How It Works: Central Air Conditioning

Central air conditioning is a general term for the most common type of whole-house air conditioning system. Most residential and commercial buildings use central air conditioning systems for heating and cooling. So it is important to know their ins and outs in case of malfunctions or replacement needs.

All central air units have the same main components, which consist of:

• The condensing unit, which contains condenser coils, a fan, and the compressor
• The evaporator coils and the evaporator fan
• Copper tubing, which runs refrigerant between the components

Variations exist across all central HVAC units, but most run on electricity and use thermostats to control temperatures. The main differences exist in the physical placement and consolidation of the units themselves.

The two different types of central air conditioning units are split systems and packaged systems.

Split-system central air conditioners have both indoor and outdoor components. The outdoor unit contains the condenser coils, the fan, and the compressor. The indoor unit contains the evaporator coils, filters, and the fan blower that pushes air throughout a building's ductwork. Refrigerant runs between the two units through a series of copper tubing.

Both units typically install on either side of an exterior wall for easy connection. Split system air conditioners often pair with gas furnaces to achieve both heating and cooling. In most cases, the indoor unit installs in your basement or utility closet. On the other hand, the outdoor unit installs on the side or behind of the building.

Benefits

Split system air conditioners are one of the most energy efficient HVAC systems, often more than split systems. This means that they are cost-effective to operate and save money on heating and air conditioner costs. Additionally, a dual unit system is easier to setup and install in a home. They also have the potential to add resale value to your home.

If you're looking to replace your central AC unit, split systems install well with existing ductwork. Though, some spaces don't have ductwork or are incapable of having it installed. In that case, there are also ductless mini split air conditioning and heat pump systems that provide heat and air. These systems require the least amount of maintenance of any home HVAC system.

Disadvantages

Because they have both interior and exterior components, split systems cost more to install. The installation costs increase the further apart the units are, as the required copper tubing and ductwork increases. The presence of an indoor unit also means indoor noise, the level of it depends on the individual unit.

Packaged systems have all the central heat and air components located in one unit. Because they have a combined air conditioner and central heater, it eliminates the need for a separate furnace. The metal structure typically sits on a roof or a concrete slab on the side of a building. The ductwork connects directly to the outdoor packaged system through the wall or roof.

Packaged units are more common for commercial use since the units occupy more space outdoors. The more robust units also are better at supplying heat and air throughout a larger space. Residential homes often favor more discreet systems for aesthetic purposes.

Benefits

Generally, packaged AC systems are less disruptive as they operate quietly and out of the way. They also have better efficiency by combining the heating and cooling process. Instead of two or more units drawing power, packaged systems have just one.

The consolidation of a packaged central air conditioner makes them easy to install and maintain. Especially in buildings that have minimal indoor space available, an entirely outdoor unit saves space. They have cheaper installation, maintenance, and replacement costs because all the components are easily accessible from one place. They also have less line connections, reducing clutter and areas where malfunction can occur.

Packaged AC systems are also more compatible with air quality devices such as filters, purifiers, and humidifiers. If having clean air is a priority in your space, consider installing a packaged system with an air filter add-on.

Disadvantages

Because the outdoor unit is larger and more exposed, they are more prone to weather damage. This also leads them to have a slightly shorter lifespan than split-system air conditioners. If one component rusts or malfunctions, it is likely to affect the whole unit.

Another disadvantage is less availability for customization in terms of placement. Packaged units have to install in a place that can easily access ductwork and is open enough to allow air flow.

Central air conditioners work by circulating air throughout your whole home to maintain a set temperature. When the indoor temperature rises above a certain set point, the central AC unit will kick on to start the cycling of air. Electricity is the power source for both split and packaged systems.

The steps of the cycle proceed as follows:

• A fan pulls warm air from indoors into the return ducts, where it then goes through filters to remove dust and other contaminants.
• The warm air then passes over the evaporator coil, where cold liquid refrigerant absorbs heat and cools the air.
• The blower fan then circulates the newly cool air through the supply ducts into the home. For ductless mini split systems, air circulates directly from fans located on multiple indoor units throughout house.
• As the refrigerant absorbs heat, it turns from a liquid into a gas. The gas refrigerant then travels through the copper tubing and into the compressor.
• The compressor increases pressure to release the absorbed heat, which turns the refrigerant back into a cool liquid. Then, the refrigerant flows to the condenser.
• The air conditioner condenser coils dissipate the leftover heat outside the building.
• The liquid refrigerant travels back to the evaporator coils to begin the cycle again.

The repetitive cycle continuously draws warm air out and circulates cold air into a space. Each component depends on the others, and when one fails, it eventually causes the whole system to fail.

Keeping the coils clean and monitoring for refrigerant leaks ensures your unit continues cycling air into your space.

According to Energy Star, the lifespan of a central air conditioner is about 15 to 20 years. Doing routine maintenance on your unit, however, can extend this lifespan even longer. Biannual tune-ups are important and easy to schedule with your local HVAC technician. These checkups are worth the long-term savings they guarantee in energy costs.

Central AC malfunctions are often the cause of one faulty component. If you can attribute the problem to one component, replacing that part often costs less than replacing the whole unit. Certain AC condensers, for example, are far cheaper than brand new units, especially if you have a packaged system. So, before investing in a total replacement the moment your unit stops working, get the exact problem diagnosed by a professional.