energy efficiency in industrial refrigeration systems_r

Energy Efficiency in Industrial Energy Efficiency in Industrial Refrigeration SystemsRefrigeration Systems

Ahmad R. Ganji, Ph.D., P.EAhmad R. Ganji, Ph.D., P.EProfessor of Mechanical Professor of Mechanical

EngineeringEngineeringSan Francisco State UniversitySan Francisco State University

2008 IAC Directors Meeting2008 IAC Directors MeetingJuly 14July 14--15 200815 2008

IACIAC--SFSUSFSU 22

OutlineOutline

•• Brief Introduction of Vapor Compression Brief Introduction of Vapor Compression CyclesCycles

•• Major Components of Industrial Major Components of Industrial Refrigeration SystemsRefrigeration Systems

•• Potential Energy Efficiency OpportunitiesPotential Energy Efficiency Opportunities

IACIAC--SFSUSFSU 33

Industrial Refrigeration ApplicationsIndustrial Refrigeration Applications

•• Space CoolingSpace Cooling•• Food ProcessingFood Processing•• ChemicalsChemicals•• PharmaceuticalsPharmaceuticals•• ………….. …………..

IAC-SFSU 4

Vapor Compression CycleSingle Stage

Pres

sure

(psi

a)

Saturated Liquid Line 1

10

100

1000

1

Ammonia

23

4

Saturated Vapor Line

Compression

Enthalpy (Btu/lbm)400200 500300100-100 600 700 8000

Motor

Receiver

vapor

vaporliquid

Compressor

1

2

3

4

liquid

EvaporativeCondenser

Evaporator

IAC-SFSU 5

Vapor Compression CycleTwo-Stage

vapor

Evaporative Condenser

vapor

liquid

liquid

Process Chiller

Flooded Drum/Low Pressure Receiver

vapor

superheatedvapor

subcooled liquid

2nd StageReciprocating Compressor

1st Stage Reciprocating Compressors

Intercooler

High Pressure Receiver

Pres

sure

(psi

a)


1

10

100

1000

1

Ammonia

45

7

3 2High-Stage

Low-Stage

Saturated Liquid Line

6

8 High Temperature Evaporators (30 F)

Low Temperature Evaporators (0 F)

Enthalpy (Btu/lbm)400200 500300100-100 600 700 8000

IAC-SFSU 6

High-Stage Reciprocating Compressors in 2-Stage System

IAC-SFSU 7

Low-Stage Screw Compressors in 2-Stage System

IACIAC--SFSUSFSU 88

Refrigeration System ComponentsRefrigeration System Components

•• CompressorCompressor–– ReciprocatingReciprocating–– Screw TypeScrew Type–– Rotary VaneRotary Vane

•• CondenserCondenser–– Air condensersAir condensers–– Evaporative CondenserEvaporative Condenser–– Cooling Tower/Heat ExchangerCooling Tower/Heat Exchanger

•• Evaporator/Chiller/Heat ExchangerEvaporator/Chiller/Heat Exchanger•• Receiver/AccumulatorReceiver/Accumulator

IACIAC--SFSUSFSU 99

Causes of Low Energy EfficiencyCauses of Low Energy Efficiency

•• Unnecessary High LoadUnnecessary High Load•• Unnecessary High System LiftUnnecessary High System Lift•• Poor PartPoor Part--Load PerformanceLoad Performance•• Poor/Outdated Control SystemsPoor/Outdated Control Systems•• Low Efficiency EquipmentLow Efficiency Equipment

IACIAC--SFSUSFSU 1010

Potential Energy Efficiency MeasuresPotential Energy Efficiency Measures

Refrigeration SystemRefrigeration System•• Insulate Suction Lines and Low Pressure ReceiversInsulate Suction Lines and Low Pressure Receivers•• Increase Ammonia System’s Suction PressureIncrease Ammonia System’s Suction Pressure•• Reduce Head Pressure Reduce Head Pressure •• Convert Ammonia Refrigeration to Floating Head Pressure Convert Ammonia Refrigeration to Floating Head Pressure •• Install High Efficiency Ammonia CompressorsInstall High Efficiency Ammonia Compressors•• Sequence Ammonia CompressorsSequence Ammonia Compressors•• Replace Single Stage Compressor with TwoReplace Single Stage Compressor with Two--Stage SystemStage System•• Use Use SubcoolingSubcooling to Reduce Compressor Powerto Reduce Compressor Power•• Recover Waste Heat from Ammonia Refrigeration SystemRecover Waste Heat from Ammonia Refrigeration System



CondensersCondensers•• Increase Evaporative Condenser CapacityIncrease Evaporative Condenser Capacity•• Replace AirReplace Air--Cooled Condensers with Cooled Condensers with

WaterWater--Cooled CondensersCooled Condensers•• Install Adjustable Speed Drives on the Install Adjustable Speed Drives on the

Evaporative Condenser FansEvaporative Condenser Fans



EvaporatorsEvaporators•• Control Evaporator Defrost Based on DemandControl Evaporator Defrost Based on Demand•• Control Evaporator Fans with VFDControl Evaporator Fans with VFD


Insulate Suction Lines/ReceiversInsulate Suction Lines/Receivers

•• Present Condition:Present Condition:The lines or receivers are bare or poorly insulated, and The lines or receivers are bare or poorly insulated, and ice formation on them is often visible.ice formation on them is often visible.

•• Remedy:Remedy:Insulate with appropriate insulation, based on Insulate with appropriate insulation, based on temperature temperature –– may need vapor barrier.may need vapor barrier.

•• Pay back:Pay back:Fairly short, depends on ambient and refrigerant Fairly short, depends on ambient and refrigerant temperaturetemperature


Increase Ammonia System’s Suction Increase Ammonia System’s Suction PressurePressure•• Present Condition:Present Condition:

The suction pressure/temperature is too low for the application,The suction pressure/temperature is too low for the application, i.e. i.e. ∆∆T between refrigerant and the refrigerated medium is too high. T between refrigerant and the refrigerated medium is too high. Typical values for Typical values for ∆∆T should be about 10T should be about 10--15 F. Other cause may be 15 F. Other cause may be pressure restriction in the suction line.pressure restriction in the suction line.

•• Remedy:Remedy:Decrease Decrease ∆∆T to 10T to 10--15 F, and make sure that evaporator/ heat 15 F, and make sure that evaporator/ heat exchanger can handle the new setting. Remove pressure restrictorexchanger can handle the new setting. Remove pressure restrictors.s.

•• Pay back:Pay back:Immediate, unless you need to change/add evaporatorImmediate, unless you need to change/add evaporator/ heat exchanger/ heat exchanger

1 F increase in the evaporator will increase the efficiency of t1 F increase in the evaporator will increase the efficiency of the he system about 2%!system about 2%!


Reduce Head PressureReduce Head Pressure•• Present Condition:Present Condition:

The head pressure/temperature is too high for the application, iThe head pressure/temperature is too high for the application, i.e. .e. ∆∆T between condensing refrigerant and the ambient (dry or wet T between condensing refrigerant and the ambient (dry or wet bulb temperature depending on the condensing system) is too highbulb temperature depending on the condensing system) is too high..

•• Remedy:Remedy:Decrease Decrease ∆∆T to 10T to 10--15 F, and make sure that the condenser can 15 F, and make sure that the condenser can handle the new setting. handle the new setting.

•• Pay back:Pay back:Immediate, unless you need to change/add condensing capacity.Immediate, unless you need to change/add condensing capacity.

Reducing condenser T by 1 F may increase compressor efficiency bReducing condenser T by 1 F may increase compressor efficiency by 1.5 to y 1.5 to 2%! Lowering the head pressure increases system capacity2%! Lowering the head pressure increases system capacity

IAC-SFSU 16

Reduce Head Pressure (cont.)

Reducing head pressure increases system capacity

Enthalpy (Btu/lbm)

Pres

sure

(psi

a)


0-200

1

10

100

1000

100-100-300-500 -400 200 300 400 500

1

Ammonia

3

4

2


3'

4'

2'


Convert Ammonia Refrigeration to Convert Ammonia Refrigeration to Floating Head PressureFloating Head Pressure•• Present Condition:Present Condition:

The head pressure setting is high to accommodate for high The head pressure setting is high to accommodate for high temperature ambient (temperature ambient (TTwbwb), but most of the time ), but most of the time TTwbwb is low.is low.

•• Remedy:Remedy:Add a floating head pressure controller and let the head pressurAdd a floating head pressure controller and let the head pressure e float based on ambient wet bulb temperature, with an approach float based on ambient wet bulb temperature, with an approach temperature of about 10temperature of about 10--15 F.15 F.

•• Pay back:Pay back:$30 k $30 k -- $50 k, will increase if additional condensing capacity is $50 k, will increase if additional condensing capacity is needed.needed.

Minimum pressure may become limited due to hot gas defrost, liquMinimum pressure may become limited due to hot gas defrost, liquid id injection or floor heating pressure requirements.injection or floor heating pressure requirements.


Install High Efficiency Ammonia Install High Efficiency Ammonia CompressorsCompressors

•• Present Condition:Present Condition:The compressor has poor performance especially at part The compressor has poor performance especially at part load (e.g. long unload periods, oversized, etc.)load (e.g. long unload periods, oversized, etc.)

•• Remedy:Remedy:Install a new reciprocating with cylinder unloading of Install a new reciprocating with cylinder unloading of VFD controlled screw VFD controlled screw compressor(scompressor(s).).

•• Pay back:Pay back:Several years, highly dependent on the specific case.Several years, highly dependent on the specific case.


Use Computer Control to Manage Use Computer Control to Manage Compressor SequencingCompressor Sequencing

•• Present Condition:Present Condition:Multiple Compressors are not sequenced properly and some of themMultiple Compressors are not sequenced properly and some of themwork partwork part--load or unloaded for significant periods of time.load or unloaded for significant periods of time.

•• RemedyRemedy::Properly sequence the compressors by computer control to minimizProperly sequence the compressors by computer control to minimize e partpart--load/unload operation for significant periods. This can be well load/unload operation for significant periods. This can be well accomplished with reciprocating compressor accomplished with reciprocating compressor unloadersunloaders and VFD and VFD controlled screw compressors.controlled screw compressors.

•• Pay back:Pay back:Immediate to a few yearsImmediate to a few years


Replace Single Stage Compressor with Replace Single Stage Compressor with TwoTwo--Stage SystemStage System

•• Present Condition:Present Condition:This is the case that there may be one or two refrigerated This is the case that there may be one or two refrigerated temperature levels, but a single stage system produces a large temperature levels, but a single stage system produces a large pressure ratio (lift, usually for subzero temperature levels) pressure ratio (lift, usually for subzero temperature levels)

•• Remedy:Remedy:Split the system into a two stage system with Split the system into a two stage system with intercoolingintercooling. Most . Most appropriate for multiappropriate for multi--level temperature systems.level temperature systems.

•• Pay back:Pay back:Can be several years because of the cost of compressor, vessels,Can be several years because of the cost of compressor, vessels,valvingvalving and controls.and controls.

IAC-SFSU 21

Vapor Compression CycleTwo-Stage

vapor

Evaporative Condenser

vapor

liquid

liquid

Process Chiller

Flooded Drum/Low Pressure Receiver

vapor

superheatedvapor

subcooled liquid

2nd StageReciprocating Compressor

1st Stage Reciprocating Compressors

Intercooler

High Pressure Receiver

Pres

sure

(psi

a)


1

10

100

1000

1

Ammonia

45

7

3 2High-Stage

Low-Stage


6

8 High Temperature Evaporators (30 F)

Low Temperature Evaporators (0 F)

Enthalpy (Btu/lbm)400200 500300100-100 600 700 8000


Use SubUse Sub--cooling to Reduce Compressor cooling to Reduce Compressor PowerPower

•• Present Condition:Present Condition:Saturated liquid refrigerant is expanded for evaporation.Saturated liquid refrigerant is expanded for evaporation.

•• Remedy:Remedy:Install an subInstall an sub--cooler through an intermediate stage cooler through an intermediate stage expansionexpansion

•• Pay back:Pay back:About one yearAbout one year

IAC-SFSU 23

Typical Subcooler

vapor

Liquid Ammoniafrom Evaporative

Condenser

Subcooled Ammonia toEvaporators

Intermediate-PressureAmmonia Vapor to

Intercooler

subcooledHPL

High-PressureReceivers

LiquidSubcooler

Expansion Valve

HPL

5

6


Recover Waste Heat from Ammonia Recover Waste Heat from Ammonia Refrigeration SystemRefrigeration System•• Present Condition:Present Condition:

No heat is recovered from hot compressor outflow. No heat is recovered from hot compressor outflow. Does not apply to cases with liquid injection!Does not apply to cases with liquid injection!

•• Remedy:Remedy:Install a heat exchanger to recover heat for any Install a heat exchanger to recover heat for any application in the plant (e.g. preheat boiler makeapplication in the plant (e.g. preheat boiler make--up up water, heat domestic water, water, heat domestic water, floorheatingfloorheating))

•• Pay back:Pay back:A couple of years depending on the need for thermal A couple of years depending on the need for thermal energy at low temperatureenergy at low temperature

IAC-SFSU 25

Recover Waste Heat from Ammonia Refrigeration System (cont.)

Schematic of Proposed Desuperheater



CondensersCondensers•• Increase Evaporative Condenser CapacityIncrease Evaporative Condenser Capacity•• Replace AirReplace Air--Cooled Condensers with Cooled Condensers with

WaterWater--Cooled CondensersCooled Condensers•• Install Adjustable Speed Drives on the Install Adjustable Speed Drives on the

Evaporative Condenser FansEvaporative Condenser Fans


Increase Evaporative Condenser Increase Evaporative Condenser CapacityCapacity

•• Present Condition:Present Condition:The condenser does not have enough heat rejection capacity, thusThe condenser does not have enough heat rejection capacity, thusthe refrigerant condenses at high pressure/head pressure remainsthe refrigerant condenses at high pressure/head pressure remainshighhigh

•• RemedyRemedy::Increase the condensation capacity.Increase the condensation capacity.

•• Pay back:Pay back:From one to few years depending on the capacity needsFrom one to few years depending on the capacity needs


Replace AirReplace Air--Cooled Condensers with Cooled Condensers with WaterWater--Cooled CondensersCooled Condensers

•• Present Condition:Present Condition:The system has an air cooled condenser working based on heat The system has an air cooled condenser working based on heat rejection to rejection to TTdbdb, , which results in high head pressurewhich results in high head pressure..

•• Remedy:Remedy:Replace the air cooled condenser with an evaporator condenser (iReplace the air cooled condenser with an evaporator condenser (if f atmospheric conditions allows!) and lower the head pressure.atmospheric conditions allows!) and lower the head pressure.

•• Pay back:Pay back:A few yearsA few years


Install VFD on the Evaporative Install VFD on the Evaporative Condenser FanCondenser Fan

•• Present Condition:Present Condition:The evaporator condenser/cooling tower has constant The evaporator condenser/cooling tower has constant speed fans and works continuously or is on/off speed fans and works continuously or is on/off controlled.controlled.

•• Remedy:Remedy:Install VFD and control the speed based on water Install VFD and control the speed based on water temperature or head pressure.temperature or head pressure.

•• Pay back:Pay back:A couple of yearsA couple of years



EvaporatorsEvaporators•• Control Evaporator Defrost Based on DemandControl Evaporator Defrost Based on Demand•• Control Evaporator Fans with VFDControl Evaporator Fans with VFD


Control Evaporator Defrost Based on Control Evaporator Defrost Based on DemandDemand

•• Present Condition:Present Condition:Defrosting of evaporators is timeDefrosting of evaporators is time--based, it is timer based, it is timer controlled.controlled.

•• Remedy:Remedy:Install demandInstall demand--based defrosting controller using defrost based defrosting controller using defrost sensors. DOE sponsored study shows 7sensors. DOE sponsored study shows 7--11% savings 11% savings

•• Pay back:Pay back:About a year, will greatly depend on the cold About a year, will greatly depend on the cold storage/freezer environment.storage/freezer environment.


Control Evaporator Fans with VFDControl Evaporator Fans with VFD

•• Present Condition:Present Condition:Evaporator fans are on all the time or they have onEvaporator fans are on all the time or they have on--off control. The off control. The environment temperature is usually controlled by refrigerant floenvironment temperature is usually controlled by refrigerant flow.w.

•• Remedy:Remedy:Install VFD on the evaporators to be controlled based on cold Install VFD on the evaporators to be controlled based on cold environment temperature.environment temperature.

•• Pay back:Pay back:A few years, will greatly depend on the cold storage/freezer loaA few years, will greatly depend on the cold storage/freezer load d variation.variation.


Potential Energy Efficiency Measures Potential Energy Efficiency Measures (cont.)(cont.)

Other MeasuresOther Measures•• Install thermoInstall thermo--siphon oil coolingsiphon oil cooling•• Optimize Intermediate Suction PressureOptimize Intermediate Suction Pressure•• Install Gas Engine Driven CompressorsInstall Gas Engine Driven Compressors•• Reduce Refrigeration Load by Various MeansReduce Refrigeration Load by Various Means


Some ReferencesSome References

Industrial Refrigeration Best Practices GuideIndustrial Refrigeration Best Practices GuideNorthwest Energy Efficiency Alliance, Dec. 2007Northwest Energy Efficiency Alliance, Dec. 2007

Industrial Refrigeration HandbookIndustrial Refrigeration HandbookWilbert F. Wilbert F. StoeckerStoecker, McGraw Hill, 1995, McGraw Hill, 1995

energy efficiency in industrial refrigeration systems_r

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