Geothermal Design - Ground Loop Design GLD2010 Software

7/24/2019 Geothermal Design - Ground Loop Design GLD2010 Software

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GLD2010 -Loopfield & Piping Workshop Week 2 - Slide 1.1 - 1

22 2010 2010

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The objective of this workshop is to provide the geothermal designer with an in-

depth look at designing practical and purgeable piping system designs

using the industry leading Ground Loop Design GLD2010 Software Suite.

You are encouraged to interact with your instructor. We are seeking to provide

the geothermal professional with the tools and familiarity that he/she needs

to optimize a wide range of GSHP systems.

By extending the user's mastery of the GLD program, it is possible to eliminate

the design and field guesswork that has often been used to connect

loopfields to the load systems. Designers will quickly discover that thedrudgery of hand calculations can be eliminated and replaced by a much

more accurate and practical tool that designs piping systems which can beeffectively purged and can be built with pipe sizes and types that are

appropriate to your operations.


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What is the CFD Module?

The computational fluid dynamics (CFD) module enables designersto easily design, build, simulate and optimize the piping systems

that comprise the foundation of ground heat exchanger systems.

Why does one want to optimize a piping system?To ensure that the system can be purged and to ensure that the

system provides effective heat transfer with minimal circulationpump costs.

Cant I do this by hand?Not really. Modeling reverse return systems is very complex and

impossible to do with any accuracy by hand or even with aspreadsheet. Plus, it takes hours to make modifications and redo

calculations. With the CFD Module, it takes a few seconds.


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What can the CFD Module model do?The CFD module can model piping systems that consist of a wide

possible range of connected components including :Manifolds/Vaults, Supply and Return Runouts, Supply and Return

Headers, single and double u-bends, the fittings that connect thesystems together and circulation pumps.

How does it do this?Utilizing a new, patent-pending visual interface for viewing and

creating a design via a drag and drop methodology, the CFDmodule can automatically design optimal flow-balanced (direct and

reverse return) systems while providing designers with the flexibilitythey need for standard and non-standard systems.


What results do I get out of the Module?Outputs include flow rates, fluid velocities, Reynold's numbers,

pressure drop, fluid volume and the like for every single point in adynamic geothermal piping system.


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GLD2010 - Loopfield & Piping Workshop Week 2 - Slide 1.1 -10

We want to design geothermal heat exchangers that are easily purged

and perform well.

We want a system that is easily purged so that we can get all the air

bubbles out and ensure stable performance.

We want a system that performs well so that the circulation pumps donot consume unnecessary energy.

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A sample system:

22,000kWh cooling5,000 kWh heating

Well Designed piping system:12 x 2 borefield10 ft. hd @ 45gpm~ 0.5 hp pump with 85% efficiency = 3,504 kWhPump penalty = 11%

Poorly Designed System:12 x 2 borefield34 ft. hd @ 45 gpm

~ 1 hp pump with 85% efficiency = 7,884 kWhPump penalty = 22%

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To achieve the goal of designing an easy-to-purge and high performance system we needto look at and understand these parameters in our designs:

FlowRate (gpm) Velocity(ft/s) Reynolds Numbers PressureDrop (ft. head)

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We use the following equations:

1) Darcy-Weisbach (calculates pressure drop from friction factor, pipeparameters, fluid density and fluid velocity)

2) Reynolds Number (calculates Reynolds Number from density, velocity, pipeparameters and viscosity)

3) A range of equivalent resistance calculations for determining pressuredrops across network nodes.

4) The Hazen-Williams equation is not used (due to very limited applicability)

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Standardized Nomenclature is critical to clear communication.


U-Tube: An assembly of two lengths of HDPE pipe connected on one end with a molded, purpose built U-bend.

GHX: Refers to a ground heat exchanger, and may include vertical, horizontal trenching, horizontal boring,pond or lake heat exchanger buried in the ground or submerged in a body of water.


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GHX Circuits: HDPE pipe buried in the ground i n horizontal or vertical orientation designed to transfer energyto and from the ground. Typically a number of GHX Circuits are fusion welded to a GHX Header that is in turnfusion welded to a Supply-Return Runout. Heat transfer fluid is circulated through the assembly to a building.

GHX Header: Connection points between Supply-Return Runout piping and GHX Circuits. GHX Headers areburied in the ground adjacent to the GHX Field and are comprised of an assembly of fusion welded fittingsand pipe. Fittings and pipe are manufactured using HDPE resin and are connected using heat fusion (butt

fusion, socket fusion or electro-fusion). Most GHX Headers are Reducing Headers


GHX Module Supply-Return Runout : Supply-Return Runout refers to the high-density polyethylene (HDPE)piping installed to connect the GHX Circuit piping to the Pump House header. The Supply-Return Runout has

both a supply pipe and a return pipe.


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GHX Module: Completed assembly of GHX components, i ncluding GHX Supply and Return Runouts, GHXheader and GHX Circuits.


GHX Field: Assembly of all GHX Modules connected to a single building or group of buildings via GHXManifold(s)/Vault(s).


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Note: Direct Return (DR) systems uncommon but useful for illustrative purposes


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This RR GHX Module is know as the horseshoe. It can offer lower pressure

drops compared to standard RR GHX Modules (i.e. 8.3 vs 10.3 ft head) . Doyou know why?


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You want to have a piping system that you can purge with available purge pumps.

A 2 ft/sec fluid velocity throughout entire system is required to purge air effectively.

Systems are purged with water and all calculations must be done with water.


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: : You want to have a piping system that you can purge with available purge pumps.




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48.27 GPM and 18.4 ft. hd:


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: : 48.27 GPM and 18.4 ft. hd:

Clearly, we need a higher flow rate to purge the GHX Header Sections on this GHX Module.


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Based on this configuration, to achieve 2 ft/s flow rates across the headering system requires:

158 GPM and 331 ft. hd

This clearly is unreasonable and justifies the use of a reducing headering system


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: : Reducing headering systems will enable purging velocities throughout a system while maintainingreasonable flow rates and pressure drops.


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Reducing headering systems enable purging velocities throughout a system while maintaining reasonable

flow rates and pressure drops.

51.75 GPM and 46.7 ft. hd


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: : Other Reducing Header Options:

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2

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2/2 5.60 / 2/2 5.79 / 2/2 8.63

1 2/2 4.79 / 2/2 4.96 / 2/2 7.41

2 2/2 4.03 / 2/2 4.18 / 2/2 6.25

3 2/2 3.30 / 2/2 3.43 / 2/2 5.14

4 2/2 2.60 / 2/2 2.71 / 2/2 4.07

5 1 /1 2.98 / 2/2 2.00 / 2/2 3.03

6 1 /1 2.55 / 1 /1 2.68 / 2/2 2.00

7 1/1 2.00 / 1/1 2.10 / 1/1 3.21

51.75 53.5 79.8

46.7 . 49.1 . 99 .


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Flow Balance and Reynolds Numbers

Flow balance is very important to ensure that all of the GHX circuits transfer an equal # of BTUS to and fromthe ground. Unbalanced systems perform poorly.

This DR system has GHX Circuit flow rates that decrease from 3.88 gpm to 2.95 gpm, a nearly 21%

imbalance, across the entire GHX Module.

Note: Propylene Glycol with freeze protection down to 20F, 27 gpm, 17.5 ft hd.


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: : Balanced Flow and Reynolds Numbers

Reynolds indicate flow type (turbulent, laminar, etc). Turbulent flow is optimal for efficient heat transfer.

This direct return system has GHX circuit flow Reynolds numbers that drop as the distance from thesupply-return runout to GHX circuit increases. In this example, the Reynolds numbers drop from3,845 to 2,944: again, a ~20% drop.

What about compact headering systems?Do reverse return systems perform better?


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: : You want to have a piping system that you can purge with available purge pumps.




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45.32 GPM and 6.6 ft. hd :

The GHX circuits are being purged but the headering is not.


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: : Based on this configuration, to achieve 2 ft/s flow rates across the headering system requires:

146 GPM and 345 ft. hd.

This clearly is unreasonable and justifies the use of a reducing headering system .


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Reducing headering systems enable purging velocities throughout a system while maintainingreasonable flow rates and pressure drops.


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: : Reducing headering systems enable purging velocities throughout a system while maintainingreasonable flow rates and pressure drops.

46.7 GPM and 46.2 ft. hd.


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Other Reducing Header Options:

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2/2 5.05 /5.05 2/2 2.34/2.34 2/2 2.69/2.69

1 2/1 4.44/2.00 2/1 2.06/2.00 2/1 2.37/2.29

2 2/1 3.81/2.54 2/1 3.84/2.56 2/2 2.03/2.93

3 2/1 3.17/2.94 2/2 3.20/2.96 2/2 3.67/2.18

4 2/2 2.53/2.53 2/2 2.55/2.55 2/2 2.92/2.92

5 1 /2 2.94/3.17 2/2 2.96/3.20 2/2 2.18/3.67

6 1 /2 2.54/3.81 1 /2 2.56/3.84 2/2 2.93/2.037 1/2 2.00/4.44 1/2 2.00/2.06 1/2 2.29/2.37

46.7 49.5 71.9

37.6 . . 42.5 . 84 . .


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: : Flow Balance and Reynolds Numbers

Flow balance is important to ensure that all of the GHX circuits exchange an equal # of BTUS with the

ground. Unbalanced systems perform poorly.

This RR system has GHX circuit fl ow rates that range from 3.31 gpm to 3.41 gpm, a less than 5% imbalanceacross the entire GHX Module. Note: Propylene Glycol with freeze protection down to 20F, 27 gpm, 20.2 ft hd.


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Balanced Flow and Reynolds Numbers

Reynolds indicate flow type (turbulent, laminar, etc). Turbulent flow is optimal for efficient heat transfer.

This RR system has GHX circuit fl ow Reynolds Numbers drop from 3,404 to 3,305, a 5% drop.


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: : Design:

Direct Return Systems are mirror images on the supply and return lines

Reverse Return Systems are palindromes on the supply and return lines

Performance:

Reverse return systems provide more balanced flow, more balanced heat transfer and are thereforesuperior. For this reason they are considered to be the gold standard design methodology.


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1) GHX Circuit Lengths

2) Number of Circuits in a GHX Module

3) Pressure Drop Maximums4) Supply Return Pipe Size Selection


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: : GHX Circuit Length and Pipe Si ze Selection: Pressure Drop Considerations

Conclusion: Choose the right pipe size for the circuit length

3/4 500 14.6

1 500 4.8

1 1/4 500 1.4

1 1/2 500 0.6

3/4 500 15.1

1 500 5.0

1 1/4 500 1.8

1 1/2 500 1.0


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GHX Circuit Length and Pipe Size Selection

General Guideline:

200

250

300 1

350 11

400 1

500 + 1


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(B) : (B) : GHX Circuit Length: Circuits of Different Length in a Single DR GHX Module

Conclusion: DR Module imbalance exacerbated by 7%. Therefore dont do it unless


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GHX Circuit Length: Circuits of Different Length in a Single DR GHX Module

Partially mitigate problem by having two GHX circuits in series (two bores per circuit for example)


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(B) : (B) : GHX Circuit Length: Circuits of Different Length in a Single DR GHX Module

Partially mitigate problem by having two GHX circuits in series (two bores per circuit for example)


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Reducing Circuit Designs: An interesting experiment

Circuits of different and reducing depths in a single DR module can lead to more balanced flow


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(B) : (B) : GHX Circuit Length: Circuits of Different Length in a Single RR GHX Module

Conclusion: RR Systems are integrated systems that are systemically very sensitive to changes.Therefore, all GHX circuits should be the same length.


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The number of GHX Circuits on a GHX Module: Flow Balancing Considerations

8 GHX circuits per GHX module: 15-25% imbalance 20 GHX circuits per GHX module: 40-60% imbalance

24 GHX circuits per GHX module: 50-80% imbalanceConclusion: Dont use a large number of GHX Circuits on a DR GHX Module


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: : The number of GHX Circuits on a GHX Module: Flow Balancing Consideration

80 gpm

Conclusion: RR systems of all sizes are inherently balanced GHX modules. The maximum number of GHXcircuits normally will be determined by supply-return runout size limits and pressure drop concerns for

purging and operations.


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If pressure drop in a GHX Module is greater than around 30 ft. hd under normal operation, the designer should:

A) Reduce the number of GHX circuits in the GHX Module

B) Increase the pipe size for the supply/return runoutC) Consider using a geothermal vault to reduce the length of the Supply-Return Runout

D) Increase the GHX circuit pipe diameter

Lets explore these designsoptions via this example:


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: : Reduce the number of GHX circuits in the GHX Module:

First look at 16 GHX Circuits per GHX Module (Propylene Glycol, 20F freeze protection)Pressure drop is 56 ft. hd = too high

Reduce the number of circuits to 11 per GHX module


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Reduce the number of GHX circuits in the GHX Module:

With 11GHX Circuits per GHX Module (Propylene Glycol, 20F freeze protection)Pressure drop is 30.7 ft. hd = ok

Aim for 28 GHX Modules with 11 GHX Circuits and 1 GHX Module with 12 GHX Circuits for 320 Circuits


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: : If pressure drop in a GHX Module is greater than around 30 ft. hd under normal operation, the designer should:

A) Reduce the number of GHX circuits in the GHX ModuleB) Increase the pipe size for the supply/return runout

C) Consider using a geothermal vault to reduce the length of the Supply-Return RunoutD) Increase the GHX circuit pipe diameter



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Increase the pipe size for the supply return runout

First look at 16 GHX Circuits per GHX Module with 2 Supply-Return Runouts

Pressure drop is 56 ft. hd = too high


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: : Increase the pipe size of the supply return runout to 3

With 16GHX Circuits per GHX Module with 3 runouts: Pressure drop is 15.8 ft. hd = ok

Aim for 20 GHX Modules with 16 GHX Circuits for a total of 320 Circuits


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: : Assume the GHX Modules are 700ft/1000ft from the building

First look at 16 GHX Circuits per GHX Module with 3 RunoutsPressure drop is 35.2 ft. hd = high

Consider using a vault because going up to 4 Supply Return runouts can be difficult


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Use a vault that connects to a building via 500 ft 4 pipe

With 16GHX Circuits per GHX Module with 3 runouts

Pressure drop is 20.3 ft. hd = ok

Aim for 20 16 Circuit GHX Modules coming off of the vault


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: : Use a vault that connects to a building via 500 ft 4 pipe


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: : Increase the GHX circuit pipe diameter


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In summary, if the pressure drop in a GHX Module is greater than around 30 ft. hd under normaloperation, the design should:

A)Reduce the number of GHX circuits in the GHX Module

B)Increase the pipe size for the supply/return runout

C)Consider using a geothermal vault to reduce the length of the Supply-Return Runout

D)Consider increasing the GHX circuit pipe diameter


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: : Supply Return Runout Pipe Size Selection: Head Loss and Flow Rates

Remember to not spec anything greater than 4 on the supply/return pipe size because anything biggeris very difficult to install in the field. Even 4 are hard to handle and require butt fusion.

Selection of a Supply Return Runout pipe size is based on:

The number of GHX circuits on the headering system: more GHX circuits = larger diameter runoutsPurging flow rate and pressure drop goals (remember you need to optimize for purging first! )The performance of the loopfield (flow rates, velocities, circulation pump costs, etc)


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Two Inch vs Three Inch Supply Return Runouts

200 ft Supply/Return runouts14 GHX Circuits

50 ft Supply/Return runouts14 GHX Circuits

Conclusion: Larger diameter pipe = smaller purge pumps and lower cost performance

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31.3 . 10.3 .

13.1 . . 4.2 .

# 5,700 5,700

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13.3 . 9.4 .

5.9 . . 3.9 .

# 5,800 5,900


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0.75 814 1420

1.00 610 1015

1.25 46 610


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Basics:

Two Key Components: the GHX Circuit and the Pipe Pair


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The GHX CircuitThe GHX Circuit

An individual GHX Circuit consists of the following fivesubcomponents:

Af - Fitting for attachment to parent header pipe (optional)A - Supply side pipeAfu - End fitting that connects Pipe A and Pipe A' (optional)A' - Return side pipe (usually length A = length A')A'f - Fitting for attachment to child header pipe (optional)

Definable features for each subcomponent: Fitting type (socket tee branch, butt tee branch, etc.) Fitting pipe size Fitting equivalent length Fitting name Fitting volume Pipe size, type, inner & outer diameter Pipe length, Extra pipe length Pipe name, volume


The Pipe PairThe Pipe Pair

An individual Pipe Pair consists of the following four subcomponents:

Af - Supply side fitting (generally before the supply side pipe)A - Supply side pipeA' - Return side pipeA'f - Return side fitting (generally after the return side pipe)

Definable features for each subcomponent: Fitting type (socket tee branch, butt tee branch, etc.) Fitting pipe size Fitting equivalent length Fitting name Fitting volume Pipe size, type, inner & outer diameter

Pipe length, Extra pipe length Pipe name, volume


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Snapping The Components Together to Form a System


Manual Design Methods Automatic Design Methods Headering Design Adding Circulation Pumps System Performance Review


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1:1:

1) Use the wizard to build a GHX Module

- Reverse Return

- 10 Circuits

- 15 ft Circuit Separation

- 325 ft one way Circuit Length

- 1 in SDR 11 Circuit Pipe Size

- 2 in SDR 11 Header Pipe Size

- 200 ft Supply-Return Runout Length

- 2 in SDR 11 Supply-Return Runout Pipe Size


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2:2:

Using the GHX Module that you built in the previous exercise:

1) Display the pipe size, pipe length and pipe type for the entire system

2) Switch to purge mode and then select the results you wish to see in purge mode

3) Auto Adjust the Purging Flow Rate so that 2 ft/s is achieved in the GHX circuits

4) Manually adjust the purging flow rate so that 2 ft/s is achieved in the entiresystem (including the headering pairs)

5) Auto Size the Headers so that 2 ft/s is achieved in the headering pairs whileminimizing flow rates


3:3:

Using the GHX Module that you optimized in the previous exercise:

1) Determine the flow rate and head loss requirements for the purge pump(write this number down for later use!)

2) Switch to PEAK LOAD mode

3) Select the results you wish to see for operational simulations

4) Enter a Peak Load Flow Rate

5) Select propylene glycol with freeze protection to 20F

6) Determine the Reynolds numbers7) Determine the Head Loss for the GHX Module under operational conditions

(write this number down for later use!)


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4:4:

1) Use the wizard to build a GHX Module

- Reverse Return

- 10 Circuits

- 15 ft Circuit Separation

- 325 ft one way Circuit Length

- 1 in SDR 11 Circuit Pipe Size

- 3 in SDR 11 Header Pipe Size

- 200 ft Supply-Return Runout Length

- 3 in SDR 11 Supply-Return Runout Pipe Size


5:5:

Using the GHX Module that you built in the previous exercise:

1) Display the pipe size, pipe length and pipe type for the entire system

2) Switch to purge mode and then select the results you wish to see in purge mode

3) Auto Adjust the Purging Flow Rate so that 2 ft/s is achieved in the GHX circuits

4) Manually adjust the purging flow rate so that 2 ft/s is achieved in the entire

system (including the headering pairs)

5) Auto Size the Headers so that 2 ft/s is achieved in the headering pairs whileminimizing flow rates


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6:6:

Using the GHX Module that you optimized in the previous exercise:

1) Determine the flow rate and head loss requirements for the purge pump(compare this result from the system you designed before with 2 in headers)

2) Switch to PEAK LOAD mode

3) Select the results you wish to see for operational simulations

4) Enter a Peak Load Flow Rate

5) Select propylene glycol with freeze protection to 20F

6) Determine the Reynolds numbers

7) Determine the Head Loss for the GHX Module under operational conditions

(compare this result from the system you designed before with 2 in headers)

Q & AQ & A

Thank you for using GLD Software and for learning how to use it correctly! Pleasetry to use some of what you have learned prior to the next session

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Geothermal Design - Ground Loop Design GLD2010 Software