Fundamentals of Water System Design - ibse.hkibse.hk/cpd/water-system/WSD_Chp_9.pdf · System load...

transcript

Fundamentals of Water System Design

17, 18, 24, 25 January 2007

ASHRAE Hong Kong Chapter Technical Workshop

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

Liquid Chilling System

Simple Chiller Schematic

Refrigeration Cycle on p-h Chart(Mollier diagram, vapor compression)

22pres

enthalpyenthalpy

evaporatorevaporator

condensercondenser

22--stage stage compressorcompressor

economizereconomizer

44expansion expansion devicesdevices

Refrigerating Effect, ΔH

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

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)

Types of Water Chiller

heat-driven compressor-driven

Vapor-Compression Cycle

compressorcompressorexpansionexpansion

devicedeviceenergy inenergy in

absorb heatabsorb heat

reject heatreject heat

condensercondenser

centrifugal

scroll

reciprocating

Compressor Types and Controls

¾¾ ~ 100 tons~ 100 tons

70 ~ 500 tons70 ~ 500 tons 300 ~ 3000 tons300 ~ 3000 tons

¾¾ ~ 60 tons~ 60 tons

Variable-Speed Drives

variablevariable--speedspeeddrivedrive

Commonly used acronym: VSD, VFD, AFD

VFD=Efficiency?

20% 30% 40% 50% 60% 70% 80% 90% 100%

n Standard Unit

Std. Unit with VFD

Performance at condenser water temperature reliefPerformance at condenser water temperature relief

20% 30% 40% 50% 60% 70% 80% 90% 100%Load

- High Eff. Unit- Std. Eff. Unit w/VFD

Performance vs ECWT85ºF (29.4ºC) ECWT

ECWT = Entering Condenser Water Temperature

kW- High Eff. Unit- Std. Eff. Unit w/VFD

80ºF (26.7ºC) ECWT

- High Eff. Unit- Std. Eff. Unit w/VFD

kW- High Efficiency Unit- Std. Eff. Unit w/VFD

VFD=Efficiency?

15% 25% 35% 45% 55% 65% 75% 85% 95%% Load

- Std. Eff. Unit w/VFD- Std. Eff Unit

Performance at Constant water temperaturePerformance at Constant water temperature

Condenser Types

water-cooled

air-cooled

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]

air-cooled or water-cooledEfficiency

1212midnightmidnight

1212noonnoon

1212midnightmidnight

dry bulbdry bulb

wet bulbwet bulb

water-cooledGreater energy efficiencyLonger equipment life

air-cooled or water-cooledComparison

air-cooledLower maintenancePackaged systemBetter low-ambient operation

Absorption Refrigeration Cycle

solution pumpsolution pumpexpansionexpansiondevicedevice

absorb heatabsorb heat

reject heatreject heatheat energy inheat energy in

reject heatreject heat

condensercondenser

absorberabsorber

generatorgenerator

Refrigerant = WaterRefrigerant = Water

Absorption Chillers Offer Choice

Avoid high electric demand chargesMinimal electricity needed during emergency situationsWaste heat recoveryCogeneration

Absorption Chiller Types

single-effect double-effect

direct-firedCapacity range:100 ~ 1600 tons

Equipment Rating Standards

Air-Conditioning & Refrigeration Institute (ARI)

Standard 550/590-2003:centrifugal and screw water chillersStandard 560-2000:absorption water chillers

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

ratingstandard

ARI550/590

ARI560

*water leaving evaporator = 44°F [6.7°C]*water entering condenser = 85°F [29.4°C]

Flow Rates and Temperatures

QBtu/hr = 500 × flow rate × ΔT

[ QW = 4,184 × flow rate × ΔT ]

equation for water onlyequation for water only

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

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:

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.

a multi-chiller system:

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

Centrifugal Chiller IPLV comparison

0 500 1000 1500 2000 2500

Nominal Cooling, tons

Lowest-stdHighest-stdHighest-VFDLowest-VFD

IPLV + VFD = Trap!

Standard Chillers

Chillers w/VFD

ASHRAE/IESNA Standard 90.1

Energy standardBuilding design and materialsMinimum equipment efficienciesHVAC system design

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]

all capacities

> 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

minimum efficiency*2.8 COP 3.05 IPLV

4.2 COP 5.05 IPLV

* as of October 29, 2001* as of October 29, 2001

standard efficiency requirements (examples)Water-Cooled Absorption Chillers

chiller typesingle-effect

double-effectindirect-fired

direct-fired

chiller typesingle-effect

double-effectindirect-fired

direct-fired

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

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

Chilled-Water System Components

chillerpumps

cooling coil

cooling tower

Chilled-Water System Piping

pumppump coilcoil

controlcontrolvalvevalve

airair--cooledcooledchillerchiller

Load-Terminal Control Options

Three-way modulating valveTwo-way modulating valveFace-and-bypass dampers

Three-Way Valve Control

threethree--waywaymodulatingmodulating

valvevalve

airflowairflow

bypassbypasspipepipe

Two-Way Valve Control

twotwo--waywaymodulating valvemodulating valve

airflowairflow

Face-and-Bypass Damper Control

bypassbypassdamperdamper

facefacedamperdamper

airflowairflow

Chiller Evaporator Flow

Constant flow is most commonVariable flow is possible

Can reduce energy consumption Use only with advanced chiller and system controls

Single-Chiller System

pumppumpcoilcoil

threethree--way valveway valve

airair--cooledcooledchillerchiller

Multiple-Chiller Systems

Redundancy or backup capacityPart-load system efficiency

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

5454°°FF[12.2[12.2°°C]C]

4242°°FF[5.6[5.6°°C]C]

offoff

60% to 70%60% to 70%of system flowof system flow

coil starved for flowcoil starved for flow

chillers piped in parallelDedicated Pumps

percent flowpercent flow

2 pumps2 pumps

1 pump1 pump

system system curvecurve

100%100%65%65%

chillers piped in parallelDedicated Pumps

Chillers Piped in Series

threethree--way valveway valve

absorptionabsorptionchillerchiller

electricelectricchillerchiller

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]

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]

Primary-Secondary (Decoupled) Configuration

productionproductionpumpspumps

twotwo--way valveway valve

distributiondistributionpumppump

distributiondistributionlooploop

productionproductionlooploop

bypass pipebypass pipe

decoupler

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

Production Loop

returnreturnteetee

supplysupplyteetee

productionproductionpumpspumps

Distribution Loop

twotwo--way valveway valve

distributiondistributionpumppumpbypass pipe

bypass pipe

returnreturnteetee

supplysupplyteetee

The bypass pipe should be free of restrictions Load terminals should use two-way modulating control valves

equal percent or linear flow

Varying Distribution Flow

pressurepressuredifferencedifference

riding the pump curvevariable-speed control

percent flowpercent flow100100505000

pumppumpcurvecurve

Multiple Distribution Pumps

distributiondistributionpumpspumps

supplysupplyto loadsto loads

returnreturnfrom loadsfrom loads

Multiple Distribution Pumps

distributiondistributionpumpspumps

supplysupplyto loadsto loads

returnreturnfrom loadsfrom loads

CA B C

Distribution Loop Characteristics

Reduced pump energy useDistribution loop sized for system diversityHigher return-water temperatures

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

System Operation

distributiondistributionlooploop

productionproductionlooploop

bypass pipe

returnreturnteetee

supplysupplyteetee

supplysupplyflowflow

demanddemandflowflow

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]

1,200 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]

Excess Flow

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]

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]

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

Types of Fluid Flow Meters

Pressure-basedPitot tubeVenturiOrifice plateDifferential pressure

Turbine and impellerVortexMagneticUltrasonic

Temperature-Based Calculations

bypass pipe

returnreturnteetee

supplysupplyteetee

systemsystem--levellevelcontrollercontroller

chiller/system Energy Performance

Chilled-Water Systems

Air Conditioning Clinic TRG-TRC016-ENAir Conditioning Clinic TRG-TRC016-EN© American Standard Inc. 2001

Electric Utility Deregulationpr

ice of

tricity

, $/kW

ice of

tricity

, $/kW

0.200.20

0.100.10

0.300.30

MayMay JuneJune JulyJuly AugustAugust SeptemberSeptember

Energy Options

absorptionthermal storage

indirectly-coupled, gas-engine chillers

control interfacecontrol interface

powerpower

Chiller Efficiency Improvementsch

iller e

fficien

iller e

fficien

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

Focus on System Energy Efficiency

Trend Towards Lower Flow Rates

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]

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]

low-flow conditionsevaporator

flow ratecondenser

flow rate

evaporatorflow rate

condenserflow rate

Low-Flow Systemsan

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

(Source: Kelly, David W. and Chan, Tumin, “Optimizing Chilled Water Plants,” Heating/Piping/Air Conditioning, January 1999)

Variable-Primary-Flow Systems

bypassbypass

twotwo--waywayvalvevalve

variablevariable--flowflowpumpspumps

controlcontrolvalvevalve

checkcheckvalvesvalves

optional bypassoptional bypasswith threewith three--way valveway valve

Capacity Controlw /o W ater Flow Com pensation

0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00Tim e (hour:m in:sec)

-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

Evaporator W ater F low

Evap Entering W ater Tem p

Evap Leaving W ater Tem pChiller off Chiller

Chiller on

Change Too Fastcan be a problem

Capacity Controlw ith W ater Flow Com pensation

0:00:00 0:10:00 0:20:00 0:30:00 0:40:00 0:50:00Tim e (hour:m in:sec)

-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

Evaporator W ater Flow

Evap Entering W ater Tem p

Evap Leaving W ater Tem p

No Problem!

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”

Sidestream Configuration

heatheat--recoveryrecoverychillerchiller

Heat-Recovery Chillerheatheat--recovery recovery

condensercondenser

standard standard condensercondenser

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

Heat-Recovery Chiller Efficiency

chiller typecoolingmode

cooling-onlycentrifugal chiller

heat-recoverycentrifugal chiller

0.57 kW/ton[6.2 COP]

heat-recoverymode

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

Asymmetric Design

50% / 50%50% / 50%

lagchillerlagchiller

60% / 40%60% / 40%

10,00010,000

8,0008,000

6,0006,000

4,0004,000

2,0002,000

leadchillerleadchiller

Different chiller capacitiesDifferent chiller efficiencies

chiller splitchiller split

Swing Chillerequalequal--capacitycapacitylarge chillerslarge chillers

smallsmall--capacity capacity ““swingswing”” chillerchiller

Swing Chillerpe

chiller 1chiller 1

100100

swing chillerswing chiller

chiller sequencechiller sequence

chiller 2chiller 2

swing chillerswing chiller

“Free” Cooling

Airside economizerWaterside economizer

Strainer cyclePlate-and-frame heat exchangerRefrigerant migration

waterside economizerPlate-and-Frame Heat Exchanger

plateplate--andand--frameframeheat exchangerheat exchanger

condensercondenserwater loopwater loop

waterside economizerRefrigerant Migration

from from compressorcompressor

to to compressorcompressor

condensercondensershutoffshutoffvalvevalve

shutoffshutoffvalvevalve

vaporvapormigrationmigration

liquidliquidflowflow

Chiller Controls

Start–stopChilled-water temperature controlMonitor and protectAdapt to unusual conditions

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

Chiller Sequencing

Turning on an additional chillerTurning off a chillerWhich chiller to turn on or off?

load indicatorsTemperature

supplysupply--waterwatertemperaturetemperature

returnreturn--waterwatertemperaturetemperature

chillerchiller--plantplantcontrollercontroller

load indicatorsFlow

flowflowmetermeter

load indicatorsCapacity

flowflowmetermeter

supplysupply--waterwatertemperaturetemperature

returnreturn--waterwatertemperaturetemperature

Chiller Rotation

equalequal--capacity chillerscapacity chillers

large electriclarge electricchillerchiller

absorptionabsorptionchillerchiller

small electricsmall electricchillerchiller

Chiller Rotation

Heat Recovery

preferentiallypreferentially--loaded loaded heatheat--recoveryrecoverychillerchiller

standardstandardelectric chillerselectric chillers

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

Soft Loadingsu

ly --wa

ter te

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]

System Optimization

ChillerDecrease condenser-water temperatureIncrease chilled-water temperature

Chilled-water pump (variable-flow system)Increase chilled-water ΔT

Cooling towerIncrease condenser-water temperature

Condenser-Water Temperaturean

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

22 24 26 28 30 32 34

Condenser water temperature (°C)

Chiller kWTower kWTotal kW

Chiller-Tower Optimization

Optimal Temp.

Control of Condensing Pressure

condensercondenser

controlcontrolpanelpanelevaporatorevaporator

Operator Training and Support

Operator Interface

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

THANK YOUPhilip Yu

Environmental and Applications Engg.Trane

E-mail: yupc@trane.com

Fundamentals of Water System Design - ibse.hkibse.hk/cpd/water-system/WSD_Chp_9.pdf · System load...

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