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1.How does basic refrigeration cycle work?

The basic refrigeration cycle for beginners 

If you are interested in learning how a refrigeration system works, it is helpful to understand

from the Ph (Pressure Enthalpy) chart perspective. It makes our life much easier.This is how the refrigeration cycle diagram looks:

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Yeah, it seems complicated at first, but it will be easier to understand once I have explained the

refrigeration cycle diagram section by section. It important to understand the basic refrigerationcycle, to comprehend what is going on within the air conditioner units, we cannot see it.

The refrigeration cycle tells us if there is air in the central air conditioner units, what to repair

after troubleshooting the refrigeration system, if there is enough air conditioner freon, or if the acfilter is dirty.

You could know the entire thing by knowing the pressure and temperature of the evaporator,

condenser, and compressor.

Once you have found the pressure and temperature, you plot in the Ph charts to determine what

and where sub-cooled and superheat take place in the Ph charts.

Here is how a Ph charts looks:

The Ph chart graphically shows where the physical states of these five mechanical components isand what is happening to the refrigerant within these components.

However, first let’s understand air conditioning theory, the basic principle, types of heat, howheat transfers and I will show you how the basic refrigeration cycle diagram works.

Air conditioning theory

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There are two laws that are significant to understand the basic refrigeration cycle and air

conditioning.

Thermodynamics’ first law explains that energy cannot be neither created nor destroyed, but can

be changed from one form to another.

Thermodynamics second law can help us better understand how the basic refrigeration cycleworks. Once of these laws state that heat always flows from a material at a high temperature to a

material at a low temperature.

As I have mentioned in the residential air conditioners section, air conditioning (the refrigeration

cycle) is a process that simply removes heat from an area that is not wanted and transfers that

heat to an area that makes no difference. The air conditioner itself does not create heat, it just

transfers heat.

For heat to transfer, there has to be a temperature and pressure difference. In the refrigeration

process there are two sections which produce a pressure difference: a high-pressure, hightemperature section (condenser) and a low-pressure, low temperature section (evaporator).

The refrigeration system removes heat from an area that is low-pressure, low temperature

(evaporator) into an area of high-pressure, high temperature (condenser).

For example, if cold refrigerant (40°F) flows through the evaporator and the air surrounding

evaporator is 75°F, the cold 40°F will absorb the heat from the 75°F space. By absorbing the heat

from the warm space, it also cools the space. It then transfers that heats to condenser (high side)

through compressor.

A hot refrigerant from the compressor flows to a cooler location the condenser medium (airsurround condenser) for example, the refrigerant will give up the hot vapor heat it absorbs fromthe indoor evaporator and becomes cool again and turns back to liquid.

You will understand it better, once I have explained this from the ph diagram point of view. This

is what the second thermodynamics’ law stated. It is more complicated, but I will describe it

briefly.

Air conditioning is a way to keep your home comfortable by controlling the temperature, air

movement, cleanliness, humidity, or dehumidify for our comfort.

To move heat from the evaporator to the condenser you need refrigerant, and other mechanicalcomponents, therefore we need to understand how heat transfers.

So how does heat transfer occur in the basic refrigeration cycle?

Maybe you are wondering how hot 75°F air transfers it heat to cool 40°F refrigerant. Well, there

are three methods of heat transfer. They are conduction, convection, and radiation or any

combination of the three methods.

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Heat transfer is the movement of heat from solid, liquid or gas materials to other solid, liquid and

gas materials.

According to the second law of thermodynamics, heat always flows from a material at a high

temperature to a material at a low temperature. For heat to transfer there has to be a temperature

difference between the two materials.

Heat transfer by conduction is when we heat a copper pipe to 100°F and grab that hot copper

with our bare hand (I don’t recommend that anyone do that, it’s just for the example). That is

molecule to molecule heat transfer.

Radiation is the transfer of heat in an invisible ray, for example, sun ray. We cannot see it, but

we can feel the sun ray hits our skin.

Convection is the transfer of heat from one place to a different location by circulating it with a

fan (force movement) or natural movement.

Air conditioner refrigerant is a chemical substance that air conditioner units use; these

refrigerants absorb heat from low-pressure, low temperature evaporator and condensing at ahigher pressure, high temperature condenser.

These refrigerants could be R-22, R 410a, or R134a. It depends on what kind of refrigerant theair conditioner units are designed for. Refrigerant can change state from vapor (by absorbing

heat) to liquid (by condensing that heat).

Basic refrigeration cycle principles: 

1. 

As refrigerant in the latent state or as vapor refrigerant in the process of changedstate to liquid, this is the phase where it absorbs or rejects large quantities of heat.

The quantities of heat absorbed or rejected can be managed by controlling the

pressure and temperature of the refrigerant.

2.  The boiling point of closed-system liquid can be controlled by changing the vaporpressure above it.

3.  Gauge pressure is used to determine the pressure inside the closed refrigeration

cycle system. It’s expressed in pounds per square inch gauge (psig).

4.  Heat flows from a material at a higher temperature to a material at low

temperature.

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5.  Heat energy is not created but converted and transferred.

Here is Principles of refrigeration video 

HVAC's video made by PublicResourceOrg

Make sure to press the Play button in the player controls to watch it. Enjoy!

What are two forms of heat and where does it take place in basic refrigeration cycle?

Sensible Heat when change in temperature can be measured by a thermometer or when you put

your hand on an object you’ll feel heat. That is sensible heat. 

Latent Heat absorbed or rejected when a refrigerant is changing state from liquid to gas, or vice

versa; however, the temperature remains the same. Heat is known to add to refrigerant but doesnot register in a thermometer, it just changed the refrigerant state (gas to liquid, or vice versa).This is also known as hidden heat.

First-lesson on how the basic refrigeration cycle works 

The refrigeration cycle explains to us what is happening to the ac freon in each of the fourcomponents within the air conditioner units. It tells us how much refrigerant the evaporator

absorbs, the refrigerant properties in the compressor, and how much refrigerant the condenser

rejects.

Understanding the basic refrigeration cycle diagram also helps us to find subcooled, superheatand to troubleshoot refrigeration processes much easier.

Finding subcooled and superheat is beyond the scope of this discussion.

As you can see in the Ph diagram below. Saturation curve this curve represents what state (vapor

or liquid) and region (sub-cooled, latent heat, and superheat) the refrigerant is in. It also splits

into two sections a saturation liquid line and a saturation vapor line.

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What do the saturated liquid line and the saturated vapor line show us in the basic

refrigeration cycle? 

These lines show us the refrigerant has reached the 100 percent point. For example, saturated

liquid means the refrigerant has reached 100 percent liquid (point 4) and there is no vapor.

Saturated vapor mean refrigerant is 100 percent in vapor state (point 3 and 8).

The area on the left side of the curve represents the sub-cooled liquid refrigerant region. The sub-

cooled region is heat removed (sensible heat) after the refrigerant has reached the 100% saturated

liquid state. The saturated liquid state in point 4 (The intercept between high-pressure line andsaturation curve).

The area under the curve represents latent heat or a mixture of vapor and liquid region (point A

to B). Heat that causes the refrigerant to change state, vapor to liquid or liquid to vapor.

Within the saturation curve a refrigerant splits into two sections vapor or liquid:

A.  To the left of the center line within the saturation curve, the refrigerant is in moreof a liquid state.

B.  To the right of the center within the saturation curve, the refrigerant is in more of a vapor state.

The area to the right of the curve represents refrigerant in a superheated vapor region. Superheat

is heat added to the refrigerant after it has reached 100% saturated vapor state. Point three andeight are saturation superheat vapor.

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Second-lesson on how the basic refrigeration cycle work 

In the typical split-air conditioning system, the four basic components are separated into two

sections indoor and outdoor.

Indoor Units Ourdoor Units

air conditioner expansion

valveair conditioner condenser

air conditioner evaporator   air conditioning compressor

In the basic refrigeration system or any air conditioner system you will have five basicmechanical components: a compressor, a condenser, an expansion device (metering device), an

evaporator and a refrigeration copper tube that connects them.

I will start the basic refrigeration cycle diagram discussion on evaporator section first. As youremember, evaporator and condenser act as a heat exchanges in the air conditioning system.

There are two pressure lines and two heat exchangers. The low-pressure line is an evaporator (itabsorbs heat) and the high pressure line is the condenser (it rejects heat).

The first heat exchange that occurs in this basic refrigeration cycle is the evaporator. The airconditioner evaporator is locate between points six and one in the basic refrigeration cycle

diagram. The evaporator is a heat exchange that is responsible for absorbing heat from whatever

 place (medium) that needs to be cooled; for our discussion it’s indoor.

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Do you remember thermodynamics’ second law? This law states that heat always flows from a

material at a high temperature to a material at a low temperature.

Since the evaporator is at a low temperature than the air surrounding it, it will absorb the

surrounding heat until the refrigerant liquid inside the evaporator coils starts boiling as result of 

absorb that heat.

As the evaporator refrigerant has boiled completely to vapor it’s now saturated vapor at point 7.Some compressors cannot pump liquid; if it does pump liquid, it will damage it. This is why we

need the entire liquid refrigerant to boil at point 7.

After, the entire liquid refrigerant turns to vapor and passes point 7. Superheat occurs. Superheat

is between point 7 and 1.

Superheat is life insurance for the compressor. It makes sure the compressor does not pull in

liquid refrigerant from the evaporator.

The air conditioner compressors located between points 1 and 2 has two important lines: a

suction line (low side pressure and back pressure) and discharge pressure (high side pressure,head pressure).

The suction line is the line that pulls the low-pressure and temperature from the evaporator andthe discharge line is the line that compresses and pushes that superheat vapor to the condenser.

Its creates a pressure difference in the air conditioning system by pulling in low-pressure, lowtemperature vapor from the evaporator suction line and increasing it to high-pressure, high

temperature superheat.

This pressure difference what makes the refrigerate flow in a refrigeration cycle. The compressor

is also known as the heart of the refrigeration system. The compressor is known as the vapor

pump.

The air conditioner condenser locate between points 2 and 5 is a heat exchange; it rejects both

sensible (measurable) and latent (hidden) heat absorbed by the indoor evaporator plus heat of compression from the compressor.

There are three important states that take place in the condenser heat rejection. The first statepoints 2 and 3 it de-superheat or simply rejects hot superheat vapor (it removes sensible heat).

At points 3 and 4 this the state where it rejects so many saturated vapors heat, it starts changingphase from vapor to liquid; as the refrigerant reaches point 4 it is 100 percent saturated liquid

refrigerant.

From points 4 and 5 it removes sensible heat from the saturated liquid refrigerant. This is where

you could use a thermometer and tell how much heat it has removed; as more heat is removed

it’s now in the subcooled region.

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The expansion device (metering Device) is normally installed in the liquid line between

condenser and evaporator (points 5 and 7). We cannot see it if you’re interested in seeing it. In aregular split central air conditioners system it’s located indoors with or near the evaporator coils.

The general principle behind any metering device is it acts as a restriction. You can see it in thediagram above. It reduces high-pressure, high temperature refrigerant from the condenser liquid

line to low-pressure, low temperature refrigerant for the evaporator.

What causes the temperature reducing is due to the restriction (orifice). The metering device is

responsible for providing the correct amount of refrigeration to the evaporator.

The operation to a metering is more complicated; however, the restriction is the principle behindevery metering device.

Check out refrigeration cycle for beginners. I explained from a split central air conditioner unit’sstandpoint.

By understanding how the basic refrigeration cycle work; you also know how air conditioningworks. The basic principles behind the refrigeration cycle and air conditioning are the same.

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2.We'll discuss the refrigeration cycle using the cycle diagram below.

Component #1 is the compressor. It takes refrigerant vapor in from the low pressure side of the

circuit, and discharges it at a much higher pressure into the high pressure side of the circuit.

The compressor is the heart of the system; it keeps the refrigerant flowing through the system at

specific rates of flow, and at specific pressures.

The rate of flow through the system will depend on the size of the unit. And the operatingpressures will depend on the refrigerant being used and the desired evaporator temperature.

Component #2 in this refrigeration cycle diagram is the condenser. The red dots inside the piping

represent discharge vapor. The solid red color represents high pressure liquid refrigerant.

Most air-cooled refrigeration systems are designed so that the refrigerant will condense at a

temperature about 25° to 30° above the ambient air temperature around the condenser.

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Most water-cooled systems are designed for 75° to 95° entering condenser water temperature,with 85° being the design temperature. With water-cooled condensers, refrigerant should

condense at a temperature about 10° above leaving condensing water temperature, or 20° above

entering condenser water temperature.

When the hot refrigerant vapor discharged from the compressor travels through the condenser,

the cool air or water flowing through the condenser coil absorbs enough heat from the vapor to

cause it to condense.

If the outside air temperature is 80°, an air-cooled system is designed so that the temperature of 

the refrigerant, right at the point where it first condenses, will be about 105° to 115°.

If the entering condenser water temperature is 85°, a water-cooled system is designed so that the

temperature of the refrigerant, right at the point where it first condenses, will be about 105°.

Why do we want the refrigerant to condense at this relatively high temperature? So that the air orwater flowing through the condenser will be very cold relative to the temperature of the

discharge vapor, which will allow the heat energy in the vapor to move into that relatively coldair or water, and cause the refrigerant to condense.

At this stage in the refrigeration cycle, high pressure liquid refrigerant will flow down the liquidline, through a filter-drier that is designed to prevent contaminants from flowing through the

system, and on to the metering device.

The metering device, component #3 on this refrigeration cycle diagram, is the dividing pointbetween the high pressure and low pressure sides of the system, and is designed to maintain a

specific rate of flow of refrigerant into the low side of the system.

If the wrong capacity of metering device is used, or if there is a problem with the meteringdevice, an incorrect quantity of refrigerant will flow into the evaporator.

When the high pressure liquid refrigerant passes through the metering device, its pressure willdrop to a low pressure that will be equivalent to about 10° to 15° below the design temperature

of the evaporator. It starts evaporating immediately, and it wouldn't be too inaccurate to imagine

it acting like warm soda when you shake the bottle and pop the top off. It shoots out into theevaporator foaming, bubbling, and boiling — and remember, it's at a low pressure, so for a

freezer it would be boiling at about -10° to -15°, and for a medium temperature refrigerator it

would be boiling at about 25°.

And that brings us to the evaporator, component #4 in the refrigeration cycle diagram. There will

be relatively warm air (or water, if the unit is an ice machine) flowing over the evaporator coil.

The refrigeration system is designed so that the refrigerant will evaporate in the evaporator at a

temperature that's about 10° to 15° below the temperature setting if it's a refrigerator or freezer,

and the temperature will drop to around 0° in the evaporator of an ice machine or ice cream

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machine.

The system is designed so that the heat in the relatively warm air, water, or ice cream mix

flowing over the evaporator will move into the cold evaporating refrigerant.

This process will continue to cool the air, water, or ice cream mix that's flowing over theevaporator until it reaches the design set point or thermostat setting.

So, when you turn on the refrigerator, freezer, ice machine, or ice cream machine, the system isdesigned so that the evaporator will stay colder than whatever it's cooling, and will continuously

remove heat from it and cool it.

I hope this article has helped you understand the refrigeration cycle a little more clearly.