhance 1:4 ratio bentonite: silica


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The drilling log above indicates that drilling becomes difficult at 200 feet when bedrock is hit.Drilling deeper into the hard limestone would be more expensive per linear foot than the first 200feet, so the VHEs specified design depth would typically not go beyond 200 feet. If there is anavailable land constraint the designer may have to consider going deeper than 200 feet with theVHE depth.

Formation Thermal Conduct ivity TestA test bore provides the necessary information required by the installing contractor for drillingpurposes. Although the design engineer is now aware of the formation makeup, he must refer totables to determine the anticipated thermal conductivity range for each soil/rock type and interpolatean overall average formation thermal conductivity. At this point, there still remains a large degree ofuncertainty so designs tend to be overly conservative. To obtain a reasonably accurate value for theformation thermal conductivity, a test measuring this value needs to be performed on a VHE at theproject site. The drilling log test bore can now be used to test the formation thermal conductivity byinstalling a u-bend pipe assembly to the anticipated design depth and then grouting the remainingborehole annulus.

This in-situ thermal conductivity testing or more commonly called heat dump testing, has water that

is heated with a constant energy input circulating through the VHE piping. The temperature of thewater with respect to time is recorded. Based on the increase in water temperature with respect totime, the formations thermal conductivity can be calculated. The longer the duration of this heatdump test, the more accurate the results are, but the cost of conducting the longer test increases.This design guide suggests a minimum of a 24-hour test duration. Industry standards tend to leantoward a 48-hour test duration producing more accurate results. The implementation of u-bend pipeseparators and/or thermally enhanced bentonite grout will make shorter test durations moreaccurate.

The graph below shows the recorded data from a 24-hour formation thermal conductivity test. Theaverage water temperature data is plotted with respect to the natural log of time. Line source theorycan be used to determine the formation thermal conductivity once the slope of the regression line

for this data is determined. There are several factors that influence the results of these tests, so it isstrongly recommended that experienced personnel analyze the data and calculate the resultingthermal conductivity (see appendix page 20 for an example report).

020

406080

100

-5.00 0.00 5.00

TEM

P(F)

LN TIME (HOURS)

FORMATION T.C. TEST

AVG


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VERTICAL HEAT EXCHANGER DESIGN LENGTH

Determining the required total VHE length can prove to be the most challenging task in thegeothermal wellfield design process. There are several wellfield design software programsthat assist designers in calculating the total required VHE lengths such as Ground Loop

Design that can be downloaded. Regardless of the software program used, designers needto have a fundamental understanding of various factors affecting VHE design lengths.Obviously, the buildings design loads, the grounds soil/rock thermal conductivity andmean ground temperature play significant roles in determining design lengths (see

Appendix page 15 for Mean Ground Water Temperature Graph). However, other influentialfactors that determine design lengths include seasonal diversification between loads,ground water movement, heat pump efficiencies, borehole resistance, and VHE spacing.

Effects of Heating Versus Cooling of Wellfield SizingThe most basic concept in understanding the geothermal wellfield loads involves not only thebuilding loads themselves, but also the effect of which load heating or cooling -- is dominant; alsoto be considered is the efficiencies of the geothermal heat pumps used. The following example isprovided to explain this concept of comparing two identical geothermal heat pumps, where one unitis heating and the other unit is cooling. These units are both operating at 300% efficiency; typicallythe efficiency in cooling is higher than in heating.

Heating: For the theological geothermal heat pump in heating, every three units of energy delivered into the conditionedenvironment comes from two units of energy extracted from the wellfield and one unit of energy provided by the electricityrequired to run the compressor. Therefore, only 2/3 of thebuildings heating load is absorbed from the wellfield.

Cooling: For the theological geothermal heat pump incooling, every three units of energy that are removed from

the conditioned environment are added to one unit of energyfrom the electricity required to run the compressor to berejected into the wellfield. Therefore, not only is the entirebuilding load rejected into the wellfield, but an additional33% of that load in electrical input is also rejected into thewellfield.

The purpose of the above example is to demonstrate theinfluence of the buildings dominant load on the sizing of thewellfield. In theory, a building that requires only coolingcould require twice the wellfield capacity as a building withthe same size load that requires only heating. Likewise, a

building with even larger loads -- seasonally diversified inheating and cooling -- may require a smaller wellfieldcapacity, then a building with smaller loads but highly coolingor heating dominant.

GEOTHERMAL HEAT PUMP

ELECTRIC

LOOPFIELD

HEATING

(300% EFFICIENT)

(3 UNITS ENEGY OUT)

(1 UNIT ENERGY IN)

(2 UNITS ENERGY IN)

LOOPFIELD LOAD = HEATING - ELECTRIC

GEOTHERMAL HEAT PUMP

ELECTRIC

LOOPFIELD

COOLING

(300% EFFICIENT)

(3 UNITS ENEGY IN)

(1 UNIT ENERGY IN)

(4 UNITS ENERGY OUT)

LOOPFIELD LOAD = COOLING + ELECTRIC


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Effects of EquipmentGeothermal heat pump equipment selection also significantly affects the wellfield design lengths.This should be clear if the basic theory presented in the preceding section is understood.Geothermal heat pump models vary in efficiencies. A more efficient heat pump will require a lowercapacity wellfield in cooling, but a larger capacity wellfield in heating, compared to a lower efficiencyheat pump. This is supported by the fact that the more efficient a heat pump is, the less electricity it

will require to provide the same capacity. This means that in the cooling mode, less electricalenergy needs to be rejected into the wellfield along with the energy removed from the building.However, in the heating mode, a more efficient geothermal heat pump will provide less electricalenergy into the heated environment, so more energy is absorbed from the wellfield to obtain thesame capacity. A geothermal heat pump that has a high heating and low cooling efficiency willrequire a much larger wellfield capacity than a geothermal heat pump that will produce the samecapacities, but has a low heating, high cooling efficiency.

Geothermal Borehole ResistanceThe performance of a VHE is largely influenced by the soil/rock surrounding the borehole; however,the backfill or grout used in the borehole and the positioning of the u-bend pipes within the boreholealso significantly contributes to the VHEs performance.

A standard VHE installation has two pipes (that make up the u-bend pipe assembly) that are eithertouching or are in close proximity of each other, thus interfering with each others ability toexchange energy with the earth. These u-bend pipes are usually encased with a 20% solidsbentonite grout (often required by State regulations) in order to seal the borehole to preventcontamination of water aquifers below ground. Although the bentonite grout mixture is excellent forsealing the borehole, it has poor heat transfer characteristics and acts as an insulator that restrictsenergy exchange between the u-bend pipes and the surrounding soil/rock. Recent technology(within the last 10 years or so) has developed products that can be utilized to decrease boreholeresistance, thereby significantly increasing the performance of a VHE and lowering the installationcosts by shortening required VHE lengths.

The two most significant breakthroughs in VHE design include thermally enhanced (T.E.) bentonitegrouts and u-bend pipe separators. Currently, there are T.E. grouts that can increase the thermalconductivity of bentonite grout ranging from 0.4 Btu/hr-ft-F up to as high as 1.4 Btu/hr-ft-F. Thisguide suggests that a grout thermal conductivity of 0.90 Btu/hr-ft-F to typically be the most costeffective for most design conditions. Most T.E. grouts add silica sand to the bentonite to increase itsthermal conductivity while maintaining a low permeability rate of less than 1X10-7cm/s. Alsoavailable are u-bend pipe separators (GeoClips) that attach to the u-bend pipes positioning themagainst the borehole wall directly across from each other. Positioning the u-bend pipes against theborehole wall and separating them as far apart as possible, significantly lowers the insulating effectof the bentonite grout, increases the area of energy absorption/rejection and decreases energyexchange between the two pipes.


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STANDARD U-BEND INSTALLATIONSTANDARD BENTONITE GROUT

TYPICAL STANDARD CAPACITYVERTICAL HEAT EXCHANGER

ENERGY APPLIED

VERTICAL HEAT EXCHANGERBOREHOLE CONFIGURATION

RESULTING ENERGY EFFECTSBASED ON BOREHOLE CONFIGURATION

U-BEND PIPE SEPARATOR

STANDARD BENTONITE GROUT

U-BEND PIPE SEPARATORT.E. GROUT

LARGE CAPACITY INCREASE

OVER STANDARD INSTALLATION

CAPACITY INCREASES EVEN MORE WITHU-BEND PIPE SEPARATOR AND T.E. GROUT

ENERGY APPLIED

ENERGY APPLIED

The diagram above illustrates how the energy flux of a VHE is affected by its configuration. The firstconfiguration uses no performance enhancing technology; therefore, the borehole resistancegreatly inhibits the exchange of energy of the circulating fluid and the earth. The energy fluxincreases significantly with the use of u-bend pipe separators in the second configuration. An evengreater increase in capacity is gained by incorporating a T.E. grout with the u-bend pipe separator

as shown in the third borehole configuration. A key point to consider is that there is a balancebetween the added cost of increasing VHE performance and the savings incurred by shortening thetotal VHE length.

Sensitivity AnalysisThe objective in sizing and designing a VHE is to obtain the required wellfield capacity for thelowest installation cost. The areas of control when designing a VHE include pipe placement, groutthermal conductivity, u-bend pipe size and VHE grid spacing. The following graphs show how eachparameter influences the VHE design lengths.

The graph to the right demonstrates the effectsthat grid spacing and u-bend pipe sizes have on

VHE design lengths. This example is typical inthat the design depth decreases dramatically asthe VHE grid spacing approaches 10 feet andcontinues to decrease as grid spacing getslarger. In this example the VHE decrease isntsignificant enough to justify the extra cost ofgoing beyond twenty-foot grid spacing. Typicaldesigns find 15 to 20 foot grid spacing optimum.However, warmer climates with cooling dominateloads and higher mean earth temperatures can

justify grid spacing greater than 20 feet. Thisexample also shows an increase in performance

by using larger diameter u-bend pipes; but, this isusually outweighed by the additional cost of thelarger pipe and increased volume of antifreezerequired. U-bend pipe size should be determinedby required flow as pertaining to head loss and/orturbulent flow (see VHE pipe sizing section formore detail).

200

250

300

350

400

450

5 10 15 20 25

VH

EDESIGN

LENGTH

(feet)

VHE GRID SPACING (feet)

VHE U-BEND SIZING & VHE GRID

SPACING COMPARISON(12,000 Btuh cooling)

3/4" U-BEND 1" U-BEND 1 1/4" U-BEND


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The graph to the right demonstrates the effectsof u-bend pipe placement within the boreholeand grout thermal conductivity on VHE designlengths. As previously mentioned, lowering theborehole resistance significantly shortens therequired VHE design length. By simply

implementing a u-bend pipe separator, thedesign length in this example is decreased by50 feet. This example also demonstrates howincreasing the grout thermal conductivitycorrelates directly with the decrease in designlengths. However, as with VHE grid spacing inthe example above, there is a point ofdiminishing returns. Higher thermalconductivity grouts are more expensive andlabor intensive to mix and pump. In mostinstances, either a 0.90 Btu/hr-ft-F thermallyenhanced grout by itself or a combination u-

bend pipe separator with a lower 0.57 Btu/hr-ft-F thermal conductivity grout optimizes costversus performance.

140

160

180

200

220

240

260

VHEDESIGN

LENGTH

(fe

et)

GROUT THERMAL COND. (Btu/hr-ft-F)

VHE DESIGN LENGTH VERSUS PIPEPLACEMENT & GROUT T.C.(12,000 Btuh Cool ing / VHE)

Random Pipe Placement U-bend Pipe Separator


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SYSTEM PIPING DESIGN

Pipe SizingExcessive head loss of circulating fluid through the wellfield can account for a large portion of theentire geothermal heat pump systems operating costs. This guide suggests keeping the entire

wellfield head loss below 50 feet of head. This can typically be achieved by designing the entirewellfield piping to have around 3 (maximum of 4) feet of head loss per 100 feet of pipe or less.

For the VHE pipe size the industry practice tries to achieve turbulent flow or a Reynolds Numbergreater than 2,500 (transition) in all of the VHEs to attain the maximum heat transfer between thecirculating fluid and the pipe during peak operation. For large wellfields that are designed aroundground thermal buildup or depletion (usually a 10 year modeling period is used), turbulent flowplays less importance because the wellfield size is significantly increased to compensate for thelong term thermal effects. If the circulating solution is pure water, turbulent flow is easily achievedbecause a flow rate of 2 GPM will be turbulent even in a 1 u-bend pipe. The flow must be muchhigher if the circulating fluid consists of a 25% propylene glycol/water solution and the solutiontemperature gets down in the 30F range. Now to be in turbulent flow the u-bends minimum flowrate for requires 3 GPM, 1 requires 4 GPM and 1 requires 5 GPM. The correspondingfeet of head loss per 100 of pipe are 4.1 for , 2.0 for 1 and 1.0 for 1. Typical designs use u-bends for flow rates up to 3 GPM, 1 u-bends for flow rates between 3 to 6 GPM and1ubends for flow rates between 6 to 12 GPM. This information pertains to DR11 (160 psi) pipe.

Header Design Using Multiple CircuitsThe wellfield header is used to connect all of the VHEs together. The planning of the header designplays an important factor on the performance, installation cost and reliability of the geothermalwellfield. A recommended design practice is to header the VHEs using multiple 2 or 3 circuitpiping. This guide recommends having at least 4 circuits when possible so that if a leak would everdevelop you could isolate that circuit and only lose 25% of your wellfield. This would allow thegeothermal system to still operate in a limited capacity while waiting for the leak to be repaired.

A common practice is to use 2 circuits on smaller commercial wellfield projects so there is greatercontrol especially for isolation purposes. On larger wellfield projects 3 circuits usually provide themost economic installations because you can significantly reduce the number of circuits.

To keep the head loss in the range previously mentioned in the Pipe Sizing section our designwould limit 2 (DR11) pipe to flow rates between 30 to 35 GPM and between 80 to 100 GPM for3 (DR15.5) pipe. With these flow rates you would typically see designs with (8 to 14) - , (6 to 8)- 1 or (3 to 6) - 1 VHEs being serviced on a single 2 circuit. A single 3 circuit would commonlyhave designs servicing (24 to 40) - , (18 to 24) - 1 and (9 to 18) - 1 VHEs. Of course thenumber VHEs on a circuit can fall outside those listed above depending on the type of circulatingsolution and the required VHE flow rates (see Appendix page 16 for Flow Characteristics of HighDensity Polyethylene (HDPE) Pipe).


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Reverse Return CircuitTo obtain balanced flow through all of theVHEs, each circuit header design shouldhave a reverse return. As illustrated to theright, with a reverse return header, the firstVHE hooked up on the supply line is the last

VHE on the return line. This headertechnique will balance flow between theVHEs on this circuit, provided that all of theu-bend pipe lengths are approximately thesame.

Reduced HeaderOnce the headering process is complete, the entire wellfield piping system needs to be flushed ofall debris and purged of air. This process is performed by circulating water through all of thewellfield piping system at high flow rates. The industrys accepted standard is to obtain a minimumvelocity of 2 feet per second through all piping. If a reduced header is not used, it may be

impossible to obtain this flow rate through portions of the header.

3/4" 1" 1 1/4" 2" 3/4"1"1 1/4"2"

The reduced piping in the above header diagram can be explained by reviewing the requiredvelocities needed to purge the VHEs (see Appendix page 16 for Flow Characteristics of HighDensity Polyethylene (HDPE) Pipe). This example uses HDPE DR11 pipe for the VHEs whichrequires a flow rate of approximately 3.75 GPM to obtain a velocity of 2 feet per second through

each VHE. The main line, which is 2 HDPE DR 11, requires a flow rate of 19 GPM to obtain thenecessary 2 feet per second velocity. If the main line does not reduce in size as it approaches thelast VHEs hooked up in parallel to the main line, the flow rates will fall well below the required 2 feetper second velocity, thus allowing air and debris to remain in that portion of the header pipe. In thisexample, 13 VHEs need to be flushed and purged, at the same time requiring a total flow rate ofabout 48 GPM at 3.75 GPM through each VHE. The reduced header system shown will flush andpurge all header piping as well as all the VHEs and not add excessive head pressure to the systemunder normal operation.

30 GPM

3GPM

3GPM

3GPM

3GPM

3GPM

3GPM

3GPM

3GPM

3GPM

3GPM


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Single Supply & Return MainsThe wellfield layout illustrated to theright shows all smaller header circuitsconnected to a single large main headerthat is brought into the building.

Although there is nothing wrong with this

type of header system from a balancedsystem flow standpoint, it is not the bestoption when considering liability. Theprimary concern is that if a leak wouldoccur, the entire wellfield is in jeopardyof going down until the leak is repaired.Locating that leak could become a majorordeal because there is no individualcircuit isolation to perform pressurechecks. The entire wellfield also needsto be flushed and purged at the sametime, which requires a very large

pumping and filtering system.

Multiple Supply & Return MainsThis guide suggests using a wellfieldheader system that has multiple valvedcircuits that are either brought into thebuilding or to a vault where they areconnected to a manifold as illustrated tothe right. The primary advantage ofimplementing this type of header systemis that if a leak occurs, only a small

percentage of the VHEs are taken out ofservice. A leaking circuit can be isolatedby shutting off valves connecting thatcircuit to an accessible manifold. Thetask of locating a leak is also mucheasier by pressure testing andidentifying which circuit needs to berepaired. Another advantage is thateach circuit can be flushed and purgedindividually. Balancing valve can beused on this system to balance flowbetween circuits.

TO BUILDING

SINGLE SUPPLY & RETURN MAINS

NOTR

ECOMMENDED

MULTIPLE SUPPLY & RETURN MAINS

TOBUILDING


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ManifoldsA typical manifold (interior manifold shown below) includes butterfly isolation valves, combinationbalancing/isolation valves and pressure/temperature ports for each circuit. With this design setup,circuit isolation, pressure testing and flow balancing can be easily performed. Each circuit can beindividually flushed and purged and accessed by connecting to the fill port. The mains should alsohave isolation valves so the wellfield contractor can complete his portion of the installation

independent of the interior mechanical. Having temperature and pressure indicators installed on themains can aid in quick system checks during startup as well as during normal operation (seeappendix page 23 for vault layout).


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MATERIALS

PipeHigh density polyethylene (HDPE) pipe is the geothermal industrys standard piping material.The specific pipe used is a PE3408 HDPE with a minimum cell classification of 345464C per

ASTM D-3035. Typically, a DR 11 (160 psi) rating is used for u-bends and header pipe diameterstwo inches and smaller; and a minimum of DR 15.5 (110 psi) is used for header pipe diametersgreater than two inches. Pipe produced specifically for the geothermal industry generally carriesa 50-year or longer warranty and has a life expectancy of over 100 years.

Advantages to using HDPE pipe include the following characteristics: toughness, durability,and chemical and corrosion resistance. Another advantage of HDPE pipe is that it requires nomechanical or glued fittings that could corrode or fail. All joints are permanently joined (welded)with heat fusion, providing a leak proof joint when properly joined. The smooth wall of this pipeaccommodates low-pressure losses.

GroutMany State and local regulatory agencies dictate grouting material and procedures for VHE

installations. In most cases, a 20% solids bentonite grout that is pumped from the bottom of theborehole up in a continuous fashion will meet those requirements. The purpose of grouting withbentonite is to form a hydraulic seal which will prevent contamination of aquifers. The permeabilityrate of bentonite is approximately 1 x 10-9centimeters per second; therefore, it is an excellentmedium for sealing a borehole. Bentonite grout products are usually bagged in a dry powder orgranular form; and, when mixed with water, will hydrate swelling to many times its dry size.

The primary drawback of using straight bentonite grout in VHEs is that it has a poor thermalconductivity (K = 0.4 Btu/hr ft-F). Since the u-bend pipes are encased in the bentonite grout,they are restricted from exchanging energy with the surrounding soil/rock. Thermally Enhancedbentonite grouts add silica sand in with the bentonite/water slurry to increase its thermalconductivity ranging up to 1.4 Btu/hr -ft-F. However, these thermally enhanced bentonite grout

products are expensive and labor intensive; therefore, it is rarely cost effective to increase thethermal conductivity higher than 0.9 Btu/hr-ft-F.

Anti freezeAn ideal antifreeze solution for use in a geothermal wellfield system would be non-corrosive,non-toxic, economical, possess low flammability and low viscosity, and meet all state & localregulations. Currently, there is no particular antifreeze product that meets all of the desiredcharacteristics. For commercial geothermal heat pump systems, the most common antifreezeused is propylene glycol (usually with inhibitors) and in many States, it is the only antifreezesolution allowed in vertical wellfields. Propylene glycol is non-corrosive, non-toxic, possesseslow flammability and moderate heat transfer characteristics and meets State regulations. On thenegative side, propylene glycol is very viscous at low temperatures and is relatively expensive.

It is not recommended to use less than 20% propylene glycol by volume, in order to avoid dilutionof the products inhibitors and to avoid the promotion of organic growth. It is also not recommendedto exceed 30% propylene glycol by volume, because it may lower the performance of thegeothermal heat pumps. At 25% propylene glycol by volume, a water/antifreeze circulating solutionis freeze protected down to around 15 F. At this same concentration, propylene glycol at lowtemperatures will increase the head loss of the circulating solution by approximately 36% overstraight water.


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APPENDIX

EXAMPLE GEOTHERMAL WELLFIELD SPECIFICATIONSClosed Circui t Heat Exchanger (VHE)

2010 GHP Systems, Inc.NOTICE: THIS DOCUMENT REPORTS ACCURATE AND RELIABLE INFORMATION TO THE BEST OF OUR KNOWLEDGE BUT OUR SUGGESTIONS AND RECOMMENDATIONS

CANNOT BE GUARANTEED BECAUSE THE CONDITIONS OF USE ARE BEYOND OUR CONTROL. THE USER OF SUCH INFORMATION ASSUMES ALL RISK CONNECTED WITH THE USE

THEREFORE. THE AUTHOR AND DISTRIBUTOR ASSUMES NO RESPONSIBILITY FOR THE USE OF THE INFORMATION PRESENTED HEREIN AND HEREBY DISCLAIMS ALL LIABILITY INREGARD TO SUCH USE.

14

MEAN WATER TEMPERATURE GRAPH


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APPENDIX

EXAMPLE GEOTHERMAL WELLFIELD SPECIFICATIONSClosed Circuit Heat Exchanger (VHE)

2010 GHP Systems, Inc.NOTICE: THIS DOCUMENT REPORTS ACCURATE AND RELIABLE INFORMATION TO THE BEST OF OUR KNOWLEDGE BUT OUR SUGGESTIONS AND RECOMMENDATIONSCANNOT BE GUARANTEED BECAUSE THE CONDITIONS OF USE ARE BEYOND OUR CONTROL. THE USER OF SUCH INFORMATION ASSUMES ALL RISK CONNECTED WITH THE USE


15

FLOW CHARACTERISTICS OF WATER IN HDPE PIPE (PE345464C)Pipe Size: DR 11, 0.86 I.D. Pipe Size: 1 DR 11, 1.075 I.D.Pipe Volume: 3.02 Gallons/100 ft Pipe Volume: 4.71 Gallons/100 ft

GPMVelocity(ft/sec)

Head Loss(ft/100ft) GPM

Velocity(ft/sec)

Head Loss(ft/100ft)

0.75 0.41 0.13 0.50 0.18 0.041.00 0.55 0.18 1.00 0.35 0.07

1.25 0.69 0.22 1.50 0.53 0.11

1.50 0.83 0.27 2.00 0.71 0.15

1.75 0.97 0.80 2.50 0.88 0.52

2.00 1.10 1.01 3.00 1.06 0.71

2.25 1.24 1.24 3.50 1.24 0.93

2.50 1.38 1.49 4.00 1.41 1.17

2.75 1.52 1.76 4.50 1.59 1.44

3.00 1.66 2.05 5.00 1.77 1.74

3.25 1.80 2.36 5.50 1.94 1.82

3.50 1.93 2.68 6.00 2.12 2.13

3.75 2.07 3.03 6.50 2.30 2.46

4.00 2.21 3.39 7.00 2.47 2.81

4.25 2.35 3.35 7.50 2.65 3.18

4.50 2.49 3.71 8.00 2.83 3.574.75 2.62 4.09 8.50 3.00 3.98

5.00 2.76 4.48 9.00 3.18 4.41

5.25 2.90 4.89 9.50 3.36 4.86

5.50 3.04 5.32 10.00 3.53 5.33

6.00 3.31 6.21 11.00 3.89 6.32

6.50 3.59 7.17 12.00 4.24 7.39

7.00 3.87 8.19 13.00 4.60 8.53

7.50 4.14 9.27 14.00 4.95 9.75

8.00 4.42 10.41 15.00 5.30 11.03

Pipe Size: 1-1/4 DR 11, 1.358 I.D. Pipe Size: 1-1/2 DR 11, 1.554 I.D.Pipe Volume: 7.52 Gallons/100 ft Pipe Volume: 9.85 Gallons/100 ft

GPMVelocity(ft/sec)


Velocity(ft/sec)

Head Loss(ft/100ft)

4.00 0.89 0.39 7.00 1.18 0.544.50 1.00 0.48 8.00 1.35 0.61

5.00 1.11 0.57 9.00 1.52 0.75

5.50 1.22 0.68 10.00 1.69 0.91

6.00 1.33 0.79 11.00 1.86 1.08

6.50 1.44 0.91 12.00 2.03 1.26

7.00 1.55 0.92 13.00 2.20 1.46

7.50 1.66 1.04 14.00 2.37 1.67

8.00 1.77 1.17 15.00 2.54 1.88

8.50 1.88 1.30 16.00 2.71 2.12

9.00 1.99 1.44 17.00 2.88 2.36

9.50 2.10 1.59 18.00 3.04 2.61

10.00 2.22 1.74 19.00 3.21 2.88

10.50 2.33 1.90 20.00 3.38 3.16

11.00 2.44 2.06 21.00 3.55 3.45

12.00 2.66 2.41 23.00 3.89 4.0613.00 2.88 2.78 25.00 4.23 4.72

14.00 3.10 3.18 27.00 4.57 5.42

15.00 3.32 3.60 29.00 4.91 6.16

16.00 3.54 4.04 31.00 5.24 6.94

17.00 3.77 4.50 33.00 5.58 7.77

18.00 3.99 4.99 35.00 5.92 8.64

19.00 4.21 5.50 37.00 6.26 9.55

20.00 4.43 6.03 39.00 6.60 10.50

21.00 4.65 6.58 41.00 6.94 11.48


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16

FLOW CHARACTERISTICS OF WATER IN HDPE PIPE (PE345464C)Pipe Size: 2 DR 11, 1.943 I.D. Pipe Size: 3 DR 15.5, 3.048 I.D.Pipe Volume: 15.40 Gallons/100 ft Pipe Volume: 37.90 Gallons/100 ft

GPMVelocity(ft/sec)


Velocity(ft/sec)

Head Loss(ft/100ft)

10.00 1.08 0.31 40.00 1.76 0.43

11.50 1.24 0.40 45.00 1.98 0.5413.00 1.41 0.50 50.00 2.20 0.65

14.50 1.57 0.61 55.00 2.42 0.77

16.00 1.73 0.73 60.00 2.64 0.90

17.50 1.89 0.85 65.00 2.86 1.04

19.00 2.06 0.99 70.00 3.08 1.19

20.50 2.22 1.13 75.00 3.30 1.34

22.00 2.38 1.28 80.00 3.52 1.51

23.50 2.54 1.45 85.00 3.74 1.68

25.00 2.71 1.62 90.00 3.96 1.86

26.50 2.87 1.79 95.00 4.18 2.06

28.00 3.03 1.98 100.00 4.40 2.25

29.50 3.19 2.17 105.00 4.62 2.46

31.00 3.35 2.38 110.00 4.84 2.68

34.00 3.68 2.81 120.00 5.28 3.13

37.00 4.00 3.27 130.00 5.72 3.6240.00 4.33 3.76 140.00 6.16 4.14

43.00 4.65 4.28 150.00 6.60 4.69

46.00 4.98 4.83 160.00 7.04 5.26

49.00 5.30 5.42 170.00 7.47 5.87

52.00 5.63 6.03 180.00 7.91 6.51

55.00 5.95 6.67 190.00 8.35 7.18

58.00 6.28 7.34 200.00 8.79 7.88

61.00 6.60 8.04 210.00 9.23 8.61

Pipe Size: 4 DR 15.5, 3.92 I.D. Pipe Size: 6 DR 15.5, 5.771 I.D.Pipe Volume: 62.69 Gallons/100 ft Pipe Volume: 135.88 Gallons/100 ft

GPMVelocity(ft/sec)


Velocity(ft/sec)

Head Loss(ft/100ft)

53.00 1.41 0.21 200.00 2.45 0.3758.50 1.56 0.26 220.00 2.70 0.44

64.00 1.70 0.30 240.00 2.94 0.51

69.50 1.85 0.35 260.00 3.19 0.59

75.00 1.99 0.40 280.00 3.43 0.67

80.50 2.14 0.46 300.00 3.68 0.76

86.00 2.29 0.51 320.00 3.93 0.86

91.50 2.43 0.57 340.00 4.17 0.96

97.00 2.58 0.64 360.00 4.42 1.06

102.50 2.72 0.70 380.00 4.66 1.17

108.00 2.87 0.77 400.00 4.91 1.28

113.50 3.02 0.85 420.00 5.15 1.40

119.00 3.16 0.92 440.00 5.40 1.52

124.50 3.31 1.00 460.00 5.64 1.65

130.00 3.46 1.08 480.00 5.89 1.78

141.00 3.75 1.25 520.00 6.38 2.06152.00 4.04 1.43 560.00 6.87 2.36

163.00 4.33 1.62 600.00 7.36 2.67

174.00 4.63 1.83 640.00 7.85 3.00

185.00 4.92 2.04 680.00 8.34 3.35

196.00 5.21 2.27 720.00 8.83 3.72

207.00 5.50 2.50 760.00 9.32 4.10

218.00 5.80 2.75 800.00 9.81 4.50

229.00 6.09 3.00 840.00 10.30 4.92

240.00 6.38 3.27 880.00 10.79 5.35


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17

FLOW CHARACTERISTICS OF WATER IN HDPE PIPE (PE345464C)

Pipe Size: 8 DR 15.5, 7.513 I.D. Pipe Size: 10 DR 15.5, 9.362 I.D.Pipe Volume: 230.30 Gallons/100 ft Pipe Volume: 357.60 Gallons/100 ft

GPMVelocity(ft/sec)


Velocity(ft/sec)

Head Loss(ft/100ft)

300.00 2.17 0.21 550.00 2.56 0.22320.00 2.32 0.24 600.00 2.80 0.26

340.00 2.46 0.27 650.00 3.03 0.30

360.00 2.61 0.30 700.00 3.26 0.34

380.00 2.75 0.33 750.00 3.50 0.39

400.00 2.89 0.36 800.00 3.73 0.44

420.00 3.04 0.39 850.00 3.96 0.49

440.00 3.18 0.43 900.00 4.19 0.54

460.00 3.33 0.46 950.00 4.43 0.60

480.00 3.47 0.50 1000.00 4.66 0.66

500.00 3.62 0.54 1050.00 4.89 0.72

520.00 3.76 0.58 1100.00 5.13 0.78

540.00 3.91 0.62 1150.00 5.36 0.85

560.00 4.05 0.66 1200.00 5.59 0.91

580.00 4.20 0.71 1250.00 5.83 0.98

620.00 4.49 0.80 1350.00 6.29 1.13660.00 4.78 0.89 1450.00 6.76 1.29

700.00 5.07 0.99 1550.00 7.22 1.46

740.00 5.36 1.10 1650.00 7.69 1.63

780.00 5.64 1.21 1750.00 8.16 1.82

820.00 5.93 1.32 1850.00 8.62 2.01

860.00 6.22 1.44 1950.00 9.09 2.21

900.00 6.51 1.57 2050.00 9.55 2.42

940.00 6.80 1.69 2150.00 10.02 2.64

980.00 7.09 1.83 2250.00 10.49 2.87


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18

EXAMPLE VERTICAL HEAT EXCHANGER REPORT


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EXAMPLE DETAIL DRAWINGS

VHE Detail Example 1

VHE Detail Example 2

6'

300''

PREMANUFACTURED U-BEND

1" HDPE PIPE DR11PE3408 CC 345464C

T.E. BENTONITE GROUT50:200 BENTONITE/SILICA SAND(K = 0.90 BTU/HR FT F)

MAINTAIN MINIMUM PIPE BENDING RADIUSOF 25 TIMES THE PIPE DIAMETER

TRACER WIRE(ALONG ENTIRE LENGTHOF HEADER PIPING)

SAND BACKFILL

FINAL GRADE

EARTH BACKFILL(COMPACT AS SPECIFIED)

18"

FOILED BACKWARNING TAPE(ALONG ENTIRE LENGTHOF HEADER PIPING)

18"

6'

10' TYP200'

PREMANUFACTURED U-BEND

U-BEND PIPE SEPARATORGEOCLIP AS MANUFACTURED BYGBT,I NC.

3/4" HDPE PIPE DR11PE3408 CC 345464C

MAINTAIN MINIMUM PIPE BENDING RADIUSOF 25 TIMES THE PIPE DIAMETER

EARTHBACKFILL(COMPACT AS SPECIFIED)

18"

SAND BACKFILL

FINAL GRADE

18"

T.E. BENTONITE GROUT50:50 BENTONITE/SILICA SAND(K = 0.57 BTU/HR FT F)

TRACER WIRE(ALONG ENTIRE LENGTHOF HEADER PIPING)

FOILED BACKWARNING TAPE(ALONG ENTIRE LENGTHOF HEADER PIPING)


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21

EXAMPLE GEOTHERMAL WELLFIELD LAYOUT


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22

Little Giant Sump Model 6 CIA-RFS

W/ Mercury Switch (Provided)

14" x 14" x 15" Stainless Steel Sump Pit

To Sump

Number ofCircuits

Typ. of 20




To Sump




To Sump

1" Electrical Conduit, Switches And

Outlet Boxes Provided But Not Wired

(Electrician Is Responsible)

Tracer Wire Conduit

Ventilation Blower And Flexible Duct

120V Sealed Utility Light With Protective Shield

4" ValvedBypass

1 1/4" HDPESump Pump

Discharge

EPDM Sump Pit Seal

2" Butterfly Valve (Typ)

P/T Port (Typ)

2" Balancing/Isolation Valve (Typ)

2" Fill Port (Typ of 2)

Sump Pit

W/ Pump

Pressure Ind.

(Typ of 2)

8" Valved Main (Typ of 2)

Temperature Ind.

(Typ of 2)

Steel Sleeve W/ Link Seals

(Typ Of All Wall Penetrations)

Number of

Circuits

Typ. of 20

EXAMPLE VAULT DETAIL


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EXAMPLE GEOTHERMAL WELLFIELD SPECIFICATIONSClosed Circuit Vertical Heat Exchanger (VHE)

DESCRIPTION OF WORK

A. This design has been prepared in accordance with the materials standards andaccepted installation practices of the International Ground Source Heat Pump

Association (IGSHPA). The wellfield contractor shall comply with these standardsand practices along with all State and local regulations pertaining to the installation.

B. The wellfield contractor is responsible for all aspects involved with the completegeothermal wellfield installation. All materials, drilling, water supply, excavation,hauling of backfill, dewatering, building penetration, manifold/vault installation, leaktesting, soil compaction, final flushing/purging, adding glycol and labor required shall

be included in the bid price.

C. The wellfield contractor shall take note: There is no guarantee to the wellfieldcontractor that the location of any existing utilities are exactly as indicated on theplans. Some areas may require hand digging to locate that utility. The wellfieldcontractor must include in the bid price, the repair of any domestic water, electrical,communication or any service line that may be damaged during the construction ofthis project. Any offsets required to route over or under existing lines shall also beincluded in the bid price of the project.

QUALIFICATIONS

A. The wellfield contractor must have on this project a certified IGSHPA installer.The wellfield contractor performing this work must have a minimum of two yearsexperience in performing underground closed circuit VHE work of this projects sizeor larger.

B. VHE fabricators must be heat fusion certified by an authorized high densitypolyethylene (HDPE) pipe manufacturers representative of the brand of pipe used.

Certification must include: successful completion of a written heat fusion exam aswell as demonstrating proper heat fusion techniques under the direct supervisionof the authorized HDPE pipe manufacturers representative.


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APPENDIX




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PRODUCTS

A. PipeThe pipe shall be PE3408 HDPE with a minimum cell classification of 345464C per

ASTM D3035 and a DR11 (160 psi) rating for u-bends and header pipe two inches

and smaller and a minimum of DR15.5 (110 psi) for header pipe greater than 2 inchin diameter. This pipe will carry a warranty of no less than 50 years.

Each pipe shall be permanently indent marked with the manufacturer's name,nominal size, pressure rating, relevant ASTM standards, cell classification numberand date of manufacture.

The VHE will have a factory fused u-bend with pipe lengths long enough to reachgrade from the bottom of the bore so no field fusions are required below the headerpit. Approved pipe manufacturer is Performance Pipe.

B. FittingsPipe fittings shall meet the requirements of ASTM D2683 (for socket fusion fittings)or ASTM D3261 (for butt/saddle fusion fittings). Each fitting shall be identified withthe manufacturer's name, nominal size, pressure rating, relevant ASTM standardsand date of manufacturer. Saddle fusion is not allowed except when performed by amanufacturer normally engaged in that type of work. No field installed saddle fittingsare allowed. Approved fabrication manufacturer is GHP Systems, Inc. and approvedfitting manufacturers are Performance Pipe, Central Plastics and Viega.

C. Manufactured Infield Extended HeadersThe header sections shall be factory assembled with all branches ready forconnection to the u-bend pipe ends. The infield extended headers used to connectthe VHE u-bends in each circuit shall be constructed as shown on project drawings.

All 2" and smaller header pipe sections will come in one complete coil that ispalletized. All 3" and larger header pipe sections will be shipped in long straightsections which are typically between 40' to 50' in length. All packaging shall be asnecessary to minimize damage in transit/handling and facilitate ease in unloadingand storage. The infield extended headers shall be GeoHeadersas manufacturedby GHP Systems, Inc. and will be manufactured with the same pipe and fittingspecifications as listed in those sections.

D. Interior Manifold (Use in place of Vault)The interior manifold shall be constructed as shown on project drawings. Themanifoldshall be the GeoManifoldas manufactured by GHP Systems, Inc. and willbe manufactured with the following specifications.

High density polyethylene (HDPE) pipe and fittings, joined together with heat fusion,shall be used for all circuit and main header piping. All HDPE pipe and heat fused


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APPENDIX

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materials shall be manufactured from high-density, high molecular weight PE 3408polyethylene compound that meets or exceeds ASTM D 3350 cell classification345464C, and is listed by the Plastic Pipe Institute in PPI TR-4 with HDB ratings of1600 psi (11.04 MPa) at 73F (23C) and 800 psi (5.52 MPa) at 140F (60C). All 3"and larger HDPE piping will be DR15.5 and all 2" and smaller HDPE piping will be

DR11. All circuits 2" and greater shall include butterfly valves constructed of lugtype/lever with cast iron body, aluminum-bronze disc, EPDM Seat, 416 stainlesssteel stem, rated at 200 psi. All circuit setter flow balancing valves will have a fixedport venture orifice, have blow-out proof stem, flow measurement functionindependent of ball position, install in any position, and serve as a service shutoffwith a tamper resistant memory stop to accurately reset to balancing. Circuitssmaller than 2" and all fill ports shall be ball valves with full port opening with blowout proof stem, 600 psi non-shock cold WOG. Pressure/temperature ports shall bebrass and have a dual seal core of Nordel, good up to 350F for water and shall berated zero leakage from vacuum to 1000 psig. Plug shall be capable of receiving a1/8" pressure or temperature probe. A stainless steel pressure gauge with "

isolation valve will be included on both supply and return mains. The pressure gaugewill be Sisco brand with 4 " dial size and read 0 100 psig. A stainless steelbimetal thermometer will be included on both supply and return mains. Thepressure gauge will be Ashcroft brand with 3" dial size with 4" stem and reads 0 250F. The manifold will be leak proof checked at factory with 100 psi pressure for aperiod of 24 hours or more.

E. Composite Steel/Concrete Vault (Use in place of interior manifold)The vault shall be a composite steel and concrete structure constructed as shownon project drawings. The vault shall be shipped from factory preformed for aconcrete pour with all reinforcement rods, manifolds, valves and piping securedin place. The vault weight by itself will overcome all buoyancy forces without anyadditional anchoring. The vault will come traffic load ready without any additionalmanhole rings, covers, bracing, or concrete pours. The approved vault is theGeoVaultas manufactured by GHP Systems, Inc and will be manufactured withthe following specifications.

Structure:The interior shell shall consist of a heavy-duty steel frame and basewhere all joints have a continuous weld. The base frame and cross bracing shall beconstructed of 1/4" 3" x 8" square steel tubing. The base cross bracing shall bespaced a maximum of 2 feet on center with " 3" x 8" square steel tubing. Thesidewall and ceiling frames and all cross bracing shall be constructed of " 3" x 3"angle iron. Sidewall and ceiling cross bracing shall be spaced a maximum of 2 feeton center. The steel interior walls/ceiling, stainless steel floor and stainless steelsump pump pit shall be constructed of 12-gage sheet that are specially treated withan epoxy coating on interior side. All interior sheet steel shall have a continuousweld on seams and a 2" weld every 12" at support framing and exterior form walls.#5 reinforcement rods shall be placed on a 12" spacing for sidewalls and #6reinforcement rods shall be placed on a 12" x 12" grid spacing for the ceiling. All


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APPENDIX

26

steel pipe sleeves will be schedule 40 and have a continuous weld on interior side.All reinforcement rods shall be located 3" within the concrete from the interior sideand welded to steel framing every 2 feet or less. The outer shell of the walls andceiling shall consist of 8" thick 4,000 psi concrete that is poured by the contractor on-site and vibrated into place. The manhole shall be constructed of " sheet steel with

a 3" flange that is anchored into ceiling concrete and welded to ceiling frame; allmanhole welds being continuous. The manhole cover shall be constructed of "steel tread plate with framing constructed of " 3" x 3" angle iron. The manifoldstands support channel shall run continuous between circuits and be constructed of" 3" x 3" angle iron with 1/8" 1" tube supports every 3 feet welded to the floor.

Manifolds: High density polyethylene (HDPE) pipe and fittings, joined together withheat fusion, shall be used for all circuit and main header piping. All HDPE pipe andheat fused materials shall be manufactured from high-density, high molecular weightPE 3408 polyethylene compound that meets or exceeds ASTM D 3350 cellclassification 345464C, and is listed by the Plastic Pipe Institute in PPI TR-4 with

HDB ratings of 1600 psi (11.04 MPa) at 73F (23C) and 800 psi (5.52 MPa) at140F (60C). All 3" and larger HDPE piping will be DR15.5 and all 2" and smallerHDPE piping will be DR11. All circuits 2" and greater shall include butterfly valvesconstructed of lug type/lever with cast iron body, aluminum-bronze disc, EPDM Seat,416 stainless steel stem, rated at 200 psi. All circuit setter flow balancing valves willhave a fixed port venture orifice, have blow-out proof stem, flow measurementfunction independent of ball position, install in any position, and serve as a serviceshutoff with a tamper resistant memory stop to accurately reset to balancing.Circuits smaller than 2" and all fill ports shall be ball valves with full port opening withblow out proof stem, 600 psi non-shock cold WOG. Pressure/temperature ports shallbe brass and have a dual seal core of Nordel, good up to 350F for water and shallbe rated zero leakage from vacuum to 1000 psig. Plug shall be capable of receivinga 1/8" pressure or temperature probe. A stainless steel pressure gauge with "isolation valve will be included on both supply and return mains. The pressure gaugewill be Sisco brand with 4 " dial size and read 0 100 psig. A stainless steelbimetal thermometer will be included on both supply and return mains. Thepressure gauge will be Ashcroft brand with 3" dial size with 4" stem and reads 0 250F. The manifold will be leak proof checked at factory with 100 psi pressure for aperiod of 24 hours or more.

Keyed Entry: The manhole cover of the vault will be fastened with four stainlesssteel pentagon head bolts requiring a special socket key for removal. These boltswill be counter sunk a minimum of 1" in a circular hole just large enough toaccommodate the socket key to inhibit tampering/removal with conventional tools.Two socket keys will be included with each vault.

Seals: All HDPE pipe penetrations in the vault will utilize a Link-Seal EPDMmodular hydrostatic seal to water proof and anchor the pipe. This seal will beremovable to allow replacement of the HDPE pipe should it ever be damaged at the


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APPENDIX

27

point of vault penetration. The manhole cover and stainless steel sump pit will utilizeEPDM gaskets for seals where bolted connections are made.

Sump Pump: A Little Giant series 6 with mercury switch will be supplied with thevault. The pump will be 1/3 HP, continuous duty rated, 60Hz, 120V - 9.0A. The pump

will discharge at a rate of 46 GPM at the point it exits the vault.

Ventilation: Vault will come with its own ventilation blower and 8" flexible ducting.The blower will be industrial grade made with heavy duty metal construction andproduce high velocity air movement. The blower will be Aloha model 39008 rated for60Hz, 120V - 1.4A. The blower will produce 1,580 CFM open and 1,200 CFMconnected to 20 feet of 8" industrial grade flexible ducting. The blower will be ceilingmounted at the opposite end of the manhole within the vault. The 8" flexible duct willbe run from the blower up to the top of the manhole entry. The blower will beswitched with the lights with this switch being located right below the manhole cover.

Electrical: The electrical service required for the vault is 60 Hz, 120V - 20A withGFCI breaker. The vault shall have all required electrical conduit and boxes ceilingmounted with 1" conduit exiting the vault. All outlets, light fixture(s), switch andweatherproof covers will be included with the vault. The vault is to be field wired by alicensed electrician in the state of installation.

The electrical components include:

1. Light Fixture(s): Sealed glass lens with aluminum guard and aluminum

ceiling mounted base. The fixture is suitable for damp locations and uses

a 100 W bulb.

2. Switch: The switch will be a 120V - 20A heavy duty double pole that will

power the lights as well the ventilation outlet

3. Outlets: The two outlets used will be 120V - 20A heavy duty duplex.

The utility outlet will be wired continuous power for sump pump and servicing

equipment. The ventilation outlet will be switched with the lights for the

blower.

All alternate vaults must at a minimum meet the following criteria to be considered

for approval by engineer.

1. Quality Assurance: The vault shall come from the factory with the HDPE

manifold mounted in place and all main and circuit piping stubbed out of vault

housing. The manufacturer shall be specialized in the manufacturing of

commercial geothermal vaults, have manufactured at least 200 geothermal

vaults and shall have manufactured geothermal vaults for a minimum of 5


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APPENDIX

28

years. Proof of experience shall be required for approval.

2. Structural Integrity: Vault shall come from the factory traffic load rated and

capable of handling all traffic and service/utility equipment loads encountered

regardless of the vaults location. If additional structural support (such as a

concrete surface pad with manhole ring and cover) is required to meet this

criterion, it must have a PE stamped design. The vault shall have a flat base

that extends out to the complete width and length of the vault. This wide base

will have a reinforced footing surface area that carries a load of no more than

12 lb per square inch of the installed vaults weight.

3. Buoyancy: The weight of the vault housing itself must overcome all bouncy

forces at the installed depth. The vault must not be able to float in a flooded

open vault pit during installation. If any additional vault weighting/anchoring is

required to meet this criterion, it must have a PE stamped design. The designcalculations will use complete saturated soil conditions.

4. Component Replacement: All vault supply/return pipe penetrations must

utilize a positive hydrostatic seal (equivalent to Link-Seal) to allow field

replacement should the pipe be damaged. Pipe cannot be heat fused (or

extrusion welded) to vault structure or be secured in any fashion which

promotes crack propagation in the pipe or hinders pipe replacement. All

valves and gauges within the vault must be able to be replaced without any

heat fusion repair required.

5. Safety/Servicing: The vault shall have switched lighting, switched fresh air

ventilation (minimum 1200 CFM), service outlet and a sump pit/pump. The

vault shall have a minimum of a 30" square manway or a 34" diameter

manway with an OSHA approved ladder and a tamper resistant non skid

cover with a gasket seal. There must be a minimum 2' wide walkway between

circuits with a minimum 6 high unobstructed ceiling. All ceiling mounted

lights, ventilation blower, outlets and etc. must be mounted to the side of this

walkway.

F. Grout (Design option 1)The thermally enhanced bentonite based grout used to seal the VHE shall have aminimum of 63% solids. This grout will also have a permeability rate of less than1X10-7cm/sec. The silica sand used will have a 4030 mesh or finer. The minimumgrout thermal conductivity is 0.90 Btu/hr-ft-F (50lb bentonite/200lb silica sand).

Approved grout manufacturers are Black Hills Bentonite (TG Lite), Wyo-Ben Inc.(ThermEx) and Baroid (Barotherm Gold).


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APPENDIX

29

G. U-bend Pipe Separators (Design option 2 - use with 0.57 TC grout)The u-bend pipe separators used to position the u-bend pipes against the boreholewall directly across from one another shall be the GeoClipbrand manufactured byGBT, Inc. These separators will be positioned every ten feet on the u-bend pipe.

H. Warning TapeWarning tape used must be foil backed, two inches wide or greater with acontinuous message printed every 36 inches or less reading: "CAUTIONGEOTHERMAL PIPELINE BURIED BELOW". The tape shall be highly resistant toalkalis, acids and other destructive agents found in the ground.

EXECUTION

A. Dri ll ingThe vertical boreholes will be drilled to a depth allowing complete insertion of theVHE to its specified depth. The maximum borehole diameter will be six inches. If alarger diameter is required, it must be approved by the design engineer.

B. U-bend Pipe AssemblyThe u-bend pipe shall be filled with water and pressurized to 100 psi to check forleaks before insertion. If necessary, an iron (sinker) bar can be attached at the baseof each u-bend to overcome buoyancy. This iron bar will have all sharp edgesadequately taped to avoid scarring and/or cutting of the polyethylene pipe. Nodriving rod that is pulled out after u-bend insertion will be allowed. The entireassembly is inserted to the specified depth in the borehole.

C. Grouting ProceduresThe VHE is to be grouted from the bottom on up in a continuous fashion using a oneinch or larger HDPE tremie pipe. The tremie pipe will be pulled out during thegrouting procedure maintaining the pipes end just below grout level within theborehole. All State regulations will be met for borehole grouting of the VHE.

D. Heat Fusion Pipe JoiningAll underground pipe joining will be heat fused by socket, butt or saddle (sidewall)fusion in accordance to ASTM D2610, ASTM D2683 and the manufacturer's heatfusion specifications. The operator shall be heat fusion certified and experienced inexecuting quality fusion joints.


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APPENDIX

30

E. Excavation and Backfill ing for PipingThe wellfield contractor shall do all excavating, backfilling, shoring, bailing andpumping for the installation of their work and perform necessary grading to preventsurface water from flowing into trenches or other excavations. Sewer lines shall not

be used for draining trenches and the end of all pipe and conduit shall be keptsealed and lines left clean and unobstructed during construction. Only materialsuitable for backfilling shall be piled a sufficient distance from banks of trenches toavoid overloading. Unsuitable backfill material shall be removed as directed by thedesign engineer.

Sheathing and shoring shall be done as necessary for protection of work andpersonnel safety. Unless otherwise indicated, excavation shall be open cut exceptfor short sections. The wellfield contractor shall install geothermal locating (warning)tape 18 inches above all horizontal/header piping.

Prior to drilling or trenching, the wellfield contractor shall be responsible forreviewing with the general contractor the location of underground utilities. Existingutility lines uncovered during excavation shall be protected from damage duringexcavation and backfilling.

F. Pipe InstallationThe u-bend pipe ends will be sealed with fusion caps or tape prior to insertion intothe borehole. Reasonable care shall be taken to ensure that the geothermal wellfieldpipe is not crushed, kinked, or cut. Should any pipe be damaged, the damagedsection shall be cut out and the pipe reconnected by heat fusion.

The VHEs must be connected as indicated on the plans. The header designaccounts for balanced flow as well as flushing and purging flow rates. No variationscan be made in the circuit hookup or the pipe sizes that are indicated withoutapproval from the design engineer. The minimum bend radius for each pipe sizeshall be 25 times the nominal pipe diameter or the pipe manufacturer'srecommendations, whichever is greater. The depth of all headers and supply andreturn piping is indicated on the plans and must be maintained.

Circuits will be pressure tested before any backfilling of the header trenches isexecuted. The individual circuits will be pressure tested with water at 60 psi;however, not to exceed DR 11 pipe working pressure at bottom of the u-bend pipe.

G. Flushing/Purging and GlycolDuring installation, all debris shall be kept out of the pipe. Ends of the HDPE pipeshall be sealed until the pipe is joined to the circuits.

Flushing and Purging: Each supply and return circuit shall be flushed and purgedwith a water velocity of two feet per second. The lines shall be left filled with clean


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APPENDIX

water and then pressure tested. If connection to the manifold is not immediate,piping must be capped. The wellfield contractor must coordinate with the mechanicalcontractor on propylene glycol antifreeze installation. The mechanical contractor isresponsible for the interior pipings propylene glycol antifreeze. See MechanicalSpecifications for antifreeze specifics.

Glycol Charging: Follow all manufacturers instructions for product handling.

1. Circuits: Isolate and charge one circuit at a time. Close all main valves andall other circuits. Gradually introduce premixed propylene glycol solution,through the fill port, until a concentration of 25% is obtained. Repeatprocedure for each remaining circuit.

2. Mains: Close valves to all circuits, isolate and charge one pair of mains at atime. Open valves on primary supply/return mains in mechanical room. Openbypass valve in mechanical room or vault.

3. Allow untreated water to be displaced from the system as solution isintroduced. Handle discharged water according to manufacturersrecommendations, state and local regulations.

4. While charging, repeatedly check concentration at vault manifolds to minimizeproduct loss. Immediately discontinue introducing solution when testingconfirms a concentration of 25%.

SHOP DRAWINGS

Before geothermal wellfield construction begins, the wellfield contractor must submit shopdrawings to the design engineer. The shop drawings shall include all applicablemanufacturers specifications, warranties, and material safety data sheets for all materialsused in the geothermal installation. No substitutions will be allowed without authorizationfrom the design engineer.

Fundamentals of Commercial Geothermal Wellfield Design

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