Refrigeration & Air Conditioining

7/28/2019 Refrigeration & Air Conditioining

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REFRIGERATION &

AIR CONDITIONING

Applications

Vapour compression cycle

Vapour absorption cycle

Energy consumption inrefrigeration systems

Air conditioning

Energy savingopportunities

Case studies



Integrated Systems Approach to

Refrigeration & Air-conditioning

Reducing the Need for Refrigeration

Increase Temperature Settings

Reduce Heat Ingress

Better Heat Exchanger Design and Maintenance

Better Monitoring & Control Techniques

New Developments for Relative Humidity Control

Energy Storage

Inter-fuel Substitution: Use of Absorption Chillers

Drive Transmission

Electric Motor



Applications

Refrigeration systems are used for process cooling by chilled wateror brine, ice plants, cold storage, freeze drying, air-conditioningsystems etc. The refrigerant temperatures for process coolingapplications may range from 15C to as low as -70C.

Comfort air-conditioning requires refrigerant temperatures in therange of 0C to 5C. Air-conditioning generally implies cooling of room air to about 24C and relative humidity of 50%-60%.

In some applications, air-conditioning involves humidification of airup to 70%-80% relative humidity (in textile industry) ordehumidification of air to less than 45% or 20% (in somepharmaceutical industries, rooms housing sophisticated electronicequipment, storage rooms for hygroscopic materials etc.).



Terms

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

COP = Refrigeration EffectWork done

EER = Refrigeration Effect (Btu/hr)Work done (Watts)

Specific Power Consumption = Power Consumption (kW)

Refrigeration effect (TR)



Vapour Compression System



Compressors

Reciprocating compressors are commonly used up to capacities of 250 TR.

Screw compressors are available for refrigeration capacities fromabout 200 TR to 1200 TR.

Centrifugal compressor are generally used beyond 150 ton singlemachine capacity.

Scroll compressor is of more recent origin. Suction, compression anddischarge are simultaneously performed in an ongoing sequence by

the orbiting motion of the scroll. Scroll compressors are available forcapacities up to 30 TR.



Performance of

Vapour Compression Machines

CapacityTR

Power kW

COP EER Btu/hr/W

Specific PowerkW/TR

Open Type Reciprocating Compressors

10.78 6.62 5.75 19.7 0.61

28.90 19.26 5.24 17.9 0.67

48.30 32.06 5.32 18.2 0.66

64.40 42.75 5.32 18.2 0.66

Semi-hermetic Reciprocating Compressors

8.77 6.25 4.94 16.9 0.71

9.26 7.00 4.62 15.8 0.76

13.90 12.10 4.03 13.8 0.87

42.00 34.50 4.28 14.6 0.82

Open Type Centrifugal Compressors

563.67 329.94 6.00 20.5 0.59



Single Effect Absorption Chiller



Performance of

Vapour Absorption MachinesCapacity

TR Steam

pressurekg/sq. cm

Steam cons.Kg/hr

COP EER Btu/hr/

W

Specificsteam cons.Kg/hr/TR

Single Effect Chiller (Steam heated)

240 3.0 2101.0 0.61 2.10 8.75

Double Effect Chiller (Steam heated)85 8.5 415.2 1.10 3.76 4.88

100 8.0 490.2 1.10 3.76 4.90

155 8.0 736.5 1.13 3.86 4.75

270 8.5 1284.0 1.13 3.86 4.76

400 8.5 2097.0 1.02 3.49 5.24500 8.0 2296.0 1.17 4.00 4.59

Double Effect Chiller (Direct fired)

78 - 27.3 m3/hrnatural gas

0.96 3.28 0.35m3/hr

150 - 54.6 lit/hr LDO 0.96 3.27 0.36lit/hr/TR



Centralised Air Conditioning Systems:

Comparison of Air Cooling Methods

Type DX chiller (air

cooled

condenser)

DX chiller (water

cooled

condenser)

Chilled water

system

Capacity, TR 100 100 100

Saturated Suction temp, C 6.1 6.1 4.4

Saturated Discharge temp, C 52.7 37.8 37.8

Compressor power, kW (a) 104.5 62.0 62.0

Chilled water pump, kW (b) 0.0 0.0 12.8

Condenser cooling fan/pump

(c)

7.8 13.5 13.5

Total power, kW (a) + (b) +(c) 112.3 75.5 88.3

Total Specific power, kW/TR 1.12 0.76 0.88



Effect of Evaporator and Condensing

temperatures on COP



Energy Saving Opportunity:

Operate at Higher Temperature

Increase the Chilled Water Temperature Set Point if Possible.

Improve Air Distribution and Circulation

Improve air Distribution in Cold Storages

CompressorType

Percent Increase in the COPfor each 1°F Reset

CondenserTemperature

EvaporationTemperature

Reciprocating 1.30% 1.13%

Centrifugal 0.50% 1.54%

Screw 2.30% 2.08%

Absorption 0.80% 0.59%



Case Study: Increase refrigerant charging to

operate at higher suction pressure

Increase of suction pressure of refrigerant compressor-chilled waterplant from 40 psig to 60 psig to increase capacity and efficiency.

This has helped in reducing the number of compressors in operationfrom 3 to 2

Under-charging of refrigerant causes poor performance of compressors

Annual energy saving was 68,000 kWh. i.e. Rs 2.8 lakhs/year ($7000)

No investment




Reduce Conditioned Volume & Heating Loads

Keep Unnecessary Heat LoadsOut

Use False Ceilings

Use Small Power Panel Coolers

Use Pre-Fabricated, ModularCold Storage Units




Reduce Heat Ingress

Check and Maintain Thermal Insulation

Insulate Pipe Fittings

Reduce Excessive Window Area

Use Low Emissivity (Sun Control) Films

Use Low Conductivity Window Frames Provide Insulation on Sun-Facing Roofs

and Walls.

Provide Evaporative Roof Cooling

Building Structure Cooling

Use Doors, Air-Curtains, PVC StripCurtains

Use High Speed Doors for Cold Storage




Use Favourable Ambient Conditions

Use Cooling Tower Water Directly for Cooling in Winter

Design New Air-conditioning Systems with Facility for 100% Fresh Air during Winter

Use Ambiators : 2-stage Air Washers in Dry Areas to get water

below ambient wet bulb temperature Use Ground Source Cooling



Energy Saving Opportunity: Improve Heat Transfer

Use Heat Exchangers with Larger Surface Area

Use Plate Heat Exchangers for Process and Refrigeration MachineCondenser Cooling

Avoid the Use of Air Cooled Condensers

Evaporative Pre-coolers for Air-cooled Condensers

1C higher temperature in the evaporator or 1C lowertemperature in the condenser can reduce the specific powerconsumption by 2 to 3%.





Energy Saving Opportunity: Routine

Maintenance

Inefficient operation of refrigeration machines is usually due to fouling of

condensers. This happens generally due to the absence of water treatmentor poor water treatment practices. Specify Appropriate Fouling Factors forCondensers

Turn fans off when they are not needed.

Clean screens, filters and fan blades regularly.

Minimise fan speed.

Check belt tension regularly.

Eliminate ductwork air leaks.



Energy Saving Opportunity: Heat Recovery

Devices

Heat Pipes, Heat Wheels, Plate Heat Exchangers

Reducing Heat Load due to Ventilation

Low Relative Humidity Air-Conditioning



Demand Saving Opportunity:

Thermal Storage

Ice banks

Salt hydrates



Case Study: Optimising Speed of Compressors

Description Brine Chiller Water Chiller

Compressor make Kirloskar Kirloskar

Compressor model KC4 KC4

Motor rating, kW 55.0 90.0 Motor power input, kW 53.0 74.1

Speed, rpm 750 780

Operating hours/day 14.5 9.0

Refrigeration capacity, TR 29.1 57.0

Specific power consumption, kW/TR (compressor shaft power)

1.6 1.2

Average energy consumption,kWh/day

768.5 666.9



Case Study:

Optimising Speed of Compressors

Description Brine Chiller Water Chiller

Motor power input, kW 32.3 35.6

Speed, rpm 480 409.5

Refrigeration capacity, TR 23.0 44.0

Specific power consumption,kW/TR (compressor shaft power)

1.23 0.7

Operating hours/day 18.0 14.0

Average energy consumption, kWh/day

581.4 498.4



Case Study: Low Relative Humidity Air

Conditioning

The Air-to-Air Heat Exchangerwas installed recover heat fromthe return air duct to eliminate orreduce the requirement of ductheaters.

The room condition at the time of

measurements was at 23.9ºC and50% relative humidity. Total HeatLoad was 7 TR (i.e Room HeatLoad plus Air Re-heating Load).

Heat Recovery was 2.8 TR (equivalent to electrical heat loadof 9.9 kW).

The annual energy saving is about97,000 kWh/annum i.e. Rs. 5.0lakhs (12,500 $) per annum. Thisis a saving of about 70%.

C t d R d i i diti i l d



Case study: Reducing air conditioning load –

Green Building

The CII-Godrej Centre for

Environmental Excellence isIndia’s first Green Building

In the air conditionedauditorium, the design freshair requirement is 4000 cfm,which would increase the air

conditioning load. A uniquemethod of natural pre-coolingof warm fresh air has beenattempted called “wind tower”.

On an average, the airconditioning load reduction is

about 10 TR. The net saving is about 76.5

kWh/day in cool climate. Thesavings are expected to behigher in summer.



COOLING TOWER

Temperature Range: It isthe difference between thecooling tower inlet andoutlet water temperatures.

Temperature Approach: It is the difference betweenthe cooling tower cold watertemperature and theambient wet bulbtemperature.



Common Causes Of Poor Cooling Tower

Performance

Scale Deposits —When water evaporates from the cooling tower, it

leaves scale deposits on the surface of the fill from the minerals thatwere dissolved in the water.

Clogged Spray Nozzles — Algae and sediment that collect in thewater basin as well as excessive solids that get into the coolingwater can clog the spray nozzles. This causes uneven water

distribution over the fill.

Poor Air Flow —Poor air flow through the tower reduces theamount of heat transfer from the water to the air. Poor air flow canbe caused by debris at the inlets or outlets of the tower or in the fill.Other causes of poor air flow are loose fan and motor mountings,

poor motor and fan alignment, poor gear box maintenance,improper fan pitch, damage to fan blades, or excessive vibration.

Poor Pump Performance — An indirect cooling tower uses acooling tower pump. Proper water flow is important to achieveoptimum heat transfer.



Energy Saving Opportunities

Automatic ON/OFF control of fans with temperaturefeedback

Multi-speed motors for fans

Variable speed drives for fans

More efficient fans

Fan inlet cone

Velocity recovery stack

Fan tip clearance

PVC fills



Case Study: Cooling Tower Rationalisation

Description Unit Induceddraft CT-1

Naturaldraft CT-2

Water flow m3/hr 278 380

Water inlet temp. C 35 35

Water outlet temp C 30 30

Heat load TR 460 630

CT pump power KW 18.7 30.5

CT fan power KW 6.8 fanless

As the natural draft cooling tower had a capacity of

1200 TR, CT-1 was shut down and the entire load wasdiverted to the natural draft tower after change of pump impeller

Net saving of 10 kW.

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Refrigeration & Air Conditioining

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