variable primary flow.ppt
TRANSCRIPT
Proprietary & Confidential1Johnson Controls
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Presentation Title
Presenters:Andrew Clancy, Business Development Sr Manager - NavyScott Schmittel, Account ExecutiveJason Richwine , Application Engineer
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Consulting Engineer’s Office
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The Project
University Classroom Building
Central Chilled Water Plant
This building cannot be connected
Cooling tower will not work
Variable Primary Flow
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Discovery
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Scott Branch Account Manager - Buddy
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Discovery
Low Delta T Syndrome
300Tons – Cooling
Two 150 Ton Chillers
Scroll
Screw
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Johnson Controls Capabilities
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Dave Jason Richwine
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Primary/Secondary System
Constant Speed Primary Pumps
Variable Speed Secondary Pumps
Common Pipe
Typical load with two way valves
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Primary/Secondary System at Design
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
1080 GPM @ 54.0 °F
Secondary Pumps
1080 GPM @ 44.0 °F
Typical Coil
No flow
44.0 °F
54.0 °F
150 ton chillers360 GPM Each54.0-44.0°F
1080 GPM @ 54.0 °F
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Primary/Secondary System at Part Load
51.5 °F
51.5 °F
51.5 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
1080 GPM @ 51.5 °F
Secondary Pumps
810 GPM @ 44.0 °F
Typical Coil
44.0 °F
54.0 °F
270 GPM @ 44.0 °F
810 GPM @ 54.0 °F
75% System Load
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Primary/Secondary System
54.0 °F
54.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
720 GPM @ 54.0 °F
Secondary Pumps
720 GPM @ 44.0 °F
Typical Coil
44.0 °F
54.0 °F
No Flow
720 GPM @ 54.0 °F
OFF 67% System LoadClean Coils
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Primary/Secondary System
54.0 °F
54.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
720 GPM @ 54.0 °F
Secondary Pumps
792 GPM @ 44.0 °F
Typical Coil
44.0 °F
53.0 °F
72 GPM @ 53.0 °F
792 GPM @ 53.0 °F
OFF 67% System LoadDirty Coils
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Primary/Secondary System
53.0 °F
53.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
720 GPM @ 53.0 °F
Secondary Pumps
792 GPM @ 44.8 °F
Typical Coil
44.8 °F
53.0 °F
72 GPM @ 53.0 °F
792 GPM @ 53.0 °F
OFF 67% System LoadDirty Coils
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Primary/Secondary System
51.9 °F
51.9 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
720 GPM @ 51.9 °F
Secondary Pumps
900 GPM @ 44.8 °F
Typical Coil
44.8 °F
51.9 °F
180 GPM @ 51.9 °F
900 GPM @ 51.9 °F
OFF 67% System LoadDirty Coils
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Primary/Secondary System
Variable Primary System
Secondary Pumps
Primary Pumps
Primary Pumps
Flow Meter
BypassValve
Automatic Isolation Valve
Typical load with 2 way valve
Typical load with 2 way valve
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Variable Primary System at Design
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
1080 GPM @ 56.0 °F
1080 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
150 ton chillers360 GPM Each54.0-44.0°F
Typical load with two way valves
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Variable Primary System – Part Load
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
270 GPM Each
810 GPM @ 54.0 °F
810 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve
75% System Load
810 GPM @ 54.0 °F
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Variable Primary System – Part Load
54.0 °F
54.0 °F
44.0 °F
44.0 °F
Primary Pumps
180 GPM Each
540 GPM @ 54.0 °F
540 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve
50% System LoadChiller off
540 GPM @ 54.0 °F
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Variable Primary System – Min Flow (120 gpm each)
51.5 °F
44.0 °F
Primary Pumps
120 GPM (one operating)
120 GPM @ 51.5 °F
90 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Open
Typical load with two way valve
System flow below chiller minimum flow
Chiller off
Chiller off
Closed
Closed
30 GPM @ 44.0
90 GPM @ 54.0 °FFlow meter
Pumps off
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Designing a VPF Bypass
Size for minimum flow through one chiller
Bypass valve shall be the normally open type
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
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Variable Primary System – Min Flow (120 gpm each)
51.5 °F
44.0 °F
Primary Pumps
120 GPM (one operating)
120 GPM @ 51.5 °F
90 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Open
Typical load with two way valve
Pumps maintain system pressure
Bypass maintains minimum flow
Chiller off
Chiller off
Closed
Closed
30 GPM @ 44.0
90 GPM @ 54.0 °FFlow meter
Pumps off
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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 120 + 120*10% = 132 gpm
Calibrate flow meter at least as often as manufacturer recommends
Buy the best
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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
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Selecting VPF Chiller Isolation Valves
All valve pressure ratings greater than pump dead head
Linear characteristic - valve position % equals flow %
Modulating valve with slow actuator
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VPF Design Considerations
Flow rate changes – Staging on additional chillers
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Variable Primary System (1 chiller running)
54.0 °F
44.0 °F
Primary Pumps
120 GPM Each
360 GPM @ 546.0 °F
360 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve360 GPM
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Variable Primary System (Staging on second chiller)
54.0 °F
45.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 55.0 °F
396 GPM @ 45.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve396 GPM
Need to add chiller
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Variable Primary System (Open isolation valve)
55.0 °F
35.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 55.0 °F
396 GPM @ 45.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve198 GPM
198 GPM55.0 °F
55.0 °F
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Variable Primary System (Open isolation valve)
55.0 °F
35.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 55.0 °F
396 GPM @ 45.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve198 GPM
198 GPM55.0 °F
55.0 °F
LCHWT approaches 35F
LWT Cutout at 40F
Off goes chiller 1
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Variable Primary System (Open isolation valve)
55.0 °F
40.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 55.0 °F
396 GPM @ 45.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve264 GPM
132 GPM55.0 °F
55.0 °F
Open slowly
Chiller 2 comes on when flow exceeds minimum
Chiller 1 unloads to maintain set point
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Variable Primary System (Open isolation valve)
54.0 °F
44.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 54.0 °F
396 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve198 GPM
198 GPM44.0 °F
54.0 °F
Both valves fully open
Flow equalizes
Chillers modulate to maintain chilled water set point
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Variable Primary System (Open isolation valve)
55.0 °F
42.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 55.0 °F
396 GPM @ 45.9 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve276 GPM
120 GPM55.0 °F
55.0 °F
Open to change flow 36gpm/min
Chiller 2 comes on when flow is 120gpm – in 3 min 20 sec
Chiller 1 is still producing 100% capacity
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Variable Primary System (Open isolation valve)
54.0 °F
44.0 °F
Primary Pumps
132 GPM Each
396 GPM @ 54.0 °F
396 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valve198 GPM
198 GPM44.0 °F
54.0 °F
Both valves fully open
Flow equalizes
Chillers modulate to maintain chilled water set point
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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
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Setting Flow Rate of Change
Start with 10% of design flow per minute
YORK 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
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Variable Primary System – Handling Rapidly Decreasing Loads
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
1080 GPM @ 56.0 °F
1080 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
150 ton chillers360 GPM Each54.0-44.0°F
Typical load with two way valves
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Variable Primary System – Handling Rapidly Decreasing Loads
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
360 GPM Each
1080 GPM @ 44.0 °F
0 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Open
150 ton chillers360 GPM Each54.0-44.0°F
Typical load with two way valves
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Variable Primary System – Handling Rapidly Decreasing Loads
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
324 GPM Each
972 GPM @ 44.0 °F
972 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valves
Close the closest valve first
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Variable Primary System – Handling Rapidly Decreasing Loads
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
288 GPM Each
864 GPM @ 44.0 °F
864 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valves
Close the next closest valve
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Variable Primary System – Handling Rapidly Decreasing Loads
54.0 °F
54.0 °F
54.0 °F
44.0 °F
44.0 °F
44.0 °F
Primary Pumps
252 GPM Each
756 GPM @ 44.0 °F
756 GPM @ 44.0 °F
Automatic Isolation Valve
Bypass Closed
Typical load with two way valves
Close the next closest valve
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Selecting a Small Tonnage Chiller for VPF
Look at all applicable selections
Evaluate based on full load performance
Evaluate based on part load performance
Evaluate based on evaporator minimum flow
Evaluate based on required temperature control accuracy
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Selecting a Small Tonnage Chiller for VPF
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Optimizing Air-cooled Chiller Operation
Optimize Chiller Efficiency
Optimize Pump Efficiency
Define loading and unloading sequences
Model annual energy use
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Optimizing Air-cooled Chiller Operation
Chiller is more efficient at 80% than at 40% for the given ambient temperature.
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288 GPM
Optimizing Air-cooled Chiller Operation
9 Ft. Head
288 GPM144 GPM each 2.5 Ft. Head
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Optimizing Air-cooled Chiller Operation
Chiller is more efficient at 40% than at 80% for the given ambient temperature.
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Optimizing Air-cooled Chiller Operation
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STC Special Case – How would you design this system?
The Setup 20 ton VPF cooling system
One chiller, one AHU
44F chilled water with 54F return
Chiller has two scroll compressors (0%, 50%, or 100% capacity)
The Problem Load remains constant at around 55% or 60% for several hours
Chiller can’t meet demand with one compressor on
Chiller severely over-cools with both compressors on
System is unstable
The Hint Start by thinking about how increasing system water volume can add stability
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Summary
How VPF systems work
How to select control components for system stability
How to sequence chillers on and off
How to control the chillers, pumps, and valves
How to size the bypass
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