2_VPF Hong Kong rv1

©2003American Standard In

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Variable Primary chilled water systems


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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


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Hyatt Singapore Hotel


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chilled water systems

From Primary Secondary

© 2003 American Standard Inc.



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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


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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


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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)


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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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∆∆∆∆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


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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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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


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Comparative Summary




• Control valve



Load determinant Temperature difference Flow through evaporator


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Comparative Summary




• Control valve



Load determinant Temperature difference Flow through evaporator

Flow-monitoring Temperature sensors orflow meter

Flow meter or differential pressure sensors



Advantages


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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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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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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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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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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


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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]


Part Load [ARI Relief]


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Part Load [no ARI Relief]


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


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Greater Flexibility Variable Primary advantages

Greater Flexibility

any flow rate …

any ∆∆∆∆T



Chiller selection considerations


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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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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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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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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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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


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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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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)


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Variable Primary Chilled Water System in Hyatt Singapore Hotel


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Saving 30% Kwhr


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Reduce 25% KW Demand


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xxxxx

Variable Primary Chilled Water System in Another Singapore Hotel


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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


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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


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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)


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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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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


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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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Answers to yourquestions


2_VPF Hong Kong rv1

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