Variable Primary Systems Add Photo/Graphic

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Lorraine Andrews
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1 Variable Primary Systems Add Photo/Graphic Richard Roberts Systems Sales Engineer January 03, 2012

2 Variable Primary Flow Only (VPF) Advantages Lower Capital Cost Installed (vs Primary/Secondary) No secondary pumps/piping/valves/electrical to buy and install Fewer piping and electrical connections less field labor No large common pipe, but smaller bypass pipe/valve/flow meter/controls Lower CHW Pumping Energy Potential Savings, may reduce pump horsepower and initial cost. Reference ARTI (Air Conditioning & Refrigeration Technology Institute) Estimated energy savings of 3 to 8 percent Estimating initial cost saving of 4 to 8 percent Estimating life cycling saving cost 3 to 5 percent

3 Variable Primary Flow Only (VPF) Advantages Smaller Footprint (vs Primary/Secondary) More space available for better access to the other equipment Higher Reliability Fewer mechanical components Any pump can serve any chiller

4 Variable Primary Flow Only (VPF) Disadvantages Potentially higher 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 Potentially longer commissioning time and start-up (ref ASHRAE Taylor article) Requires greater operator sophistication Sudden flow variation through the chiller More of an issue when additional machines are staged on More complexity bypass control

5 Primary/Secondary System Variable Speed Secondary Pumps Constant Speed Common Pipe valves

6 Primary/Secondary System at Design 150 ton chillers 360 GPM Each - Secondary Pumps 1080 Coil 360 GPM Each No flow

7 Primary/Secondary System at Part Load % System Load 51.5 Secondary Pumps Coil 360 GPM Each

8 Primary/Secondary System OFF 67% System Load Clean Coils Secondary Pumps 720 Coil 360 GPM Each No Flow

9 Primary/Secondary System OFF 67% System Load Dirty Coils Secondary Pumps Coil 360 GPM Each

10 Primary/Secondary System OFF 67% System Load Dirty Coils Secondary Pumps Coil 360 GPM Each

11 Primary/Secondary System Secondary Pumps 2 valve Automatic Isolation Valve Variable Primary System Flow Meter Valve 2 valve

12 Variable Primary System at Design Automatic Isolation Valve 150 ton chillers 360 GPM Each GPM Each valves

13 Variable Primary System Part Load Automatic Isolation Valve 75% System Load GPM Each valve

14 Variable Primary System Part Load Automatic Isolation Valve Chiller off 50% System Load GPM Each valve

15 Variable Primary System Min Flow (120 gpm each) Automatic Isolation Valve Chiller off System flow below chiller minimum flow Chiller off Pumps off GPM (one operating) 51.5 Open 30 valve Flow meter 90

16 Variable Primary System Min Flow (120 gpm each) Automatic Isolation Valve Chiller off Pumps maintain system pressure maintains minimum flow Chiller off Pumps off GPM (one operating) 51.5 Open 30 valve Flow meter 90

17 Designing a VPF Size for minimum flow through one chiller Valve head ratings must be higher than pump dead head Linear characteristic - valve position % equals flow % Fast actuator Valve control range 100:1 Flow meter controls bypass to maintain chiller minimum flow

18 Selecting a VPF Flow Meter for Small Tonnage Systems Best accuracy job can afford Minimum +/- 5% at evaporator minimum flow Set bypass to open when flow equals minimum plus 2 times flow meter accuracy rating Example: 120 gpm minimum, flow meter +/- 5%, set minimum flow at *10% = 132 gpm Calibrate flow meter at least as often as manufacturer recommends Buy the best

19 Selecting VPF AHU Control Valves All valve pressure ratings greater than pump dead head Sized by pressure % valve position equals % coil capacity Control range 200:1

20 Selecting VPF Chiller Isolation Valves All valve pressure ratings greater than pump dead head Linear characteristic - valve position % equals flow % Modulating valve slow actuator

21 Variable Primary System (1 chiller running) Automatic Isolation Valve GPM Each 360 GPM valve

22 Variable Primary System (Staging on second chiller) Automatic Isolation Valve Need to add chiller GPM Each 396 GPM 45.0 valve

23 Variable Primary System (Open isolation valve) Automatic Isolation Valve GPM GPM Each GPM 35.0 valve

24 Variable Primary System (Open isolation valve) Automatic Isolation Valve LCHWT approaches 35F LWT Cutout at 40F Off goes chiller GPM GPM Each GPM 35.0 valve

25 Variable Primary System (Open isolation valve) Automatic Isolation Valve Open slowly Chiller 2 comes on when flow exceeds minimum GPM 55.0 Chiller 1 uns to maintain set point GPM Each GPM 40.0 valve

26 Variable Primary System (Open isolation valve) Automatic Isolation Valve Open to change flow 36gpm/min Chiller 2 comes on when flow is 120gpm in 3 min 20 sec GPM 55.0 Chiller 1 is still producing 100% capacity GPM Each GPM 42.0 valve

27 Variable Primary System (Open isolation valve) Automatic Isolation Valve Both valves fully open Flow equalizes Chillers modulate to maintain chilled water set point 198 GPM GPM Each 198 GPM valve 396

28 Staging on Chiller 2 in VPF Systems Maintain minimum flow through the operating chiller Avoid sudden changes in flow anywhere in the system Prefer schemes that work when bringing on any chiller

29 Setting Flow Rate of Change Start 10% of design flow per minute Most small tonnage chillers can handle faster changes If the project requires rapid flow changes, contact application engineering If problems occur during operation, adjust the rate

30 Variable Primary System Handling Rapidly Decreasing Loads Automatic Isolation Valve 150 ton chillers 360 GPM Each GPM Each valves

31 Variable Primary System Handling Rapidly Decreasing Loads Automatic Isolation Valve 150 ton chillers 360 GPM Each GPM Each Open valves 1080

32 Variable Primary System Handling Rapidly Decreasing Loads Automatic Isolation Valve Close the closest valve first GPM Each valves 972

33 Variable Primary System Handling Rapidly Decreasing Loads Automatic Isolation Valve Close the next closest valve GPM Each valves 864

34 Variable Primary System Handling Rapidly Decreasing Loads Automatic Isolation Valve Close the next closest valve GPM Each valves 756

35 Questions?

Commissioning chilled water TES systems

Commissioning chilled water TES systems Chilled water thermal energy storage systems should be as simple as possible. The success of a project depends on documenting and continually evaluating the owner