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Chilled Water Piping Systems (VPF Focus). Agenda – Chilled Water Distribution Systems Chilled Water Distribution Systems Primary (Constant) / Secondary.

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Presentation on theme: "Chilled Water Piping Systems (VPF Focus). Agenda – Chilled Water Distribution Systems Chilled Water Distribution Systems Primary (Constant) / Secondary."— Presentation transcript:

1 Chilled Water Piping Systems (VPF Focus)

2 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

3 Primary (Constant Flow) / Secondary (Variable Flow)

4 Primary/Secondary System Primary Pumps Secondary Pumps Common Pipe Typical load with two way valve

5 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

6 Primary/Secondary System at Design 56.0 °F 44.0 °F Primary Pumps 1000 GPM Each °F Secondary Pumps °F Typical Coil No flow 44.0 °F 56.0 °F 500 ton chillers 1000 GPM Each °F

7 Primary/Secondary System at Part Load 53.0 °F 44.0 °F Primary Pumps 1000 GPM Each °F Secondary Pumps °F Typical Coil 44.0 °F 56.0 °F °F °F 75% System Load

8 Primary/Secondary System 53.0 °F 44.0 °F Primary Pumps 1000 GPM Each °F Secondary Pumps °F Typical Coil 44.0 °F 56.0 °F °F °F OFF 50% System Load

9 Low Delta T Syndrome

10 10 Dirty Coils Major Causes of Low Delta T

11 Chilled Water Coil

12 12 Dirty Coils Controls Calibration Leaky 2 Way Valves 3 Way Valves at end of Index circuit Major Causes of Low Delta T

13 Primary/Secondary System Primary Pumps Secondary Pumps Common Pipe

14 Primary/Secondary System Primary Pumps Secondary Pumps Common Pipe

15 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

16 Chilled Water Coil

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

18 18 100% Load = 100% Sec Flow Primary (Constant) / Secondary (Variable) Ideal Operation Secondary Pumps Primary Pumps Decoupler /Bypass 100% Flow = 3000 gpm 0 gpm 1212

19 Secondary Pumps Primary Pumps Decoupler /Bypass 67% Flow = 2000 gpm 0 gpm 19 67% Load = 67% Sec Flow Primary (Constant) / Secondary (Variable) Ideal Operation 1212

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

21 Secondary Pumps Primary Pumps Decoupler /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 1010

22 Higher Secondary Pump Energy Higher CHW Plant Chiller/Auxiliary Energy Major Effects of Low Delta T

23 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).

24 Primary/Secondary System Primary Pumps Secondary Pumps Common Pipe P

25 Primary Only (Variable Flow)

26 Primary/Secondary System Variable Primary System Secondary Pumps Primary Pumps Flow Meter Bypass Valve Automatic Isolation Valve Typical load with 2 way valve

27 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

28 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

29 Variable-Primary-Flow System Primary Pumps Flow Meter Typical load with two way valve Automatic Isolation Valve Bypass

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

31 Variable Primary System – Part Load 56.0 °F 44.0 °F Primary Pumps 750 GPM Each °F °F Automatic Isolation Valve Bypass Closed Typical load with two way valve 75% System Load

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

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

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

35 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

36 Chiller Design Considerations Flow rate changes – Staging on additional chillers

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

38 Variable Primary System (Staging on second chiller) 57.0 °F 45.0 °F Primary Pumps 333 GPM Each °F °F Automatic Isolation Valve Bypass Closed Typical load with two way valve 1100 GPM Need to add chiller

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

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

41 Variable Primary System (Open isolation valve slowly) 57.0 °F 45.0 °F Primary Pumps 333 GPM Each °F °F Automatic Isolation Valve Bypass Closed Typical load with two way valve 1100 GPM Open over 1.5 to 2 min

42 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 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 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 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 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 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)

47 Chilled Water Piping Systems (VPF Focus) Questions?

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

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


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