Fundamentals of Water System Design - ibse.hkibse.hk/cpd/water-system/WSD_Chp_9.pdf · System load...
Transcript of Fundamentals of Water System Design - ibse.hkibse.hk/cpd/water-system/WSD_Chp_9.pdf · System load...
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© 2007 ASHRAE Hong Kong Chapter Slide 1
Fundamentals of Water System Design
17, 18, 24, 25 January 2007
ASHRAE Hong Kong Chapter Technical Workshop
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© 2007 ASHRAE Hong Kong Chapter Slide 2
Chapter 9:Water Chillers and Load Control
1. Basic water chiller components2. Refrigeration cycle3. Heat transfer chiller4. Refrigeration power5. Chiller types and control6. Chiller piping arrangements7. Chiller energy performance8. Thermal storage
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© 2007 ASHRAE Hong Kong Chapter Slide 3
Liquid Chilling System
Chi
ller
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© 2007 ASHRAE Hong Kong Chapter Slide 4
Simple Chiller Schematic
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© 2007 ASHRAE Hong Kong Chapter Slide 5
Refrigeration Cycle on p-h Chart(Mollier diagram, vapor compression)
11
22pres
sure
pres
sure
enthalpyenthalpy
evaporatorevaporator
condensercondenser
PPee
PPcc
PP11
C B A
66
77
99
55
22--stage stage compressorcompressor
economizereconomizer
33
44expansion expansion devicesdevices
1010
88
Refrigerating Effect, ΔH
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© 2007 ASHRAE Hong Kong Chapter Slide 6
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© 2007 ASHRAE Hong Kong Chapter Slide 7
Heat Transfer Chiller
W = (Specific Heat)(Density) × flow rate × ΔT
kW = 4.19 × flow rate × ΔT
equation for water only
equation for brine or glycol mixture
mass flow rate
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© 2007 ASHRAE Hong Kong Chapter Slide 8
Refrigeration Power
COP = kW ÷ chiller power input
kW = refrigerant mass rate × ΔH
chiller capacity
chiller efficiency
(RT or ton = 3.516 × kW)
(kW/ton = 3.516 ÷ COP)
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© 2007 ASHRAE Hong Kong Chapter Slide 9
Types of Water Chiller
heat-driven compressor-driven
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© 2007 ASHRAE Hong Kong Chapter Slide 10
Vapor-Compression Cycle
compressorcompressorexpansionexpansion
devicedeviceenergy inenergy in
absorb heatabsorb heat
reject heatreject heat
evaporatorevaporator
condensercondenser
A B
CD
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© 2007 ASHRAE Hong Kong Chapter Slide 11
centrifugal
scroll
reciprocating
screw
Compressor Types and Controls
¾¾ ~ 100 tons~ 100 tons
70 ~ 500 tons70 ~ 500 tons 300 ~ 3000 tons300 ~ 3000 tons
¾¾ ~ 60 tons~ 60 tons
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© 2007 ASHRAE Hong Kong Chapter Slide 12
Variable-Speed Drives
variablevariable--speedspeeddrivedrive
Commonly used acronym: VSD, VFD, AFD
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© 2007 ASHRAE Hong Kong Chapter Slide 13
VFD=Efficiency?
0.3
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0.5
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0.7
0.8
20% 30% 40% 50% 60% 70% 80% 90% 100%
Load
kW/to
n Standard Unit
Std. Unit with VFD
Performance at condenser water temperature reliefPerformance at condenser water temperature relief
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© 2007 ASHRAE Hong Kong Chapter Slide 14
0
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20% 30% 40% 50% 60% 70% 80% 90% 100%Load
kW
- High Eff. Unit- Std. Eff. Unit w/VFD
Performance vs ECWT85ºF (29.4ºC) ECWT
ECWT = Entering Condenser Water Temperature
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20%
30%
40%
50%
60%
70%
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90%
100%
Load
kW- High Eff. Unit- Std. Eff. Unit w/VFD
80ºF (26.7ºC) ECWT
ECWT = Entering Condenser Water Temperature
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100%
Load
kW
- High Eff. Unit- Std. Eff. Unit w/VFD
70ºF (21.1ºC) ECWT
ECWT = Entering Condenser Water Temperature
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0
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Load
kW- High Efficiency Unit- Std. Eff. Unit w/VFD
60ºF (15.5ºC) ECWT
ECWT = Entering Condenser Water Temperature
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© 2007 ASHRAE Hong Kong Chapter Slide 18
VFD=Efficiency?
0.300
0.500
0.700
0.900
1.100
15% 25% 35% 45% 55% 65% 75% 85% 95%% Load
kW/to
n
- Std. Eff. Unit w/VFD- Std. Eff Unit
Performance at Constant water temperaturePerformance at Constant water temperature
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© 2007 ASHRAE Hong Kong Chapter Slide 19
Condenser Types
water-cooled
air-cooled
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© 2007 ASHRAE Hong Kong Chapter Slide 20
Air-Cooled or Water-Cooled
0 tons0 tons[0 kW][0 kW]
1,000 tons1,000 tons[3,517 kW][3,517 kW]
2,000 tons2,000 tons[7,034 kW][7,034 kW]
chiller capacitychiller capacity
waterwater--cooledcooled
airair--cooledcooled
1,500 tons1,500 tons[5,276 kW][5,276 kW]
2,500 tons2,500 tons[8,793 kW][8,793 kW]
500 tons500 tons[1,759 kW][1,759 kW]
3,000 tons3,000 tons[10,551 kW][10,551 kW]
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© 2007 ASHRAE Hong Kong Chapter Slide 21
air-cooled or water-cooledEfficiency
outdo
or te
mper
ature
outdo
or te
mper
ature
1212midnightmidnight
1212noonnoon
1212midnightmidnight
dry bulbdry bulb
wet bulbwet bulb
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© 2007 ASHRAE Hong Kong Chapter Slide 22
water-cooledGreater energy efficiencyLonger equipment life
air-cooled or water-cooledComparison
air-cooledLower maintenancePackaged systemBetter low-ambient operation
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© 2007 ASHRAE Hong Kong Chapter Slide 23
Absorption Refrigeration Cycle
solution pumpsolution pumpexpansionexpansiondevicedevice
absorb heatabsorb heat
reject heatreject heatheat energy inheat energy in
reject heatreject heat
evaporatorevaporator
condensercondenser
absorberabsorber
generatorgenerator
A B
CD
Refrigerant = WaterRefrigerant = Water
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© 2007 ASHRAE Hong Kong Chapter Slide 24
Absorption Chillers Offer Choice
Avoid high electric demand chargesMinimal electricity needed during emergency situationsWaste heat recoveryCogeneration
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© 2007 ASHRAE Hong Kong Chapter Slide 25
Absorption Chiller Types
single-effect double-effect
direct-firedCapacity range:100 ~ 1600 tons
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© 2007 ASHRAE Hong Kong Chapter Slide 26
Equipment Rating Standards
Air-Conditioning & Refrigeration Institute (ARI)
Standard 550/590-2003:centrifugal and screw water chillersStandard 560-2000:absorption water chillers
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© 2007 ASHRAE Hong Kong Chapter Slide 27
chiller typeevaporatorflow rate
vapor-compression• reciprocating• scroll• helical-rotary• centrifugal
2.4 gpm/ton[0.043 L/s/kW]
absorption• single-effect
• double-effect,indirect-fired
• double-effect,direct-fired
Standard Rating Conditionscondenserflow rate
3.0 gpm/ton[0.054 L/s/kW]
2.4 gpm/ton[0.043 L/s/kW]
3.6 gpm/ton[0.065 L/s/kW]
2.4 gpm/ton[0.043 L/s/kW]
4.0 gpm/ton[0.072 L/s/kW]
ratingstandard
ARI550/590
ARI560
*water leaving evaporator = 44°F [6.7°C]*water entering condenser = 85°F [29.4°C]
4.5 gpm/ton[0.081 L/s/kW]
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© 2007 ASHRAE Hong Kong Chapter Slide 28
Flow Rates and Temperatures
QBtu/hr = 500 × flow rate × ΔT
[ QW = 4,184 × flow rate × ΔT ]
equation for water onlyequation for water only
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© 2007 ASHRAE Hong Kong Chapter Slide 29
Part-Load Efficiency Rating
Integrated Part-Load Value (IPLV)Weighted-average load curvesBased on an “average” single-chiller installationStandard operating conditions
Non-Standard Part-Load Value (NPLV)Weighted-average load curvesBased on an “average” single-chiller installationNon-standard operating conditions
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© 2007 ASHRAE Hong Kong Chapter Slide 30
Part-Load Efficiency Rating
Do not use for System Efficiency!Do not use for System Efficiency!
1IPLV/NPLV = .01 .42 .45 .12
A B C DA= kW/Ton @ 100% Load, 85ºF (29.4ºC) ECWT B= kW/Ton @ 75% Load, 75ºF (23.9ºC) ECWTC= kW/Ton @ 50% Load, 65ºF (18.3ºC) ECWTD= kW/Ton @ 25% Load, 65ºF (18.3ºC) ECWT
ARI Standard 550/590:
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© 2007 ASHRAE Hong Kong Chapter Slide 31
Example
System load 100% 90% 80% 70% 60% 50% 40% 30% 20% 10%Unit chillers loadChiller A-30% 100% 100% 88.8% 100% 100% 83.3% 0% 100% 0% 0%Chiller B-30% 100% 100% 88.8% 0% 100% 83.3% 0% 0% 0% 0%Chiller C-30% 100% 100% 88.8% 100% 0% 0% 100% 0% 66.6% 0%Chiller D-10% 100% 0% 100% 0% 0% 100% 0% 0% 100%
Over 80% chillers are installed in multi-chiller plant with sequencing controls, i.e. turned on/off one by one to match system load. Therefore, under normal operation, most chillers should be loaded heavily or close to full-load.
Over 80% chillers are installed in multi-chiller plant with sequencing controls, i.e. turned on/off one by one to match system load. Therefore, under normal operation, most chillers should be loaded heavily or close to full-load.
Part-Load Efficiency Rating
a multi-chiller system:
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© 2007 ASHRAE Hong Kong Chapter Slide 32
System load profile different from single chillerSystem energy performance determined by also cooling tower, pump and other accessoriesARI recommend energy simulation software to better evaluate part-load performance
better IPLV ≠ more energy-savingsbetter IPLV ≠≠ more energy-savings
Part-Load Efficiency:Multi-chiller System
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© 2007 ASHRAE Hong Kong Chapter Slide 33
Centrifugal Chiller IPLV comparison
0.3
0.35
0.4
0.45
0.5
0.55
0 500 1000 1500 2000 2500
Nominal Cooling, tons
Ener
gy E
ffici
ency
, kW
/ton
Lowest-stdHighest-stdHighest-VFDLowest-VFD
IPLV + VFD = Trap!
Standard Chillers
Chillers w/VFD
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© 2007 ASHRAE Hong Kong Chapter Slide 34
ASHRAE/IESNA Standard 90.1
Energy standardBuilding design and materialsMinimum equipment efficienciesHVAC system design
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© 2007 ASHRAE Hong Kong Chapter Slide 35
standard 90.1 efficiency requirements (examples)Electric Vapor-Compression Chillerschiller typeair-cooled
water-cooledreciprocating
screw, scroll
centrifugal
chiller typeair-cooled
water-cooledreciprocating
screw, scroll
centrifugal
capacityall capacities
all capacities
< 150 tons [528 kW]150 to 300 tons [528 to 1,056 kW]
> 300 tons [1,056 kW]
< 150 tons [528 kW]150 to 300 tons [528 to 1,056 kW]
> 300 tons [1,056 kW]
capacityall capacities
all capacities
< 150 tons [528 kW]150 to 300 tons [528 to 1,056 kW]
> 300 tons [1,056 kW]
< 150 tons [528 kW]150 to 300 tons [528 to 1,056 kW]
> 300 tons [1,056 kW]
minimum efficiency*2.8 COP 3.05 IPLV
4.2 COP 5.05 IPLV
4.45 COP 5.2 IPLV4.9 COP 5.6 IPLV5.5 COP 6.15 IPLV
5.0 COP 5.25 IPLV5.55 COP 5.9 IPLV6.1 COP 6.4 IPLV
minimum efficiency*2.8 COP 3.05 IPLV
4.2 COP 5.05 IPLV
4.45 COP 5.2 IPLV4.9 COP 5.6 IPLV5.5 COP 6.15 IPLV
5.0 COP 5.25 IPLV5.55 COP 5.9 IPLV6.1 COP 6.4 IPLV
* as of October 29, 2001* as of October 29, 2001
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© 2007 ASHRAE Hong Kong Chapter Slide 36
standard efficiency requirements (examples)Water-Cooled Absorption Chillers
chiller typesingle-effect
double-effectindirect-fired
direct-fired
chiller typesingle-effect
double-effectindirect-fired
direct-fired
capacityall capacities
all capacities
all capacities
capacityall capacities
all capacities
all capacities
minimum efficiency*0.7 COP
1.0 COP 1.05 IPLV
1.0 COP 1.0 IPLV
minimum efficiency*0.7 COP
1.0 COP 1.05 IPLV
1.0 COP 1.0 IPLV
* as of October 29, 2001* as of October 29, 2001
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© 2007 ASHRAE Hong Kong Chapter Slide 37
ASHRAE Standard 15
Safety standard for refrigerating systemsMechanical equipment room
Refrigerant monitorsAlarmsMechanical ventilationPressure-relief piping
Further reading:Trane, Applications Engineering Manual: Application Considerations for Compliancewith ASHRAE Standard 15
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© 2007 ASHRAE Hong Kong Chapter Slide 38
Chilled-Water System Components
chillerpumps
cooling coil
cooling tower
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© 2007 ASHRAE Hong Kong Chapter Slide 39
Chilled-Water System Piping
pumppump coilcoil
controlcontrolvalvevalve
airair--cooledcooledchillerchiller
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© 2007 ASHRAE Hong Kong Chapter Slide 40
Load-Terminal Control Options
Three-way modulating valveTwo-way modulating valveFace-and-bypass dampers
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© 2007 ASHRAE Hong Kong Chapter Slide 41
Three-Way Valve Control
threethree--waywaymodulatingmodulating
valvevalve
airflowairflow
bypassbypasspipepipe
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© 2007 ASHRAE Hong Kong Chapter Slide 42
Two-Way Valve Control
twotwo--waywaymodulating valvemodulating valve
airflowairflow
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© 2007 ASHRAE Hong Kong Chapter Slide 43
Face-and-Bypass Damper Control
bypassbypassdamperdamper
facefacedamperdamper
airflowairflow
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© 2007 ASHRAE Hong Kong Chapter Slide 44
Chiller Evaporator Flow
Constant flow is most commonVariable flow is possible
Can reduce energy consumption Use only with advanced chiller and system controls
evaporatorevaporator
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© 2007 ASHRAE Hong Kong Chapter Slide 45
Single-Chiller System
pumppumpcoilcoil
threethree--way valveway valve
airair--cooledcooledchillerchiller
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© 2007 ASHRAE Hong Kong Chapter Slide 46
Multiple-Chiller Systems
Redundancy or backup capacityPart-load system efficiency
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© 2007 ASHRAE Hong Kong Chapter Slide 47
5454°°FF[12.2[12.2°°C]C]
4242°°FF[5.6[5.6°°C]C]
5454°°FF[12.2[12.2°°C]C]offoff
onon4848°°FF[8.9[8.9°°C]C]
chillers piped in parallelSingle Pump
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© 2007 ASHRAE Hong Kong Chapter Slide 48
5454°°FF[12.2[12.2°°C]C]
4242°°FF[5.6[5.6°°C]C]
offoff
onon
60% to 70%60% to 70%of system flowof system flow
coil starved for flowcoil starved for flow
chillers piped in parallelDedicated Pumps
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© 2007 ASHRAE Hong Kong Chapter Slide 49
head
pres
sure
head
pres
sure
percent flowpercent flow
2 pumps2 pumps
1 pump1 pump
system system curvecurve
100%100%65%65%
chillers piped in parallelDedicated Pumps
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© 2007 ASHRAE Hong Kong Chapter Slide 50
Chillers Piped in Series
threethree--way valveway valve
absorptionabsorptionchillerchiller
electricelectricchillerchiller
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© 2007 ASHRAE Hong Kong Chapter Slide 51
chillers piped in seriesEqual Set Points
5454°°FF[12.2[12.2°°C]C]
4242°°FF[5.6[5.6°°C]C]
set point = set point = 4242°°F F [5.6[5.6°°C]C] set point = set point = 4242°°F F [5.6[5.6°°C]C]
4848°°FF[8.9[8.9°°C]C]
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© 2007 ASHRAE Hong Kong Chapter Slide 52
chillers piped in seriesStaggered Set Points
5252°°FF[11.1[11.1°°C]C]
4242°°FF[5.6[5.6°°C]C]
set point = set point = 4848°°F F [8.9[8.9°°C]C] set point = set point = 4242°°F F [5.6[5.6°°C]C]
4848°°FF[8.9[8.9°°C]C]
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© 2007 ASHRAE Hong Kong Chapter Slide 53
Primary-Secondary (Decoupled) Configuration
productionproductionpumpspumps
twotwo--way valveway valve
distributiondistributionpumppump
distributiondistributionlooploop
productionproductionlooploop
bypass pipebypass pipe
decoupler
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© 2007 ASHRAE Hong Kong Chapter Slide 54
Primary-Secondary System Rules
The bypass pipe should be free of restrictions Sized for minimal pressure dropAvoid random mixing of supply- and return-water streamsNo check valve
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© 2007 ASHRAE Hong Kong Chapter Slide 55
Production Loop
returnreturnteetee
supplysupplyteetee
productionproductionpumpspumps
bypass pipebypass pipe
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© 2007 ASHRAE Hong Kong Chapter Slide 56
Distribution Loop
twotwo--way valveway valve
distributiondistributionpumppumpbypass pipe
bypass pipe
returnreturnteetee
supplysupplyteetee
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© 2007 ASHRAE Hong Kong Chapter Slide 57
Primary-Secondary System Rules
The bypass pipe should be free of restrictions Load terminals should use two-way modulating control valves
equal percent or linear flow
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© 2007 ASHRAE Hong Kong Chapter Slide 58
Varying Distribution Flow
pressurepressuredifferencedifference
riding the pump curvevariable-speed control
head
pres
sure
head
pres
sure
percent flowpercent flow100100505000
B
A
pumppumpcurvecurve
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© 2007 ASHRAE Hong Kong Chapter Slide 59
Multiple Distribution Pumps
distributiondistributionpumpspumps
bypass pipebypass pipe
supplysupplyto loadsto loads
returnreturnfrom loadsfrom loads
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© 2007 ASHRAE Hong Kong Chapter Slide 60
Multiple Distribution Pumps
distributiondistributionpumpspumps
bypass pipebypass pipe
supplysupplyto loadsto loads
returnreturnfrom loadsfrom loads
A
B
CA B C
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© 2007 ASHRAE Hong Kong Chapter Slide 61
Distribution Loop Characteristics
Reduced pump energy useDistribution loop sized for system diversityHigher return-water temperatures
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© 2007 ASHRAE Hong Kong Chapter Slide 62
Primary-Secondary System Rules
The bypass pipe should be free of restrictions Load terminals should use two-way modulating control valvesAll chillers should be selected for the same leaving chilled-water temperature and ΔT
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© 2007 ASHRAE Hong Kong Chapter Slide 63
System Operation
distributiondistributionlooploop
productionproductionlooploop
bypass pipe
bypass pipe
returnreturnteetee
supplysupplyteetee
supplysupplyflowflow
demanddemandflowflow
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© 2007 ASHRAE Hong Kong Chapter Slide 64
Deficit Flow
1,200 1,200 gpmgpm at 56at 56°°FF[76 L/s at 13.3[76 L/s at 13.3°°C]C]
1,000 1,000 gpmgpm at 56at 56°°FF[63 L/s at 13.3[63 L/s at 13.3°°C]C]
1,000 1,000 gpmgpm at 42at 42°°FF[63 L/s at 5.6[63 L/s at 5.6°°C]C]
1,200 1,200 gpmgpm at 44.3at 44.3°°FF[76 L/s at 6.8[76 L/s at 6.8°°C]C]200 200 gpmgpm at 56at 56°°FF
[13 L/s at 13.3
[13 L/s at 13.3°°C]C]
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© 2007 ASHRAE Hong Kong Chapter Slide 65
Excess Flow
1,800 1,800 gpmgpm at 56at 56°°FF[114 L/s at 13.3[114 L/s at 13.3°°C]C]
2,000 2,000 gpmgpm at 54.6at 54.6°°FF[126 L/s at 12.6[126 L/s at 12.6°°C]C]
2,000 2,000 gpmgpm at 42at 42°°FF[126 L/s at 5.6[126 L/s at 5.6°°C]C]
1,800 1,800 gpmgpm at 42at 42°°FF[114 L/s at 5.6[114 L/s at 5.6°°C]C]200 200 gpmgpm at 42at 42°°FF
[13 L/s at 5.6
[13 L/s at 5.6°°C]C]
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© 2007 ASHRAE Hong Kong Chapter Slide 66
Control of Primary-Secondary System
condition
deficit flow for specified period of time
excess flow greater than 110% to 115% of next pump to turn off
neither
condition
deficit flow for specified period of time
excess flow greater than 110% to 115% of next pump to turn off
neither
response
start another chiller and pump
turn off next chiller and pump
do nothing
response
start another chiller and pump
turn off next chiller and pump
do nothing
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© 2007 ASHRAE Hong Kong Chapter Slide 67
Types of Fluid Flow Meters
Pressure-basedPitot tubeVenturiOrifice plateDifferential pressure
Turbine and impellerVortexMagneticUltrasonic
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© 2007 ASHRAE Hong Kong Chapter Slide 68
Temperature-Based Calculations
bypass pipe
bypass pipe
returnreturnteetee
supplysupplyteetee
systemsystem--levellevelcontrollercontroller
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chiller/system Energy Performance
Chilled-Water Systems
Air Conditioning Clinic TRG-TRC016-ENAir Conditioning Clinic TRG-TRC016-EN© American Standard Inc. 2001
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© 2007 ASHRAE Hong Kong Chapter Slide 70
Electric Utility Deregulationpr
ice of
elec
tricity
, $/kW
hpr
ice of
elec
tricity
, $/kW
h
0.200.20
0.100.10
0.300.30
MayMay JuneJune JulyJuly AugustAugust SeptemberSeptember
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© 2007 ASHRAE Hong Kong Chapter Slide 71
Energy Options
absorptionthermal storage
indirectly-coupled, gas-engine chillers
control interfacecontrol interface
powerpower
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© 2007 ASHRAE Hong Kong Chapter Slide 72
Chiller Efficiency Improvementsch
iller e
fficien
cy (k
W/to
n)ch
iller e
fficien
cy (k
W/to
n)
19701970yearyear
19801980 20002000
COPCOP
kW/tonkW/ton
19901990
chiller efficiency (COP)chiller efficiency (COP)
0.90.9
0.80.8
0.70.7
0.60.6
0.50.5
8.08.0
7.07.0
6.06.0
5.05.0
4.04.0
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© 2007 ASHRAE Hong Kong Chapter Slide 73
Focus on System Energy Efficiency
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© 2007 ASHRAE Hong Kong Chapter Slide 74
Trend Towards Lower Flow Rates
2.4 gpm/ton[0.043 L/s/kW]
4444°°F F [6.7[6.7°°C]C]
5454°°FF[12.2[12.2°°C]C]
8585°°FF[29.4[29.4°°C]C]
9595°°FF[35[35°°C]C]
3.0 gpm/ton[0.054 L/s/kW]
ARI conditions1.5 gpm/ton[0.027 L/s/kW]
4141°°F F [5[5°°C]C]
5757°°FF[13.9[13.9°°C]C]
8585°°FF[29.4[29.4°°C]C]
100100°°FF[37.8[37.8°°C]C]
2.0 gpm/ton[0.036 L/s/kW]
low-flow conditionsevaporator
flow ratecondenser
flow rate
evaporatorflow rate
condenserflow rate
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© 2007 ASHRAE Hong Kong Chapter Slide 75
Low-Flow Systemsan
nual
ener
gy co
nsum
ption
, kW
han
nual
ener
gy co
nsum
ption
, kW
h
base casebase casebase case
chillerchiller
cooling tower fanscooling tower fanslow flowlow flowlow flow
750,000750,000
600,000600,000
450,000450,000
300,000300,000
150,000150,000 pumpspumps
00
(Source: Kelly, David W. and Chan, Tumin, “Optimizing Chilled Water Plants,” Heating/Piping/Air Conditioning, January 1999)
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© 2007 ASHRAE Hong Kong Chapter Slide 76
Variable-Primary-Flow Systems
bypassbypass
twotwo--waywayvalvevalve
variablevariable--flowflowpumpspumps
controlcontrolvalvevalve
checkcheckvalvesvalves
optional bypassoptional bypasswith threewith three--way valveway valve
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© 2007 ASHRAE Hong Kong Chapter Slide 77
Capacity Controlw /o W ater Flow Com pensation
30
40
50
60
70
80
90
100
110
120
130
0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00Tim e (hour:m in:sec)
Wat
er T
emp
[deg
F]
-500.00
-300.00
-100.00
100.00
300.00
500.00
700.00
900.00
1,100.00
1,300.00
1,500.00
Wat
er F
low
[gpm
]
Evaporator W ater F low
Evap Entering W ater Tem p
Evap Leaving W ater Tem pChiller off Chiller
ff
Chiller on
Change Too Fastcan be a problem
Variable-Primary-Flow Systems
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© 2007 ASHRAE Hong Kong Chapter Slide 78
Capacity Controlw ith W ater Flow Com pensation
30
40
50
60
70
80
90
100
110
120
130
0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00Tim e (hour:m in:sec)
Wat
er T
emp
[deg
F]
-500.00
-300.00
-100.00
100.00
300.00
500.00
700.00
900.00
1,100.00
1,300.00
1,500.00
Wat
er F
low
[gpm
]
Evaporator W ater Flow
Evap Entering W ater Tem p
Evap Leaving W ater Tem p
No Problem!
Variable-Primary-Flow Systems
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© 2007 ASHRAE Hong Kong Chapter Slide 79
Variable-Primary-Flow Systems
ARTI: 2004 March reportSavings relative to conventional primary-secondary systemTotal annual plant energy 3~8%First cost 4~8%Life cycle cost 3~5%Cure “low delta-T syndrome”
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© 2007 ASHRAE Hong Kong Chapter Slide 80
Sidestream Configuration
bypass pipebypass pipe
distributiondistributionpumppump
heatheat--recoveryrecoverychillerchiller
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© 2007 ASHRAE Hong Kong Chapter Slide 81
Heat-Recovery Chillerheatheat--recovery recovery
condensercondenser
standard standard condensercondenser
evaporatorevaporator
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© 2007 ASHRAE Hong Kong Chapter Slide 82
Heat-Recovery Chiller Optionsheat-recovery(dual) condenser
auxiliarycondenser
No extra condenserLarge base-heating loads or continuous operationHigh hot-water temperaturesControlledGood heating efficiency
Second, full-size condenserLarge heating loadsHigh hot-water temperaturesControlledDegrades chiller efficiency
Second, smaller-size condenserPreheating loadsModeratehot-water temperaturesUncontrolled Improves chiller efficiency
heat pump
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© 2007 ASHRAE Hong Kong Chapter Slide 83
Heat-Recovery Chiller Efficiency
chiller typecoolingmode
cooling-onlycentrifugal chiller
heat-recoverycentrifugal chiller
0.57 kW/ton[6.2 COP]
heat-recoverymode
0.60 kW/ton[5.9 COP]
0.69 kW/ton[5.1 COP]
cooling mode conditions:• evaporator ΔT = 44°F to 54°F [6.7°C to 12.2°C]• condenser ΔT = 85°F to 95°F [29.4°C to 35.0°C]
heat-recovery mode conditions:• evaporator ΔT = 44°F to 54°F [6.7°C to 12.2°C]• condenser ΔT = 85°F to 105°F [29.4°C to 40.6°C]
notapplicable
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© 2007 ASHRAE Hong Kong Chapter Slide 84
Asymmetric Design
annu
al op
erati
ng ho
urs
annu
al op
erati
ng ho
urs
50% / 50%50% / 50%
lagchillerlagchiller
60% / 40%60% / 40%
10,00010,000
8,0008,000
6,0006,000
4,0004,000
2,0002,000
00
leadchillerleadchiller
Different chiller capacitiesDifferent chiller efficiencies
chiller splitchiller split
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© 2007 ASHRAE Hong Kong Chapter Slide 85
Swing Chillerequalequal--capacitycapacitylarge chillerslarge chillers
smallsmall--capacity capacity ““swingswing”” chillerchiller
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© 2007 ASHRAE Hong Kong Chapter Slide 86
Swing Chillerpe
rcent
cooli
ng lo
adpe
rcent
cooli
ng lo
ad
chiller 1chiller 1
100100
8080
6060
4040
2020
00
swing chillerswing chiller
chiller sequencechiller sequence
chiller 2chiller 2
swing chillerswing chiller
swing chillerswing chiller
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© 2007 ASHRAE Hong Kong Chapter Slide 87
“Free” Cooling
Airside economizerWaterside economizer
Strainer cyclePlate-and-frame heat exchangerRefrigerant migration
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© 2007 ASHRAE Hong Kong Chapter Slide 88
waterside economizerPlate-and-Frame Heat Exchanger
bypass pipebypass pipe
distributiondistributionpumppump
plateplate--andand--frameframeheat exchangerheat exchanger
condensercondenserwater loopwater loop
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© 2007 ASHRAE Hong Kong Chapter Slide 89
waterside economizerRefrigerant Migration
from from compressorcompressor
to to compressorcompressor
evaporatorevaporator
condensercondensershutoffshutoffvalvevalve
shutoffshutoffvalvevalve
vaporvapormigrationmigration
liquidliquidflowflow
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© 2007 ASHRAE Hong Kong Chapter Slide 90
Chiller Controls
Start–stopChilled-water temperature controlMonitor and protectAdapt to unusual conditions
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© 2007 ASHRAE Hong Kong Chapter Slide 91
Chiller-Plant Controls
When to turn a chiller on or offWhich chiller to turn on or offHow to recover from an equipment failureHow to optimize system efficiencyHow to communicate with the operator
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© 2007 ASHRAE Hong Kong Chapter Slide 92
Chiller Sequencing
Turning on an additional chillerTurning off a chillerWhich chiller to turn on or off?
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© 2007 ASHRAE Hong Kong Chapter Slide 93
load indicatorsTemperature
supplysupply--waterwatertemperaturetemperature
returnreturn--waterwatertemperaturetemperature
chillerchiller--plantplantcontrollercontroller
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© 2007 ASHRAE Hong Kong Chapter Slide 94
bypass pipebypass pipe
load indicatorsFlow
flowflowmetermeter
chillerchiller--plantplantcontrollercontroller
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© 2007 ASHRAE Hong Kong Chapter Slide 95
load indicatorsCapacity
flowflowmetermeter
supplysupply--waterwatertemperaturetemperature
returnreturn--waterwatertemperaturetemperature
chillerchiller--plantplantcontrollercontroller
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© 2007 ASHRAE Hong Kong Chapter Slide 96
Chiller Rotation
equalequal--capacity chillerscapacity chillers
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© 2007 ASHRAE Hong Kong Chapter Slide 97
large electriclarge electricchillerchiller
absorptionabsorptionchillerchiller
small electricsmall electricchillerchiller
Chiller Rotation
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© 2007 ASHRAE Hong Kong Chapter Slide 98
Heat Recovery
preferentiallypreferentially--loaded loaded heatheat--recoveryrecoverychillerchiller
standardstandardelectric chillerselectric chillers
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© 2007 ASHRAE Hong Kong Chapter Slide 99
System Timers
Load-confirmation timerAvoids transient conditions
Staging-interval timerAllows time for the system to respond to turning a chiller on
Minimum-cycle timerPrevents excessive cycling
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© 2007 ASHRAE Hong Kong Chapter Slide 100
Soft Loadingsu
pply
supp
ly --wa
ter te
mper
ature
water
temp
eratu
re
operating time, minutesoperating time, minutes
two chillerstwo chillers
soft loadingsoft loading(one chiller)(one chiller)
set pointset point
6060303000
8080°°FF[26.7[26.7°°C]C]
6060°°FF[15.6[15.6°°C]C]
4040°°FF[4.4[4.4°°C]C]
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© 2007 ASHRAE Hong Kong Chapter Slide 101
System Optimization
ChillerDecrease condenser-water temperatureIncrease chilled-water temperature
Chilled-water pump (variable-flow system)Increase chilled-water ΔT
Cooling towerIncrease condenser-water temperature
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© 2007 ASHRAE Hong Kong Chapter Slide 102
Condenser-Water Temperaturean
nual
ener
gy co
nsum
ption
, kW
han
nual
ener
gy co
nsum
ption
, kW
h
cooling towercooling tower
300,000300,000
chillerchiller
condenser-water temperature set pointcondensercondenser--water temperature set pointwater temperature set point
85°F[29.4°C]8585°°FF
[29.4[29.4°°C]C]70°F
[21.1°C]7070°°FF
[21.1[21.1°°C]C]55°F
[12.8°C]5555°°FF
[12.8[12.8°°C]C]optimalcontroloptimalcontrol
200,000200,000
100,000100,000
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© 2007 ASHRAE Hong Kong Chapter Slide 103
0
100
200
300
400
22 24 26 28 30 32 34
Condenser water temperature (°C)
kW
Chiller kWTower kWTotal kW
Chiller-Tower Optimization
Optimal Temp.
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© 2007 ASHRAE Hong Kong Chapter Slide 104
Control of Condensing Pressure
condensercondenser
controlcontrolpanelpanelevaporatorevaporator
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© 2007 ASHRAE Hong Kong Chapter Slide 105
Operator Training and Support
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© 2007 ASHRAE Hong Kong Chapter Slide 106
Operator Interface
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© 2007 ASHRAE Hong Kong Chapter Slide 107
chiller operating logASHRAE Guideline 3
Chilled-water inlet and outlet temperatures and pressuresChilled water flowEvaporator-refrigerant temperature and pressuresEvaporator approach temperatureCondenser-water inlet and outlet temperatures and pressuresCondenser water flowCondenser-refrigerant temperature and pressuresCondenser approach temperature
Compressor-refrigerant suction and discharge temperaturesOil pressures, temperature, and levels
Refrigerant level
Vibration levels
Addition of refrigerant or oil