1. Chilled Water Piping Systems (VPF Focus)

2. Agenda – Chilled Water Distribution Systems
Primary (Constant) / Secondary (Variable – 2W Valves)
Low Delta T
Primary Only (Variable Flow - 2W Valves)
VPF Design/Control Considerations

3. Primary (Constant Flow) / Secondary (Variable Flow)

4. Primary/Secondary System
Secondary Pumps
Typical load with two way valve
Primary Pumps
Common Pipe

5. Primary (Constant Flow) / Secondary (Variable Flow)
2 Way Valves
Higher Capital Cost Installed (vs Constant Flow 3W Valve system)
Lower CHW Pumping Energy (vs Constant Flow 3W Valve system)
Well Understood & Easy to Control

6. Primary/Secondary System at Design
500 ton chillers
1000 GPM Each °F
44.0 °F
56.0 °F
Secondary Pumps °F
56.0 °F
44.0 °F
44.0 °F
56.0 °F
Typical Coil
44.0 °F
Primary Pumps
1000 GPM Each
No flow
56.0 °F °F

7. Primary/Secondary System at Part Load
75% System Load
44.0 °F
53.0 °F
Secondary Pumps °F
53.0 °F
44.0 °F
44.0 °F
53.0 °F
Typical Coil
44.0 °F
Primary Pumps
1000 GPM Each °F
56.0 °F °F °F

8. Primary/Secondary System
50% System Load
OFF
Secondary Pumps °F
53.0 °F
44.0 °F
44.0 °F
53.0 °F
Typical Coil
44.0 °F
Primary Pumps
1000 GPM Each °F
56.0 °F °F °F

9. Low Delta T Syndrome

10. Major Causes of Low Delta T
Dirty Coils 10 10

11. Chilled Water Coil

12. Major Causes of Low Delta T
Dirty Coils
Controls Calibration
Leaky 2 Way Valves
3 Way Valves at end of Index circuit 12 12

13. Primary/Secondary System
Secondary Pumps
Primary Pumps
Common Pipe

14. Primary/Secondary System
Secondary Pumps
Primary Pumps
Common Pipe

15. Major Causes of Low Delta T
Dirty Coils
Controls Calibration
Leaky 2 Way Valves
3 Way Valves at end of Index circuit
Coils piped up backwards 15 15

16. Chilled Water Coil

17. Primary (Constant) / Secondary (Variable)
P Load = Flow X Delta T
S Load = Flow X Delta T
Secondary Pumps
Primary Pumps
Typical load with 2 way valve
Decoupler
/Bypass 17 17

18. Primary (Constant) / Secondary (Variable) Ideal Operation
100% Load = 100% Sec Flow
Secondary Pumps
Primary Pumps
Decoupler
/Bypass
100% Flow = 3000 gpm
0 gpm 12 18 18

19. Primary (Constant) / Secondary (Variable) Ideal Operation
67% Load = 67% Sec Flow
Secondary Pumps
Primary Pumps
Decoupler
/Bypass
67% Flow = 2000 gpm
0 gpm 12 19 19

20. Primary / Secondary Rule of Flow
Primary flow must always be equal to or greater than Secondary flow. 20 20

21. Primary (Constant) / Secondary (Variable) Low Delta T Operation
67% Load = 80% Sec Flow
Secondary Pumps
Primary Pumps
Decoupler
/Bypass
100% Flow = 3000 gpm
80% Flow = 2400 gpm (400 gpm over-pumped)
600 gpm 10 21 21

22. Major Effects of Low Delta T
Higher Secondary Pump Energy
Higher CHW Plant Chiller/Auxiliary Energy

23. Solution to (or reduce effects of) Low Delta T
Address the causes
Clean Coils
Calibrate controls occasionally
Select proper 2W valves (dynamic/close-off ratings) and maintain them
no 3W valves in design
find and correct piping installation errors
Over pump chillers at ratio of Design Delta T / Actual Delta T
Increase Delta T across chillers with CHW Re-set (down).
Use Variable Speed Chillers & sequence to operate from 30 to 70% Load
Use VPF Systems (mitigates energy waste in plant)
Header pumps & operate more pumps than chillers
If dedicated pumping, over-size (design at 80% speed). 23 23

24. Primary/Secondary System
Secondary Pumps P
Primary Pumps
Common Pipe

25. Primary Only (Variable Flow)

26. Primary/Secondary System
Secondary Pumps
Typical load with 2 way valve
Primary Pumps
Automatic Isolation Valve
Variable Primary System
Primary Pumps
Typical load with 2 way valve
Bypass
Valve
Flow Meter

27. Primary Only (Variable Flow)
2 Way Valves
Lower Capital Cost Installed (vs Primary/Secondary)
No secondary pumps/piping/valves/electrical to buy and install
No large Common pipe, but smaller Bypass pipe/valve/flow meter/controls
Lower CHW Pumping Energy
Smaller Footprint (vs Primary/Secondary)
Relatively New & More Complex Controls
Reduces Negative Impacts from Low Delta T
Chillers are not staged on by flow requirements
Chillers can load up and are staged on load

28. Primary Only (Variable Flow)
Disadvantages
Higher (potentially) PSID rated 2-Way valves in system
Requires more robust (complex and calibrated) control system
Requires coordinated control of chillers, isolation valves, and pumps in sequencing
Longer (potentially) Commissioning time
Requires greater operator sophistication

29. Variable-Primary-Flow System
Automatic Isolation Valve
Typical load with two way valve
Primary Pumps
Bypass
Flow Meter

30. Variable Primary System at Design
500 ton chillers
1000 GPM Each °F
Automatic Isolation Valve
56.0 °F
44.0 °F
56.0 °F
44.0 °F °F
Typical load with two way valve
56.0 °F
Primary Pumps
1000 GPM Each
44.0 °F
Bypass Closed °F

31. Variable Primary System – Part Load
75% System Load
Automatic Isolation Valve
56.0 °F
44.0 °F
56.0 °F
44.0 °F °F
Typical load with two way valve
56.0 °F
Primary Pumps
750 GPM Each
44.0 °F
Bypass Closed °F

32. Variable Primary System – Part Load
Chiller off
50% System Load
Automatic Isolation Valve
Pump off
56.0 °F
44.0 °F °F
Typical load with two way valve
56.0 °F
Primary Pumps
750 GPM Each
44.0 °F
Bypass Closed °F

33. Variable Primary System – Part Load
Chiller off
50% System Load
Low Δ T
Automatic Isolation Valve
Pump on
52.0 °F
44.0 °F °F
Typical load with two way valve
52.0 °F
Primary Pumps
750 GPM Each
44.0 °F
Bypass Closed °F

34. Variable Primary System – Min Flow (400 gpm each)
Chiller off
System flow below chiller minimum flow
Automatic Isolation Valve
Closed
Chiller off
Pumps off
Closed °F
Typical load with two way valve
50.0 °F
Primary Pumps
400 GPM (one operating)
44.0 °F
Bypass Open °F
Flowmeter °F

35. Bypass Valve Control Bypass Valve Control
Maintain a minimum chilled water flow rate through the chillers
Differential pressure measurement across each chiller evaporator
Flow meter
Bypass valve modulates open to maintain the minimum flow through operating chiller(s).
Bypass valve shall be the normally open type.
Pipe and valve sized for Min flow of operating chillers

36. Chiller Design Considerations
Flow rate changes – Staging on additional chillers

37. Variable Primary System (1 chiller running)
Automatic Isolation Valve °F
Typical load with two way valve
56.0 °F
Primary Pumps
333 GPM Each
44.0 °F
1000 GPM
Bypass Closed °F

38. Variable Primary System (Staging on second chiller)
Automatic Isolation Valve
Need to add chiller °F
Typical load with two way valve
57.0 °F
Primary Pumps
333 GPM Each
45.0 °F
1100 GPM
Bypass Closed °F

39. Variable Primary System (Open isolation valve)
Load = F X DT DT = 12 = 24
Automatic Isolation Valve
Load = 1/2F X 2DT DT = 24
LCHWT = 35! °F
550 GPM
Typical load with two way valve
57.0 °F
Primary Pumps
333 GPM Each
45.0 °F
550 GPM
Bypass Closed °F

40. Variable Primary System (Open isolation valve)
LCHWT approaches 35
LWT Cutout at 4 deg below
44 set-point or 40
Off goes chiller 1
Automatic Isolation Valve °F
550 GPM
Typical load with two way valve
57.0 °F
Primary Pumps
333 GPM Each
45.0 °F
550 GPM
Bypass Closed °F

41. Variable Primary System (Open isolation valve slowly)
Automatic Isolation Valve
Open over 1.5 to 2 min °F
Typical load with two way valve
57.0 °F
Primary Pumps
333 GPM Each
45.0 °F
1100 GPM
Bypass Closed °F

42. VPF Systems Design/Control Considerations Summary
Chillers
Equal Sized Chillers preferred, but not required
Maintain Min flow rates with Bypass control (1.5 fps)
Maintain Max flow rates (11.0 to 12.0 fps)
Isolation Valves (Modulating or Stroke-able to 1.5 to 2 min)
Don’t vary flow too quickly through chillers (VSD Ramp function – typical setting of 10%/min)
Chiller Type
System Water Volume
Chiller Load
Active Loads
Sequence
If Constant Speed – run chiller to max load (Supply Temp rise). Do not run more chillers than needed (water-cooled)
If Variable Speed – run chillers between 30% and 70% load (depending on ECWT). Run more chillers than load requires.
Add Chiller - CHW Supply Temp or Load (Adjusted* Flow X Delta T) or amps (if CSD)
Subtract Chiller - Load (Adjusted* Flow X Delta T) or Amps (if CSD) 42 42

43. VPF Systems Design/Control Considerations Summary
Pumps
Variable Speed Driven
Headered arrangement preferred
Sequence
with chillers (run more pumps than chillers for over-pumping capability)
on flow (add pump when existing inadequate, subtract when can)
optimized algorithm (total kW of more pumps, lower than less pumps)
Stay within pump/motor limits (25% to 100% speed)
Subtract a Pump at 25 to 30% speed
Add a pump back when speed of operating pumps high enough
Speed controlled by pressure sensors at end of index circuit 43 43

44. VPF Systems Design/Control Considerations Summary
Bypass Valve
Maintain a minimum chilled water flow rate through the chillers
Differential pressure measurement across each chiller evaporator
Flow meter preferred
Modulates open to maintain the minimum flow through operating chiller(s).
Bypass valve is normally open, but closed unless Min flow breeched
Pipe and valve sized for Min flow of operating chillers
High Rangeability (100:1 preferred)
PSID Ratings for Static, Dynamic, And Close Off = Shut Off Head of Pumps
Linear Proportion (Flow to Valve Position) Characteristic preferred
Fast Acting Actuator
Locate in Plant around chillers/pumps (preferrred)
Energy
Avoid Network traffic 44 44

45. VPF Systems Design/Control Considerations Summary
Load Valves
High Rangeability (200:1 preferred)
PSID Ratings for Static, Dynamic, And Close Off = Shut Off Head of Pumps
Equal Percentage (Flow to Load) Characteristic
Slow Acting Actuator
Staging Loads
Sequence AHUs On/Off in 10 to 15 min intervals 45 45

46. Summary on VPF Design 46 Size equally with same WPDs (best)
Chillers
Size equally with same WPDs (best)
Respect Min/Max Flows through chillers
Set Pump VSD Ramp function to about 10%/min (600 sec 0 to Max Speed)
Use Modulating or Strokeable Valves (preferred) on chiller evaps, headered pumping
Use 2 Position Valves (1 min stroke) on chiller evaps, dedicated pumping
Pumps
VSD Controllers
Headered Pumping Arrangement (preferred)
Dedicated Pumping OK (over-size pumps)
2 Way Valves
Select for Static, Dynamic, Close-off ratings (PSID) equal to pump SOH (plus fill pressure)
Range-ability 100 to 200:1
If Bypass – fast acting, linear proportion
If Coils – slow acting, equal percentage, “On-Off” stagger air units (10-15 min intervals)
Controls
Set-point far out in index circuit (lower the value, the better the pump energy)
Set Ramp function in VSD Controller (10%/min average)
Run 1 more pump than chillers (when headered)
Chillers On by common Supply Temp, Load, Amps, Adj Flow (Adj for Low Delta T)
Chillers Off by Amps, Load, Adj Flow (Adj for Low Delta T)
Over-pump Chillers to combat Low Delta T and get Max Cap out of chillers
Bypass controlled by Min flow (preferred) or Min WPD of largest chiller (locate in plant for best energy, but can go anywhere in system) 46 46

47. Chilled Water Piping Systems (VPF Focus)
Questions?

48. Supply Terminal Balance and Service Valve 2-Way Control Return
2 Way Valve/Coil Detail
Supply
Terminal
Balance
and
Service
Valve
2-Way
Control
Return
Service Valve
Air

49. Electric Energy Cost Equations
Mass Flow/t X Lift
33,015 X Efficiency X
Hours
Cost/Unit Energy =
0.7459
Mot Eff
Lbs Refrig/hr X Head
33,015 X Comp Eff
0.7459
Mot Eff
Chiller
Energy Cost = X X
Hours X
Cost/Unit Energy
GPM X Head
3960 X Pump Eff
0.7459
Mot Eff
Pump
Energy Cost = X X
Hours X
Cost/Unit Energy
CFM X TSP
6356 X Fan Eff
0.7459
Mot Eff
Fan
Energy Cost = X X
Hours X
Cost/Unit Energy 36