Transcription
Roy Hubbard
AgendaUnderstanding the three basic piping systemsDesign and Off-design operationAdvantages and DisadvantagesLow DeltaT Syndrome – causes, effects, and solutionsDesign & Control Considerations (VPF)ChillersCHW PumpsBypass Valve2
Chilled Water Piping System Types (typical)ConfigurationLoadValvesInstalled CostPumping CostConstant Primary Flow3-wayLowestHighestPrimary / Secondary2-wayHighestMediumVariable Primary Flow2-wayMediumLowest3
Load EquationSecondary PumpsLoad Flow X DeltaT4
Constant Primary Flow (CPF)Secondary Pumps5
Load Flow X DeltaTConstant Primary Flow (CPF)Dedicated PumpingSecondary Pumps6
Constant Primary Flow at DesignLoadPer ChillerSystem500 Tons(1760kW)1500 Tons(5280kW)Primary56 ºF(13.3 ºC)Flow3000gpm (189 l/s)Delta T12oF (6.7oC)Secondary Pumps56 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
Constant Primary Flow at 75% LoadPer ChillerSystem375 Tons(1320kW)1125 Tons(3960kW)LoadPrimary75%53 ºF(11.7 ºC)Flow3000gpm (189 l/s)Delta T9oF (5.6oC)Secondary Pumps53 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(189 l/s) @ 11.7 ºC)853 ºF(11.7 ºC)
Constant Primary Flow at 50% LoadPer ChillerSystem250 Tons(880kW)750 Tons(2640kW)LoadPrimary50%50 ºF(10 ºC)Flow3000gpm (189 l/s)Delta T6oF (3.3oC)Secondary Pumps50 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(189 l/s) @ 10 ºC)950 ºF(10 ºC)
Constant Primary Flow at 25% LoadPer ChillerSystem125 Tons(440kW)375Tons (1320kW)LoadPrimary25%47 ºF(8.3 ºC)Flow3000gpm (189 l/s)Delta T3oF (1.7oC)Secondary Pumps47 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(189 l/s) @ 8.3 ºC)1047 ºF(8.3 ºC)
Constant Flow PrimaryAdvantagesLowest installed costLess plant space than P/SEasy to Control & OperateEasy to CommissionDisadvantagesHighest Plant Energy Cost (must run all, even at low loads)11
Primary (Constant) / Secondary (Variable)12
Primary (Constant) / Secondary (Variable)SLoad Flow X DeltaTSecondary PumpsPLoad Flow X DeltaT13
Primary (Constant) / Secondary (Variable)Headered PumpingSecondary Pumps14
Primary (Constant) / Secondary (Variable)Dedicated PumpingSecondary Pumps15
Primary (Constant) / Secondary (Variable)Rule of FlowPrimary flow must always be equalto or greater than Secondary flow.Secondary Pumps16
LoadPrimary/Secondary at DesignPer ChillerSystem500 Tons (1760kW)1500 Tons (5280kW)PrimarySecondaryBypassFlow3000gpm (189 l/s)3000gpm (189 l/s)0gpm (0 l/s)Delta T12oF (6.7oC)12oF (6.7oC)----100% Load 100% Sec Flow56 ºF(13.3 ºC)Secondary Pumps3000 GPM @ 44 ºF189 l/s @ 6.7 ºC100 ft (303 kPa) Head56 ºF(13.3 ºC)56 ºF(13.3 ºC)44.0 F(6.7 C)(1760 kW)(63 l/s)(189 l/s) @ 13.3 ºC)50 ft (152 kPa) Head170 GPM @ 44 ºF0 l/s @ 6.7 ºC3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
LoadPrimary/Secondary at 75% LoadPer ChillerSystem375 Tons (1320kW)1125 Tons (3960kW)PrimarySecondaryBypassFlow3000gpm (189 l/s)2250gpm (142 l/s)750gpm (47 l/s)Delta T9oF (5oC)12oF (6.7oC)----75% Load75% 75% Sec Flow53 ºF(11.7 ºC)Secondary Pumps2250 GPM @ 44 ºF142 l/s @ 6.7 ºC53 ºF(11.7 ºC)53 ºF(11.7 ºC)44.0 F(6.7 C)(1760 kW)(63 l/s)3000 GPM @ 53 ºF(189 l/s) @ 11.7 ºC)18750 GPM @ 44 ºF47 l/s @ 6.7 ºC2250 GPM @ 56 ºF(142 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
LoadPrimary/Secondary at 50% LoadPer ChillerSystem375 Tons (1320kW)750 Tons (2640kW)PrimarySecondaryBypassFlow2000gpm (126 l/s)1500gpm (95 l/s)500gpm (32 l/s)Delta T9oF (5oC)12oF (6.7oC)----50% Load50% 50% Sec FlowSecondary Pumps1500 GPM @ 44 ºF95 l/s @ 6.7 ºC53 ºF(11.7 ºC)53 ºF(11.7 ºC)44.0 F(6.7 C)(1760 kW)(63 l/s)2000 GPM @ 53 ºF(126 l/s) @ 11.7 ºC)19500 GPM @ 44 ºF32 l/s @ 6.7 ºC1500 GPM @ 56 ºF(95 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
LoadPrimary/Secondary at 25% LoadPer ChillerSystem375 Tons (1320kW)375 Tons (1320kW)PrimarySecondaryBypassFlow1000gpm (126 l/s)750gpm (47 l/s)250gpm (16 l/s)Delta T9oF (5oC)12oF (6.7oC)----25% Load25% 25% Sec FlowSecondary Pumps750 GPM @ 44 ºF47 l/s @ 6.7 ºC53 ºF(11.7 ºC)44.0 F(6.7 C)(1760 kW)(63 l/s)1000 GPM @ 53 ºF(63 l/s) @ 11.7 ºC)20250 GPM @ 44 ºF16 l/s @ 6.7 ºC750 GPM @ 56 ºF(47l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
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) LATT23
Valve Controls Leaving Air Temperature (LAT)Set Point 55º (12.8º) LATT24
Valve Controls Leaving Air Temperature (LAT)Set Point 55º (12.8º) LATT25
As Valve Opens, Pressure in loop lowersAs Valve Closes, Pressure in loop rises26
Pressure Differential Sensor Controls Secondary Pump SpeedDifferential Pressure sensor on last coilcontrols speedto Set Point (coil WPD Valve PD Piping PD Safety)located at end of Index Circuit for best efficiencyP27Set PointP 25 ft (76 kPa)
Primary (Constant) / Secondary (Variable)AdvantagesEasy to ControlEasy to CommissionLoop separationEasier trouble-shootingSeparating isolated loads/buildings for lower total pump energyLower Plant Energy (can sequence chillers and ancillary equipment)Versatile – multi-circuit capabilityDisadvantagesMedium Pump Energy CostHighest Installed Cost (Sec Pumps, Piping, etc.)Potential for higher plant energy loss because of Low Delta T syndrome28
Variable Primary Flow29
Load Flow X DeltaTVariable Primary FlowVariable Primary Flowat 100% System LoadTwo-way valves control capacityBy varying flow of water in coilsPrimary PumpsChillers30Closed
Primary/Secondary SystemThree Differences?Variable Primary SystemPrimaryPumps31Chillers
LoadVariable Primary Flow at DesignPer ChillerSystem500 Tons (1760kW)1500 Tons (5280kW)PrimaryBypassFlow3000gpm (189 l/s)0gpm (0 l/s)Delta T12oF (6.7oC)----Variable Primary Flow100%LoadSystem 100%LoadFlowat 100%56 ºF(13.3 ºC)Two-way valves control capacityBy varying flow of water in coils3000 GPM @ 44 ºF189 l/s @ 6.7 ºC56 ºF(13.3 ºC)56 ºF(13.3 ºC)Primary Pumps1000 GPM each(63 l/s)44.0 F(6.7 C)500 Ton (1760 kW)Chillers3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)320 GPM @ 44 ºF0 l/s @ 6.7 ºCClosed3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
LoadVariable Primary Flow at 75% LoadPer ChillerSystem375 Tons (1320kW)1125 Tons (3960 kW)PrimaryBypassFlow2250 gpm (189 l/s)0 gpm (0 l/s)Delta T12oF (6.7oC)----Variable Primary Flow75% 75% Flowat Load75% SystemLoad56 ºF(13.3 ºC)Two-way valves control capacityBy varying flow of water in coils2250 GPM @ 44 ºF142 l/s @ 6.7 ºC56 ºF(13.3 ºC)56 ºF(13.3 ºC)Primary Pumps750 GPM each(47 l/s)2250 GPM @ 56 ºF(142 l/s) @ 13.3 ºC)3344.0 F(6.7 C)0 GPM @ 44 ºF0 l/s @ 6.7 ºCClosed2250 GPM @ 56 ºF(142 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
LoadVariable Primary Flow at 50% LoadPer ChillerSystem375 Tons (1320kW)750 Tons (2640 kW)PrimaryBypassFlow1500 gpm (95 l/s)0 gpm (0 l/s)Delta T12oF (6.7oC)----Variable Primary Flow50% 50% Flowat Load50% SystemLoadTwo-way valves control capacityBy varying flow of water in coils1500 GPM @ 44 ºF95 l/s @ 6.7 ºC56 ºF(13.3 ºC)56 ºF(13.3 ºC)Primary Pumps750 GPM each(47 l/s)1500 GPM @ 56 ºF(95 l/s) @ 13.3 ºC)3444.0 F(6.7 C)0 GPM @ 44 ºF0 l/s @ 6.7 ºCClosed1500 GPM @ 56 ºF(95 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
LoadVariable Primary Flow at 25% LoadPer ChillerSystem375 Tons (1320kW)375 Tons (1320 kW)PrimaryBypassFlow750 gpm (95 l/s)0 gpm (0 l/s)Delta T12oF (6.7oC)----Variable Primary Flow25% 25% Flowat Load25% SystemLoadTwo-way valves control capacityBy varying flow of water in coils750 GPM @ 44 ºF47 l/s @ 6.7 ºC56 ºF(13.3 ºC)Primary Pumps750 GPM(47 l/s)750 GPM @ 56 ºF(47 l/s) @ 13.3 ºC)3544.0 F(6.7 C)0 GPM @ 44 ºF0 l/s @ 6.7 ºCClosed750 GPM @ 56 ºF(47 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
Variable Primary Flow in Bypass ModeSystem flow below chiller min flow (250 gpm)LoadPer ChillerSystem50 Tons (176kW)50Tons (176 kW)PrimaryBypassFlow250 gpm (95 l/s)150 gpm (9.5 l/s)Delta T12oF (6.7oC)----Variable Primary Flowat 25% System LoadTwo-way valves control capacityBy varying flow of water in coils100 GPM @ 44 ºF6.3 l/s @ 6.7 ºC48.8 ºF(9.3 ºC)Primary Pumps250 GPM(15.8 l/s)250 GPM @ 48.8 ºF(15.8 l/s) @ 9.3 ºC)3644.0 F(6.7 C)150 GPM @ 44 ºF9.5 l/s @ 6.7 ºCOpen100 GPM @ 56 ºF(6.3 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
Varying Flow Through Chillers - IssuesIssue During Normal OperationChiller Type (centrifugal fast, absorbers slow)Chiller Load (min load - no variance, full load - max variance)System Water Volume (more water, more thermal capacitance, faster variance allowed)Active Loads (near or far from plant)Typical VSD pump ramp rate setting of 10%/minute (accel/decel rates set to 600 seconds)37
Varying Flow Through Chillers - IssuesIssue During Normal OperationChiller Type (centrifugal fast, absorbers slow)Chiller Load (min load - no variance, full load - max variance)System Water Volume (more water, more thermal capacitance, faster variance allowed)Active Loads (near or far from plant)Typical VSD pump ramp rate setting of 10%/minute (accel/decel rates set to 600 seconds)38
Varying Flow Through Chillers - IssuesIssue During Normal OperationChiller Type (centrifugal fast, absorbers slow)Chiller Load (min load - no variance, full load - max variance)System Water Volume (more water, more thermal capacitance, faster variance allowed)Active Loads (near or far from plant)Typical VSD pump ramp rate setting of 10%/minute (accel/decel rates set to 600 seconds)Issue Adding ChillersModulating isolation valves on chillers39
Variable Primary System – Staging on chillers & changes in flow rateCurrent Situation – 1 chiller runningPer ChillerSystem500 Tons (1760kW)500 Tons (1934kW)LoadVariablePrimary Flowat 100% System LoadTwo-way valves control capacityBy varying flow of water in coils1000 GPM @ 44 ºF63 l/s @ 6.7 ºC44.0 F(6.7 C)Primary Pumps500 GPM each(32 l/s)1000 GPM @ 56 ºF(63 l/s) @ 13.3 ºC)40Closed56 ºF(13.3 ºC)
Variable Primary System – Staging on chillers & changes in flow rateCurrent Situation –building load increases, valve opens, second chiller startsPer ChillerSystem275 Tons (967kW)550 Tons (1934kW)LoadVariablePrimary FlowIf valve Systemopens too quick:at 100%LoadChiller1 shuts down on low chilledTwo-way valves controlcapacitywater temp cutoutBy varying flow of water in coils1100 GPM @ 45 ºF69 l/s @ 7.2 ºCBest practice!Open valve over 1.5 to 2 minutes toallow for system stabilization45.0 F(7.2 C)Primary Pumps550 GPM each(35 l/s)1100 GPM @ 57 ºF(69 l/s) @ 13.9 ºC)41Closed57 ºF(13.9 ºC)
Variable Primary Flow (VPF) System ArrangementAdvantagesLower Installed Cost (approx. 5% compared P/S)No secondary Pumps or piping, valves, electrical, installation, etc.Offset somewhat by added 2W Bypass Valve and more complex controlsLess Plant Space NeededBest Chilled Water Pump Energy Consumption (most optimeady configuration)VSD energy savingsLower Pump Design Head42
Primary/Secondary56 ºF(13.3 ºC)Secondary Pumps3000 GPM @ 44 ºF189 l/s @ 6.7 ºC100 ft (303 kPa) Head56 ºF(13.3 ºC)56 ºF(13.3 ºC)44.0 F(6.7 C)(1760 kW)(63 l/s)(189 l/s) @ 13.3 ºC)50 ft (152 kPa) Head430 GPM @ 44 ºF0 l/s @ 6.7 ºC3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
Variable Primary FlowVariable Primary Flowat 100% System Load56 ºF(13.3 ºC)Two-way valves control capacityBy varying flow of water in coils3000 GPM @ 44 ºF189 l/s @ 6.7 ºC56 ºF(13.3 ºC)56 ºF(13.3 ºC)Primary Pumps1000 GPM each(63 l/s)44.0 F(6.7 C)500 Ton (1760 kW)Chillers3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)140 ft (424 kPa) Head440 GPM @ 44 ºF0 l/s @ 6.7 ºCClosed3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)56 ºF(13.3 ºC)
Pump EnergyBHP 45GPM X Head3960 X PumpEff
Variable Primary Flow (VPF) System ArrangementAdvantagesLower Installed Cost (approx. 5% compared P/S)No secondary Pumps or piping, valves, electrical, installation, etc.Offset somewhat by added 2W Bypass Valve and more complex controlsLess Plant Space NeededBest Chilled Water Pump Energy Consumption (most optimeady configuration)VSD energy savingsLower Pump Design HeadHigher Pump Efficiency46
Pump Curves - Pump Efficiency47
Pump Curves - Pump Efficiency48With VPF you will need larger pumps compared to P/S, but they willbe operating at a more efficient point, yielding energy savings
Pump EnergyBHP 49GPM X Head3960 X PumpEff
Variable Primary Flow (VPF) System ArrangementAdvantagesMedium Installed Cost (approx. 5% compared P/S)No secondary Pumps or piping, valves, electrical, installation, etc.Offset somewhat by added 2W Bypass Valve and more complex controlsLess Plant Space Needed (vs P/S)Best Chilled Water Pump Energy Consumption (most optimeady configuration)VSD energy savingsLower Pump Design HeadHigher Pump EfficiencyLower potential impact from Low Delta T (can over pump chillers if needed)50
Variable Primary Flow (VPF) System ArrangementAdvantagesMedium Installed Cost (approx. 5% compared P/S)No secondary Pumps or piping, valves, electrical, installation, etc.Offset somewhat by added 2W Bypass Valve and more complex controlsLess Plant Space Needed (vs P/S)Best Chilled Water Pump Energy Consumption (most optimeady configuration)VSD energy savingsLower Pump Design HeadHigher Pump EfficiencyLower potential impact from Low Delta T (can over pump chillers if needed)DisadvantagesRequires more robust (complex and properly calibrated) control systemRequires coordinated control of chillers, isolation valves, and pumpsPotentially longer commissioning times to tune the systemNeed experienced facility manager to operate/maintain properly51
Low Delta T SyndromeSecondary PumpsDesign Delta T 12ºF44 F56 F52
Major Causes of Low Delta TDirty Coils53
Chilled Water CoilT54
Chilled Water CoilLoad Flow X Delta T55
Chilled Water CoilLoad Flow X Delta T56
Major Causes of Low Delta TDirty CoilsControls CalibrationLeaky 2-Way ValvesCoils Piped-Up Backwards57
Chilled Water CoilT58
Major Causes of Low Delta TDirty CoilsControls Calibrati
Chiller Load (min load - no variance, full load - max variance) System Water Volume (more water, more thermal capacitance, faster variance allowed) Active Loads (near or far from plant) Typical VSD pump ramp rate setting of 10%/minute (accel/decel rates set to 600 seconds) 3377. Varying Flow Through Chillers - Issues Issue During Normal Operation Chiller Type (centrifugal fast, absorbers slow .
