The Effects of A/C Refrigerant Properties on their Performance
6 mins read

The Effects of A/C Refrigerant Properties on their Performance

There are many things that can have an effect on the performance of your air conditioning. As air conditioning units become more in the public eye because of the coming phase out of R22 it is becoming increasingly important to pay close attention to the properties of the alternative refrigerants and how they are used.

How Air Conditioners Work

Air conditioners are simply a form of heat exchanger. They take heat energy from one place (the room in your property that you are trying to cool) and they transfer that heat energy elsewhere. Air conditioners cannot ‘make heat disappear’, because that would go against the laws of thermodynamics. Rather, they take the heat out of the air, heat up the ‘refrigerant’, and then transfer that air to the outside world.

The refrigerant is the substance that makes the air conditioning work. It is a fluid which can transition between being liquid to gas with relative ease. When it is a gas, it behaves under what is known as the ‘ideal gas law’. The pressure, temperature and density of the gas are linked. Raise the pressure of the gas and it will get hotter. Lower the pressure of the gas, and it will cool down.  Turning the refrigerant from liquid to gas takes energy. Refrigerants transition from liquid to gas at high temperatures. At low pressures, the transition will happen at a lower temperature. The temperature, pressure and energy that it takes for the transition to happen will depend on the refrigerant that is being used.

To cool your home, the air conditioner will compress the refrigerant in a compressor that is outside of your home. This increases the temperature of the refrigerant. A fan will blow outside air across the coils that contain the hot refrigerant. The air outside is cooler than the refrigerant, so the energy will flow from the refrigerant to the air, warming the air and cooling the gas.

The high temperature, high-pressure liquid will pass into an expander which will convert the refrigerant to a low-temperature liquid at a lower pressure. There is another fan in your home that will blow the air from your house across the coils. This air should, in theory, be warmer than the refrigerant in the coils. The warm air will transfer heat to the coils, which means the air cools down and the refrigerant warms up. The refrigerant will turn back into a gas and enter the compressor where the cycle will begin again.

The Efficiency of Different Refrigerants

There are many different refrigerants, and different ones will work at different temperatures and pressures. For example, R22 was a common and popular refrigerant for a long time but it is now being phased out because it has found to be harmful to the environment.

R401a is a popular refrigerant for small and medium-sized systems that provide both heating and air conditioning. It is supercritical at temperatures above 71 degrees Celcius and above this temperature there cannot be a difference made between the gaseous and liquid phases. It is very good for smaller systems and is quite affordable, but it is also less efficient than some other modern refrigerants.

For bigger systems, R134a is popular.  It is very efficient but it operates at lower pressures and therefore you need to put higher volumes through the compressor and this means that bigger investments are needed for installation.

R717 is often used in industrial environments and particular for refrigeration. It is known as ammonia, and it has a mixed reputation. Ammonia is known to be toxic, but it is easily detected because it has a strong odor. Because ammonia has been used in refrigeration for so long there is a lot of expertise and knowledge already out there. Ammonia is a natural refrigerant that will not contribute to the greenhouse effect. It is known to be very efficient at temperatures below 80 degrees Celsius, but is less effective at higher temperatures. Because of this, it is not typically used in air conditioning in warm climates.

R718 is another fascinating refrigerant. This one is also known as ‘water’.  As surprising as it sounds, water can be used as a refrigerant as well, but only at very high temperatures. At temperatures above 100 degrees Celsius, other refrigerants can sometimes be unusable because they would be at too high of a pressure. Water has a comparatively low density in a gaseous form, making it more suitable. However, you would still need a compressor with a quite high capacity to use this.

Choosing a Refrigerant

There are dozens of refrigerants to choose from. Some are drop in replacements for R22 such as that from Some will require certain modifications. Some have high boiling points. Some will work at pressures that are similar to older refrigerants.  Some are ‘natural’ and therefore good options for those whose primary concern is picking an environmentally friendly refrigerant. Some are designed to operate well at specific temperatures (very high or very low), while others prioritize broad energy efficiency.

If you are not sure what air conditioning refrigerant is most suitable for your specific circumstances, then you should call an HVAC technician. They would be happy to give you some advice and help you to figure out what would work best. If you are changing from an older HCFC refrigerant then you might need to limit yourself to refrigerants that will work with your existing unit.

Older HCFC refrigerants are still found in a lot of units that are 10 or more years old, and it is not illegal to have those units in operation. It will, however, become increasingly difficult to find replacement refrigerant for those units as the phase out continues. After January 2020 you will only be able to purchase refrigerant that has been stockpiled ahead of time or reclaimed from decommissioned units. For this reason, it is a good idea to start looking for a low GWP and low ODP refrigerant as soon as possible, that is energy efficient and suitable for your planned application.