Transcript Chilled Water Piping Systems (VPF Focus)

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
Secondary Pumps
Typical
load
with
two
way
valve
Primary Pumps
Common Pipe
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
44.0 °F
500 ton chillers
1000 GPM Each
56.0-44.0°F
Secondary Pumps
3000 GPM @ 44.0 °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
3000 GPM @ 56.0 °F
Primary/Secondary System at Part Load
53.0 °F
44.0 °F
75% System Load
Secondary Pumps
2250 GPM @ 44.0 °F
53.0 °F
44.0 °F
44.0 °F
53.0 °F
Typical
Coil
44.0 °F
Primary Pumps
1000 GPM Each
750 GPM @ 44.0 °F
56.0 °F
3000 GPM @ 53.0 °F
2250 GPM @ 56.0 °F
Primary/Secondary System
50% System Load
OFF
Secondary Pumps
1500 GPM @ 44.0 °F
53.0 °F
44.0 °F
44.0 °F
53.0 °F
Typical
Coil
44.0 °F
Primary Pumps
1000 GPM Each
500 GPM @ 44.0 °F
56.0 °F
2000 GPM @ 53.0 °F
1500 GPM @ 56.0 °F
Low Delta T Syndrome
Major Causes of Low Delta T
 Dirty Coils
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Chilled Water Coil
Major Causes of Low Delta T
 Dirty Coils
 Controls Calibration
 Leaky 2 Way Valves
 3 Way Valves at end of Index circuit
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Primary/Secondary System
Secondary Pumps
Primary Pumps
Common Pipe
Primary/Secondary System
Secondary Pumps
Primary Pumps
Common Pipe
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
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Chilled Water Coil
Primary (Constant) / Secondary (Variable)
P Load = Flow X Delta T
S Load = Flow X Delta T
Secondary Pumps
Typical load with 2 way valve
Primary Pumps
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Decoupler
/Bypass
Primary (Constant) / Secondary (Variable)
Ideal Operation
100% Load = 100% Sec Flow
Secondary Pumps
100% Flow = 3000 gpm
Primary Pumps
100% Flow = 3000 gpm
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1
2
Decoupler
/Bypass
0 gpm
Primary (Constant) / Secondary (Variable)
Ideal Operation
67% Load = 67% Sec Flow
Secondary Pumps
67% Flow = 2000 gpm
Primary Pumps
67% Flow = 2000 gpm
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1
2
Decoupler
/Bypass
0 gpm
Primary / Secondary Rule of Flow
Primary flow must always be equal
to or greater than Secondary flow.
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Primary (Constant) / Secondary (Variable)
Low Delta T Operation
67% Load = 80% Sec Flow
Secondary Pumps
80% Flow = 2400 gpm (400 gpm over-pumped)
Primary Pumps
100% Flow = 3000 gpm
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1
0
Decoupler
/Bypass
600 gpm
Major Effects of Low Delta T
 Higher Secondary Pump Energy
 Higher CHW Plant Chiller/Auxiliary Energy
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).
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Primary/Secondary System
Secondary Pumps
P
Primary Pumps
Common Pipe
Primary Only (Variable Flow)
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
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
Automatic
Isolation Valve
Primary Pumps
Bypass
Flow Meter
Typical
load
with
two
way
valve
Variable Primary System at Design
Automatic
Isolation Valve
500 ton chillers
1000 GPM Each
56.0-44.0°F
56.0 °F
44.0 °F
56.0 °F
44.0 °F
Primary Pumps
3000 GPM @ 44.0 °F
Typical
load
with
two
way
valve
56.0 °F
1000 GPM Each
44.0 °F
Bypass
Closed
3000 GPM @ 56.0 °F
Variable Primary System – Part Load
75% System Load
Automatic
Isolation Valve
56.0 °F
44.0 °F
56.0 °F
44.0 °F
Primary Pumps
2250 GPM @ 44.0 °F
56.0 °F
750 GPM Each
44.0 °F
Bypass
Closed
2250 GPM @ 56.0 °F
Typical
load
with
two
way
valve
Variable Primary System – Part Load
Chiller off
50% System Load
Automatic
Isolation Valve
Pump off
56.0 °F
44.0 °F
Primary Pumps
1500 GPM @ 44.0 °F
56.0 °F
750 GPM Each
44.0 °F
Bypass
Closed
1500 GPM @ 56.0 °F
Typical
load
with
two
way
valve
Variable Primary System – Part Load
Chiller off
50% System Load
Low Δ T
Automatic
Isolation Valve
Pump on
52.0 °F
44.0 °F
Primary Pumps
2250 GPM @ 44.0 °F
52.0 °F
750 GPM Each
44.0 °F
Bypass
Closed
2250 GPM @ 52.0 °F
Typical
load
with
two
way
valve
Variable Primary System – Min Flow (400 gpm each)
Chiller off
Automatic
Isolation Valve
System flow below chiller
minimum flow
Closed
Chiller off
Pumps
off
Closed
200 GPM @ 44.0 °F
Primary Pumps
400 GPM (one
operating)
50.0 °F
44.0 °F
Bypass
Open
200 GPM @ 44.0
400 GPM @ 50.0 °F
Flowmeter
200 GPM @ 56.0 °F
Typical
load
with
two
way
valve
Chiller Design Considerations
Flow rate changes – Staging on additional chillers
Variable Primary System (1 chiller running)
Automatic
Isolation Valve
1000 GPM @ 44.0 °F
Primary Pumps
Typical
load
with
two
way
valve
56.0 °F
44.0 °F
333 GPM Each
1000 GPM
Bypass
Closed
1000 GPM @ 56.0 °F
Variable Primary System (Staging on second chiller)
Automatic
Isolation Valve
Need to add chiller
1100 GPM @ 45.0 °F
Primary Pumps
Typical
load
with
two
way
valve
57.0 °F
45.0 °F
333 GPM Each
1100 GPM
Bypass
Closed
1100 GPM @ 57.0 °F
Variable Primary System (Open isolation valve)
Load = F X DT DT = 12 = 57- 45
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Load = 1/2F X 2DT
DT = 24
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LCHWT = 35!
Automatic
Isolation Valve
1100 GPM @ 45.0 °F
550 GPM
Primary Pumps
Typical
load
with
two
way
valve
57.0 °F
45.0 °F
333 GPM Each
550 GPM
Bypass
Closed
1100 GPM @ 57.0 °F
Variable Primary System (Open isolation valve)
LCHWT approaches 35
Automatic
Isolation Valve
LWT Cutout at 4 deg below
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Off goes chiller 1
1100 GPM @ 45.0 °F
550 GPM
Primary Pumps
Typical
load
with
two
way
valve
57.0 °F
45.0 °F
333 GPM Each
550 GPM
Bypass
Closed
1100 GPM @ 57.0 °F
Variable Primary System (Open isolation valve slowly)
Automatic
Isolation Valve
Open over 1.5 to 2 min
1100 GPM @ 45.0 °F
Primary Pumps
Typical
load
with
two
way
valve
57.0 °F
45.0 °F
333 GPM Each
1100 GPM
Bypass
Closed
1100 GPM @ 57.0 °F
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)
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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
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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
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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
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Summary on VPF Design
Chillers
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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
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VSD Controllers
Headered Pumping Arrangement (preferred)
Dedicated Pumping OK (over-size pumps)
2 Way Valves
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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
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
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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?
2 Way Valve/Coil Detail
Air
2-Way
Control
Valve
Service Valve
Return
Supply
Terminal
Balance
and
Service
Valve
Electric Energy Cost Equations
Mass Flow/t X Lift
Energy Cost =
Chiller
=
Energy Cost
Pump
=
Energy Cost
Fan
=
Energy Cost
0.7459
X Hours X Cost/Unit Energy
X
33,015 X Efficiency
Mot Eff
Lbs Refrig/hr X Head
0.7459
X Hours X Cost/Unit Energy
X
33,015 X Comp Eff
Mot Eff
GPM X Head
0.7459
X Hours X Cost/Unit Energy
X
3960 X Pump Eff
Mot Eff
CFM X TSP
0.7459
X Hours X Cost/Unit Energy
X
6356 X Fan Eff
Mot Eff