Chilled Water Piping Distribution Systems ASHRAE 3-12-14

1 Roy HubbardAgenda Understandingthe three basic Piping Systems Design and Off-design operation Advantages and Disadvantages Low DeltaT Syndrome causes, effects, and solutions Design & Control Considerations (VPF) Chillers CHW pumps Bypass Valve2 Chilled Water Piping system Types (typical)ConfigurationLoadValvesInstalle d CostPumping CostConstant Primary Flow3-wayLowestHighest3 Primary / Secondary2-wayHighestMediumVariable Primary Flow2-wayMediumLowestSecondary pumps =Flow X DeltaTLoadLoad Equation=Flow X DeltaTLoad4 Secondary PumpsConstant Primary Flow (CPF)5 Secondary pumps = Flow X DeltaTLoadConstant Primary Flow (CPF)Dedicated Pumping 6 Secondary Pumps56 F( C)56 F( C)(189 l/s) @ C)Constant Primary Flow at DesignPrimaryFlow3000gpm (189 l/s)Delta T12oF ( )Per ChillerSystemLoad500 Tons(1760kW)1500 Tons(5280kW)56 F( C)(63 l/s)56 F( C)(189 l/s) @ C)(1760 kW)(189 l/s) @ C)7 Secondary Pumps53 F( C)53 F( C)75%(189 l/s) @ C)Constant Primary Flow at 75% LoadPrimaryFlow3000gpm (189 l/s)Delta T9oF ( )Per ChillerSystemLoad375 Tons(1320kW)1125 Tons(3960kW)53 F( C)(63 l/s)56 F( C)(1760 kW)53 F( C)(189 l/s) @ C)

2 53 F(189 l/s) @ C)8 Secondary Pumps50 F(10 C)50 F(10 C)50%(189 l/s) @ C)Constant Primary Flow at 50% LoadPrimaryFlow3000gpm (189 l/s)Delta T6oF ( )Per ChillerSystemLoad250 Tons(880kW)750 Tons(2640kW)50 F(10 C)(63 l/s)56 F( C)(1760 kW)50 F(10 C)(189 l/s) @ 10 C)50 F(189 l/s) @ C)9 Secondary Pumps47 F( C)47 F( C)25%(189 l/s) @ C)Constant Primary Flow at 25% LoadPrimaryFlow3000gpm (189 l/s)Delta T3oF ( )Per ChillerSystemLoad125 Tons(440kW)375 Tons (1320kW)47 F( C)(63 l/s)56 F( C)(1760 kW)47 F( C)(189 l/s) @ C)47 F(189 l/s) @ C)10 Advantages Lowest installed cost Less plant space than P/S Easy to Control & Operate Easy to Commission Disadvantages Highest Plant Energy Cost (must run all, even at low loads)Constant Flow Primary Highest Plant Energy Cost (must run all, even at low loads)11 Primary (Constant) / Secondary (Variable)12 Primary (Constant) / Secondary (Variable)Secondary pumps =FlowX DeltaTSLoad= Flow X DeltaTPLoad13 Primary (Constant) / Secondary (Variable)Headered PumpingSecondary Pumps14 Primary (Constant) / Secondary (Variable)Dedicated Pumping Secondary Pumps15 Primary (Constant) / Secondary (Variable)

3 Rule of FlowSecondary PumpsPrimary flow must always be equal toor greater thanSecondary at DesignSecondary Pumps3000 GPM @ 44 F189 l/s @ C56 F( C)56 F( C)Per ChillerSystemLoad500 Tons (1760kW)1500 Tons (5280kW)PrimarySecondaryBypassFlow3000gp m (189 l/s)3000gpm (189 l/s)0gpm (0 l/s)Delta T12oF ( )12oF ( )----100 ft (303 kPa) Head100% Load = 100% Sec Flow(63 l/s)(1760 kW)56 F( C)56 F( C)(189 l/s) @ C)50 ft (152 kPa) Head0 GPM @ 44 F0 l/s @ C3000 GPM @ 56 F(189 l/s) @ C) F( C)17 Primary/Secondary at 75% LoadSecondary Pumps2250 GPM @ 44 F142 l/s @ C53 F( C)53 F( C)Per ChillerSystemLoad375 Tons (1320kW)1125 Tons (3960kW)PrimarySecondaryBypassFlow3000gp m (189 l/s)2250gpm (142 l/s)750gpm (47 l/s)Delta T9oF (5oC)12oF ( )----75%75% Load = 75% Sec Flow(63 l/s)(1760 kW)53 F( C)56 F( C)750 GPM @ 44 F47 l/s @ C2250 GPM @ 56 F(142 l/s) @ C)3000 GPM @ 53 F(189 l/s) @ C) F( C)18 Primary/Secondary at 50% LoadSecondary Pumps1500 GPM @ 44 F95 l/s @ C53 F( C)Per ChillerSystemLoad375 Tons (1320kW)750 Tons (2640kW)PrimarySecondaryBypassFlow2000gp m (126 l/s)1500gpm (95 l/s)500gpm (32 l/s)Delta T9oF (5oC)12oF ( )

4 ----50%50% Load = 50% Sec Flow(63 l/s)(1760 kW)53 F( C)56 F( C)500 GPM @ 44 F32 l/s @ C1500 GPM @ 56 F(95 l/s) @ C)2000 GPM @ 53 F(126 l/s) @ C) F( C)19 Primary/Secondary at 25% LoadSecondary Pumps750 GPM @ 44 F47 l/s @ CPer ChillerSystemLoad375 Tons (1320kW)375 Tons (1320kW)PrimarySecondaryBypassFlow1000gp m (126 l/s)750gpm (47 l/s)250gpm (16 l/s)Delta T9oF (5oC)12oF ( )----25%25% Load = 25% Sec Flow(63 l/s)(1760 kW)53 F( C)56 F( C)250 GPM @ 44 F16 l/s @ C750 GPM @ 56 F(47l/s) @ C)1000 GPM @ 53 F(63 l/s) @ C) F( C)20 But what controls the VSD s?What Controls the Flow of the Secondary Loop?

5 21 Valve Controls Leaving Air Temperature (LAT)22 Valve Controls Leaving Air Temperature (LAT)Set Point = 55 ( ) LATT23 Valve Controls Leaving Air Temperature (LAT)Set Point = 55 ( ) LATT24 Valve Controls Leaving Air Temperature (LAT)Set Point = 55 ( ) LATT25As Valve Opens, Pressure in loop lowersAs Valve Closes, Pressure in loop rises26 Pressure Differential Sensor Controls Secondary Pump SpeedDifferential 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 efficiencySet PointP=25 ft (76 kPa)P27 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)Primary (Constant) / Secondary (Variable) Lower Plant Energy (can sequence chillers and ancillary equipment) Versatile multi-circuit capabilityDisadvantages Medium Pump Energy Cost Highest Installed Cost (Sec pumps , Piping , etc.)

6 Potential for higher plant energy loss because of Low Delta T syndrome28 Variable Primary Flow29 Variable Primary Flow=FlowX DeltaTLoadVariable Primary Flowat 100% system LoadTwo-way valves control capacityBy varying flow of Water in coilsPrimary PumpsChillersClosed30 Primary/Secondary SystemVariable Primary SystemThree Differences?Variable Primary SystemPrimary PumpsChillers31 Variable Primary Flow at DesignVariable Primary Flowat 100% system LoadTwo-way valves control capacityBy varying flow of Water in coilsPer ChillerSystemLoad500 Tons (1760kW)1500 Tons (5280kW)PrimaryBypassFlow3000gpm (189 l/s)0gpm (0 l/s)Delta T12oF ( )----3000 GPM @ 44 F189 l/s @ C56 F( C)56 F( C)100% Load = 100% Flow56 F( C)0 GPM @ 44 F0 l/s @ C3000 GPM @ 56 F(189 l/s) @ C) F( C)3000 GPM @ 56 F(189 l/s) @ C)Primary Pumps1000 GPM each(63 l/s)500 Ton (1760 kW)Chillers56 F( C)

7 Closed32 Variable Primary Flow at 75% LoadVariable Primary Flowat 75% system LoadTwo-way valves control capacityBy varying flow of Water in coilsPer ChillerSystemLoad375 Tons (1320kW)1125 Tons (3960 kW)PrimaryBypassFlow2250 gpm (189 l/s)0 gpm (0 l/s)Delta T12oF ( )----2250 GPM @ 44 F142 l/s @ C56 F( C)56 F( C)75% Load = 75% Flow56 F( C)0 GPM @ 44 F0 l/s @ C2250 GPM @ 56 F(142 l/s) @ C) F( C)2250 GPM @ 56 F(142 l/s) @ C)Primary Pumps750 GPM each(47 l/s)56 F( C)Closed33 Variable Primary Flow at 50% LoadVariable Primary Flowat 50% system LoadTwo-way valves control capacityBy varying flow of Water in coilsPer ChillerSystemLoad375 Tons (1320kW)750 Tons (2640 kW)PrimaryBypassFlow1500 gpm (95 l/s)0 gpm (0 l/s)Delta T12oF ( )----1500 GPM @ 44 F95 l/s @ C56 F( C)50% Load = 50% Flow56 F( C)0 GPM @ 44 F0 l/s @ C1500 GPM @ 56 F(95 l/s) @ C) F( C)1500 GPM @ 56 F(95 l/s) @ C)Primary Pumps750 GPM each(47 l/s)56 F( C)

8 Closed34 Variable Primary Flow at 25% LoadVariable Primary Flowat 25% system LoadTwo-way valves control capacityBy varying flow of Water in coilsPer ChillerSystemLoad375 Tons (1320kW)375 Tons (1320 kW)PrimaryBypassFlow750 gpm (95 l/s)0 gpm (0 l/s)Delta T12oF ( )----750 GPM @ 44 F47 l/s @ C25% Load = 25% Flow56 F( C)0 GPM @ 44 F0 l/s @ C750 GPM @ 56 F(47 l/s) @ C) F( C)750 GPM @ 56 F(47 l/s) @ C)Primary Pumps750 GPM(47 l/s)56 F( C)Closed35 Variable Primary Flow in Bypass ModeSystem flow below chiller min flow (250 gpm)Variable Primary Flowat 25% system LoadTwo-way valves control capacityBy varying flow of Water in coilsPer ChillerSystemLoad50 Tons (176kW)50 Tons (176 kW)PrimaryBypassFlow250 gpm (95 l/s)150 gpm ( l/s)Delta T12oF ( )----100 GPM @ 44 @ C56 F( C)150 GPM @ 44 @ C100 GPM @ 56 F( ) @ C) F( C)250 GPM @ F( ) @ C)Primary Pumps250 GPM( l/s) F( C)36 Varying Flow Through Chillers - Issues Issue During Normal Operation Chiller Type (centrifugal fast, absorbers slow) Chiller Load (min load - no variance, full load - max variance)

9 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)3737 Varying Flow Through Chillers - Issues Issue During Normal Operation Chiller 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)3838 Varying Flow Through Chillers - Issues Issue During Normal Operation Chiller Type (centrifugal fast, absorbers slow) Chiller Load (min load - no variance, full load - max variance) system Water Volume (more Water , more thermal capacitance, faster varianc)