What Are Superheat and Subcooling and How Do They Affect AC Performance?

From the outside, air conditioners often look almost like large fans – a simple technology that takes hot air out of a property and blows in cold air. But there is an incredible amount of science and technology that goes into each AC, far more than a person can see just by looking at the system.

An example of this is the “Superheat” and “Subcooling” components of the air conditioning system. Very few homeowners have ever heard of these terms before, but for AC repair companies like Cal Energy, they are a very important part of the air conditioning process and measured during tune-ups to improve AC performance.

What is Subcooling?

Subcooling is a process of cooling the refrigerant liquid below its saturation temperature at a given pressure. The refrigerant vaporizes and absorbs heat into its evaporator coil. It then enters the compressor. The compressor then compresses the refrigerant, which increases both its pressure and its temperature.

The hot, pressurized refrigerant then flows into the condenser coil, where it releases heat into the outdoor air. Once it is released, the refrigerant then transforms from a high pressure vapor to a high pressure liquid. In this condensed, liquid form, the system can then cool the liquid to an even lower temperature by transferring additional heat out of the liquid through the AC’s subcooling techniques.

The techniques may include:

A liquid subcooling coil.
A subcooling refrigerant circuit.
A subcooling refrigerant loop.
Additional compression.
A heat recovery system.

Different ACs use different processes to provide additional subcooling. Talk to your Cal Energy AC repair technician to learn more about your specific air conditioner if you would like to learn more.

What is Superheating?

Superheating is the opposite of Subcooling. It is the temperature increase of the refrigerant gas above its saturation temperature at a given pressure.

After the subcooled liquid refrigerant passes through the expansion device, it enters the evaporator coil. At this point, it has been allowed to expand (so it is no longer condensed) and evaporate. As it expands, it absorbs heat from the surrounding indoor air. This absorbed heat then turns the refrigerant into a vapor/gas. At this stage, the AC has its own superheating techniques depending on the make and model:

Larger sized evaporator coil.
Higher evaporator coil temperature.
Thermal or electronic expansion valves.
Suction line heat exchanges.
Vapor injection.

Once again, most ACs won’t use all of these systems. They’ll likely have their own specific approach for Superheating.

Superheating and Subcooling – AC Model Based

Every AC, no matter the brand or price, uses some level of superheating or subcooling. But the system itself varies depending on the make and model. Different size ACs may also play a role. That is why it is so important to make sure that you choose the right AC model when you are buying a new air conditioner and replacing an existing AC. The same size property may benefit from a different type of air conditioner compared to someone else’s home. It is our job to match you with the best model.

Optimization and Problems with Superheating and Subcooling Elements

When we examine your air conditioner during our AC repair trips or tune-ups, one of the things we’re looking for is whether or not your subcooling and superheating elements are working property and as efficiently as possible for your home. When they’re working properly, they provide:

Better Energy Efficiency – Your home is able to cool faster and stay cool for longer using less energy.
Better Cooling – The cooling efficiency of the system works far more efficiently, resulting in a more comfortable home.
System Longevity – AC systems that are have properly working subcooling and superheating systems last longer. The systems protect the internal working parts.

Superheating and subcooling also affect the system’s ability to cool the home with precision. When they begin to work improperly, the system struggles to release a precise temperature, and the result is a home that can be too hot OR too cold.

AC Tuneups in Sacramento, Orangevale, Rancho Cordova, and More

There is a reason that it is highly recommended that property owners have their ACs tuned up at least once a year, with their entire HVAC systems receiving at least two separate visits. That is because the components that make up superheating and subcooling are complex and need to be precisely working for your system to do its job.

This is especially important here in the Sacramento region. It gets hot here. Any issues with your AC, no matter how small can cost you potentially hundreds of dollars on your energy bills and potentially lead to an AC system that isn’t working properly. These are complex pieces of machinery, no matter how simple they may look on the outside. Superheating and subcooling are just two of the many parts that make your AC function properly.

Phillip Isaacs