While passing through the condenser, refrigerant is in three different states. what are they?

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Posted On: July 10, 2018

Air conditioners rely on a number of different components in order to effectively cool your home. The condenser is one of the most important such components. Unfortunately, it is also one of the least understood. This lack of understanding stems from the fact that a condenser accomplishes several different tasks as it runs.

The more you know about how your air conditioning system works, the better you will be able to recognize potential problems. If you would like to learn more about the components inside of your air conditioner, read on. This article will introduce you to the three key jobs performed by an air conditioner’s condenser.

1. Desuperheating

Refrigerant exits your evaporator coil as a gas, having absorbed heat from inside of your home. This gaseous refrigerant then enters the compressor, which packs it more tightly together, increasing its temperature in the process. The condenser’s job involves lowering the refrigerant’s temperature enough for it to transform back into a liquid.

The first task a condenser must accomplish goes by the name of desuperheating. To understand desuperheating, you must first understand the related concept known as saturation temperature. Saturation temperature refers to the boiling point of a liquid at a given pressure. Once the liquid reaches its saturation temperature, it begins turning into a gas.

When the temperature of a gas continues to rise beyond its saturation temperature, the gas is said to be in a superheated state. An air conditioner’s refrigerant exists in a superheated state as it flows out of the compressor to the condenser. Superheated refrigerant must be cooled back down to its saturation temperature before it can be condensed into a liquid.

This initial cooling process goes by the name of desuperheating. The gaseous refrigerant passes through the condenser as many times as needed in order to reject its superheat.

2. Condensation

Once all of a refrigerant superheat has been rejected, the actual process of condensation may begin. Condensation involves the transformation of the gaseous refrigerant into its liquid state. The mechanics of this operation remain the same as in desuperheating — in other words, the refrigerant continues to circulate through the condenser in multiple passes.

As the refrigerant flows through the condenser, the condenser’s multitude of fins allow heat to transfer to the surrounding air. A fan on top of the condenser unit ensures that this heated air cools off quickly, enabling the process to continue. As the refrigerant’s temperature lowers beneath its saturation temperature, it automatically begins transforming into a liquid.

3. Subcooling

After all of the refrigerant has converted to a liquid state, it is said to be a fully saturated liquid. At this point, however, the refrigerant will still be quite volatile. Even a small temperature increase will cause part of it to shift back to a gas. This places a severe limitation on the potential cooling that the refrigerant can achieve.

The condenser increases the effectiveness of the refrigerant by continuing to cool it beyond its saturation temperature. This process, known as subcooling, improves the stability of the refrigerant. As a result, the refrigerant will be sure to remain a liquid on its continued journey back to the evaporator coil in your home.

All air conditioners have a pre-determined subcooling limit. As the system ages, however, wear and tear will make it harder and harder time cooling the refrigerant to this level. Consequently, your system’s efficiency will go down. Fortunately, you can ensure ideal functionality by having your system regularly serviced and maintained.

For more information about what it takes to keep your condenser working at peak capacity, please don’t hesitate to contact the cooling professionals at C.B. Lucas.

In an air conditioning system, refrigerant are present in three forms:

1. Liquid
2. Vapor
3. Mixture of liquid and vapor

When the refrigerant leaves the compressor, the refrigerant in the discharge line is all vapor. As the refrigerant moves through the condenser it begins to cool, and changes state. At this point the refrigerant is a mixture of liquid and vapor. As the refrigerant exits the condenser, the refrigerant has now changed to all liquid. At this point, if a site glass is installed you should not see any bubbles.  A solid column of liquid moving to the expansion device is required for a properly operating AC system.

As the refrigerant passes through the expansion device, the refrigerant once again changes into liquid/vapor mixture and continues to stay in this state through most of the evaporator coil. Near the exit point of the evaporator and entrance to the suction line, the refrigerant has changed to all vapor once again.

Remember – when using your PT chart as a diagnostics tool, it only pertains to the refrigerant in the liquid/vapor state, meaning the refrigerant in the condenser and evaporator coils. When the refrigerant exists in a liquid and vapor state, it is in a condition called saturated.

Superheat and Subcooling

Superheat is measured at the places where the only vapor is present (the suction line) and is the difference between the saturation temperature and the measured temperature. In a properly operating HVAC system, the measured temperature will always be above the saturation temperature, usually 5-20F depending on the manufacturer and system conditions.

Subcooling is measured at the places where only liquid is present (the liquid line) and is the difference between the saturation temperature and the measured temperature. In a properly operating HVAC system, the measured temperature will always be below the saturation temperature, usually 5-15F depending on the manufacturer and system conditions.

So, if we can determine the pressure at any of the points where the refrigerant is in the saturated state, we can find the corresponding saturation temperature on our PT chart. You can even determine the pressure of the refrigerant in the saturated state by measuring the temperature, although it is much easier and more convenient to measure the pressures.

If you would like to become an HVAC technician and learn more about refrigeration and refrigerant, sign up for our online HVAC course. We have interactive superheat and subcooling exercises for measuring superheat and subcooling.

by Ron Walker

A fluid, known as a refrigerant, moves between four key stages in refrigeration cycle. As it does so, it changes in pressure and temperature, this allows the fluid to absorb heat from one place and discharge it in another.

For a refrigeration cycle to work, it requires five main components. The four key stages of temperature and pressure change occur within these components.

• The compressor
• The condenser
• The expansion valve
• The evaporator
• The pipework which connects them all

To cool a room down, you need to collect the heat and dump it somewhere else. The air in this “somewhere else” must be a lower temperature than the refrigerant for you to be able to dump the heat. To make sure this is possible, the refrigerant is compressed so that the temperature increases. That way when the refrigerant reaches the condenser, the refrigerant within the pipe will be hotter than the air on the outside of the pipe, so it will be able to dump the heat. If the pipe was the same temperature as the air then you wouldn’t be able to reject any heat and you wouldn’t cool the room down.

The refrigerant enters the compressor as a warm, saturated low pressure gas, it is then compressed within the compressor (hence the name). During compression, the quantity of fluid remains the same but the volume decreases, this increases the pressure and temperature. The refrigerant leaves the compressor as a superheated (hot) high pressure gas.

Next this superheated high pressure gas enters the condenser, the condenser is a coil of pipework which runs between metal fins.

The metal fins help carry heat away from the pipe via conduction. A fan also blows air across the coil and fins to remove the heat via convection.

As the air is blown across the pipework and fins, it picks up the heat from the refrigerant and moves it away so that the refrigerant cools down. As it cools down the high pressure gas condenses into liquid, which is still at a high pressure.

The refrigerant enters the condenser as a superheated (hot) high pressure gas, it dumps its heat into the air being blown across by the fan, this drop in temperature condenses the refrigerant. The refrigerant leaves the condenser as a regular temperature, saturated high pressure liquid.

To cool a room down, the heat within that room must be collected and dumped somewhere else. The refrigeration cycle collects this heat by sending the refrigerant at a low temperature and pressure into the evaporator within that room.

To cool the refrigerant down it is passed through the expansion valve, this will reduce the pressure of the refrigerant by restricting how much can flow through the valve. This restriction means that there will be less refrigerant in the next section of pipe, so the refrigerant which is allowed to pass through can expand a little. This expansion reduces the temperature and gives it some storage room to collect the heat.

The expansion valve restricts the flow of refrigerant through use of an internal spring loaded valve which is connected to a diaphragm.

A thin tube, known as the capillary tube, runs between the expansion valve and a thermal bulb. The thermal bulb is in contact with the pipe just after the evaporator, the liquid/vapour inside the thermal bulb expands and contracts with the change in temperature of the refrigerant leaving the evaporator. This expansion and contraction causes the diaphragm to move which in turn controls the spring loaded valve that limits the flow of refrigerant into the evaporator.

The refrigerant enters the expansion valve as a regular temperature, saturated high pressure liquid. The expansion valve will limit how much refrigerant can pass through at one time, this results in the refrigerant dropping in pressure and temperature. The refrigerant leaves the expansion valve as a cold, saturated low pressure liquid.

The final key stage of the refrigeration cycle is the component called the evaporator. This is similar to the condenser in construction, but the refrigerant behaves differently inside.

In the evaporator, the refrigerant enters as a cold, low pressure liquid but quickly begins to boil. The refrigerant has a very low boiling temperature, typically of -23ºc (minus twenty-three degrees Celsius). As the refrigerant boils it evaporates, this evaporation picks up the rooms heat and carries it away towards the compressor where the refrigeration cycle will begin again.

The refrigerant enters the evaporator as a cold, low pressure liquid, the refrigerant begins to boil and evaporate, this evaporation causes a cooling effect in the room and the heat is carried away to be dumped in the condenser after the compressor. The refrigerant leaves the evaporator as a warm, saturated low pressure gas.