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RDI Product

Training

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Refrigeration 101

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Table of Contents

Refrigeration 101 3-68

What is Refrigeration? 4

BTU 5

Latent & Sensible Heat 6

Latent Heat 7-12

Saturation Temperature 13

Superheat 14

Sub-cooled Liquid 15

Refrigerants 16-17

Refrigeration Capacity 18

Pressure to Control 19

Refrigeration Cycle 20-68

Compression System 21

Basic System 22

Heat Rejection 23

Compressors 25-29

Oil Separator 30-31

Condenser 32-33

Headmaster Valve 34-36

Liquid Receiver Tank 37-38

Filter/Drier 39-40

Sight Glass 41-42

Solenoid Valve 43-44

Pump-Down 45

TXV 46-49

Superheat 50-52

Evaporators 53-56

EPR & CPR Valve 57-62

Suction Accumulator 63-65

Suction Filter 66-67

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What is Refrigeration?

Process of Heat Removal

Heat ALWAYS travels from a warm object to

a colder objectHeat travels from the air or product inside a walk-

in to the refrigerant inside the evaporatorHeat travels from the refrigerant in the condenser

to the air surrounding the condenser

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BTU

British Thermal UnitEnergy required to increase temperature of 1 pound

of water 1 degree FahrenheitApproximately equal to energy of one wooden

match

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Latent Heat & Sensible Heat

Latent HeatHeat that has the effect of changing the state of a

substance without changing its temperatureHidden heat; heat that cannot be sensed with a

thermometer

Sensible Heat Heat that causes a change in the temperature of a

substanceA rise in temperature that can be sensed with a

thermometer

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Latent Heat

Latent Heat of Vaporization Liquid to VaporThe amount of heat that must be added to 1 lb. of liquid

at its boiling point to change it into 1 lb. of vapor

Latent Heat of CondensationVapor to Liquid The amount of heat that must be released by 1 lb. of

vapor at its boiling point to change it into 1 lb. of liquid

This is the Essence of Modern Refrigeration

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Latent Heat

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Latent Heat

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Latent Heat

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Latent Heat

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Latent Heat

When one pound of water boils it absorbs 970 BTU’s at a constant temperature of 212° F

When one pound of steam condenses into water, 970 BTU’s must be extracted constant temperature of 212° F

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Saturation Temperature

A saturated liquid or vapor is one at its boiling point; for water at sea level, the saturation temperature is 212° F

At higher pressures, the saturation temperature

increases, and with a decrease in pressure, the saturation temperature decreases

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Superheated Vapor

The amount of sensible heat over a vapors evaporation point

Water At Sea Level at 220° F has 8° F of Superheat

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Sub-cooled Liquid

Any liquid which has a temperature lower than the saturation temperature corresponding to its pressure is said to be sub-cooled

Water at any temperature less than its boiling temperature (212°F at sea level) is sub cooled

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Refrigerants

The ability of liquids to absorb enormous quantities of heat as they vaporize is the basis of the mechanical refrigeration system

R-22Liquid at +25°F and 48.8 psig has a Latent Heat of

Vaporization of 90.3 BTU/lb.

R-404ALiquid at -20°F and 16.3 psig has a Latent Heat of

Vaporization of 81.6 BTU/lb

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Alternative Refrigerants

We are constantly looking for new technology and continue to pursue alternative refrigerants

Look for possible refrigerant modifications in the future

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Refrigeration Capacity

Measured in BTUs or in Tons Not HP

Ton= energy needed to freeze one ton of ice

Each pound of water has a latent heat of fusion of 144 BTU

Ton = 2000 (LBS)*144 (LHF) = 288,000 BTU

288,000/24 = 12,000 BTU/HR

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Pressure to Control State

At Sea Level Water Saturation Point 212°

At 10,000 Feet Water Saturation Point 193°

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The Refrigeration Cycle

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Compression System

There are two pressures existing in a compression system

1. Evaporating or low pressure2. Condensing or high pressure

The refrigerant acts as a transportation medium to move heat from the evaporator to the condenser where it is given off to the ambient air

The change of state from liquid to vapor and back to liquid allows the refrigerant to absorb and discharge large quantities of heat efficiently

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Basic System

Flow

Flow

Flow

Flow

High Pressure Gas

Low Pressure Liquid

High Pressure Liquid

Low Pressure Gas

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Heat Rejection

The condenser is the exit door for the heat that the refrigerant has absorbed in the evaporator and compressor

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Refrigeration System Components

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Compressor

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Compressor

Forces (pumps) the refrigerant through the refrigeration system

Compresses the refrigerant from a low pressure gas to a high pressure gas First it removes the refrigerant vapor from the

evaporator and reduces the pressure in the evaporator to a point where the desired evaporating temperature can be maintained

Second, the compressor raises the pressure of the refrigerant vapor to a level high enough so that the saturation temperature is higher than the temperature of the cooling medium (air or water) used for condensing the refrigerant vapor to a liquid refrigerant

We use Reciprocating and Scroll Compressors

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Hermetic Compressor

Most Prevalent in Smaller Systems

Costs Less

Refrigerant Acts as Coolant

Simple Replacement

Cannot be Repaired in Field

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Semi-Hermetic Compressor

More Robust

The “Old Standard”

Reputation of Quality

More Expensive

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Scroll

Hermetic System

Different Compression System

More Expensive than Standard Hermetic

Less Expensive than Semi-Hermetic

Limited to Larger Systems

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Oil Separator

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Oil Separator

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Condenser

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Condenser

As heat is given off by the high temperature high pressure vapor, its temperature falls to the saturation point and the vapor condenses to a liquid, hence the name condenser

Air Cooled vs. Water Cooled

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Headmaster Valve

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Headmaster Valve

Designed to maintain head pressure during low ambient conditions

Limits the flow of liquid refrigerant from the condenser while at the same time regulating the flow of hot gas around the condenser to the receiver

The two primary controlling pressures are the dome pressure, opposed by the discharge pressure which bleeds around the pushrods to the underside of the diaphragm

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Headmaster Valve

Pressure Pre-Set

Not Adjustable

Liquid

Gas

Mixture

Maintains

High Pressure

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Liquid Receiver Tank

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Liquid Receiver Tank

Liquid storage tank for refrigerant which is not in circulation

Contain high pressure liquid refrigerant and some high pressure refrigerant gas

CVD Technology uses the gas here for defrost mode

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Filter/Drier

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Filter/Drier

The liquid line filter/drier absorbs moisture, acid and sludge/varnish

It also filters (collects) small foreign particles from the system

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Sight Glass

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Sight Glass

Also know as the “liquid level moisture indicator”

Provides a visual means to determine if the refrigerant charge is low

Bubbles or foaming in the sight glass indicate a shortage in the flow of refrigerant

Provides a visual means to determine the approximate moisture level within the system GREEN – Moisture level should be at acceptable range YELLOW – Moisture level too high. The sight glass

should be located in the liquid line after the liquid line filter drier

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Solenoid Valve

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Solenoid Valve

Located in the liquid line just before the expansion valve inside the evaporator housing

Used in conjunction with the thermostat (temperature control) and a low pressure control in order to achieve an automatic pumpdown

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Pump-Down

Sequence1. The thermostat senses that the interior walk-in temperature has

become cool enough. The thermostat opens, de-energizing the normally closed liquid solenoid valve

2. The solenoid valve closes (stops the flow of refrigerant at the valve). The compressor continues to run. The pressure in the low side of the system is reduced and all remaining liquid in the evaporator changes to vapor

3. When the low-side pressure has dropped to satisfy the low pressure control setting, the electrical circuit through the low pressure control opens and turns off the compressor

Purpose1. It removes the refrigerant from the low side, making it impossible for

the oil to become diluted with liquid refrigerant. (Refrigerant vapor will always migrate to the coldest point of the system)

2. It prevents the compressor from having to start-up with a high suction pressure that could overload the compressor motor

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TXV

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TXV

The Thermostatic Expansion Valve (TXV) controls the flow of refrigerant to the evaporator and also reduces the high pressure liquid to a low pressure liquid and gas

Intelligent device that modulates in order to allow the correct amount of refrigerant to enter the evaporator

Senses the pressure and the temperature of the refrigerant leaving the evaporator, and determine the number of degrees of superheat

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TXV

Liquid

Liquid

(Starting to Boil)

Sensing

Superheat

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TXV

Sensing

Superheat

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Superheated Vapor

The amount of sensible heat over a vapors evaporation point

Water At Sea Level at 220° F has 8° F of Superheat

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Superheat

A vapor that is at a temperature higher than its saturation (boiling) temperature

How to Determine Evaporator Superheat:1. Measure the temperature of the suction line at the point the bulb

is clamped2. Obtain the suction pressure that exists in the suction line at the

bulb location3. Convert the pressure obtained in 2 above to saturated

evaporator temperature by using a temperature-pressure chart4. Subtract the two temperatures obtained in 1 and 3 (1 minus 3).

The difference is the evaporator superheat

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Calculating Super Heat

R-22Temperature at bulb is 33°F Pressure is 49 PSIG Super Heat Equals

33°F

-25°F 8°F

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Evaporator

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Evaporator

Condenser Evaporator

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Evaporator

The cold refrigerant is allowed to absorb heat from the warmer material that needs to be cooled

In our design application: The air inside the walk-in absorbs heat from its surroundings. Some

possible heat sources are:Product being stored (if above walk-in design temperature)Heat transferred through the insulated walls from the exterior of the

walk-inPeople entering the walk-inWarm exterior air through wall penetrations not sealed properlyHeat generated by other sources inside the walk-in (lights, fan motors,

heaters, forklifts, etc.) The evaporator coil surface absorbs heat from the air The refrigerant flowing inside the evaporator absorbs heat from the

evaporator coil surface

REMEMBER: Heat ALWAYS travels from a warm object to a colder object

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Evaporator TD

Difference in temperature between the temperature of the air entering the evaporator, usually taken as the walk-in interior design temperature, and the saturation temperature of the refrigerant corresponding to the pressure at the evaporator outlet

EXAMPLE:WALK-IN DESIGN TEMP. 35 °FSuction Pressure at EvapOutlet is 49PSIG 25 °F

(Refrigerant R-22) _____EVAPORATOR TD 10 °F

The most important factor governing the humidity in the refrigerated space is the evaporator TD The smaller the difference in temperature between the evaporator and

the space, the higher is the relative humidity in the space Likewise, the greater the evaporator TD, the lower is the relative

humidity in the space The colder the surface of an object, the more moisture it will attract

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EPR or CPR Valve

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EPR Valve

The Evaporator Pressure Regulating (EPR) Valve prevents the evaporator pressure from falling below the predetermined value for which the EPR valve has been set

By controlling the evaporator pressure, the evaporator temperature is also controlled

An EPR valve modulates from fully open to fully closed, closing on a fall in inlet pressure

Located in the suction line near evaporator outlet

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EPR Valve

Some typical applications where an EPR valve might be used:On multiple evaporator applications where each

evaporator is intended to operate at a different temperature

On multiple evaporator installations where evaporators vary in size, style and capacity

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EPR Valve

Flow

Flow

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CPR Valve

The Crankcase Pressure Regulating (CPR) Valve limits the suction pressure at the compressor below a preset limit to prevent overloading of the compressor motor

The CPR valve modulates from fully open to fully closed. The valve responds to outlet pressure, closing on a rise in outlet pressure

A CPR valve is typically used to prevent motor overloading on low temperature units during start-up after a defrost cycle or on systems in applications where high back pressures might be encountered during pulldown

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CPR Valve

Flow

Flow

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Suction Accumulator

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Suction Accumulator

Primary purpose is to intercept liquid refrigerant before it can reach the compressor

Prevents slugging the Compressor

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Suction Accumulator

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Suction Filter

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Suction Filter

Protects the refrigeration compressor by collecting all foreign material and preventing it from entering the compressor where it could damage the internal working parts

Must be on remote systems with long lines

The filter will collect any dirt that is in the evaporator or suction line at start up, and thus protect the new compressor

Any field built up system which requires cutting and/or brazing of lines needs the protection of a suction filter

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Refrigeration System Components