1. Sizing Variable Flow Piping – An Opportunity for Reducing Energy

2. 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
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

3. Overview Pipe Sizing Considerations Pipe Sizing Methods
Work Through a Pipe Sizing Example
Discuss Pump & System Energy Costs as They Relate to Pipe Sizing
As we move through the content of this training the we will cover the following topics:
Pipe Sizing Considerations
Pipe Sizing Methods
Work Through a Pipe Sizing Example
Discuss Pump & System Energy Costs as They Relate to Pipe Sizing

4. Importance Pipe size selection impacts: Pump head
Hydronic system performance
Energy consumption
This training presentation has been developed to address the need to save energy in buildings. To date much of the focus of efficiency savings has been on individual system components such as motors and pumps. This effort has been important and successful but there are limitations as to how much more efficient individual components can become. The next step towards optimizing efficiency need to focus on the system operation – how all the pieces of the system work together. Hydronic piping is not new and designers have been sizing it for decades but little attention has been given to how this pipe sizing influences the overall system performance. Even more interesting is that many designers do not even know why they size the piping the way they do besides they have always done it that way. We will cover the background of why we select pipe the way we do and what needs to be considered as we move forward with better and more efficient designs.

5. Sizing Considerations
Pipe size depends on:
Material
First cost
Pump energy costs
Internal pipe erosion
Noise
Budget
All these items material type, first cost, pump energy costs, internal pipe erosion, noise, and budget influence pipe sizing procedure but rarely are they all considered.

6. 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
The first item we will consider is the pipe material. There are many different pipe materials used in hydronic systems but the two most common include: copper and steel. For this reason we will limit our discussion to only these two materials although the principles could apply to any material.

7. Copper has the more restrictive ID Nominal 2” Copper ID=1.985”
Nominal 2” Steel ID=2.067”
It is important to clarify that pipe of different materials although the same nominal size do not have the same inside diameter. The inside diameter influences the performance because it impacts the free area of the pipe. The smaller the ID, the greater the velocity and in turn the higher the fiction loss or head. For this presentation we will focus on the most common pipe types used in commercial design – copper type L and Steel Schedule 40 (the 40 and the L reference the wall thinkness of the pipe). As illustrated here the 2” copper pipe has a smaller inside diameter than a 2” steel pipe.

8. Typical Procedure Size pipe based on: Constant Friction Rate Velocity
Use rule of thumb or common values
The common methods of sizing pipe are using the constant friction rate or velocity. When applying either of these methods there are rules of thumb or commonly applied values used to set limits when making a selection.

9. 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
The constant friction rate as pipe sizing method does just as the name implies – sizes the pipe to maintain a constant friction. The fiction rate ranges from 1’ of head per 100’ of pipe length to 4’ of head per 100’ of pipe length. 2.5’/100’ is the value used on average per the ASHRAE Handbook unless the pipe diameters exceed 2” in which case the friction loss is increased to 4’/100’. Commonly in practice designers utilize values anywhere within this range.

10. ASHRAE Fundamentals 2009 Chapter 22
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
The second common method of pipe sizing is using a maximum velocity. Commonly designers use a max value of 4 fps for pipes 2” or below and 8 fps when pipe sizes exceed 2” but there is not a standard that defines the values used. The primary reason velocity is limited is to prevent noise and internal erosion of the pipe. The table here from ASHRAE Fundamentals reinforces these velocities as being acceptable values. One thing worth noting, is that that the most recent research, 1976, on this topic is long before may of the technologies applied in our hydronic systems existed such as variable flow/volume systems (1976).
Close loop systems can exceed these velocities since the air that does most of the erosion damage and creates the noise is removed from the system. This being said the absolute highest acceptable velocity is 15 fps.
ASHRAE Fundamentals 2009 Chapter 22

11. Velocity - Material Impact
Maximum velocity per Copper Tube Handbook*
Chilled Water 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
The piping material selected will also influence the acceptable water velocity. Copper pipe velocity limits have been researched by the Copper Development Association and are published in the Copper Tue Handbook. It is important for a designer to be sensitive to information published by many different sources and as noted here water temperature can be an influencing factor. Also in very small pipe sizes the maximum velocities should be reduced because craftsmanship and abrupt changes in flow direction will have a greater impact.
*Copper Development Association

12. Commercial Steel Pipe (schedule 40)
ASHRAE Fundamentals 2009 Chapter 22 Figure 4
Pipe sizing tables can be used to size pipe. This table published in ASHRAE fundamentals is for steel schedule 40 pipe. On this table you will find the flow, head loss, pipe size, and velocity.

13. Commercial Steel Pipe (schedule 40)
ASHRAE Fundamentals 2009 Chapter 22 Figure 4
If using the constant friction rate method for sizing you would look first to the verticle axis and reference the rate that will be used. In this case we are indicating the 2.5’/100’ rate with a blue line.
2.5’/100’ hd loss

14. Commercial Steel Pipe (schedule 40)
ASHRAE Fundamentals 2009 Chapter 22 Figure 4
A designer could also choose to use a higher head loss value 4’/100’ as represented by the green line.
2.5’/100’ hd loss
4’/100’ hd loss

15. Commercial Steel Pipe (schedule 40)
ASHRAE Fundamentals 2009 chapter 22 Figure 4
If maximum velocity is the preferred method this can also be located on this chart. For this example the red line highlights a velocity equal to 4 fps.
2.5’/100’ hd loss
4’/100’ hd loss
4 fps

16. Commercial Steel Pipe (schedule 40)
ASHRAE Fundamentals 2009 chapter 22 Figure 4
Each of the lines correlating to values 2.5’/100’, 4.0’/100’, and 4 fps can then be looked at to see where they cross a specific pipe size. From there the maximum flow rate can them be determined. The 1” pipe has been identified in yellow and the orange arrows to the horizontal axis allow GPM value to be established.
2.5’/100’ = 5.5 GPM
4’/100’ = 7 GPM
4 fps = 11 GPM
2.5’/100’ hd loss
4’/100’ hd loss
4 fps

17. Schedule 40 Steel Pipe Sizing Chart
This same process can be done for all the pipe sizes and a chart can be created.

18. Copper Tubing (Types K, L, M)
ASHRAE Fundamentals 2009 chapter 22 Figure 5
ASHRAE also publishes tables for copper pipe. When selecting pipe sizes one must use the chart that correlates with the correct material since they are not the same to account for the fact the inside diameters are different. If we look for the same intersections of lines as we did on the steel chart we can create a copper sizing chart.
2.5’/100’ hd loss
4’/100’ hd loss
4 fps

19. Copper Type L Pipe Sizing Chart

20. Material Comparison Copper Steel
What is interesting is looking at the charts side by side. You will notice that the GPM values for pipe sizes are very similar – this is a result of using the ASHRAE chart the correlates to the corresponding pipe material.
Steel

21. 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.
Noise has been mentioned a couple of times as being a factor in pipe sizing. Most hydronic systems are closed loop systems therefore this is not a significant concern since the air that will typically cause the noise has been removed. When this is an issue maximum velocity is difficult to determine do the many variables including: pipe insulation, number of turns, fittings, and valves, and partial flow.

22. Erosion
Velocities < 10 fps – erosion is not significant as long as there is no cavitation
As long as velocity is below 10 fps erosion is not a significant concern. The limits can be higher than 10 fps if the operational hours per year is not high.
ASHRAE Fundamentals 2009 Chapter 22

23. 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
Aging is another issue that can effect the free area and the friction loss in a hydronic system. Recognizing that this is an issue, it is fair to say that it is typically ignored because it is unpredictable and research has not been done to establish values that should be used. Aging is typically only addressed in open systems if accounted for at all.
Evaluation of internal pipe condition is best practice in a retrofit situation since the water treatment during the life of the system is unknown.  Either a section (or two) should be removed and examined or a pressure drop analysis should be conducted.

24. Having had some exposure to pipe sizing methods lets apply them an example closed loop chilled water system in a building.
Example

25. Example 4 Story Office Building Located in Houston, Texas
HVAC system: Fan Coil Units with Chilled Water coils
The example is a 4 story office building located in Houston, Texas. The building cooling is accomplished with an air cooled chiller serving Fan Coil Units at the zone level.

26. Zoning 2 3 1 4 5 6 Basement Mechanical Room
The office basement level is broken into 6 different zones plus a mechanical room that houses the pumps. Each zone has its own thermostat connected to a fan coil unit as is the case on all the floors.
Basement
Mechanical Room

27. Zoning 1 2 3 5 4 6 8 7 11 9 10
The main floor is broken into smaller zones than the basement since these spaces are primarily occupied spaces compared to the basement that is mostly utility type space use.
Main Floor 12 13

28. Zoning 3 2 1 4 7 6 5 9 8
The Second and Third floor layout and zoning are identical.
2nd/3rd Floor 10 11

29. Riser Steel Schedule 40 2.5’/100’ Copper 3RD 23.7 GPM 2”, 2”
2ND
46 GPM ½”, 2½”
24.3 GPM ”, 2”
MAIN
The total peak load for the building is just less than 40 tons cooling. 81 GPM of chilled water will be delivered to the fan coil units located within each zone. This graphic represents the riser diagram of the supply piping to each of the floors of the building. In addition to the GPM being listed the associated pipe size is also indicated. The pipe is sized using the constant friction rate method using the value of 2.5’ of head per 100’ run. You will notice that material choice has no impact on the nominal pipe size selected in this situation.
70.3 GPM 3”, 3”
10.7 GPM ¼”, 1¼”
BASE
81 GPM ”, 3”

30. Example Basement Steel Schedule 40 2.5’/100’ Copper Fan Coil Unit
0-2
(2.2)
0-3
(2.2)
Fan Coil Unit
¾”, 1”
1¼”, 1¼”
0-1
(0.9)
½”, ½”
1”, 1”
0-4
(1.7)
0-5
(1.7)
1¼”, 1¼”
0-6
(1.1)
Each of the floors of the building are shown with hatched boxes representing the fan coil units (the number is the unit reference number and the value in () is the unit GPM) and the chilled water main routed to each of the units. The return piping is not shown to simply the plan for the purposed of this example. The piping is sized based on the flow (GPM) that will be carried to serve the units down stream. The pipe to the furthest unit will only need to carry 0.9 GMP to this unit therefore the pipe size is small (1/2”). The only discrepancy between pipe sizes due to material selection is highlighted by the blue circle.
3”, 3”
Basement
3”, 3” co
MECH ROOM
(0.8)

31. Example Main Floor Steel Schedule 40 2.5’/100’ Copper Fan Coil Unit
1-1
(1.5)
1-2
(0.95)
1-3
(0.8)
Fan Coil Unit
1-4
(1.6)
1”, 1”
1¼”, 1¼”
1-5
(1.9)
1-6
(0.8)
1¼”, 1¼”
1-8
(1.9)
1 ¼”, 1 ½”
1-7
(2.0)
1-11
(1.4)
1-10
(1.0)
1½”, 1½”
1-9
(2.0)
2”, 2”
Completing the same pipe sizing exercise for the main floor, it can be seen that again there is only one minor difference in line size between copper and steel. This is further evident in the second and third floor piping.
Main Floor co
1-12
(3.7)
1-13
(4.9)

32. Example 2nd Floor Steel Schedule 40 2.5’/100’ Copper Fan Coil Unit
2-2
(2.1)
2-3
(1.2)
Fan Coil Unit
2-4
(2.0)
1”, 1”
2-7
(1.5)
1¼”, 1¼”
1¼”, 1¼”
2-1
(1.6)
2-6
(1.3)
2-5
(3.0)
1¼”, 1½”
2-9
(2.6)
1½”, 2”
2-8
(3.0)
2nd Floor co
2-11
(2.2)
2-10
(1.9)
2”, 2”

33. Example 3rd Floor Steel Schedule 40 2.5’/100’ Copper Fan Coil Unit
3-2
(2.2)
3-3
(1.3)
Fan Coil Unit
3-4
(2.1)
3-7
(1.6)
1”, 1”
1¼”, 1½”
3-1
(2.2)
3-5
(3.0)
3-6
(1.4)
1½”, 1½”
3-9
(2.8)
3-8
(3.1)
The 3rd floor pipe sizing is different than that for the second floor even though broken into the same number of zones. The difference is attributed to the roof load seen only by the top floor.
2”, 1½”
3rd Floor
3-11
(2.2)
3-10
(1.9)
2”, 2”

34. Riser Steel Schedule 40 2.5’/100’ 4’/100’ 4fps(≤2”); 8fps(>2”)
3RD
23.7 GPM ”, 2”, 1½”
22.3 GPM 2”, 1½”, 1 ½”
2ND
46 GPM ½”, 2½”, 2½”
24.3 GPM 2”, 2”, 1 ½”
MAIN
We have just seen that the material selected has a negligible impact on the size of the pipe selected so now lets consider the different sizing methodologies. When we look at the raiser diagram again, we see that depending on the fiction value used and the maximum acceptable velocity the pipe size can vary.
70.3 GPM ”, 2½”, 2½”
10.7 GPM 1¼”, 1¼”, 1”
BASE
81 GPM 3”, 3”, 2½”

35. Example Steel Schedule 40 2.5’/100’ 4’/100’ 4fps(≤2”); 8fps(>2”)
¾”, ¾”, ¾”
0-2
(2.2)
0-3
(2.2)
1 ¼”, 1”, 1”
0-1
(0.9)
½” ½” ½”
1” 1” ¾”
0-4
(1.7)
0-5
(1.7)
1¼”, 1¼”, 1”
0-6
(1.1)
This variance in pipe size applies the individual floors as well as the riser diagram. 3”
2½” co
2½”
Basement
MECH ROOM
(0.8)

36. Example Steel Schedule 40 2.5’/100’ 4’/100’ 4fps(≤2”); 8fps(>2”)
1-1
(1.5)
1-2
(0.95)
1-3
(0.8)
1¼” 1”
1-4
(1.6) 1” ¾” ½”
1¼” 1”
1-5
(1.9)
1-6
(0.8)
1-8
(1.9)
1¼”, 1¼”, 1¼”
1-7
(2.0)
1-11
(1.4)
1-10
(1.0)
1½”, 1¼”, 1¼”
1-9
(2.0)
Main Floor co
1-12
(3.7) 2”
1½”
1-13
(4.9)

37. Example Steel Schedule 40 2.5’/100’ 4’/100’ 4fps(≤2”); 8fps(>2”)
2-2
(2.1)
2-3
(1.2)
1”, ¾”, ½”
2-4
(2.0)
2-7
(1.5)
1¼”, 1¼”, 1”
1¼”, 1¼”, 1¼”
2-1
(1.6)
2-5
(3.0)
2-6
(1.3)
2-9
(2.6)
1¼”, 1¼”, 1”
1½”, 1½”, 1½”
2-8
(3.0)
2nd Floor co
2-11
(2.2)
2-10
(1.9)
2”, 1½”, 1½”

38. Example Steel Schedule 40 2.5’/100’ 4’/100’ 4fps(≤2”); 8fps(>2”)
3-2
(2.2)
3-3
(1.3)
3-4
(2.1)
3-7
(1.6)
1”, 1”, 1”
1¼”, 1¼”, 1”
1½”
1¼”
3-1
(2.2)
3-5
(3.0)
3-6
(1.4)
3-9
(2.8)
3-8
(3.1)
2”, 1½”, 1½”
3rd Floor
3-11
(2.2)
3-10
(1.9)
2”, 2”, 1½”

39. 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
We have spent quite a bit of time talking about pipe sizing but what is most important to this discussion is how the pipe sizing is related to the energy consumed by the system and ultimately the pump energy costs. The pump must work to overcome the resistance (head) in the system that occurs as a result of the piping layout, equipment applied, and the pipe sizing. The work or energy exerted is then converted into costs depending on the price of energy, the efficiency in the operation of the system – pump control and efficiency, and the hours of operation.

40. 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
Manufacturer Literature
The pump must exert enough energy to overcome the pressure drop or the head imposed by the critical circuit. The critical circuit is the water path that sees the greatest pressure drop – often the longest run or the path with the a piece of equipment that imposes a large pressure drop. Some pressure drops are attained from manufacturer literature such as coils and valves whereas fitting and piping resistance can be calculated using ASHRAE tables.
ASHRAE Tables

41. 1.5’ of Head/100’ of pipe length
Pipe Resistance
Based on pipe size, flow, and material, length
Example: 3” Schedule 40 pipe with 80 GPM, 50’ long
1.5’ of Head/100’ of pipe length
50’ of pipe X1.5’/100’ = 0.75’ Hd
Pipe resistance is determined using the same sizing tables used before from the ASHRAE Fundamentals. What is the pressure loss imposed by 50’ of 3” Schedule 40 pipe with 81 GPM of water flow?
First find the two variables that are given – yellow line for 3” pipe and green line for the 81 GPM. Where these two lines intersect a horizontal line can be drawn to determine the head loss – orange line.
The head loss value is 1.5’ of head per 100’ of pipe length. The head loss as a result of the 50’ of pipe length is calculated to be 0.75’ of head. This process needs to be done for all the straight lengths of pipe in the critical circuit and those value are totaled.
1.5’/100’
ASHRAE Fundamentals 2009 Chapter 22 Figure 4

42. Fitting Resistance Based on pipe size and velocity
In addition to the straight length of pipe in the critical circuit, fittings must also be considered since they also create resistance. The resistance for a fitting is given in terms of equivalent length of pipe that can then be converted to head as done with the straight pipe length. The tables for equivalent length are based on the velocity, pipe size, and the type of fitting.
ASHRAE Fundamentals 2009 Chapter 22

43. Pipe Resistance Based on pipe size, flow, and material, length
Example: 3” Schedule 40 pipe with 81 GPM
3.3 fps
Velocity = 3.3 fps
Lets first consider the velocity. Staying with our same example of a 3” pipe distributing 81 GPM of chilled water, we can determine the velocity using our pipe sizing chart.
Again locate the two variables that are given – yellow line for 3” pipe and green line for the 81 GPM. Where these two lines intersect the velocity can be determined - red line. For this example the velocity is 3.3 fps.
ASHRAE Fundamentals 2009 Chapter 22 Figure 4

44. Fitting Resistance Based on pipe size and velocity 90⁰ Elbow
The equivalent length table can now be referenced to determine the loss associated with a fitting. The velocity of 3.3 fps is located in the first column. We then look for the column associated with the pipe size of 3”. We can then read from the table the equivalent length is 8.1’ for a 90 degree elbow.
ASHRAE Fundamentals 2009 Chapter 22
90⁰ Elbow
Resistance = 8.1’ of straight pipe

45. Fitting Resistance ASHRAE Fundamentals 2009 Chapter 22
If the fitting is something other than a 90 degree elbow a correction multiplier should be applied. What if a 45 degree elbow? Use a multiplier of 0.7.
ASHRAE Fundamentals 2009 Chapter 22

46. Fitting Resistance Based on pipe size and velocity
Example: 3.5 FPS, 3” Steel pipe
This means that the resistance of (1) 45 degree 3” elbow is equal to 5.7’ of straight pipe.
45⁰ Elbow
Multiply by the 0.7 correction value
Resistance = 8.1’ x 0.7
5.7’ of straight pipe

47. 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
The pressure drop calculation to determine the system head can be very time consuming. For this reason the process is often simplified by the designer. If the pipe had been sized using the limit of 2.5’/100’, this value is applied to the entire pipe length. This will result in over estimating the head in many situations since much of the pipe was not sized at the upper limit of what is acceptable. The other time saving practice is to apply a multiplier such as 1.5 to the total length to account for fittings rather than calculating the loss for each fitting independently.
The result of this lack of precision during the design phase often generates a head value that is over estimated and in turn a pump that is over sized.

48. ASHRAE Standard 90.1-2010 Prescriptive Path requirements
Section – Hydronic Systems and Control
ASHRAE Standard 90.1 has a section under the prescriptive path requirements that addresses pipe sizing. This table defines the maximum flow rate for different sizes of pipe. The maximum GPM is dependent on operating hours and system operation in addition to pipe size. The reason this is included in Standard 90.1 is because undersized piping results in additional pump energy consumption to over come the extra head resulting from increased friction. The table includes operating hours because 90.1 requires all requirements to be economically justifiable meaning that the energy saving must pay for the increased first cost over the life of the system.
A couple of clarification items related to this table are:
These limits are only applicable to the chilled and condenser water systems*.
The table primarily focuses on energy, not the issues of erosion or noise. Since the pipe sizes effected begin at 2 ½”, the piping being considered is primarily distribution piping that will be located outside sound sensitive areas and likely be insulated.
*Hot water not included because the pipe size can be smaller since the heat of the pump is transferred to the water

49. Hours of Operation
To apply standard 90.1 limits to our example we need to know the hours of operation. Our 4 story office building peak load is nearly 40 tons with total cooling hours.

50. ASHRAE Standard 90.1-2010 Example: Schedule 40 pipe with 81 GPM
→ 3” pipe using traditional sizing methods
Using traditional sizing methods the pipe size required to address our flow of 81 GPM at peak load is 2 ½” or 3”.

51. ASHRAE Standard 90.1-2010 Example: Schedule 40 pipe with 81 GPM
→Constant Speed = 3”;
→VV/VS = 2 ½”
This is consistent with ASHRAE Standard 90.1 except 3” is the minimum pipe size for a constant flow system but 2 ½” is acceptable for a VV/VS system.

52. ASHRAE Standard
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
5.2 fps
ASHRAE Fundamentals 2009 chapter 22 Figure 4
4.5’/100’
Since 90.1 only defines the MAXIMUM water flow in a pipe, in the case of a VV/VS system being applied to our example the designer could choose to use 2 ½” or 3” pipe.
There is something that should not be forgotten as we make this decision – Standard 90.1 concentrates on primarily energy does not account for things such as noise or erosion.
What are the operating conditions if a 2 ½” pipe is selected? Head loss is 4.5’/100’ and velocity is 5.2 fps.

53. ASHRAE Standard
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
3.5 fps
ASHRAE Fundamentals 2009 chapter 22 Figure 4
1.75’/100’
What are the operating conditions if a 3” pipe is selected? Head loss is 1.75’/100’ and velocity is 3.5 fps.

54. Pipe Size 2 ½” pipe 4.5’/100’ head loss 5.2 fps 3” pipe
For lowest head loss the 3” pipe is preferable
3” pipe is more expensive than 2 ½”
REMEMBER:
System will operate at peak (81 GPM) only 19 hrs/yr
Comparing operating conditions between the 2 ½” and 3” we see that the 3” pipe has the lower head loss but the material first cost will be higher. A factor not previously considered is that the demand for peak cooling will only occur 19 hours per year for this building.

55. This graphically represents the load profile for our example 4 story office building in Houston, TX. Most of the cooling operational hours occur at less than 50% of the design load. Therefore, when we size the pipe for the peak load alone we are greatly oversizing the pipe a good portion of the time.

56. Pipe Size 2 ½” pipe 4.5’/100’ head loss 5.2 fps 3” pipe
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
Recognizing the fact that peak load occurs so infrequently, one could conclude that the head loss and velocity will be much less than those listed here 4.5’/100’ and 5.2 fps because it is a VV/VS system. Having stated this, even when at peak these values would be considered acceptable. The fact that this is a closed loop chilled water system makes concerns related to noise an erosion insignificant.

57. Decreased Pipe Size Justification
2 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
Specifying a 2 ½” pipe is certainly justifiable and may be selected because saves money in piping first costs and it requires little to no sacrifice in system life or performance. The hesitancy will likely come from those that design using the equal friction rate method as it will require a change from what they have done in the past.
The best way to make this decision is to consider the system LLC since ultimately the decision comes down to financial impact.

58. Software for Economic Analysis
Free from Energy Design Resources: Pipe Optimization Tool
A free software tool for pipe size optimization is available for download from Energy Design Resources. The software allows a designer to enter the conditions of their system and it performs an economic life cycle analysis for pipe sizing. The program allows the user to dictate whether they are designing a constant or variable volume system, their utility rates, the first cost of the components, etc.

59. Economic Analysis
Using this software and its defaults, an economic analysis was performed for a constant and variable volume system
Constant Volume
GPM = 81
Total Head = 34
Larger Pipe Size
1st Cost = $32,234
LCC = $44,040
Variable Volume
GPM = 81
Total Head = 36
Smaller Pipe Size, VFD
1st Cost = $35,678
LCC = $39,470
This software was used to analyze the critical circuit for our example building. The program defaults on unit pricing, utility rates, etc. were used rather than altering them to the specifics for our example. The program recommends the optimum pipe size as well as determines the life cycle cost for the system. As shown here, the LCC is less for the VV/VS pump system which can be attributed to the energy savings since its first costs are higher.
An item that requires clarification is related to the first costs shown here. In prior slides we stated that decreasing pipe size would result in savings in first cost. This is true but does not show up in the first costs listed here because the first cost also includes an increase in system cost to change from a constant volume to a variable volume system - VFD. If we were to look at only piping costs the VV system would be less than the constant volume system due to the reduced pipe size.
One thing that should be noted is that the software generic pump performance curves were used in this calculation with an efficiency of 58%. It can be expected that the energy saving using the Magna3 would be even greater having a efficiency of 74%.
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)

60. Retrofit
Concern with limitation on pipe sizing by ASHRAE Standard 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)
Primarily we have been discussing new system design in this presentation. Recognizing the opportunity for more retrofit work in the future, one concern is the limitations imposed by ASHRAE Standard 90.1 in regard to pipe sizing. The flow limits applied to pipe based on size are a concern especially when an existing piping system would like to be reused but the system capacity has needs to be increased to address new loads. There are two options that should be considered –
Change the system to a VV/VS system allows higher flow limits (same pipe allowed to carry more GPM)
Maintain the same GPM but increase capacity by increasing the difference between delivery and return water temperatures.

61. Other Free Resources
Chilled Water design Guide
Energy Calculator for Horizontal Piping
Temperature Drop Calculator for Hydronic Piping
This presentations has focused on pipe sizing considerations and how this ultimately impacts a system’s efficiency. As you invest more time into this topic you may find the following free resources also helpful.