Sizing Variable Flow Piping – An Opportunity for Reducing Energy 1

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Sizing Variable Flow Piping – An Opportunity for Reducing

Energy

Learning Outcomes

Upon completion of this training one should be able to:

• Compare pipe sizing methods

• Understand the impact of pipe sizing on the system performance

• Apply ASHRAE Standard 90.1 to pipe sizing

• Understand how VV/VS pumping influences pipe sizing

• Utilize life cycle cost economics to justify the use of Magna3 in both new and renovated systems

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Overview

• Pipe Sizing Considerations• Pipe Sizing Methods• Work Through a Pipe Sizing Example• Discuss Pump & System Energy Costs as They

Relate to Pipe Sizing

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Importance

Pipe size selection impacts:• Pump head• Hydronic system performance • Energy consumption

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Sizing Considerations

Pipe size depends on: •Material• First cost• Pump energy costs

• Internal pipe erosion• Noise• Budget

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Pipe Material

•Material selection influences pipe size• Nominal pipe size may be the same but different inside diameter (free area) • Influencing the friction loss and velocity

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Copper has the more restrictive ID

Nominal 2” Copper ID=1.985”Nominal 2” Steel ID=2.067”

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Typical Procedure

Size pipe based on: • Constant Friction Rate• Velocity

• Use rule of thumb or common values

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Constant Friction Rate

• Range: 1’/100’ - 4’/100’ • 2.5’/100’ used on average (ASHRAE Fundamentals 2009

Chpt 22)

• 4’/100’ when > 2” pipe diameter

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Velocity

• Define a maximum (Common: 4 fps ≤ 2”, 8 fps > 2”)• Limited primarily for noise & erosion • Higher values acceptable when air is removed from system

ASHRAE Fundamentals 2009 Chapter 22

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Velocity - Material Impact

Maximum velocity per Copper Tube Handbook* • Chilled Water 8 fps• Hot Water (<140ºF) 5 fps• Hot water (>140ºF) 3 fps

≤ ½” diameter pipe, lower velocities should be used due to craftsmanship and abrupt changes in flow direction

*Copper Development Association

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Commercial Steel Pipe (schedule 40)

ASHRAE Fundamentals 2009 Chapter 22 Figure 4

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2.5’/100’ hd loss


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2.5’/100’ hd loss

4’/100’ hd loss


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ASHRAE Fundamentals 2009 chapter 22 Figure 4

4 fps

2.5’/100’ hd loss

4’/100’ hd loss

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4 fps

2.5’/100’ hd loss

4’/100’ hd loss

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Schedule 40 Steel Pipe Sizing Chart

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Copper Tubing (Types K, L, M)


4 fps

2.5’/100’ hd loss

4’/100’ hd loss

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Copper Type L Pipe Sizing Chart

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Material Comparison

Steel

Copper

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Noise

• Noise velocity limits are difficult to pin point as it is dependent on many variables:• Insulation• Number of turns, fittings, valves• Air quantity• Partial flow

• Typically not a significant concern as long as entrained air has been eliminated from a closed loop system.

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Erosion

• Velocities < 10 fps – erosion is not significant as long as there is no cavitation


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Aging

•Build up and increased roughness occurs in pipe over time •Narrow the pipe free area increasing head•Often ignored •Unpredictable•Research data is not available •A greater concern for open systems

•Consider as a factor in retrofit • removed and examine section of pipe•Conduct a pressure drop analysis

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EXAMPLE

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Example

• 4 Story Office Building• Located in Houston, Texas• HVAC system: Fan Coil Units with Chilled Water coils

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Basement

2

1

3

4

Mechanical Room

5

6

Zoning

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Main Floor

5

1 2

4

3

6

7

8

9 10 11

12 13

Zoning

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2nd/3rd Floor

1

2

4

5

3

7

8

6

9

10 11

Zoning

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23.7 GPM 2”, 2”

3RD

2ND

MAIN

BASE

22.3 GPM 2”, 2”

46 GPM 2½”, 2½”

24.3 GPM 2”, 2”

10.7 GPM 1¼”, 1¼”

70.3 GPM 3”, 3”

81 GPM 3”, 3”

Steel Schedule 402.5’/100’

Copper2.5’/100’

Riser

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Basement

0-1(0.9)

0-2(2.2)

0-3(2.2)

0-4(1.7)

0-5(1.7)

0-6(1.1)

co

½”, ½”

¾”, 1”

1”, 1”

1¼”, 1¼”

1¼”, 1¼”

3”, 3”

MECH ROOM(0.8)

3”, 3”

Fan Coil Unit


Copper2.5’/100’

Example

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Main Floor

1-5(1.9)

1-1(1.5)

1-2(0.95)

1-3(0.8)

1-7(2.0)

1-9(2.0)

1-8(1.9)

1-4(1.6)

1-10(1.0)

1-11 (1.4)

1-12 (3.7)

1-13 (4.9)

co

1”, 1” 1¼”, 1¼”

1¼”, 1¼”

1 ¼”, 1 ½”

1½”, 1½”

2”, 2”

Fan Coil Unit


Copper2.5’/100’

Example

1-6 (0.8)

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2nd Floorco

2-1(1.6)

2-2(2.1)

2-5(3.0)

2-3(1.2)

2-7(1.5)

2-6(1.3)

2-8(3.0)

2-9 (2.6)

2-11(2.2)2-10

(1.9)

1”, 1”

1¼”, 1¼”

2”, 2”

1¼”, 1½”

1¼”, 1¼”

1½”, 2”

2-4(2.0)

Fan Coil Unit


Copper2.5’/100’

Example

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3rd Floor

3-1(2.2)

3-2(2.2)

3-5(3.0)

3-3(1.3)

3-7(1.6)

3-4(2.1)

3-6(1.4)

3-8(3.1)

3-9 (2.8)

3-11 (2.2)3-10

(1.9)

1”, 1”

1¼”, 1½”

2”, 2”

1½”, 1½”

2”, 1½”

Fan Coil Unit


Copper2.5’/100’

Example

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Steel Schedule 402.5’/100’4’/100’4fps(≤2”); 8fps(>2”)

23.7 GPM 2”, 2”, 1½”

3RD

2ND

MAIN

BASE

22.3 GPM 2”, 1½”, 1 ½”

46 GPM 2½”, 2½”, 2½”

24.3 GPM 2”, 2”, 1 ½”

10.7 GPM 1¼”, 1¼”, 1”

70.3 GPM 3”, 2½”, 2½”

81 GPM 3”, 3”, 2½”

Riser

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Basement

0-1(0.9)

0-2(2.2)

0-3(2.2)

0-4(1.7)

0-5(1.7)

0-6(1.1)

co

½” ½” ½”

¾”, ¾”, ¾”

1” 1” ¾”

1 ¼”, 1”, 1”

1¼”, 1¼”, 1”

2½”2½” 2½”

MECH ROOM(0.8)

3” 3”

2½”


Example

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Main Floor

1-5(1.9)

1-1(1.5)

1-2(0.95)

1-3(0.8)

1-7(2.0)

1-9(2.0)

1-8(1.9)

1-4(1.6)

1-10(1.0)

1-11 (1.4)

1-12 (3.7)

1-13 (4.9)

co

1”¾”½”

1¼”1”1”

1¼”1”1”

1¼”, 1¼”, 1¼”

1½”, 1¼”, 1¼”

2”2”1½”


Example

1-6 (0.8)

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2nd Floorco

2-1(1.6)

2-2(2.1)

2-5(3.0)

2-3(1.2)

2-7(1.5)

2-6(1.3)

2-8(3.0)

2-9 (2.6)

2-11(2.2)2-10

(1.9)

1”, ¾”, ½”

1¼”, 1¼”, 1”

2”, 1½”, 1½”

1¼”, 1¼”, 1”

1¼”, 1¼”, 1¼”

1½”, 1½”, 1½”

2-4(2.0)


Example

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3rd Floor

3-1(2.2)

3-2(2.2)

3-5(3.0)

3-3(1.3)

3-7(1.6)

3-4(2.1)

3-6(1.4)

3-8(3.1)

3-9 (2.8)

3-11(2.2)3-10

(1.9)

1”, 1”, 1” 1¼”, 1¼”, 1”

2”, 2”, 1½”

1½”1¼”1¼”

2”, 1½”, 1½”


Example

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Pump Energy Costs

• Pressure drop (head)• Hours of operation• Annual flow profile• Pump control: constant vs variable pump flow• Energy rates• Efficiency of the pump

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Pressure Drop

• Energy must exerted to overcome resistance seen by the critical circuit• Poor hydronic system design and pipe lay out influences energy consumed• Items that impose resistance:• Valves• Coils• Fittings• Pipe ASHRAE Tables

Manufacturer Literature

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Pipe Resistance

• Based on pipe size, flow, and material, length Example: 3” Schedule 40 pipe with 80 GPM, 50’ long


1.5

’/100’

1.5’ of Head/100’ of pipe length

50’ of pipe X1.5’/100’ = 0.75’ Hd

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Fitting Resistance

• Based on pipe size and velocity


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Pipe Resistance

• Based on pipe size, flow, and material, length Example: 3” Schedule 40 pipe with 81 GPM


Velocity = 3.3 fps

3.3 fps

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Fitting Resistance

• Based on pipe size and velocity

ASHRAE Fundamentals 2009 Chapter 2290⁰ ElbowResistance = 8.1’ of straight pipe

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Fitting Resistance


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Fitting Resistance

• Based on pipe size and velocityExample: 3.5 FPS, 3” Steel pipe

45⁰ ElbowMultiply by the 0.7 correction valueResistance = 8.1’ x 0.75.7’ of straight pipe

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Pressure Drop Calculation

• The calculation is cumbersome and time consuming• Often simplified• Sized pipe using 2.5’/100’, apply this value to the total pipe length of critical circuit• Much of the pipe likely to operate at less than 2.5’/100’ at full load as in example • More common to multiply value by a factor such as 1.5

• Result: Over estimated head

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Prescriptive Path requirements Section 6.5.4.5 – Hydronic Systems and Control

ASHRAE Standard 90.1-2010

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Hours of Operation

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Example: Schedule 40 pipe with 81 GPM

→ 3” pipe using traditional sizing methods


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Example: Schedule 40 pipe with 81 GPM→Constant Speed = 3”; →VV/VS = 2 ½”


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• Should a 2 ½” pipe be used for a VV/VS system?• Remember that 90.1 concentrates on energy only!• Does not account for noise or erosion


4.5

’/100’

5.2 fps


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• Should a 2 ½” pipe be used for a VV/VS system?• Remember that 90.1 concentrates on energy only!• Does not account for noise or erosion


1.7

5’/

100’

3.5 fps


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Pipe Size

3” pipe• 1.75’/100’ head loss• 3.5 fps

For lowest head loss the 3” pipe is preferable3” pipe is more expensive than 2 ½”REMEMBER:System will operate at peak (81 GPM) only 19 hrs/yr

2 ½” pipe• 4.5’/100’ head loss• 5.2 fps

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Pipe Size

3” pipe• 1.75’/100’ head loss• 3.5 fps

For lowest head loss the 3” pipe is preferable

REMEMBER:• System will operate at peak (81 GPM) only 19 hrs/yr• Head loss & velocity for 2 ½” pipe will be much less most of the time • Closed loop system will have little issues with noise and erosion since air is eliminated

2 ½” pipe• 4.5’/100’ head loss• 5.2 fps

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Decreased Pipe Size Justification2 ½” pipe is potentially justifiable:• Decrease first cost• Little to no sacrifice in system life/performance• Inconsistent with pipe sizing using the constant friction rate method• Designer must consider LLC and system operation

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Software for Economic Analysis

• Free from Energy Design Resources: Pipe Optimization Tool

• http://www.energydesignresources.com/resources/software-tools/cool-tools/cooltools-pipe-size-optimization-tool.aspx

http://www.energydesignresources.com/resources/software-tools/cool-tools/cooltools-pipe-size-optimization-tool.aspx











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Economic Analysis

• Using this software and its defaults, an economic analysis was performed for a constant and variable volume system

Variable VolumeGPM = 81Total Head = 36Smaller Pipe Size, VFD1st Cost = $35,678LCC = $39,470

Constant VolumeGPM = 81Total Head = 34Larger Pipe Size1st Cost = $32,234LCC = $44,040

Note: generic pump performance curves utilized for this analysis (58% Eff)

Actual savings in energy by a Magna3 pump will exceed these values (74% Eff)

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• Concern with limitation on pipe sizing by ASHRAE Standard 90.1-2010 on retrofits:• Pipes exist and there is a need for increased capacity• These limitations can restrict the design

• Change to VV/VS pumping allows for increased GPM • Increased capacity without increasing GPM• Change the water ∆T GPM=BTUh/(500∆T)

Retrofit

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Other Free Resources

• Chilled Water design Guide http://www.energydesignresources.com/resources/publications/design-guidelines/design-guidelines-cooltools-chilled-water-plant.aspxOptimizing

• Energy Calculator for Horizontal Piping http://www.wbdg.org/design/midg_design_echp.php

• Temperature Drop Calculator for Hydronic Piping http://www.wbdg.org/design/midg_design_tdchp.php

http://www.wbdg.org/design/midg_design_echp.php

http://www.wbdg.org/design/midg_design_echp.php

http://www.wbdg.org/design/midg_design_tdchp.php

Documents

Sizing Variable Flow Piping – An Opportunity for Reducing Energy 1