c oncerns ltd ool energy efficient refrigeration jane gartshore, cool concerns ltd

Concerns Ltdool

Energy Efficient Refrigeration

Jane Gartshore, Cool Concerns Ltd

Concerns Ltdool

Outline

• Revision - the basics• Component operation• Factors effecting efficiency

– load reduction– operating conditions

• The low hanging fruit

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• Common principles• How a system works• Importance of operating conditions:

– evaporating temperature– condensing temperature– superheat– subcooling

Concerns LtdoolA Simple System


COSP = capacity / total power input

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COSP

• What do you expect the COSP to be?

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COSP

• What do you expect the COSP to be?

Typically …• LT ~ 0.5 to 1.5• HT ~ 2 to 4• AC ~ 4 to 6


Saturated mixturelow pressure

Superheated gaslow pressure

Superheated gashigh pressure

Saturated liquidhigh pressure

Saturated mixturehigh pressure

Subcooled liquidhigh pressure

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How Many Times Round the Circuit?

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20,0

00

How Many Times Round the Circuit?

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Compressor

Most efficient if:• compression ratio low• suction superheat low• cooling adequate

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Evaporator

Evaporator effectiveness depends on ...• evaporating temperature / pressure

– size / condition of evaporator– temperature of cooled space / fluid

• degree of useful superheat• degree of subcooling

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Condenser

Condenser effectiveness depends on ...• condensing temperature / pressure

– size / condition of condenser– cooling medium– temperature of cooling medium

• head pressure control

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Superheat

Useful superheat• in evaporator• aim for ~ 5KNon useful superheat• in suction line• minimiseRefrigerant arriving at compressor must be

superheated (but not too much!)

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Subcooling

• 10K subcooling ~ 7% capacity increase– natural cooling or by subcooler– insulate liquid line when using a subcooler

• No subcooling ~ ??% capacity reduction– condensing temperature too low– liquid line passes through hot area– loss of refrigerant

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Expansion Valve

• Subcooled liquid at entry• Useful superheat setting important• TEV, minimum 6 bar pressure drop• EEV, minimum 4 bar pressure drop

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Central Plant Systems

• Several smaller compressors for better capacity matching to load

• Can be unevenly sized• Controlled on suction pressure

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Central Plant Systems

30

40

50

60

70

80

90

100

33 66 100

% loading

pow

er

screw withslide valve

Single 6cylinder

3 compressorpack

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Central Plant Control

EV

S

EV

S

EV

S

EV

S

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Evaporator Temperatures

EV

S

EV

S

EV

S

EV

S

-12 -8 -8 -6

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An Efficient System ...

…has minimum load…has minimum temperature lift…uses an efficient combination of

components…is well controlled

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Keeping the Load Low

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Load - Door ManagementOpen door:Freezer, £6/hChiller, £3/h

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Load - Product Loading

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Load - Defrost

• Does the defrost work?

• Is it controlled correctly

• Defrost on demand can improve efficiency

Concerns LtdoolLoad - Auxiliaries

Switching off fans can save up to 14%

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Load - Sec. Ref. Pumps

• Contribute twice to energy use– direct electricity consumption– heat into secondary fluid

• Variable Speed Drive – will reduce pump power, e.g. by 25%– will reduce heat load

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Load - Insulation

Cold store / cabinet insulationSecondary fluid pipe work insulation• ensure in good condition• ensure sufficient thickness• ensure well joined / sealedSuction lineLiquid line

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Temperature Lift

• Evaporating temperature• Condensing temperature• Control

1°C = 2% to 4%

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Evaporating Temperature

• Cooled space / fluid temperature- as high as possible

e.g. increasing frozen food store temperature from -25°C to -20°C saves over 10% (and reduces breakdown)

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• Ensure evaporator is clean

• Ensure evaporator is clear of frost

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• Refrigerant charge is critical– leak test– repair– re-charge

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Reduce Leak Potential

• Brazed joints• Minimum charge• Minimum pressures • Charge monitoring• Effective leak testing

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Condensing Temperature

• Ensure condensers are clean

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What’s the problem here?

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Condensing Temperature• Recommend replacement

– take opportunity to fit larger condenser

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Non condensable gases increase condensing temperature

• Purge air / nitrogen– use an automatic (refrigerated) air

purger– portable versions available

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Control

• Highest possible evaporating temperature– thermostat / controller (LP) setting

• Lowest possible condensing temperature– minimum head pressure control

• Appropriate useful superheat– TEV / EEV adjustment

• Optimum compressor strategy

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Low Hanging Fruit

• Cold store air change load reduction

• Auxiliary load reduction• Reducing refrigerant leaks• System control• Re commissioning• Maintenance

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Air Change Reduction

• Heat and moisture• Door management• Strip curtains / air lock• Try dehumidification

– e.g. 8% reduction

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Aux Load Reduction

Double impact / saving• Evaporator fan motors

– E.g. 14% reduction on HT area

• Process fluid pump control

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Leak Reduction

15% leakage doubles power input• Maintenance

– Leak test method– Regime

• Fixed leak detection• Charge monitoring

Tuesday05/02/2002

3 9 15 216 1812Wednesday

06/02/2002

3 9 15 216 1812Thursday

07/02/2002

3 9 15 216 1812Friday

08/02/2002

3 9 15 216 1812

PPM

0

50

100

150

200

250

300

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Control

• Suction and discharge pressure optimisation– ~10% savings

• Defrost on demand– ~2.5% savings

• Floating head pressure– ~ 7% savings

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Re Commissioning

Re set suction & discharge set pointsExample savings:• 21.2% on HT pack• 13.6% saving on LT pack• 6.9% on total site energy

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Maintenance is Vital

Ensure there is a maintenance regime which at least …

…cleans condensers and evaporators…checks for leaks (and repairs them!)…does an eyes & ears system check

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Energy Efficient Refrigeration

Jane Gartshore, Cool Concerns Ltd

c oncerns ltd ool energy efficient refrigeration jane gartshore, cool concerns ltd

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