Chilled Water Piping Distribution Systems ASHRAE 3-12-14

Roy Hubbard Agenda

ß Understanding the three basic piping systems ß Design and Off-design operation ß Advantages and Disadvantages ß Low DeltaT Syndrome – causes, effects, and solutions ß Design & Control Considerations (VPF) ß Chillers ß CHW Pumps ß Bypass Valve

2 Chilled Water Piping System Types (typical)

Load Configuration Valves Installed Cost Pumping Cost

Constant Primary Flow 3-way Lowest Highest

Primary / Secondary 2-way Highest Medium

Variable Primary Flow 2-way Medium Lowest

3 Load Equation

Secondary Pumps

Load = Flow X DeltaT

4 Constant Primary Flow (CPF)

Secondary Pumps

5 Constant Primary Flow (CPF) Load = Flow X DeltaT Dedicated Pumping

Secondary Pumps

6 Per Chiller System Constant Primary Flow at Design 500 Tons 1500 Tons Load (1760kW) (5280kW)

Primary

Flow 3000gpm (189 l/s)

Delta T 12 oF (6.7 oC) 56 ºF (13.3 ºC)

Secondary Pumps

56 ºF (13.3 ºC) (189 l/s) @ 6.7 ºC)

56 ºF (13.3 ºC)

(1760 kW)

(63 l/s) 56 ºF (13.3 ºC)

(189 l/s) @ 13.3 ºC)

7 Per Chiller System Constant Primary Flow at 75% Load 375 Tons 1125 Tons Load (1320kW) (3960kW)

Primary

Flow 3000gpm (189 l/s)

Delta T 9oF (5.6 oC) 53 ºF 75% (11.7 ºC)

Secondary Pumps

53 ºF (11.7 ºC) (189 l/s) @ 6.7 ºC)

53 ºF (11.7 ºC)

(1760 kW)

(63 l/s) 56 ºF (13.3 ºC) 53 ºF 53 ºF (189 l/s) @ 11.7 ºC) (11.7 ºC)

8 Per Chiller System Constant Primary Flow at 50% Load 250 Tons 750 Tons Load (880kW) (2640kW)

Primary

Flow 3000gpm (189 l/s)

Delta T 6oF (3.3 oC) 50 ºF 50% (10 ºC)

Secondary Pumps

50 ºF (10 ºC) (189 l/s) @ 6.7 ºC)

50 ºF (10 ºC)

(1760 kW)

(63 l/s) 56 ºF (13.3 ºC) 50 ºF 50 ºF (189 l/s) @ 10 ºC) (10 ºC)

9 Per Chiller System Constant Primary Flow at 25% Load 125 Tons Load 375Tons (1320kW) (440kW)

Primary

Flow 3000gpm (189 l/s)

Delta T 3oF (1.7 oC) 47 ºF 25% (8.3 ºC)

Secondary Pumps

47 ºF (8.3 ºC) (189 l/s) @ 6.7 ºC)

47 ºF (8.3ºC)

(1760 kW)

(63 l/s) 56 ºF (13.3 ºC) 47 ºF 47 ºF (189 l/s) @ 8.3 ºC) (8.3 ºC)

10 Constant Flow Primary

ß Advantages ß Lowest installed cost ß Less plant space than P/S ß Easy to Control & Operate ß Easy to Commission ß Disadvantages ß Highest Plant Energy Cost (must run all, even at low loads)

11 Primary (Constant) / Secondary (Variable)

12 Primary (Constant) / Secondary (Variable)

SLoad = Flow X DeltaT

Secondary Pumps

PLoad = Flow X DeltaT

13 Primary (Constant) / Secondary (Variable) Headered Pumping

Secondary Pumps

14 Primary (Constant) / Secondary (Variable) Dedicated Pumping

Secondary Pumps

15 Primary (Constant) / Secondary (Variable) Rule of Flow

Primary flow must always be equal to or greater than Secondary flow .

Secondary Pumps

16 Per Chiller System Primary/Secondary at Design Load 500 Tons (1760kW) 1500 Tons (5280kW) Primary Secondary Bypass

Flow 3000gpm (189 l/s) 3000gpm (189 l/s) 0gpm (0 l/s)

Delta T 12 oF (6.7 oC) 12 oF (6.7 oC) ----

56 ºF 100% Load = 100% Sec Flow (13.3 ºC) Secondary Pumps 3000 GPM @ 44 ºF 189 l/s @ 6.7 ºC

100 ft (303 kPa) Head 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

(1760 kW) 0 GPM @ 44 ºF 0 l/s @ 6.7 ºC (63 l/s)

3000 GPM @ 56 ºF 56 ºF (189 l/s) @ 13.3 ºC) (189 l/s) @ 13.3 ºC) (13.3 ºC) 50 ft (152 kPa) Head 17 Per Chiller System Primary/Secondary at 75% Load Load 375 Tons (1320kW) 1125 Tons (3960kW) Primary Secondary Bypass

Flow 3000gpm (189 l/s) 2250gpm (142 l/s) 750gpm (47 l/s)

Delta T 9oF (5 oC) 12 oF (6.7 oC) ----

53 ºF 75% Load75% = 75% Sec Flow (11.7 ºC) Secondary Pumps 2250 GPM @ 44 ºF 142 l/s @ 6.7 ºC

53 ºF (11.7 ºC)

53 ºF 44.0 °F (11.7 ºC) (6.7 °C)

(1760 kW) 750 GPM @ 44 ºF 47 l/s @ 6.7 ºC (63 l/s)

3000 GPM @ 53 ºF 2250 GPM @ 56 ºF 56 ºF (189 l/s) @ 11.7 ºC) (142 l/s) @ 13.3 ºC) (13.3 ºC)

18 Per Chiller System Primary/Secondary at 50% Load Load 375 Tons (1320kW) 750 Tons (2640kW) Primary Secondary Bypass

Flow 2000gpm (126 l/s) 1500gpm (95 l/s) 500gpm (32 l/s)

Delta T 9oF (5 oC) 12 oF (6.7 oC) ----

50% Load50% = 50% Sec Flow Secondary Pumps 1500 GPM @ 44 ºF 95 l/s @ 6.7 ºC

53 ºF (11.7 ºC)

53 ºF 44.0 °F (11.7 ºC) (6.7 °C)

(1760 kW) 500 GPM @ 44 ºF 32 l/s @ 6.7 ºC (63 l/s)

2000 GPM @ 53 ºF 1500 GPM @ 56 ºF 56 ºF (126 l/s) @ 11.7 ºC) (95 l/s) @ 13.3 ºC) (13.3 ºC)

19 Per Chiller System Primary/Secondary at 25% Load Load 375 Tons (1320kW) 375 Tons (1320kW) Primary Secondary Bypass

Flow 1000gpm (126 l/s) 750gpm (47 l/s) 250gpm (16 l/s)

Delta T 9oF (5 oC) 12 oF (6.7 oC) ----

25% Load25% = 25% Sec Flow Secondary Pumps 750 GPM @ 44 ºF 47 l/s @ 6.7 ºC

53 ºF 44.0 °F (11.7 ºC) (6.7 °C)

(1760 kW) 250 GPM @ 44 ºF 16 l/s @ 6.7 ºC (63 l/s)

1000 GPM @ 53 ºF 750 GPM @ 56 ºF 56 ºF (63 l/s) @ 11.7 ºC) (47l/s) @ 13.3 ºC) (13.3 ºC)

20 What Controls the Flow of the Secondary Loop?

But what controls the VSD’s?

21 Valve Controls Leaving Air Temperature (LAT)

22 Valve Controls Leaving Air Temperature (LAT) Set Point = 55º (12.8º) LAT

23 Valve Controls Leaving Air Temperature (LAT) Set Point = 55º (12.8º) LAT

24 Valve Controls Leaving Air Temperature (LAT) Set Point = 55º (12.8º) LAT

25 As Valve Opens, Pressure in loop lowers As Valve Closes, Pressure in loop rises

26 Pressure Differential Sensor Controls Secondary Pump Speed

Differential Pressure sensor on last coil ° controls speed ° to Set Point (coil WPD+Valve PD+Piping PD+Safety) ° located at end of Index Circuit for best efficiency

P Set Point P=25 ft (76 kPa)

27 Primary (Constant) / Secondary (Variable)

Advantages ° Easy to Control ° Easy to Commission ° Loop separation ° Easier trouble-shooting ° Separating isolated loads/buildings for lower total pump energy ° Lower Plant Energy (can sequence chillers and ancillary equipment) ° Versatile – multi-circuit capability Disadvantages ° Medium Pump Energy Cost ° Highest Installed Cost (Sec Pumps, Piping, etc.) ° Potential for higher plant energy loss because of Low Delta T syndrome

28 Variable Primary Flow

29 Variable Primary Flow Load = Flow X DeltaT

Variable Primary Flow at 100% System Load Two-way valves control capacity By varying flow of water in coils

Primary Pumps Chillers Closed

30 Primary/Secondary System

Three Differences?

Variable Primary System

Primary Chillers Pumps

31 Per Chiller System Variable Primary Flow at Design Load 500 Tons (1760kW) 1500 Tons (5280kW) Primary Bypass

Flow 3000gpm (189 l/s) 0gpm (0 l/s)

Delta T 12 oF (6.7 oC) ---- Variable Primary Flow 56 ºF 100%at 100% LoadSystem = 100% Load Flow (13.3 ºC) Two-way valves control capacity By varying flow of water in coils

3000 GPM @ 44 ºF 189 l/s @ 6.7 ºC 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

0 GPM @ 44 ºF Primary Pumps 500 Ton (1760 kW) 0 l/s @ 6.7 ºC 1000 GPM each Chillers Closed (63 l/s)

3000 GPM @ 56 ºF 3000 GPM @ 56 ºF 56 ºF (189 l/s) @ 13.3 ºC) (189 l/s) @ 13.3 ºC) (13.3 ºC)

32 Per Chiller System Variable Primary Flow at 75% Load Load 375 Tons (1320kW) 1125 Tons (3960 kW) Primary Bypass

Flow 2250 gpm (189 l/s) 0 gpm (0 l/s)

Delta T 12 oF (6.7 oC) ---- Variable Primary Flow 56 ºF 75%at Load75% System = 75% Flow Load (13.3 ºC) Two-way valves control capacity By varying flow of water in coils

2250 GPM @ 44 ºF 142 l/s @ 6.7 ºC 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

0 GPM @ 44 ºF Primary Pumps 0 l/s @ 6.7 ºC 750 GPM each Closed (47 l/s)

2250 GPM @ 56 ºF 2250 GPM @ 56 ºF 56 ºF (142 l/s) @ 13.3 ºC) (142 l/s) @ 13.3 ºC) (13.3 ºC)

33 Per Chiller System Variable Primary Flow at 50% Load Load 375 Tons (1320kW) 750 Tons (2640 kW) Primary Bypass

Flow 1500 gpm (95 l/s) 0 gpm (0 l/s)

Delta T 12 oF (6.7 oC) ---- Variable Primary Flow 50%at Load50% System = 50% Flow Load Two-way valves control capacity By varying flow of water in coils

1500 GPM @ 44 ºF 95 l/s @ 6.7 ºC 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

0 GPM @ 44 ºF Primary Pumps 0 l/s @ 6.7 ºC 750 GPM each Closed (47 l/s)

1500 GPM @ 56 ºF 1500 GPM @ 56 ºF 56 ºF (95 l/s) @ 13.3 ºC) (95 l/s) @ 13.3 ºC) (13.3 ºC)

34 Per Chiller System Variable Primary Flow at 25% Load Load 375 Tons (1320kW) 375 Tons (1320 kW) Primary Bypass

Flow 750 gpm (95 l/s) 0 gpm (0 l/s)

Delta T 12 oF (6.7 oC) ---- Variable Primary Flow 25%at Load25% System = 25% Flow Load Two-way valves control capacity By varying flow of water in coils

750 GPM @ 44 ºF 47 l/s @ 6.7 ºC

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

0 GPM @ 44 ºF Primary Pumps 0 l/s @ 6.7 ºC 750 GPM Closed (47 l/s)

750 GPM @ 56 ºF 750 GPM @ 56 ºF 56 ºF (47 l/s) @ 13.3 ºC) (47 l/s) @ 13.3 ºC) (13.3 ºC)

35 Per Chiller System Variable Primary Flow in Bypass Mode Load 50 Tons (176kW) 50Tons (176 kW) System flow below chiller min flow (250 gpm) Primary Bypass Flow 250 gpm (95 l/s) 150 gpm (9.5 l/s)

Delta T 12 oF (6.7 oC) ---- Variable Primary Flow at 25% System Load Two-way valves control capacity By varying flow of water in coils

100 GPM @ 44 ºF 6.3 l/s @ 6.7 ºC

48.8 ºF 44.0 °F (9.3 ºC) (6.7 °C)

150 GPM @ 44 ºF Primary Pumps 9.5 l/s @ 6.7 ºC 250 GPM Open (15.8 l/s)

250 GPM @ 48.8 ºF 100 GPM @ 56 ºF 56 ºF (15.8 l/s) @ 9.3 ºC) (6.3 l/s) @ 13.3 ºC) (13.3 ºC)

36 Varying Flow Through Chillers - Issues

ß Issue During Normal Operation ß Chiller Type (centrifugal fast, absorbers slow) ß Chiller Load (min load - no variance, full load - max variance) ß System Water Volume (more water, more thermal capacitance, faster variance allowed) ß Active Loads (near or far from plant) ß Typical VSD pump ramp rate setting of 10%/minute (accel/decel rates set to 600 seconds)

3737 Varying Flow Through Chillers - Issues

3838 Varying Flow Through Chillers - Issues

ß Issue Adding Chillers

ß Modulating isolation valves on chillers

39 Variable Primary System – Staging on chillers & changes in flow rate Current Situation – 1 chiller running

Per Chiller System VariableLoad 500 Primary Tons (1760kW) Flow 500 Tons (1934kW) at 100% System Load Two-way valves control capacity By varying flow of water in coils

1000 GPM @ 44 ºF 63 l/s @ 6.7 ºC

44.0 °F (6.7 °C)

Primary Pumps 500 GPM each Closed (32 l/s)

1000 GPM @ 56 ºF 56 ºF (63 l/s) @ 13.3 ºC) (13.3 ºC)

40 Variable Primary System – Staging on chillers & changes in flow rate Current Situation –building load increases, valve opens, second chiller starts

Per Chiller System VariableLoad 275 Primary Tons (967kW) Flow 550 Tons (1934kW) at 100%If valve Systemopens too quick: Load Chiller shuts down on low chilled Two-way valves control1 capacity water temp cutout By varying flow of water in coils Best practice! Open valve over 1.5 to 2 minutes to 1100 GPM @ 45 ºF allow for system stabilization 69 l/s @ 7.2 ºC

45.0 °F (7.2 °C)

Primary Pumps 550 GPM each Closed (35 l/s)

1100 GPM @ 57 ºF 57 ºF (69 l/s) @ 13.9 ºC) (13.9 ºC)

41 Variable Primary Flow (VPF) System Arrangement

ß Advantages ß Lower Installed Cost (approx. 5% compared P/S) ß No secondary Pumps or piping, valves, electrical, installation, etc. ß Offset somewhat by added 2W Bypass Valve and more complex controls ß Less Plant Space Needed ß Best Chilled Water Pump Energy Consumption (most optimeady configuration) ß VSD energy savings ß Lower Pump Design Head

42 Primary/Secondary

56 ºF (13.3 ºC) Secondary Pumps 3000 GPM @ 44 ºF 189 l/s @ 6.7 ºC

100 ft (303 kPa) Head 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

(1760 kW) 0 GPM @ 44 ºF 0 l/s @ 6.7 ºC (63 l/s)

3000 GPM @ 56 ºF 56 ºF (189 l/s) @ 13.3 ºC) (189 l/s) @ 13.3 ºC) (13.3 ºC) 50 ft (152 kPa) Head 43 Variable Primary Flow

Variable Primary Flow 56 ºF at 100% System Load (13.3 ºC) Two-way valves control capacity By varying flow of water in coils

3000 GPM @ 44 ºF 189 l/s @ 6.7 ºC 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

0 GPM @ 44 ºF Primary Pumps 500 Ton (1760 kW) 0 l/s @ 6.7 ºC 1000 GPM each Chillers Closed (63 l/s)

3000 GPM @ 56 ºF 3000 GPM @ 56 ºF 56 ºF (189 l/s) @ 13.3 ºC) (189 l/s) @ 13.3 ºC) (13.3 ºC) 140 ft (424 kPa) Head 44 Pump Energy

BHP = GPM X Head

3960 X PumpEff

45 Variable Primary Flow (VPF) System Arrangement

46 Pump Curves - Pump Efficiency

47 Pump Curves - Pump Efficiency

With VPF you will need larger pumps compared to P/S, but they will be operating at a more efficient point, yielding energy savings 48 Pump Energy

BHP = GPM X Head

3960 X PumpEff

49 Variable Primary Flow (VPF) System Arrangement

50 Variable Primary Flow (VPF) System Arrangement

ß Advantages ß Medium Installed Cost (approx. 5% compared P/S) ß No secondary Pumps or piping, valves, electrical, installation, etc. ß Offset somewhat by added 2W Bypass Valve and more complex controls ß Less Plant Space Needed (vs P/S) ß Best Chilled Water Pump Energy Consumption (most optimeady configuration) ß VSD energy savings ß Lower Pump Design Head ß Higher Pump Efficiency ß Lower potential impact from Low Delta T (can over pump chillers if needed) ß Disadvantages ß Requires more robust (complex and properly calibrated) control system ß Requires coordinated control of chillers, isolation valves, and pumps ß Potentially longer commissioning times to tune the system ß Need experienced facility manager to operate/maintain properly

51 Low Delta T Syndrome

Secondary Pumps

Design Delta T = 12ºF

44 °F

56°F

52 Major Causes of Low Delta T

ß Dirty Coils

53 Chilled Water Coil

54 Chilled Water Coil

Load = Flow X Delta T

55 Chilled Water Coil

Load = Flow X Delta T

56 Major Causes of Low Delta T

ß Dirty Coils ß Controls Calibration ß Leaky 2-Way Valves ß Coils Piped-Up Backwards

57 Chilled Water Coil

58 Major Causes of Low Delta T

ß Dirty Coils ß Controls Calibration ß Leaky 2-Way Valves ß Coils Piped-Up Backwards ß Mixing 2-Way with 3-Way Valves in the same system

59 Low Delta T Syndrome 3 Way Valves Mixed with 2 Way

Secondary Pumps

44 °F

56°F

60 Per Chiller System Primary/Secondary at Design Load 500 Tons (1760kW) 1500 Tons (5280kW) Ideal Operation Primary Secondary Bypass Flow 3000gpm (189 l/s) 3000gpm (189 l/s) 0 gpm (0 l/s)

Delta T 12 oF (6.7 oC) 12 oF (6.7 oC) ----

56 ºF 100% Load = 100% Sec Flow (13.3 ºC) Secondary Pumps 3000 GPM @ 44 ºF 189 l/s @ 6.7 ºC

44 ºF (6.7 ºC) 56 ºF (13.3 ºC)

56 ºF 44.0 °F 12ºF (13.3 ºC) (6.7 °C) (6.7ºC)

(1760 kW) 0 GPM @ 44 ºF 0 l/s @ 6.7 ºC (63 l/s)

3000 GPM @ 56 ºF 56 ºF (189 l/s) @ 13.3 ºC) (189 l/s) @ 13.3 ºC) (13.3 ºC)

61 Per Chiller System Primary/Secondary at 67% Load Load 500 Tons (1760kW) 1000 Tons (3518kW) Ideal Operation Primary Secondary Bypass Flow 2000gpm (126 l/s) 2000gpm (126 l/s) 0 gpm (0 l/s)

Delta T 12 oF (4.4 oC) 12 oF (6.7 oC) ----

67% Load = 67% Sec Flow Secondary Pumps 2000 GPM @ 44 ºF 126 l/s @ 6.7 ºC

44 ºF (6.7 ºC) 56 ºF (13.3 ºC)

56 ºF 44.0 °F 12ºF (13.3 ºC) (6.7 °C) (6.7ºC)

(1760 kW) 0 GPM @ 44 ºF 0 l/s @ 6.7 ºC (63 l/s)

2000 GPM @ 56 ºF 2000 GPM @ 56 ºF 56 ºF (189(126 l/s)l/s) @@ 13.313.3 ºC)ºC) (126 l/s) @ 13.3 ºC) (13.3 ºC)

62 Per Chiller System Primary/Secondary at 67% Load Load 500 Tons (1760kW) 1000 Tons (3518kW) Low DeltaT Primary Secondary Bypass Flow 2000gpm (126 l/s) 2280gpm (144 l/s) 280 gpm (0 l/s)

Delta T 10 oF (5.6 oC) 10 oF (5.6 oC) ----

67% Load = 76% Sec Flow Secondary Pumps 2280 GPM @ 44 ºF 144 l/s @ 6.7 ºC

44 ºF (6.7 ºC) 54 ºF (12.2 ºC)

54 ºF 44 °F 10ºF (12.2 ºC) (6.7 °C) (5.6ºC)

(1760 kW) 280 GPM @ 54 ºF 17.7 l/s @ 7.3 ºC (63 l/s)

2000 GPM @ 54 ºF 2280 GPM @ 54 ºF 54 ºF (189(126 l/s)l/s) @@ 13.312.2 ºC)ºC) (144 l/s) @ 12.2 ºC) (12.2 ºC)

63 Per Chiller System Primary/Secondary at 67% Load Load 417 Tons (1467kW) 934 Tons (3286kW) Low DeltaT Primary Secondary Bypass Flow 2000gpm (126 l/s) 2280gpm (144 l/s) 280 gpm (18l/s)

Delta T 10 oF (5.6 oC) 10 oF (5.6 oC) ----

67% Load = 76% Sec Flow Secondary Pumps 2280 GPM @ 45.2 ºF 144 l/s @ 7.3 ºC

45.2 ºF (7.3 ºC) 54 ºF ? (12.2 ºC ?)

54 ºF ? 45.2 °F ??? (12.2 ºC ?) (7.3 °C)

(1760 kW) 280 ? GPM @ 54 ºF ? 17.7 ?+ l/s @ 12.2 ºC ? (63 l/s)

2000 GPM @ 54 ºF ? 2280? GPM @ 54 ºF ? 54 ºF ? (126(189 l/s)l/s) @@ 12.213.3 ºCºC) ?) (144? l/s) @ 12.2 ºC ?) (12.2 ºC ?)

64 Per Chiller System Primary/Secondary at 67% Load Load 333 Tons (1172kW) 1000 Tons (3518kW) Low DeltaT Primary Secondary Bypass Flow 3000gpm (189 l/s) 2280gpm (144 l/s) 720 gpm (0 l/s)

Delta T 8oF (4.4 oC) 10 oF (5.6 oC) ----

52 ºF 67% Load = 76% Sec Flow (11.1 ºC) Secondary Pumps 2280 GPM @ 44 ºF 144 l/s @ 6.7 ºC

44 ºF (6.7 ºC) 52 ºF (11.1 ºC)

52 ºF 44 °F 10ºF (11.1 ºC) (6.7 °C) (5.6ºC)

(1760 kW) 720 GPM @ 44 ºF 45 l/s @ 6.7 ºC (63 l/s)

3000 GPM @ 52 ºF 2280 GPM @ 54 ºF 54 ºF (189(189 l/s)l/s) @@ 13.311.1 ºC)ºC) (144 l/s) @ 12.2 ºC) (12.2 ºC)

65 Primary (Constant) / Secondary (Variable) Rule of Flow

Primary flow must always be equal to or greater than Secondary flow . Secondary Pumps

66 Negative Effects of Low Delta T in P/S Systems

Consequences: ß Higher secondary pump energy ß pumps run faster

ß Higher chilled water plant energy ß Ancillary equipment

ß Can’t load up chillers ß more than ratio Act DT / Des DT ß 10/12 = 83% or 417 tons

67 Per Chiller System Variable Primary Flow at 67% Load Load 500 Tons (1760kW) 1000 Tons (3518kW) Ideal Operation Primary Bypass Flow 2000gpm (126l/s) 0gpm (0 l/s)

Delta T 12 oF (6.7 oC) ---- Variable Primary Flow 56 ºF at 100% System Load (13.3 ºC) 67%Two-way Load valves = control 67% capacity Sec Flow By varying flow of water in coils

2000 GPM @ 44 ºF 126 l/s @ 6.7 ºC 56 ºF (13.3 ºC)

56 ºF 44.0 °F (13.3 ºC) (6.7 °C)

0 GPM Primary Pumps 500 Ton (1760 kW) 0 l/s 666 GPM each Chillers Closed (42 l/s)

2000 GPM @ 56 ºF 2000 GPM @ 56 ºF 56 ºF (126 l/s) @ 13.3 ºC) (126 l/s) @ 13.3 ºC) (13.3 ºC)

68 Per Chiller System Variable Primary Flow at 67% Load Load 500 Tons (1760kW) 1000 Tons (3518kW) Low DeltaT (can over-pump chillers) Primary Bypass Flow 2280gpm (144l/s) 0gpm (0 l/s)

Delta T 10 oF (5.6 oC) ---- Variable Primary Flow 54 ºF at 100% System Load (12.2 ºC) 67%Two-way Load valves = control 76% capacity Sec Flow By varying flow of water in coils

2280 GPM @ 44 ºF 144 l/s @ 6.7 ºC 54 ºF (12.2 ºC)

54 ºF 44.0 °F (12.2 ºC) (6.7 °C)

0 GPM Primary Pumps 1140 GPM 0 l/s 760 GPM each (72 l/s) Closed (48 l/s) ea Chiller Flow

2280 GPM @ 54 ºF 2280 GPM @ 54 ºF 54 ºF (144 l/s) @ 12.2 ºC) (144 l/s) @ 12.2 ºC) (12.2 ºC)

69 Negative Effects of Low Delta T in VPF Systems

Consequences: ß Higher secondary pump energy ß pumps run faster

ß Higher chilled water plant energy ß Ancillary equipment

ß Can’t load up chillers ß more than ratio Act DT / Des DT ß 10/12 = 83% or 417 tons

70 VPF Systems mitigate Low Delta T Impacts

But: ß No additional energy from running more chillers than required. ß Can fully load up chillers by over-pumping. ß more than ratio Des DT / Act DT ß 12/10 = 120% or 1200 gpm (1000 des) ß 20% increase in flow is 44% increase in WPD, so 15 ft would rise to 22 ft. ß Max WPD for YKs 2P is 45 ft , 3P is 67 ft

71 Solution to (or reduce effects of) Low Delta T

ß Address the causes ß Clean Coils ß Calibrate controls periodically ß Select proper 2W valves (dynamic/close-off ratings) and maintain them ß No 3W valves in design ß Find and correct piping installation errors ß Over deltaT chillers by resetting supply water down (P/S) ß Over pump chillers at ratio of Design Delta T / Actual Delta T (VPF) ß Use VSD Chillers & Energy-based sequencing (from 30 to 80% Load)

Solve at Load, Mitigate at Plant

72 VPF Systems Design/Control Considerations

ß Chillers ß Equal Sized Chillers preferred, but not required ß Maintain Min flow rates with Bypass control (1.5 fps) ß Maintain Max flow rates (11.0 to 12.0 fps) and max WPDs (45’ for 2P, 67’ for 3P) ß Modulating Isolation Valves (or 2-position stroke-able) set to open in 1.5 to 2 min ß Don’t vary flow too quickly through chillers (VSD pump Ramp rate – typical setting of 10%/min) ß Sequence ß If CSD Chillers – run chillers to max load (Supply Temp rise). Do not run more chillers than needed (water-cooled, single compressor assumed) ß If VSD Chillers – run chillers between 30% and 80% load (depending on ECWT and actual off- design performance curves). Run more chillers than load requires. ß Add Chiller - CHW Supply Temp or Load (Flow X Delta T) or amps (if CSD) ß Subtract Chiller - Load (Flow X Delta T) or Amps (if CSD)

73 VPF Systems Design/Control Considerations

ß Pumps ß Variable Speed Driven ß Headered arrangement preferred ß Sequence ß with chillers (run more pumps than chillers for over-pumping capability) ß Flow-based sequencing ß Energy -based sequencing (most efficient combination of pumps) ß Speed controlled by pressure sensors at end of index circuit (fast response important) ß Direct wired ß Piggyback control for large distances ß Optimized - Reset pressure sensor by valve position of coils

74 VPF Systems Design/Control Considerations

ß Bypass Valve ß Maintain a minimum chilled water flow rate through the chillers ß Differential pressure measurement across each chiller evaporator ß Flow meter preferred ß Modulates open to maintain the minimum flow through operating chiller(s). ß Bypass valve is normally open, but closed unless Min flow breeched ß Pipe and valve sized for Min flow of operating chillers ß High Range-ability (100:1 or better preferred) ß PSID Ratings for Static, Dynamic, And Close Off = Shut Off Head of Pumps ß Linear Proportion (Flow to Valve Position) Characteristic preferred ß Fast Acting Actuator ß Locate in Plant around chillers/pumps (preferred) ß Energy ß Avoid Network traffic (response time is critical to protect chillers from potential freeze-up)

75 VPF Systems Design/Control Considerations

ß Load Valves ß High Range-ability (200:1 preferred) ß PSID Ratings for Static, Dynamic, and Close Off = Shut-off Head of Pumps ß Equal Percentage (Flow to Load) Characteristic ß Slow Acting Actuator ß Staging Loads ß Sequence AHUs On/Off in 10 to 15 min intervals

76 Summary on VPF Design (optimal design criteria)

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

77 Questions?

Roy Hubbard