Chilled Water Piping Systems (VPF Focus)

Agenda – 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 500 ton chillers 1000 GPM Each 56.0-44.0°F 44.0 °F 56.0 °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 75% System Load 44.0 °F 53.0 °F 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 10 10

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 12 12

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 15 15

Chilled Water Coil

Primary (Constant) / Secondary (Variable) P Load = Flow X Delta T S Load = Flow X Delta T Secondary Pumps Primary Pumps Typical load with 2 way valve Decoupler /Bypass 17 17

Primary (Constant) / Secondary (Variable) Ideal Operation 100% Load = 100% Sec Flow Secondary Pumps Primary Pumps Decoupler /Bypass 100% Flow = 3000 gpm 0 gpm 12 18 18

Primary (Constant) / Secondary (Variable) Ideal Operation 67% Load = 67% Sec Flow Secondary Pumps Primary Pumps Decoupler /Bypass 67% Flow = 2000 gpm 0 gpm 12 19 19

Primary / Secondary Rule of Flow Primary flow must always be equal to or greater than Secondary flow. 20 20

Primary (Constant) / Secondary (Variable) Low Delta T Operation 67% Load = 80% Sec Flow Secondary Pumps Primary Pumps Decoupler /Bypass 100% Flow = 3000 gpm 80% Flow = 2400 gpm (400 gpm over-pumped) 600 gpm 10 21 21

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). 23 23

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 Typical load with two way valve Primary Pumps Bypass Flow Meter

Variable Primary System at Design 500 ton chillers 1000 GPM Each 56.0-44.0°F Automatic Isolation Valve 56.0 °F 44.0 °F 56.0 °F 44.0 °F 3000 GPM @ 44.0 °F Typical load with two way valve 56.0 °F Primary Pumps 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 2250 GPM @ 44.0 °F Typical load with two way valve 56.0 °F Primary Pumps 750 GPM Each 44.0 °F Bypass Closed 2250 GPM @ 56.0 °F

Variable Primary System – Part Load Chiller off 50% System Load Automatic Isolation Valve Pump off 56.0 °F 44.0 °F 1500 GPM @ 44.0 °F Typical load with two way valve 56.0 °F Primary Pumps 750 GPM Each 44.0 °F Bypass Closed 1500 GPM @ 56.0 °F

Variable Primary System – Part Load Chiller off 50% System Load Low Δ T Automatic Isolation Valve Pump on 52.0 °F 44.0 °F 2250 GPM @ 44.0 °F Typical load with two way valve 52.0 °F Primary Pumps 750 GPM Each 44.0 °F Bypass Closed 2250 GPM @ 52.0 °F

Variable Primary System – Min Flow (400 gpm each) Chiller off System flow below chiller minimum flow Automatic Isolation Valve Closed Chiller off Pumps off Closed 200 GPM @ 44.0 °F Typical load with two way valve 50.0 °F Primary Pumps 400 GPM (one operating) 44.0 °F Bypass Open 200 GPM @ 44.0 400 GPM @ 50.0 °F Flowmeter 200 GPM @ 56.0 °F

Bypass Valve Control Bypass Valve Control Maintain a minimum chilled water flow rate through the chillers Differential pressure measurement across each chiller evaporator Flow meter Bypass valve modulates open to maintain the minimum flow through operating chiller(s). Bypass valve shall be the normally open type. Pipe and valve sized for Min flow of operating chillers

Chiller Design Considerations Flow rate changes – Staging on additional chillers

Variable Primary System (1 chiller running) Automatic Isolation Valve 1000 GPM @ 44.0 °F Typical load with two way valve 56.0 °F Primary Pumps 333 GPM Each 44.0 °F 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 Typical load with two way valve 57.0 °F Primary Pumps 333 GPM Each 45.0 °F 1100 GPM Bypass Closed 1100 GPM @ 57.0 °F

Variable Primary System (Open isolation valve) Load = F X DT DT = 12 = 57- 45 24 Automatic Isolation Valve Load = 1/2F X 2DT DT = 24 24 LCHWT = 35! 1100 GPM @ 45.0 °F 550 GPM Typical load with two way valve 57.0 °F Primary Pumps 333 GPM Each 45.0 °F 550 GPM Bypass Closed 1100 GPM @ 57.0 °F

Variable Primary System (Open isolation valve) LCHWT approaches 35 LWT Cutout at 4 deg below 44 set-point or 40 Off goes chiller 1 Automatic Isolation Valve 1100 GPM @ 45.0 °F 550 GPM Typical load with two way valve 57.0 °F Primary Pumps 333 GPM Each 45.0 °F 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 Typical load with two way valve 57.0 °F Primary Pumps 333 GPM Each 45.0 °F 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) 42 42

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 43 43

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 44 44

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 45 45

Summary on VPF Design 46 Size equally with same WPDs (best) 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 pumping Pumps 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) 46 46

Chilled Water Piping Systems (VPF Focus) Questions?

Supply Terminal Balance and Service Valve 2-Way Control Return 2 Way Valve/Coil Detail Supply Terminal Balance and Service Valve 2-Way Control Return Service Valve Air

Electric Energy Cost Equations Mass Flow/t X Lift 33,015 X Efficiency X Hours Cost/Unit Energy = 0.7459 Mot Eff Lbs Refrig/hr X Head 33,015 X Comp Eff 0.7459 Mot Eff Chiller Energy Cost = X X Hours X Cost/Unit Energy GPM X Head 3960 X Pump Eff 0.7459 Mot Eff Pump Energy Cost = X X Hours X Cost/Unit Energy CFM X TSP 6356 X Fan Eff 0.7459 Mot Eff Fan Energy Cost = X X Hours X Cost/Unit Energy 36