rac fundamentals

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SYSTEM COMPONENTS, ACCESSORIES and TEST INSTRUMENTS

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Academic Year 2004 2005, Semester 2

Prepared By: Nolasco K. Malabago, Ph.D

LEARNING OBJECTIVES

Upon completing this module you will be able to:

1. Identify the four major refrigeration components.2. Identify the high and low sides of the system.3. Define the difference between air conditioning and refrigeration.4. Differentiate between 'split systems' and 'package systems.'5. Trace the refrigeration cycle.6. Describe some of today's current issues regarding air conditioning--industry concerns and

future modifications.

REFRIGERATION FUNDAMENTALS

TERMINOLOGY

Refrigeration is a process of removing heat from a material or its content and transferring this heatto a place where it makes no difference.

Evaporation is the term used when enough heat is added to a liquid substance to cause it tochange into a vapor (gas). At sea level, water boils and vapor (steam) is given off at a sensible temperature of 212 F. Although

evaporation is the term of choice when describing a change of state, we will use the terms "boil" and"evaporation" interchangeably.

Condensation is the term used to describe the opposite of the evaporation process. If enough

heat quantity is removed from the vapor or gas, a change of state occurs. The vapor becomesa liquid. The change of vapor to a liquid is called condensation.

Freezing is another change of state. If additional heat' is removed from, a liquid, it will becomea solid.

Specific Heat is the amount of heat required to change the temperature of a substance 1 0Fwithout causing a change of state. The specific heat of, water is the standard used incomparisons. Water has different specific heats depending on, its state. Ice has a specific heat of .5 BTU per degree. Liquid has a specific heat of 1 BTU per degree.

Water vapor has a specific heat of .5 BTU per degree. Other substances have different

specific heats.

Latent Heat is the heat required to cause a change of state.

The term latentmeans "hidden" and latent heat is "hidden heat" since it cannot bemeasured by a thermometer.

The heat absorbed while water is boiling is called the "Latent Heat of Evaporation." The heat released during condensation is called the "Latent Heat of Condensation."


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While water is absorbing or releasing heat, there is no change in sensible temperatureoccurs. In other words, as long as water is boiling, both the liquid and the vapor given offare at the same temperature (212 0F).

Regardless of how much heat is added, the temperature of the liquid never rises above itsboiling point. The quantity of heat increases but the intensity of heat remains the same.Likewise, when the vapor is condensing, no change in temperature occurs.

THE REFRIGERATION CYCLE

1. The compressor and metering device set up the pressure differences required to first boil (evaporate)the refrigerant and then condense it.

2. As cool, high pressure liquid enters the evaporator, the low pressure in the evaporator coil reduces theboiling point of the refrigerant and causes it to boil violently. As it boils, the refrigerant absorbs the heatnecessary to change its state from a liquid to a vapor.

3. The compressor draws the heated vapor from the evaporator and pushes it into the condenser underhigh pressure. Because the vapor enters the condenser at a faster rate than the metering device allowsit to exit, pressure builds up and the vapor molecules are pushed closer together. Condensation of thevapor occurs. As the vapor condenses, the heat that was absorbed during evaporation is given off.

4. The cool, high pressure liquid travels through the metering device and enters the evaporator where theliquid once again boils and the cycle is repeated.

REFRIGERATION SYSTEM COMPONENTS


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PRODUCTSpecific Heat BTU's / Lb. Per F Latent Heat of Fusion in

BTU's Per Lb.Freezing Temp.

In FAbove Freezing Below Freezing

Water 1.00 0.50 144 32

Beef (Fresh) 0.75 0.40 98 27

Ham and Pork 0.68 0.38 86.5 27

Lamb 0.67 0.30 83.5 29Poultry 0.79 0.37 106 27

Sausage 0.89 0.56 93 26

Veal 0.71 0.39 91 29

VEGETABLES

Beets 0.86 0.48 128 27

Cabbage 0.93 0.47 132 31

Carrots 0.86 0.45 126 29

Celery and Lettuce 0.91 0.46 136 30

Potatoes 0.86 0.47 113 29

Tomatoes 0.92 0.46 152 30.5

FRUITS

Apples 0.90 0.49 122 28.5Cantaloupe 0.56 0.33 66 30.5

Strawberries 0.92 0.48 131 30

Pineapples 0.90 0.50 128 28

AIR CONDITIONING FUNDAMENTALS

TERMINOLOGY

Air Conditioning is the process of treating air so as to control simultaneously its temperature, humidity,cleanliness and distribution to meet the comfort requirements of the occupants of the conditioned space.

Air Conditioners are basically refrigeration devices cooling air and rooms rather then food

compartments.

Absolute Humidity is the weight of water vapor per unit volume.

Dehumidification is the condensation of water vapor from air by cooling below the dew point or

removal of water vapor from air by chemical or physical methods.

Dehumidifier is an air cooler or washer used for lowering the moisture content of the air passing

through it. An absorption or adsorption device for removing moisture from air.

Dehumidifying is the removal of moisture from the air.

Humidifying is adding moisture to the air.

Humidity is the dampness of air.

Humidity Ratio is the ratio of the mass of the water vapor to the mass of dry air contained in the

sample.

Relative Humidity is the ratio of the mol fraction of water vapor present in the air, to the mol fraction of

water vapor present in saturated air at the same temperature and barometric pressure; approximately, itequals the ratio of the partial pressure or density of the water vapor in the air, to the saturation pressureor density, respectively, of water vapor at the same temperature.


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CLASSIFICATION

According to heat rejection methods

Largely classified into water cooled and air cooled. As a tendency, air cooled is preferable since it isfree from increase of maintenance work.

Features of air cooled and water cooled types

Item Air cooled type Water cooled type

Condensing Medium Outdoor air Well water

Cooling water together

Incidental works Power supply

Refrigerant piping for Splittype

Power supply, coolingwater piping

Pump for well water orcirculating pump

Noise Comparatively high (outdoor

unit) Low

Check points

Conditions of outdoor airintake (chemicals, dust anddirt)

Short circuit of distributed air

Outdoor air temp.

Quantity and quality ofcooling water

Position of cooling tower


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According to Structures

Water cooled air conditioners are of the single packaged type.

Air cooled air conditioners come in either single packaged type or split type.

Water cooled, single packaged type is installed in either window or roof top.

Air cooled, single packaged type is installed in either pair system or multi - pair.

The split type consists of two units and installed in the indoor and outdoor separately connected byrefrigerant piping.

Features of single packaged type and split type

Item Single Packaged type Split type

Installation of work (thruhole)

A large hole is necessary for heatradiation ( for ducting or installation)

A small hole is necessary forrefrigerant piping

Operation noise (indoorside)

Comparatively high for window typecompared with split type

Compared with the single packagedtype, operation noise is small but takeheed of noise of the outdoor unit

Position of InstallationBecause hot air is extracted one sideof the room must be facing outdoor

(only window type)

Two refrigerant pipes and link wiringconnect the two units


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