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WINDOW AND SPLIT AIRCONDITIONERS

- SELECTION AND ENERGY

PERFORMANCE

S. Jothibasu, Engineering Officer,

CPRI, ERC, Thiruvananthapuram

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Refrigeration

Refrigeration means removal of heat from lowtemperature heat source (conditioned space)and rejecting in to high temperature sink

(ambient) by using a liquid (ie. refrigerant)having low boiling point.

Air conditioningTemperature (Cooling)

Relative humidity (5060 %)

Dust filtration

Ventilation

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Indian Air Conditioning Industry(Source: Kirloskar Copeland)

2 Major segments

Room Air Conditioners, up to 2T, constitutes 85% of Market size

Package Air Conditioners, constitutes,10-15% of Market size

Room Air ConditioningMarket size

Current Market Size 1 Million Nos. / Annum

Growing @ 15-20%/ annum. Expected to reach 2.5 Mn/ annum by 2010.

Current Population

6 Million Room Air Conditioners are operating in the field

1.7 Million, installed prior to 1996, are Energy guzzlers.

4.3 Million, installed post 1996, are relatively Energy Efficient.12000 MW Generating Capacity, is consumed by Room A/C.

Population by 2010

Above 15 Million Nos , Room A/C in the field.

30000MW Generating Capacity, required for Room A/Cs, in the field.

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Conditioned Space (22-25 C)

Room AirChilled air

Motor

FanExpansion

ValveCompressor

motor

Ambient air

Hot air

Typical Window mounted A/C System

Condenser

Evaporator

40 70

2 22

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Split Air Conditioner

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Pressure Enthalpy Diagram for Vapour

Compression System (Source: BEE codes)

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Wall mounted Split A/CWindow A/C

Floor mounted Split A/C

(Source: Kirloskar Copeland)

Floor mounted Split A/C

Some of the commercial window & split A/Cs

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Sl.No. Window A/C Split A/C1 Compact single unit Compressor & Consensor portion

are kept far away

2 Noisier Quiet indoor

3 Security problem No security problem

4 Programmable controlnot common

Programmable control is common

5 Cheaper Slightly costlier

6 Power consumption isslightly lower

Power consumption is slightlyhigher

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Instruments required for Energy

Performance Evaluation

Digital AnemometerDigital RTD temperature indicator

Digital RH meter / Wet bulb thermometer

Portable power analyser

Measuring tape

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Estimation cooling produced

Cooling produced (TR) = AV (hi- ho) / 3.51

where - Density of air, kg/m3

A - Area of air flow, m2

V -Average air velocity, m/s

hi -Enthalpy of air at inlet, kJ/kg

ho -Enthalpy of air at outlet, kJ/kg

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Energy Performance Indices

1 Ton of Refrigeration (TR) = 3023 kcal/h= 3.51 kWthermal= 12000 Btu/hr

Specific power consumption (SPC) = Compressor, kW / TR

COP = Refrigeration Effect (kW) = (3.51 / SPC)

Work done (kW)

COP = Cooling produced (TR) X 3.51 / Shaft power of compressor (kW)

EER = Refrigeration Effect (Btu/hr) = (12 / SPC)

Work done (Watts)

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Typical power consumption pattern

Compressor consumes 90 % of power

Condenser fan consumes 6 % of power

Evaporator fan consumes 4 % of power

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Improvement of EER over a period of time

(Source: DOE, US)

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Some of natural cooling strategies to

reduce cooling load

Light coloured roof & wall

Upgraded insulation in walls & roof

Low emissivity windows

Shading

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A/C Load depends on

Room size

No. of windows

Near by building shade

Windows, walls and roofInsulation of ceiling and walls

Air infiltration

Heat added by occupants and appliances in the

room.

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A/C - SelectionSelect A/C based on both initial procurement price

and also annual energy consumption

Select A/C for minimum life cycle cost

Select A/C with higher EER (9 or more)

Average life of room air conditioner is 10-15 years

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3000 running hours / Annum & 12 years of life

Typical life cycle cost analysis of room air

conditioners.

Energy cost

76.0%

Capital cost

12.0%

Maintenance

cost

12.0%

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(Source: BEE codes)

Grooved Tubes to IncreaseSurface Area

Tube Inserts to IncreaseTurbulence

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Thumb Rules for Calculating Comfort Air-conditioning Load

Type of Office Heat Load

TR per m2

Small office cabins 0.10

Medium size offices

(seating 10 to 30 people, withcentralised air-conditioning)

0.06

Large multistoreyed office buildings(with centralised air-conditioning)

0.04

(Source: BEE codes)

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(Source: Washington state University)

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Disadvantages ofOversized A/C Units

Does not provide more comfort

Larger-than-necessary air conditioner short

cycles - on and off more frequently, reducing its

efficiency

Frequent cycling makes indoor temperatures

fluctuate more and results in a less comfortableenvironment.

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Disadvantages of Oversized A/C Units

Frequent cycling inhibits moisture removal.

The indoor coil never gets cold enough tocondense and remove excess moisturefrom the room

Cycling wears out the compressor and

electrical parts more rapidly.

A larger air conditioner uses more electricity

and creates added demands on electrical

generation and delivery systems.

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Disadvantages ofOversized A/C Units

Larger the size, more the noise

Larger the size, more the maintenance required

Larger the size, more the initial cost

A small unit running for an extended periodoperates more efficiently and is more effective indehumidifying than a large unit that cycles on and off

too frequently.

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Variation of EER with running time

(Source: DOE, US)

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Installation Tips

Allow adequate indoor space for the installation,

maintenance, and repair of the new system

Provide way to clean the evaporator coil.

Locate the condensing unit where its noise willnot disturb.

Place the condensing unit in a shady spot, ifpossible, which can reduce your air conditioning

costs by 1% to 2%.

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Installation Tips

Verify that the newly installed air conditioner

has the exact refrigerant charge and air flow

rate specified by the manufacturer.

Locate the air conditioner in a window or wall

area near the Centre of the room and on theshadiest side of the house.

Minimize air leakage by fitting the room airconditioner exactly into its opening and sealing

gaps with a foam weather stripping material.

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Factors affecting Energy Consumption in

R & AC

Product Heat LoadHeat Leakage in to the

Conditioned/Refrigerated space.Equipment Selection

Equipment EfficiencyEquipment Maintenance

# RAC Equipment Efficiency depends on Heat Exchanger Selectionand Compressor Efficiency.

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Commonly encountered problem

Low refrigerant under charge / leak

Poor Maintenance: Dirty air filter, dirty evaporator& condenser coil / fins

Bent Aluminium fins (both evaporator & condenser)

Electric control failure: Wear due to frequent ON &

OFF (oversized compressor)

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Case study # 1: Removing heat generating loads

Conditioned space

Deep freezers

(to store chemicals)

2 TR each split A/C

Two deep freezers were run inside an A/C room

Recommendation

Shift the two deep freezers to non A/C room One of the split A/C can be put off

Other examples: Heaters, UPS, Transformer, etc.

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Other measures

A/C optimum room temperatures

Optimum running hours (meeting halls)Recommended maintenance of compressor,

AHU air filters, Condenser

Use of Electronic thermostats

Use of air curtain in Entrances

If you replace 10 year old A/C with new energy

efficient model, you can save 20-30 %

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Commonly used compressors

Reciprocating compressor

Costs more

Maximum EER of 10.8

Rotary compressors

Less cost

Maximum EER of 10.4

R i ti C

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Reciprocating Compressors

Hermetic system (sealed unit ) - small A/Cs,refrigerators

Semi-hermetic system

Open system larger capacity Similar to automobile engine

SPC 0.8 1.4 kW/ TR

Refrigeration temperature range: - 30 to 7C

Capacity control

Small capacity: On and Off control Larger capacity : Multiple cylinder Unloading

Variable speed drive

Reciprocationg Compressor

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Reciprocationg Compressor

(Source: BEE codes)

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Rotary Sliding Vane CompressorRoller compressor

Some of rotary compressors(Source: BEE codes)

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Comparison of Normal and High EER

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p gcompressors

Sl.No.

Area Normal EER Recip

High EERRecip

1 Power needed for Compression

of Gas( Useful power)

Same Same

2 Motor Loss Normal Low

3 Frictional Loss Normal Low

4 Suction Gas Super Heat Loss High Low

5 Suction Valve/Muffler loss High Low

6 Discharge Valve/Muffler Loss High Low7 Piston blow-by Normal Low

8 Re-expansion Loss Normal Normal to Low

(Source: Kirloskar Copeland)