fundamentals of commercial geothermal wellfield design€¦ · fundamentals of commercial...

APPENDIX

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 IN REGARD TO SUCH USE.

Fundamentals of Commercial Geothermal

Wellfield Design

Intended for general distribution to: Geothermal Wellfield Designers, Engineers & Architects

Distributed by: GHP Systems, Inc.

1000 N 32nd Ave Brookings, 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 wellfield products. Jeppesen has been involved in the geothermal industry

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

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

FUNDAMENTALS OF COMMERCIAL GEOTHERMAL WELLFIELD DESIGN 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 IN REGARD TO SUCH USE. 2010 GHP Systems, Inc.

1

INDEX

INTRODUCTION • Definition ............................................................................................. 2 GROUND CONDITIONS • Land Area Availability and Drilling 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 .......................................................................................... 8 • Header Design Using Multiple Circuits ............................................. 9 • Reverse Return ................................................................................... 9 • Reduced Header ................................................................................. 9 • Single Supply and Return Mains ..................................................... 10 • Multiple Supply and Return Mains .................................................. 10 • Manifolds ........................................................................................... 11 MATERIALS • Pipe .................................................................................................... 12 • Grout .................................................................................................. 12 • Antifreeze .......................................................................................... 12 APPENDIX • Mean Water Temperature Graph ..................................................... 13 • Flow Characteristics of HDPE Pipe ................................................. 14 • Example VHE Report ....................................................................... 17 • Example Formation Thermal Conductivity Analysis ..................... 18 • Detailed Drawings VHE Borehole Detail ........................................................................ 19 Geothermal Wellfield Layout ............................................................ 20 Vault Detail ...................................................................................... 21 • Example Geothermal Wellfield Specifications ............................... 22


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INTRODUCTION With the rapidly growing interest in commercial geothermal heat pump systems, the demand for qualified designers, engineers and architects who can successfully tackle these projects 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 poor system performance, excessive installation costs, and unnecessary liability. The intent of this design guide is to outline procedures and design techniques necessary to optimize the geothermal wellfield design. Definition A closed-loop geothermal wellfield exchanges energy with the earth by circulating a water or water/antifreeze solution through plastic pipe buried beneath the earth’s surface. A vertical closed-loop geothermal wellfield typically consists of multiple vertical heat exchangers (VHEs). VHEs are constructed by drilling holes generally ranging from 50 to 400 feet deep in the earth and then inserting two pipes with a fitting joining the two pipe ends at the bottom (called a u-bend pipe assembly). The remaining open annulus of the drilled borehole is then backfilled or grouted, thereby encasing 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 Conditions A geothermal system can usually be implemented by any heating/cooling application—providing that favorable conditions exist to do the geothermal wellfield installation. Available and suitable land 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 Btu/hr) of design load capacity. However, designing longer VHE depths and/or tighter VHE grid 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 the geothermal wellfield is installed, this land area can become a parking lot, park, football field or a variety of other applications.


3

Another significant factor in determining the feasibility of the wellfield is whether or not the drilling conditions are favorable. Drilling logs from wells drilled in the area can usually be obtained from the State and can provide the designer with general expectations of the subsoil formation. Additional information 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 Bore The primary unknown factor that changes from one geothermal wellfield project to the next is the VHE’s borehole composition. The borehole soil/rock composition plays a significant role in determining 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 test bore should be drilled on site to obtain accurate drilling conditions and to increase the design reliability 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 conductivity test can be performed as described in the following section. Drilling contractors will assume the worst drilling conditions in their bids if they are unfamiliar with 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. A detailed drilling log similar to the one below should be included with bid documents.

TEST BORE DRILLING LOG

DRILLING LOCATION GHP SYSTEMS, INC. 1000 N 32ND AVE. BROOKINGS, SD 57006

PERMIT NO NA CONTRACTOR JOHN JAMES DRILLING LICENSE XXXX1234

DEPTH IN FEET FROM TO DESCRIPTION

0 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 – ¾″ HDPE PIPE GROUT TYPE Thermally Enhanced 1:4 ratio bentonite: silica

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 200 feet, so the VHE’s specified design depth would typically not go beyond 200 feet. If there is an available land constraint, the designer may have to consider going deeper than 200 feet with the VHE depth.


4

Formation Thermal Conductivity Test A test bore provides the necessary information required by the installing contractor for drilling purposes. Although the design engineer is now aware of the formation makeup, he must refer to tables to determine the anticipated thermal conductivity range for each soil/rock type and interpolate an overall average formation thermal conductivity. At this point, there still remains a large degree of uncertainty, so designs tend to be overly conservative. To obtain a reasonably accurate value for the formation thermal conductivity a test measuring this value needs to be performed on a VHE at the project site. The drilling log test bore can now be used to test the formation thermal conductivity by installing a u-bend pipe assembly to the anticipated design depth and then grouting the remaining borehole 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 the water with respect to time is recorded. Based on the increase in water temperature with respect to time, the formations thermal conductivity can be calculated. The longer the duration of this heat dump test, the more accurate the results are—but the cost of conducting the longer test increases. This design guide suggests a minimum of 24 hours test duration. Industry standards tend to lean toward a 48-hour test duration producing more accurate results. The implementation of u-bend pipe separators and/or thermally enhanced bentonite grout will make shorter test durations more accurate. The graph below shows the recorded data from a 24-hour formation thermal conductivity test. The average water temperature data is plotted with respect to the natural log of time. Line source theory can 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 is strongly recommended that experienced personnel analyze the data and calculate the resulting thermal conductivity (see appendix page 20 for an example report).

020406080

100

-5.00 0.00 5.00

TEM

P (°

F)

LN TIME (HOURS)

FORMATION T.C. TEST

AVG WATER TEMP


5

VERTICAL HEAT EXCHANGER DESIGN LENGTH Determining the required total VHE length can prove to be the most challenging task in the geothermal wellfield design process. There are several wellfield design software programs that 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 need to have a fundamental understanding of various factors affecting VHE design lengths. Obviously, the building’s design loads, the ground’s soil/rock thermal conductivity and mean ground temperature play significant roles in determining design lengths (see Appendix page 13 for “Mean Ground Water Temperature Graph”). However, other influential factors 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 Sizing The most basic concept in understanding the geothermal wellfield loads involves not only the building loads themselves, but also the effect of which load–heating or cooling–is dominant; also to be considered are the efficiencies of the geothermal heat pumps used. The following example is provided to explain this concept of comparing two identical geothermal heat pumps, where one unit is heating and the other unit is cooling. These units are both operating at 300% efficiency; typically the 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 conditioned environment comes from two units of energy extracted from the wellfield and one unit of energy provided by the electricity required to run the compressor. Therefore, only two thirds of the building’s heating load is absorbed from the wellfield. Cooling: For the theological geothermal heat pump in cooling, every three units of energy that are removed from the conditioned environment are added to one unit of energy from the electricity required to run the compressor to be rejected into the wellfield. Therefore, not only is the entire building load rejected into the wellfield, but an additional 33% of that load in electrical input is also rejected into the wellfield. The purpose of the example is to demonstrate the influence of the building’s dominant load on the sizing of the wellfield. In theory, a building that requires only cooling could require twice the wellfield capacity as a building with the same size load that requires only heating. Likewise, a building with even larger loads—seasonally diversified in heating and cooling—may require a smaller wellfield capacity, then a building with smaller loads but highly cooling or 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 Equipment Geothermal 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 lower capacity wellfield in cooling, but a larger capacity wellfield in heating, compared to a lower efficiency heat 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 electrical energy 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 electrical energy into the heated environment, so more energy is absorbed from the wellfield to obtain the same capacity. A geothermal heat pump that has a high heating and low cooling efficiency will require a much larger wellfield capacity than a geothermal heat pump that will produce the same capacities, but has a low heating, high cooling efficiency. Geothermal Borehole Resistance The 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 borehole also significantly contribute to the VHE’s performance. A standard VHE installation has two pipes (that make up the u-bend pipe assembly) that are either touching or are in close proximity of each other, thus interfering with each other’s ability to exchange energy with the earth. These u-bend pipes are usually encased with a 20% solids bentonite grout (often required by State regulations) in order to seal the borehole to prevent contamination of water aquifers below ground. Although the bentonite grout mixture is excellent for sealing the borehole, it has poor heat transfer characteristics and acts as an insulator that restricts energy 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 borehole resistance, thereby significantly increasing the performance of a VHE and lowering the installation costs by shortening required VHE lengths. The two most significant breakthroughs in VHE design include thermally enhanced (T.E.) bentonite grouts and u-bend pipe separators. Currently, there are T.E. grouts that can increase the thermal conductivity of bentonite grout ranging from 0.4 Btu/hr-ft-°F up to as high as 1.4 Btu/hr-ft-°F. This guide suggests that a grout thermal conductivity of 0.90 Btu/hr-ft-°F to typically be the most cost effective for most design conditions. Most T.E. grouts add silica sand to the bentonite to increase its thermal conductivity while maintaining a low permeability rate of less than 1X10-7 cm/s. Also available are u-bend pipe separators (GeoClips®) that attach to the u-bend pipes positioning them against the borehole wall directly across from each other. Positioning the u-bend pipes against the borehole wall and separating them as far apart as possible, significantly lowers the insulating effect of the bentonite grout, increases the area of energy absorption/rejection and decreases energy exchange between the two pipes.


7

The diagram above illustrates how the energy flux of a VHE is affected by its configuration. The first configuration uses no performance enhancing technology; therefore, the borehole resistance greatly inhibits the exchange of energy of the circulating fluid and the earth. The energy flux increases significantly with the use of u-bend pipe separators in the second configuration. An even greater 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 balance between the added cost of increasing VHE performance and the savings incurred by shortening the total VHE length. Sensitivity Analysis The objective in sizing and designing a VHE is to obtain the required wellfield capacity for the lowest installation cost. The areas of control when designing a VHE include pipe placement, grout thermal conductivity, u-bend pipe size and VHE grid spacing. The following graphs show how each parameter influences the VHE design lengths. The graph to the right demonstrates the effects that grid spacing and u-bend pipe sizes have on VHE design lengths. This example is typical in that the design depth decreases dramatically as the VHE grid spacing approaches 10 feet and continues to decrease as grid spacing gets larger. In this example the VHE decrease isn’t significant enough to justify the extra cost of going beyond twenty-foot grid spacing. Typical designs find fifteen- to twenty-foot grid spacing optimum. However, warmer climates with cooling dominate loads and higher mean earth temperatures can justify grid spacing greater than twenty feet. This example also shows an increase in performance by using larger diameter u-bend pipes; but, this is usually outweighed by the additional cost of the larger pipe and increased volume of antifreeze required. U-bend pipe size should be determined by required flow as pertaining to head loss and/or turbulent flow (see VHE “Pipe Sizing” section for more detail).

200

250

300

350

400

450

5 10 15 20 25

VHE

DES

IGN

LEN

GTH

(fee

t)

VHE GRID SPACING (feet)

VHE U-BEND SIZING & VHE GRID SPACING COMPARISON (12,000 Btu/hr cooling)

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


8

The graph to the right demonstrates the effects of u-bend pipe placement within the borehole and grout thermal conductivity on VHE design lengths. As previously mentioned, lowering the borehole resistance significantly shortens the required VHE design length. By simply implementing a u-bend pipe separator, the design length in this example is decreased by 50 feet. This example also demonstrates how increasing the grout thermal conductivity correlates directly with the decrease in design lengths. However, as with VHE grid spacing in the example above, there is a point of diminishing returns. Higher thermal conductivity grouts are more expensive and labor intensive to mix and pump. In most instances, either a 0.90 Btu/hr-ft-°F thermally enhanced grout by itself or a combination u-bend pipe separator with a lower 0.57 Btu/hr-ft-°F thermal conductivity grout optimizes cost versus performance. SYSTEM PIPING DESIGN Pipe Sizing Excessive head loss of circulating fluid through the wellfield can account for a large portion of the entire geothermal heat pump system’s operating costs. This guide suggests keeping the entire wellfield head loss below 50 feet of head. This can typically be achieved by designing the entire wellfield 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 Number greater than 2,500 (transition) in all of the VHEs to attain the maximum heat transfer between the circulating fluid and the pipe during peak operation. For large wellfields that are designed around ground thermal buildup or depletion (usually a 10-year modeling period is used), turbulent flow plays less importance because the wellfield size is significantly increased to compensate for the long term thermal effects. If the circulating solution is pure water, turbulent flow is easily achieved because a flow rate of 2 GPM will be turbulent even in a 1¼" u-bend pipe. The flow must be much higher if the circulating fluid consists of a 25% propylene glycol/water solution and the solution temperature gets down in the 30°F range. Now to be in turbulent flow the u-bends minimum flow rate for ¾" requires 3½ GPM, 1" requires 4½ GPM and 1¼" requires 5½ GPM. The corresponding feet of head loss per 100' of pipe are 4.1' for ¾", 2.0' for 1" and 1.0' for 1¼". Typical designs use ¾" u-bends for flow rates up to 3½ GPM, 1" u-bends for flow rates between 3½ to 6½ GPM and 1¼" u-bends for flow rates between 6½ to 12 GPM. This information pertains to DR11 (160 psi) pipe.

140

160

180

200

220

240

260

VHE

DES

IGN

LEN

GTH

(fee

t)

GROUT THERMAL COND. (Btu/hr-ft-°F)

VHE DESIGN LENGTH VERSUS PIPE PLACEMENT & GROUT T.C.(12,000 Btu/hr Cooling / VHE)

Random Pipe Placement U-bend Pipe Separator


9

Header Design Using Multiple Circuits The wellfield header is used to connect all of the VHEs together. The planning of the header design plays an important factor on the performance, installation cost and reliability of the geothermal wellfield. A recommended design practice is to header the VHEs using multiple 2" or 3" circuit piping. This guide recommends having at least 4 circuits when possible so that if a leak would ever develop you could isolate that circuit and only lose 25% of your wellfield. This would allow the geothermal 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 greater control especially for isolation purposes. On larger wellfield projects 3" circuits usually provide the most 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 design would limit 2" (DR11) pipe to flow rates between 30 to 35 GPM and between 80 to 100 GPM for 3" (DR15.5) pipe. With these flow rates you would typically see designs with (8 to 14) - ¾", (6 to 8) - 1" or (3 to 6) - 1 ¼" VHEs being serviced on a single 2" circuit. A single 3" circuit would commonly have designs servicing (24 to 40) - ¾", (18 to 24) - 1" and (9 to 18) - 1 ¼" VHEs. Of course the number VHEs on a circuit can fall outside those listed above depending on the type of circulating solution and the required VHE flow rates (see Appendix page 14 for “Flow Characteristics of High Density Polyethylene (HDPE) Pipe”). Reverse Return Circuit To obtain balanced flow through all of the VHEs, each circuit header design should have a reverse return. As illustrated to the right, with a reverse return header, the first VHE hooked up on the supply line is the last VHE on the return line. This header technique will balance flow between the VHEs on this circuit, provided that all of the u-bend pipe lengths are approximately the same. Reduced Header Once the headering process is complete, the entire wellfield piping system needs to be flushed of all debris and purged of air. This process is performed by circulating water through all of the wellfield piping system at high flow rates. The industry’s accepted standard is to obtain a minimum velocity 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 required velocities needed to purge the VHEs (see Appendix page 14 for “Flow Characteristics of High Density Polyethylene (HDPE) Pipe”). This example uses ¾" HDPE DR11 pipe for the VHEs which

30 GPM

3 G

PM

3 G

PM

3 G

PM

3 G

PM

3 G

PM

3 G

PM

3 G

PM

3 G

PM

3 G

PM

3 G

PM


10

MULTIPLE SUPPLY & RETURN MAINS

TO BUILDINGU

requires 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 the necessary 2 feet per second velocity. If the main line does not reduce in size as it approaches the last VHEs hooked up in parallel to the main line, the flow rates will fall well below the required 2 feet per second velocity, thus allowing air and debris to remain in that portion of the header pipe. In this example, 13 VHEs need to be flushed and purged, at the same time requiring a total flow rate of about 48 GPM at 3.75 GPM through each VHE. The reduced header system shown will flush and purge all header piping as well as all the VHEs and not add excessive head pressure to the system under normal operation.

Single Supply & Return Mains The wellfield layout illustrated to the right shows all smaller header circuits connected to a single large main header that is brought into the building. Although there is nothing wrong with this type of header system from a balanced system flow standpoint, it is not the best option when considering liability. The primary concern is that if a leak would occur, the entire wellfield is in jeopardy of going down until the leak is repaired. Locating that leak could become a major ordeal because there is no individual circuit isolation to perform pressure checks. The entire wellfield also needs to be flushed and purged at the same time, which requires a very large pumping and filtering system. Multiple Supply & Return Mains This guide suggests using a wellfield header system that has multiple valved circuits that are either brought into the building or to a vault where they are connected to a manifold as illustrated to the right. The primary advantage of implementing this type of header system is that if a leak occurs, only a small percentage of the VHEs are taken out of service. A leaking circuit can be isolated by shutting off valves connecting that circuit to an accessible manifold. The task of locating a leak is also much easier by pressure testing and identifying which circuit needs to be repaired. Another advantage is that each circuit can be flushed and purged individually. Balancing valves can be used on this system to balance flow between circuits.

TO BUILDING

SINGLE SUPPLY & RETURN MAINS

NOT RECOMMENDED


11

Manifolds A typical manifold (interior manifold shown below) includes butterfly isolation valves, combination balancing/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 be individually flushed and purged and accessed by connecting to the fill port. The mains should also have 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 the mains can aid in quick system checks during startup as well as during normal operation (see appendix page 21 for “Vault Detail”).


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MATERIALS Pipe High density polyethylene (HDPE) pipe is the geothermal industry’s standard piping material. The specific pipe used is a PE3408 HDPE with a minimum cell classification of 345464C per ASTM D-3035. Typically, a DR11 (160 psi) rating is used for u-bends and header pipe diameters two inches and smaller; and a minimum of DR 15.5 (110 psi) is used for header pipe diameters greater than two inches. Pipe produced specifically for the geothermal industry generally carries a 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 no mechanical 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 pipe accommodates low-pressure losses. Grout Many 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 the borehole up in a continuous fashion will meet those requirements. The purpose of grouting with bentonite is to form a hydraulic seal which will prevent contamination of aquifers. The permeability rate of bentonite is approximately 1 x 10-9 centimeters per second; therefore, it is an excellent medium for sealing a borehole. Bentonite grout products are usually bagged in a dry powder or granular 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 thermal conductivity (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 Enhanced bentonite grouts add silica sand in with the bentonite/water slurry to increase its thermal conductivity 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 the thermal conductivity higher than 0.9 Btu/hr-ft-°F. Antifreeze An 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 & local regulations. Currently, there is no particular antifreeze product that meets all of the desired characteristics. For commercial geothermal heat pump systems, the most common antifreeze used is propylene glycol (usually with inhibitors) and in many states, it is the only antifreeze solution allowed in vertical wellfields. Propylene glycol is non-corrosive, non-toxic, possesses low flammability and moderate heat transfer characteristics and meets State regulations. On the negative 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 dilution of the product’s inhibitors and to avoid the promotion of organic growth. It is also not recommended to exceed 30% propylene glycol by volume, because it may lower the performance of the geothermal heat pumps. At 25% propylene glycol by volume, a water/antifreeze circulating solution is freeze protected down to around 15 °F. At this same concentration, propylene glycol at low temperatures will increase the head loss of the circulating solution by approximately 36% over straight water.

APPENDIX

EXAMPLE GEOTHERMAL WELLFIELD SPECIFICATIONS—Closed Circuit Heat Exchanger (VHE) 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 IN REGARD TO SUCH USE. 2010 GHP Systems, Inc.

13

MEAN WATER TEMPERATURE GRAPH

APPENDIX

EXAMPLE GEOTHERMAL WELLFIELD SPECIFICATIONS—Closed Circuit Heat Exchanger (VHE) 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 IN REGARD TO SUCH USE. 2010 GHP Systems, Inc. 14

FLOW CHARACTERISTICS OF WATER IN HDPE PIPE (PE345464C) Pipe Size: ¾" 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

GPM

Velocity (ft/sec)

Head Loss (ft/100ft)

GPM

Velocity (ft/sec)


0.75 0.41 0.13 0.50 0.18 0.04 1.00 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 3.57 4.75 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

GPM

Velocity (ft/sec)


GPM

Velocity (ft/sec)


4.00 0.89 0.39 7.00 1.18 0.54 4.50 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 4.06 13.00 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

APPENDIX


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

GPM

Velocity (ft/sec)


GPM

Velocity (ft/sec)


10.00 1.08 0.31 40.00 1.76 0.43 11.50 1.24 0.40 45.00 1.98 0.54 13.00 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 3.62 40.00 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

GPM

Velocity (ft/sec)


GPM

Velocity (ft/sec)


53.00 1.41 0.21 200.00 2.45 0.37 58.50 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 2.06 152.00 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

APPENDIX


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

GPM

Velocity (ft/sec)


GPM

Velocity (ft/sec)


300.00 2.17 0.21 550.00 2.56 0.22 320.00 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 1.13 660.00 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

APPENDIX


EXAMPLE VERTICAL HEAT EXCHANGER REPORT

APPENDIX


FORMATION T.C. TEST

0

20

40

60

80

0 10 20 30

TIME (HOURS)

TEM

P (°

F)AVG WATER TEMP

FORMATION T.C. TEST

y = 3.1385x + 66.348

5060708090

100

0.00 2.00 4.00

LN TIME (HOURS)

TEM

P (°F

) AVG WATERTEMPLinear (AVGWATER TEMP)

.

EXAMPLE FORMATION THERMAL CONDUCTIVITY ANALYSIS Project: Washington School 1000 32nd Ave Brookings, SD 57006

Test Date: 01/01/03 – 01/02/03 Test Conducted By: ACME Drilling, Inc. Test Analyzed By: GHP Systems, Inc. Drilling Log: 0 - 3' TOP SOIL 3 - 10' SAND/GRAVEL 10 - 191' CLAY 191 - 200' GRAY SHALE Vertical Heat Exchanger: VHE Type 2 pipe U-bend depth 200' U-bend pipe size 3/4" Borehole diameter 5" Grout ( Bentonite) 20% solids U-bend pipe separator 10’ spacing

In-situ Testing/Analysis: Circulating Fluid Water Average input volts 215.71 Average input amps 12.86 Average power (watts) 2,774 Test duration 24 hours Time period analyzed 12 - 24 hours

20.1)1385.3(4

34.474

.. ===ππm

QCT

where: Q = Power input (Btu/hr) per liner foot of VHE m = slope of the regression line Calculated Thermal Conductivity: 1.20 Btu/hr-ft-°F

APPENDIX


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 RADIUS OF 25 TIMES THE PIPE DIAMETER

TRACER WIRE(ALONG ENTIRE LENGTH OF HEADER PIPING)

SAND BACKFILL

FINAL GRADE

EARTH BACKFILL(COMPACT AS SPECIFIED)

18"

FOILED BACK WARNING TAPE(ALONG ENTIRE LENGTH OF HEADER PIPING)

18"

6'

10' TYP200'

PREMANUFACTURED U-BEND

U-BEND PIPE SEPARATORGEOCLIP AS MANUFACTURED BY GBT, INC.

3/4" HDPE PIPE DR11PE3408 CC 345464C

MAINTAIN MINIMUM PIPE BENDING RADIUS OF 25 TIMES THE PIPE DIAMETER

EARTH BACKFILL(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 LENGTH OF HEADER PIPING)

FOILED BACK WARNING TAPE(ALONG ENTIRE LENGTH OF HEADER PIPING)

APPENDIX


EXAMPLE GEOTHERMAL WELLFIELD LAYOUT

APPENDIX


Little Giant Sump Model 6 CIA-RFSW/ 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 AndOutlet 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 PitW/ 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 ofCircuits

Typ. of 20

EXAMPLE VAULT DETAIL

APPENDIX


EXAMPLE GEOTHERMAL WELLFIELD SPECIFICATIONS Closed Circuit Vertical Heat Exchanger (VHE)

DESCRIPTION OF WORK A. This design has been prepared in accordance with the materials standards and

accepted installation practices of the International Ground Source Heat Pump Association (IGSHPA). The wellfield contractor shall comply with these standards and practices along with all State and local regulations pertaining to the installation.

B. The wellfield contractor is responsible for all aspects involved with the complete

geothermal wellfield installation. All materials, drilling, water supply, excavation, hauling of backfill, dewatering, building penetration, manifold/vault installation, leak testing, 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 wellfield

contractor that the location of any existing utilities are exactly as indicated on the plans. Some areas may require hand digging to locate that utility. The wellfield contractor 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 of this project. Any offsets required to route over or under existing lines shall also be included 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 years experience in performing underground closed circuit VHE work of this project’s size or larger.

B. VHE fabricators must be heat fusion certified by an authorized high density

polyethylene (HDPE) pipe manufacturer’s representative of the brand of pipe used. Certification must include: successful completion of a written heat fusion exam as well as demonstrating proper heat fusion techniques under the direct supervision of the authorized HDPE pipe manufacturer’s representative.

APPENDIX


PRODUCTS A. Pipe

The 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 inch in 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 number and date of manufacture. The VHE will have a factory fused u-bend with pipe lengths long enough to reach grade from the bottom of the bore so no field fusions are required below the header pit. Approved pipe manufacturer is Performance Pipe.

B. Fittings

Pipe 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 with the manufacturer's name, nominal size, pressure rating, relevant ASTM standards and date of manufacturer. Saddle fusion is not allowed except when performed by a manufacturer normally engaged in that type of work. No field installed saddle fittings are allowed. Approved fabrication manufacturer is GHP Systems, Inc. and approved fitting manufacturers are Performance Pipe, Central Plastics and Viega.

C. Manufactured Infield Extended Headers The header sections shall be factory assembled with all branches ready for

connection to the u-bend pipe ends. The infield extended headers used to connect the 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 is palletized. All 3" and larger header pipe sections will be shipped in long straight sections which are typically between 40' to 50' in length. All packaging shall be as necessary to minimize damage in transit/handling and facilitate ease in unloading and storage. The infield extended headers shall be GeoHeaders® as manufactured by GHP Systems, Inc. and will be manufactured with the same pipe and fitting specifications as listed in those sections.

D. Interior Manifold (Use in place of Vault) The interior manifold shall be constructed as shown on project drawings.

The manifold shall be the GeoManifold® as manufactured by GHP Systems, Inc. and will be manufactured with the following specifications.

High density polyethylene (HDPE) pipe and fittings, joined together with heat fusion,

APPENDIX

24

shall be used for all circuit and main header piping. All HDPE pipe and heat-fused materials shall be manufactured from high-density, high molecular weight PE 3408 polyethylene compound that meets or exceeds ASTM D 3350 cell classification 345464C, and is listed by the Plastic Pipe Institute in PPI TR-4 with HDB ratings of 1600 psi (11.04 MPa) at 73°F (23°C) and 800 psi (5.52 MPa) at 140°F (60°C). 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 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 will have a fixed port venture orifice, have blow-out proof stem, flow measurement function independent of ball position, install in any position, and serve as a service shutoff 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 with blow out proof stem, 600 psi non-shock cold WOG. Pressure/temperature ports shall be brass and have a dual seal core of Nordel, good up to 350°F for water and shall be rated zero leakage from vacuum to 1000 psig. Plug shall be capable of receiving a 1/8" pressure or temperature probe. A stainless steel pressure gauge with ¼" isolation valve will be included on both supply and return mains. The pressure gauge will be Sisco brand with 4 ½" dial size and read 0 – 100 psig. A stainless steel bimetal thermometer will be included on both supply and return mains. The pressure gauge will be Ashcroft brand with 3" dial size with 4" stem and reads 0 – 250°F. The manifold will be leak proof checked at factory with 100 psi pressure for a period 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 shown

on project drawings. The vault shall be shipped from factory pre-formed for a concrete pour with all reinforcement rods, manifolds, valves and piping secured in place. The vault weight by itself will overcome all buoyancy forces without any additional anchoring. The vault will come traffic load ready without any additional manhole rings, covers, bracing, or concrete pours. The approved vault is the GeoVault® as manufactured by GHP Systems, Inc. and will be manufactured with the following specifications:

Structure: The interior shell shall consist of a heavy-duty steel frame and base

where all joints have a continuous weld. The base frame and cross bracing shall be constructed of 1/4" – 3" x 8" square steel tubing. The base cross bracing shall be spaced a maximum of 2 feet on center with ¼" – 3" x 8" square steel tubing. The sidewall and ceiling frames and all cross bracing shall be constructed of ¼" – 3" x 3" angle iron. Sidewall and ceiling cross bracing shall be spaced a maximum of 2 feet on center. The steel interior walls/ceiling, stainless steel floor and stainless steel sump pump pit shall be constructed of 12-gauge sheet that are specially treated with an epoxy coating on interior side. All interior sheet steel shall have a continuous weld 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 #6

APPENDIX

25

reinforcement rods shall be placed on a 12" x 12" grid spacing for the ceiling. All 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 side and welded to steel framing every 2 feet or less. The outer shell of the walls and ceiling 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 ¼" sheet steel with a 3" flange that is anchored into ceiling concrete and welded to ceiling frame; all manhole welds being continuous. The manhole cover shall be constructed of ¼" steel tread plate with framing constructed of ¼" – 3" x 3" angle iron. The manifold stand’s support channel shall run continuous between circuits and be constructed of ¼" – 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 with

heat fusion, shall be used for all circuit and main header piping. All HDPE pipe and heat fused materials shall be manufactured from high-density, high molecular weight PE 3408 polyethylene compound that meets or exceeds ASTM D 3350 cell classification 345464C, and is listed by the Plastic Pipe Institute in PPI TR-4 with HDB ratings of 1600 psi (11.04 MPa) at 73°F (23°C) and 800 psi (5.52 MPa) at 140°F (60°C). 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 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 will have a fixed port venture orifice, have blow-out proof stem, flow measurement function independent of ball position, install in any position, and serve as a service shutoff 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 with blow out proof stem, 600 psi non-shock cold WOG. Pressure/temperature ports shall be brass and have a dual seal core of Nordel, good up to 350°F for water and shall be rated zero leakage from vacuum to 1000 psig. Plug shall be capable of receiving a 1/8" pressure or temperature probe. A stainless steel pressure gauge with ¼" isolation valve will be included on both supply and return mains. The pressure gauge will be Sisco brand with 4 ½" dial size and read 0 – 100 psig. A stainless steel bimetal thermometer will be included on both supply and return mains. The pressure gauge will be Ashcroft brand with 3" dial size with 4" stem and reads 0 – 250°F. The manifold will be leak proof checked at factory with 100 psi pressure for a period of 24 hours or more.

Keyed Entry: The manhole cover of the vault will be fastened with four stainless

steel pentagon head bolts requiring a special socket key for removal. These bolts will be counter sunk a minimum of 1" in a circular hole just large enough to accommodate 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® – EPDM

modular hydrostatic seal to water proof and anchor the pipe. This seal will be removable to allow replacement of the HDPE pipe should it ever be damaged at the

APPENDIX

26

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

Sump Pump: A Little Giant series 6 with mercury switch will be supplied with the

vault. 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 and produce high velocity air movement. The blower will be Aloha model 39008 rated for 60Hz, 120V - 1.4A. The blower will produce 1,580 CFM open and 1,200 CFM connected to 20 feet of 8" industrial grade flexible ducting. The blower will be ceiling mounted at the opposite end of the manhole within the vault. The 8" flexible duct will be run from the blower up to the top of the manhole entry. The blower will be switched 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 with

GFCI breaker. The vault shall have all required electrical conduit and boxes ceiling mounted with 1" conduit exiting the vault. All outlets, light fixture(s), switch and weatherproof covers will be included with the vault. The vault is to be field wired by a licensed 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

APPENDIX

27

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 vault’s 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 design calculations 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 a minimum of 63% solids. This grout will also have a permeability rate of less than 1X10-7cm/sec. The silica sand used will have a 4030 mesh or finer. The minimum grout thermal conductivity is 0.90 Btu/hr-ft-°F (50lb bentonite/200lb silica sand). Approved grout manufacturers are Wyo-Ben Inc. (THERM-EX) and Baroid (Barotherm Gold).

APPENDIX

28

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 borehole wall directly across from one another shall be the GeoClips® brand manufactured by GBT, Inc. These separators will be positioned every ten feet on the u-bend pipe.

H. Warning Tape

Warning tape used must be foil backed, two inches wide or greater with a continuous message printed every 36 inches or less reading: "CAUTION GEOTHERMAL PIPE BURIED BELOW". The tape shall be highly resistant to alkalis, acids and other destructive agents found in the ground.

EXECUTION A. Drilling

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

B. U-Bend Pipe Assembly The u-bend pipe shall be filled with water and pressurized to 100 psi to check for leaks before insertion. If necessary, an iron (sinker) bar can be attached at the base of each u-bend to overcome buoyancy. This iron bar will have all sharp edges adequately taped to avoid scarring and/or cutting of the polyethylene pipe. No driving rod that is pulled out after u-bend insertion will be allowed. The entire assembly is inserted to the specified depth in the borehole.

C. Grouting Procedures

The VHE is to be grouted from the bottom on up in a continuous fashion using a one inch or larger HDPE tremie pipe. The tremie pipe will be pulled out during the grouting procedure maintaining the pipe’s end just below grout level within the borehole. All State regulations will be met for borehole grouting of the VHE.

D. Heat Fusion Pipe Joining

All 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 heat fusion specifications. The operator shall be heat fusion certified and experienced in executing quality fusion joints.

APPENDIX

29

E. Excavation and Backfilling for Piping

The wellfield contractor shall do all excavating, backfilling, shoring, bailing and pumping for the installation of their work and perform necessary grading to prevent surface 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 kept sealed and lines left clean and unobstructed during construction. Only material suitable for backfilling shall be piled a sufficient distance from banks of trenches to avoid overloading. Unsuitable backfill material shall be removed as directed by the design engineer. Sheathing and shoring shall be done as necessary for protection of work and personnel safety. Unless otherwise indicated, excavation shall be open cut except for 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 for reviewing with the general contractor the location of underground utilities. Existing utility lines uncovered during excavation shall be protected from damage during excavation and backfilling.

F. Pipe Installation

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

The VHEs must be connected as indicated on the plans. The header design accounts for balanced flow as well as flushing and purging flow rates. No variations can be made in the circuit hookup or the pipe sizes that are indicated without approval from the design engineer. The minimum bend radius for each pipe size shall be 25 times the nominal pipe diameter or the pipe manufacturer's recommendations, whichever is greater. The depth of all headers and supply and return piping is indicated on the plans and must be maintained.

Circuits will be pressure tested before any backfilling of the header trenches is executed. The individual circuits will be pressure tested with water at 60 psi; however, not to exceed DR11 pipe working pressure at bottom of the u-bend pipe.

G. Flushing/Purging and Glycol During installation, all debris shall be kept out of the pipe. Ends of the HDPE pipe

shall be sealed until the pipe is joined to the circuits. Flushing and Purging: Each supply and return circuit shall be flushed and purged

with a water velocity of two feet per second. The lines shall be left filled with clean

APPENDIX

30

water and then pressure tested. If connection to the manifold is not immediate, piping must be capped. The wellfield contractor must coordinate with the mechanical contractor on propylene glycol antifreeze installation. The mechanical contractor is responsible for the interior piping’s propylene glycol antifreeze. See Mechanical Specifications 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 and

all other circuits. Gradually introduce premixed propylene glycol solution, through the fill port, until a concentration of 25% is obtained. Repeat procedure for each remaining circuit.

2. Mains: Close valves to all circuits, isolate and charge one pair of mains at a

time. Open valves on primary supply/return mains in mechanical room. Open bypass valve in mechanical room or vault.

3. Allow untreated water to be displaced from the system as solution is

introduced. Handle discharged water according to manufacturer’s recommendations, state and local regulations.

4. While charging, repeatedly check concentration at vault manifolds to minimize

product loss. Immediately discontinue introducing solution when testing confirms a concentration of 25%.

SHOP DRAWINGS Before geothermal wellfield construction begins, the wellfield contractor must submit shop drawings to the design engineer. The shop drawings shall include all applicable manufacturer’s specifications, warranties, and material safety data sheets for all materials used in the geothermal installation. No substitutions will be allowed without authorization from the design engineer.

fundamentals of commercial geothermal wellfield design€¦ · fundamentals of commercial...

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