©2003American Standard In
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©2003American Standard In
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Variable Primary chilled water systems
©2003American Standard In
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©2003American Standard In
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variable primary chilled water systems
Today’s Topicsvariable primary chilled water systems
Today’s Topics
� Hyatt Singapore Hotel
� From Primary–Secondary to Variable Primary
� Variable Primary advantages
� Chiller selection for Variable Primary
� More System efficiency
� Reference
� Answers to your questions
©2003American Standard In
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©2003American Standard In
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Hyatt Singapore Hotel
©2003American Standard In
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©2003American Standard In
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chilled water systems
From Primary Secondary
© 2003 American Standard Inc.
© 2003 American Standard Inc.
©2003American Standard In
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©2003American Standard In
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12.0°C392 lps
7.0°C 392 lps
12.0°C
12. 0 C 7.0°C
2
12.0°C 7.0°C650 tons
3
12.0°C 7.0°C650 tons
498 lps(each)
bypass(decoupler)
Primary–Secondarydesign
Primary–Secondarydesign
primarypumps
primarypumps
secondarypumps
secondarypumps
12. 0 C 7.0°C650 tons
1
650 tons
©2003American Standard In
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©2003American Standard In
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12.0°C320 lps
7.0°C 392 lps
12.0°C
11.1°C 7.0°C
2
11.1°C 7.0°C650 tons
3
11.1°C 7.0°C650 tons
498 lps(each)
bypass(decoupler)
primarypumps
primarypumps
secondarypumps
secondarypumps
11.1°C 7.0°C650 tons
1
650 tons
Primary–Secondarypart load
Primary–Secondarypart load
7.0°C72 lps
©2003American Standard In
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©2003American Standard In
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∆∆∆∆P
(typical)
Variable Primary
design
Variable Primary
design
12.0°C
331 lps
7.0°C
331 lps
12.0°C
12.0°C 7.0°C800 tons
1
12.0°C 7.0°C700 tons
2
12.0°C 7.0°C700 tons
383 lps(each)
©2003American Standard In
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©2003American Standard In
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12.0°C300 lps
12.0°C
7.0°C300 lps
Variable Primarypart load
Variable Primarypart load
12.0°C 7.0°C100 lps
1
12.0°C 7.0°C100 lps
2
12.0°C 7.0°C100 lps
3
∆∆∆∆P
(typical)
300 lps
0 lps
75 lps(each)
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©2003American Standard In
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∆∆∆∆P
(typical)
12.0°C20 lps
11.1°C
7.0°C20 lps
Variable Primarysystem flow< minimumchiller flow rate
Variable Primarysystem flow< minimumchiller flow rate
11.1 °C 7.0°C24 lps
1
off
2
off
3
4 lps
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primary–secondary variable primary
From primary–secondary to variable primary
Comparative SummaryFrom primary–secondary to variable primary
Comparative Summary
production pumps (primary)
• 1 per chiller None, so
• Occupies less space
• Requires fewer connections
©2003American Standard In
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©2003American Standard In
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primary–secondary variable primary
From primary–secondary to variable primary
Comparative SummaryFrom primary–secondary to variable primary
Comparative Summary
production pumps (primary)
• 1 per chiller None, so
• Occupies less space
• Requires fewer connections
• Selected for distribution pressure drop (piping,coil, valve)
• Controlled from system∆P sensor
distribution pumps (secondary)
• Selected for system pressure drop (coil, piping, valve, plus chiller)
• Controlled from system∆P sensor
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©2003American Standard In
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primary–secondary variable primary
From primary–secondary to variable primary
Comparative SummaryFrom primary–secondary to variable primary
Comparative Summary
Bypass line • No obstructions
• Sized for 120% largest chiller flow
• “Open” most often
• Control valve
• Sized for largest minimum chiller flow
• Closed most often
©2003American Standard In
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©2003American Standard In
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primary–secondary variable primary
From primary–secondary to variable primary
Comparative SummaryFrom primary–secondary to variable primary
Comparative Summary
Bypass line • No obstructions
• Sized for 120% largest chiller flow
• “Open” most often
• Control valve
• Sized for largest minimum chiller flow
• Closed most often
Load determinant Temperature difference Flow through evaporator
©2003American Standard In
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©2003American Standard In
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primary–secondary variable primary
From primary–secondary to variable primary
Comparative SummaryFrom primary–secondary to variable primary
Comparative Summary
Bypass line • No obstructions
• Sized for 120% largest chiller flow
• “Open” most often
• Control valve
• Sized for largest minimum chiller flow
• Closed most often
Load determinant Temperature difference Flow through evaporator
Flow-monitoring Temperature sensors orflow meter
Flow meter or differential pressure sensors
© 2003 American Standard Inc.
Variable Primary chilled water systems
Advantages
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©2003American Standard In
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variable primary chilled water systems
Advantagesvariable primary chilled water systems
Advantages
� Reduces capital investment
� Saves mechanical-room space
� Simplifies control
� Improves system reliability
� Improved chiller performance
� Saves energy
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©2003American Standard In
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Variable Primary advantages
Lower Capital CostVariable Primary advantages
Lower Capital Cost
� Fewer …
� Pumps
� Motors
� Pump bases
� Starters and wiring
� Fittings and piping
� Controls
� Less labor
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Variable Primary advantages
More Available SpaceVariable Primary advantages
More Available Space
Opportunity to …
� Add other equipment
� Select larger, more efficient chillers
� Improve service access
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Variable Primary advantages
Simplified ControlVariable Primary advantages
Simplified Control
� Unfetters chillers from flow-based control
� Operates distribution pumps to transport water
… not to start/stop chillers
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©2003American Standard In
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Variable Primary advantages
Improved ReliabilityVariable Primary advantages
Improved Reliability
Provides system with …
� Fewer pumps and accessories
� Fewer chiller recovery options
� Fewer pump recovery options
� Better balance between pumps and chillers online
©2003American Standard In
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©2003American Standard In
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0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
10 20 30 40 50 60 70 80 90 100
CenTraVac Part Load Performance CTV-1% Load vs. kW/ton -- using ARI Relief Method
Version 24.08, REVL 55066
kW
/ton
% Load
Improved Chiller Performance
Part Load [ARI Relief]
Improved Chiller Performance
Part Load [ARI Relief]
©2003American Standard In
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©2003American Standard In
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Improved Chiller Performance
Part Load [no ARI Relief]
Improved Chiller Performance
Part Load [no ARI Relief]
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
20 30 40 50 60 70 80 90 100
CenTraVac Part Load Performance CTV-1% Load vs. kW/ton -- using Constant Condenser Method
Version 24.08, REVL 55066
kW
/ton
% Load
primary/secondary
variable primary
©2003American Standard In
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©2003American Standard In
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Variable Primary advantages
Greater Flexibility Variable Primary advantages
Greater Flexibility
any flow rate …
any ∆∆∆∆T
© 2003 American Standard Inc.
Variable Primary chilled water systems
Chiller selection considerations
©2003American Standard In
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©2003American Standard In
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chiller selection
Considerationschiller selection
Considerations
� Evaporator flow limits
� Rate-of-change tolerance
� Flow “range-ability”
� Difference between design flow rate and evaporator’s minimum flow limit
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©2003American Standard In
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chiller selection considerations
Evaporator Flow Limitschiller selection considerations
Evaporator Flow Limits
Flooded or falling-film evaporators …
� Refrigerant circulates around tubes
� Water flows through tubes
� Water velocity delimits acceptable flow rates
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©2003American Standard In
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chiller selection considerations
Evaporator Flow Limitschiller selection considerations
Evaporator Flow Limits
traditional limits 0.92(3.0) 3.4 – 3.6 (11–12)
revised limits: standard 0.46(1.5) —tubes
high- 0.61(2.0) —performancetubes
flooded or falling-film evaporators
water velocity, m/s (fps)
minimum maximum
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©2003American Standard In
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chiller selection considerations
Rate-of-Change Tolerancechiller selection considerations
Rate-of-Change Tolerance
allowable flow-rate change*chiller (compressor) type (% of design flow per minute)
• centrifugal 10% for process cooling30% for comfort cooling
* Tolerances pertain specificallyto Trane chillers
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©2003American Standard In
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chiller selection considerations
Rate-of-Change Tolerancechiller selection considerations
Rate-of-Change Tolerance
New chiller control technology:
� Centrifugal … •“feed forward”Control
•flow compensation
•50% per minute,all applications
©2003American Standard In
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Minimum Flow RateMinimum Flow Rate
design flow
minimum flow
minimum flow= 1 meter per second
Evaporator
Condenser
= greater than 2
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©2003American Standard In
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unsuited for
Variable Primaryunsuited for
Variable Primary
� Inadequate control capability
� Reciprocating chillers
� Return-water thermostats
� Insufficient chiller unloading
� Vintage chiller controls
� Poor financial return
(Consider chilled water reset instead)
©2003American Standard In
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©2003American Standard In
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Variable Primary Chilled Water System in Hyatt Singapore Hotel
©2003American Standard In
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©2003American Standard In
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Saving 30% Kwhr
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©2003American Standard In
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Reduce 25% KW Demand
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©2003American Standard In
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xxxxx
Variable Primary Chilled Water System in Another Singapore Hotel
©2003American Standard In
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©2003American Standard In
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Summary variable primary chilled water systems
AdvantagesSummary variable primary chilled water systems
Advantages
� Reduces capital investment
� Saves mechanical-room space
� Simplifies control
� Improves system reliability
� Improved chiller performance
� Saves energy
©2003American Standard In
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©2003American Standard In
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System Efficiency in Hotel
MoreSystem Efficiency in Hotel
More
� Increase chilled water supply temperature difference to 7°C(5°C/12°C)
� Increase range of cooling tower to 7°C (30°C/37°C)
� Side stream heat recovery
� Stepless FCU
©2003American Standard In
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©2003American Standard In
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∆∆∆∆P
(typical)
Chilled Water Range (5.0°C / 12.0°C )
Chilled Water Range (5.0°C / 12.0°C )
12.0°C
240 lps
5.0°C
240 lps
12.0°C
12.0°C 5.0°C800 tons
1
12.0°C 5.0°C700 tons
2
12.0°C 5.0°C700 tons
360 lps(each)
©2003American Standard In
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©2003American Standard In
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∆∆∆∆P
(typical)
Chilled Water Range (from 414 l/s ,30°C/ 35°C)
(to 300 l/s ,30°C / 37°C)
Chilled Water Range (from 414 l/s ,30°C/ 35°C)
(to 300 l/s ,30°C / 37°C)
300 lps
37.0°C
300 lps
30.0°C
30.0°C 37.0°C800 tons
1
30.0°C 37.0°C700 tons
2
30.0°C 37.0°C700 tons
3
coolingtower
coolingtower
coolingtower
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©2003American Standard In
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heat-recoverychiller
∆∆∆∆P
(typical)
Side stream Heat recovery design
Side stream Heat recovery design
12.0°C
240 lps
5.0°C
240 lps
12.0°C
12.0°C 5.0°C800 tons
1
12.0°C 5.0°C700 tons
2
12.0°C 5.0°C700 tons
3
©2003American Standard In
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©2003American Standard In
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Reference
• VARIABLE PRIMARY FLOW CHILLED
WATER SYSTEMS: POTENTIAL
BENEFITS AND APPLICATION ISSUES
Final Report Volume 1, March 2004, ARI CR21
• Variable Primary Flow Systems by Mick Schwedler,
P.41-44, HPAC April 2000
• Primary-Only vs. Primary-Secondary Variable Flow
Systems by Steven T. Taylor, P.E. , vol. 44, no.
2, p. 25-29 ,ASHRAE Journal, February 2002
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©2003American Standard In
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Answers to yourquestions
Variable Primary chilled water systems