705 ac & refrigeration plants

7/30/2019 705 AC & Refrigeration Plants

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Refrigeration

andAir Conditioning


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References Introduction to Naval Engineering,

Chapter 19, pp. 341-351

Principles of Naval Engineering,

Chapter 22, pp. 22-1 -

22-17


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AC &RObjectives Basic operation

Principle components

Safety considerations

Thermodynamic principles


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Uses of AC&R Systems Cooling of stores and cargo

Cooling of electronic spaces and equipment

CIC (computers and consoles)

Radio (communications gear)

Radars

Cooling of magazines

Air conditioning for crew comfort


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Definition Review Specific heat (Cp)

Amount of heat required to raise the

temperature of 1 pound of substance 1F

(water is 1 Btu/lb F) Sensible heat - add energy and temp rises

Latent heat of vaporization - liquid to vapor

BTU (British Thermal Unit) Refrigeration - Cooling of an object and the

maintenance of its temp below that of

surroundings


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Generic Cycle


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Thermodynamic Cycle

Evaporator

Condenser

CompressorTXV


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Vapor-Compression

Refrigeration Cycle Refrigerant

Receiver

Thermostatic expansion valve (TXV)

Evaporator

Compressor Condenser


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RefrigerationCycle


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Refrigerant

Must have the following properties

High latent heat of vaporization - max cooling

Non-toxicity - not a health hazard

Desirable saturation temperature - for operating

pressures

Stability - nonflammable/nonexplosive

Ease of leak detection

Low cost

Readily available

R-12, R-114


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Expansion

Liquid Freon enters the expansion valve at

high pressure

Refrigerant leaves TXV at a much lower

pressure

As pressure drops, vapor formation begins

as Freon enters saturation region


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Evaporation

From TXV - Freon is a saturated mixture of

liquid and vapor

Cooling coil acts as a heat exchanger

Absorbs its latent heat of vaporization from

the surroundings

Slightly superheated (10F) - ensures no

liquid goes to compressor


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Compression

Low pressure, superheated Freon vapor

enters the suction side of the compressor

Refrigerant is compressed from a lowpressure vapor to a high pressure vapor

Increase in energy provides the driving

force to allow the Freon to flow through thesystem


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Condensation

Refrigerant returned to starting point as a

high pressure/temperature subcooled liquid

Latent heat of condensation (LHC)

Sea water heat exchanger is used to absorb

the LHC and discharge it overboard


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Receiver

Temporary storage space and surge tank for

the sub-cooled refrigerant

Serves as a vapor seal to prevent vapor fromentering the expansion valve


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Air Conditioning

Principles of Operation Air Conditioning

Maintaining the atmosphere of an enclosedspace at a required temp, humidity and purity

Cools / Dehumidifies air via cooling coils

within ventilation system

Heaters in ventilation system

Humidification units may be present


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Air Conditioning

Systems Refrigerant circulating system

Directly cools cooling coils

Chilled water circulating system

Refrigeration system cools chill water, which

cools cooling coils

Self-Contained System Added on to ships which originally did not

have AC plants

Not located in ventilation system (window unit)


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Basic AC System


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Safety Associated

AC&R Phosgene gas hazard (created when

refrigerant is exposed to high temperatures)

Handling procedures: Wear goggles and

gloves to avoid eye irritation and frostbite

Asphyxiation hazard in non-ventilatedspaces (bilges since heavier than air)


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Summary

705 ac & refrigeration plants

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