roy hubbard

Chilled Water Piping Systems (VPF Focus)

Agenda – Chilled Water Distribution Systems

Chilled Water Distribution Systems

Primary (Constant) / Secondary (Variable – 2W Valves)

Low Delta T

Primary Only (Variable Flow - 2W Valves)

VPF Design/Control Considerations

Primary (Constant Flow) / Secondary (Variable Flow)

Primary/Secondary System

Primary Pumps

Secondary Pumps

Common Pipe

Typical load with two way valve

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

Primary/Secondary System at Design

56.0 °F

56.0 °F

56.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

1000 GPM Each

3000 GPM @ 56.0 °F

Secondary Pumps

3000 GPM @ 44.0 °F

Typical Coil

No flow

44.0 °F

56.0 °F

500 ton chillers1000 GPM Each56.0-44.0°F

Primary/Secondary System at Part Load

53.0 °F

53.0 °F

53.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

1000 GPM Each

3000 GPM @ 53.0 °F

Secondary Pumps

2250 GPM @ 44.0 °F

Typical Coil

44.0 °F

56.0 °F

750 GPM @ 44.0 °F

2250 GPM @ 56.0 °F

75% System Load

Primary/Secondary System

53.0 °F

53.0 °F

44.0 °F

44.0 °F

Primary Pumps

1000 GPM Each

2000 GPM @ 53.0 °F

Secondary Pumps

1500 GPM @ 44.0 °F

Typical Coil

44.0 °F

56.0 °F

500 GPM @ 44.0 °F

1500 GPM @ 56.0 °F

OFF 50% System Load

Low Delta T Syndrome

10

Dirty Coils

Major Causes of Low Delta T

Chilled Water Coil

12

Dirty Coils

Controls Calibration

Leaky 2 Way Valves

3 Way Valves at end of Index circuit

Major Causes of Low Delta T

Primary/Secondary System

Primary Pumps

Secondary Pumps

Common Pipe

Primary/Secondary System

Primary Pumps

Secondary Pumps

Common Pipe

15

Dirty Coils

Controls Calibration

Leaky 2 Way Valves

3 Way Valves at end of Index circuit

Coils piped up backwards

Major Causes of Low Delta T

Chilled Water Coil

17

P Load = Flow X Delta T S Load = Flow X Delta T

Primary (Constant) / Secondary (Variable)

Secondary Pumps

Primary Pumps

Typical load with 2 way valve

Decoupler/Bypass

18

100% Load = 100% Sec Flow

Primary (Constant) / Secondary (Variable)Ideal Operation

Secondary Pumps

Primary PumpsDecoupler/Bypass

100% Flow = 3000 gpm

100% Flow = 3000 gpm

0 gpm

12

Secondary Pumps

Primary PumpsDecoupler/Bypass

67% Flow = 2000 gpm

67% Flow = 2000 gpm

0 gpm

19

67% Load = 67% Sec Flow

Primary (Constant) / Secondary (Variable)Ideal Operation

12

20

Primary / Secondary Rule of Flow

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

Secondary Pumps

Primary PumpsDecoupler/Bypass

100% Flow = 3000 gpm

80% Flow = 2400 gpm (400 gpm over-pumped)

600 gpm

21

67% Load = 80% Sec Flow

Primary (Constant) / Secondary (Variable)Low Delta T Operation

10

Higher Secondary Pump Energy

Higher CHW Plant Chiller/Auxiliary Energy

Major Effects of Low Delta T

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).

Primary/Secondary System

Primary Pumps

Secondary Pumps

Common Pipe

P

Primary Only (Variable Flow)

Primary/Secondary System

Variable Primary System

Secondary Pumps

Primary Pumps

Primary Pumps

Flow Meter

BypassValve

Automatic Isolation Valve

Typical load with 2 way valve

Typical load with 2 way valve

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

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

Variable-Primary-Flow System

Primary Pumps

Flow Meter

Typical load with two way valve

Automatic Isolation Valve

Bypass

Variable Primary System at Design

56.0 °F

56.0 °F

56.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

1000 GPM Each

3000 GPM @ 56.0 °F

3000 GPM @ 44.0 °F

Automatic Isolation Valve

Bypass Closed

500 ton chillers1000 GPM Each56.0-44.0°F

Typical load with two way valve

Variable Primary System – Part Load

56.0 °F

56.0 °F

56.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

750 GPM Each

2250 GPM @ 56.0 °F

2250 GPM @ 44.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve

75% System Load

Variable Primary System – Part Load

56.0 °F

56.0 °F

44.0 °F

44.0 °F

Primary Pumps

750 GPM Each

1500 GPM @ 56.0 °F

1500 GPM @ 44.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve

50% System LoadChiller off

Pump off

Variable Primary System – Part Load

52.0 °F

52.0 °F

44.0 °F

44.0 °F

Primary Pumps

750 GPM Each

2250 GPM @ 52.0 °F

2250 GPM @ 44.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve

50% System LoadLow Δ T

Chiller off

Pump on

Variable Primary System – Min Flow (400 gpm each)

50.0 °F

44.0 °F

Primary Pumps

400 GPM (one operating)

400 GPM @ 50.0 °F

200 GPM @ 44.0 °F

Automatic Isolation Valve

Bypass Open

Typical load with two way valve

System flow below chiller minimum flow

Chiller off

Chiller off

Closed

Closed

200 GPM @ 44.0

200 GPM @ 56.0 °FFlowmeter

Pumps off

Chiller Design Considerations

Flow rate changes – Staging on additional chillers

Variable Primary System (1 chiller running)

56.0 °F

44.0 °F

Primary Pumps

333 GPM Each

1000 GPM @ 56.0 °F

1000 GPM @ 44.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve1000 GPM

Variable Primary System (Staging on second chiller)

57.0 °F

45.0 °F

Primary Pumps

333 GPM Each

1100 GPM @ 57.0 °F

1100 GPM @ 45.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve1100 GPM

Need to add chiller

Variable Primary System (Open isolation valve)

57.0 °F

45.0 °F

Primary Pumps

333 GPM Each

1100 GPM @ 57.0 °F

1100 GPM @ 45.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve550 GPM

550 GPM

Load = F X DT DT = 12 = 57- 45 24

Load = 1/2F X 2DT DT = 24 24 LCHWT = 35!

Variable Primary System (Open isolation valve)

57.0 °F

45.0 °F

Primary Pumps

333 GPM Each

1100 GPM @ 57.0 °F

1100 GPM @ 45.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve550 GPM

550 GPM

LCHWT approaches 35

LWT Cutout at 4 deg below44 set-point or 40

Off goes chiller 1

Variable Primary System (Open isolation valve slowly)

57.0 °F

45.0 °F

Primary Pumps

333 GPM Each

1100 GPM @ 57.0 °F

1100 GPM @ 45.0 °F

Automatic Isolation Valve

Bypass Closed

Typical load with two way valve1100 GPM

Open over 1.5 to 2 min

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)

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

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

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

46

Summary on VPF Design

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 pumpingPumps 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)

Chilled Water Piping Systems (VPF Focus)

Questions?

Su

pply

Terminal

Balanceand

Service Valve

2-WayControlValve

Re

turnService Valve

Air

2 Way Valve/Coil Detail

Electric Energy Cost Equations

ChillerEnergy Cost

Lbs Refrig/hr X Head

33,015 X Comp EffX Hours X Cost/Unit Energy=

PumpEnergy Cost

GPM X Head

3960 X Pump EffX Hours X Cost/Unit Energy=

FanEnergy Cost

CFM X TSP

6356 X Fan EffX Hours X Cost/Unit Energy=

0.7459

Mot Eff

0.7459

Mot Eff

0.7459

Mot Eff

X

X

X

Energy Cost Mass Flow/t X Lift

33,015 X EfficiencyX Hours X Cost/Unit Energy=

0.7459

Mot EffX