How Does Central Air Conditioning Work?

new dual central air conditioning units outside of a residential home

Cooling Trend

Central air conditioning is a modern necessity that a significant number of homes in hot summer locations can’t do without. In the past, the most common air conditioning unit was one you hung out from the window. Today, nearly 90 percent of homes have some form of air conditioning, most of which is central air conditioning.

Central air conditioning just makes more sense than window air conditioners. Central air conditioning is more efficient, less obtrusive, and less noisy. Properly sized for the home and professionally installed, central air conditioning keeps you cool on the hottest days, and does it far more efficiently than an air conditioner in every window. And it certainly keeps you cooler than just opening all those windows and hoping for a summer breeze to come by.

What’s more, central air conditioning improves indoor air quality (IAQ). That’s because central air conditioning filters air to remove dust, allergens, and other airborne particulates. And because central air conditioning is connected to your furnace or air handler, it keeps air clean year-round, not just when you need cool air.

But how exactly does central air conditioning work? Basically, a central air conditioning system pulls heat from outdoor air using a refrigerant, and then circulates the cooled air throughout the house. 

Let’s take a look at the details of how this exactly works:

In addition, let’s also look at what a heat pump is, as well as familiarize you with some key terms.  

Supply Systems: Ducts and Registers

Ducts are run inside walls, crawl spaces, and attics. The purpose of ducts is to efficiently distribute conditioned air throughout your home. There are two kinds of ducts: supply and return. Supply ducts distribute conditioned air to the rooms of your house. Return ducts return air back to be filtered and conditioned again.

Each room requires at least two registers, one for the supply duct located near or on the floor and the other for the return duct located near or on the ceiling. Registers are grilles usually colored to match the ceiling or wall paint or the floor covering. 

Split Systems: Inside and Out

A central air conditioning system with two units–an indoor air outlet and a compressor located outdoors–is called a split system because it is, well, split into two parts. The two units are connected by pipes rather than ductwork. This is probably the most common type of central air conditioning. 

There is another type of split system, called a mini-split system (it is sometimes just called a split system, which is a little confusing, but that’s what we’re here to clear up). A mini-split system also has two split units–an outdoor heat pump (which we’ll talk about more below) or condenser and an indoor air handler or handlers. The indoor component comprises multiple mini units, one for each room or zone, which is why it’s called a “mini split.” It’s ideal for applications where running ductwork is impractical. 

Indoor Air Handler

The air handler is an indoor unit that keeps your indoor temperature comfortable, based on the setting of your thermostat. The unit comprises:

  • Indoor evaporator coils. Contain low-pressure, low-temperature refrigerant gas. Humidity and heat are removed from indoor air as it passes over these coils.
  • Air filter. Traps dust, dirt, and other airborne particles from air before it circulates it throughout the house. 
  • Blower motor. Moves air to the connected ductwork. At one time, blower motors operated at only one speed, but newer multi- and variable-speed blower motors provide greater operating efficiency. 
  • Electronic components. Required to regulate and make everything mentioned above work well.

Outdoor Condenser Unit

The outdoor unit consists of the compressor, condenser, evaporator coil, and fan. This unit takes warm refrigerant from the house to cool it. It is located behind or to the side of the house, and two insulated lines that circulate refrigerant connect to the indoor air handler. 

The compressor moves refrigerant over the evaporator coil, where refrigerant absorbs heat and turns from a liquid to a gas. The gaseous refrigerant then moves over the condenser and is cooled back into a liquid, releasing heat energy. 

Heat Pump

A heat pump is sort of like an outdoor condenser unit except, as you might expect from the name, can heat as well as cool. In winter, refrigerant flow reverses and carries heat indoors. 

Heat pumps are best suited to climates with hot summers and cold (not frigid) winters. They are highly efficient, which can significantly reduce annual heating and cooling costs. In many cases, heat pumps are backed up by traditional HVAC systems when they are incapable of providing sufficient heat during much colder weather.

Key Central Air Conditioning Terms

Ton is a measurement of an air conditioning system’s cooling capacity, or the number of BTUs (British Thermal Units) removed per hour to keep a ton of ice from melting in a day. The typical residential unit is three tons. Only a professional HVAC technician can properly size a system to meet the cooling needs of a specific house, based on the number of rooms, climate conditions, number of windows and window orientation, and insulation levels, among other considerations. 

The SEER (Seasonal Energy Efficiency Ratio) indicates how well an air conditioning system converts electricity into cool air during a typical cooling season. The higher the SEER, the better the efficiency. Currently, the top SEER for a split air conditioning system is 26. Energy Star designates equipment with a SEER rating of 15 or higher. An Energy Star rating is often required for a system to qualify for tax and utility rebates.

EER (Energy Efficiency Ratio) is the amount of cooling a central air conditioning system delivers for each watt, minus seasonal averaging. In hot, dry climates, 12.2 is the minimum EER for units of 3.5 tons or smaller.

MERV (Minimum Efficiency Reporting Value) rates how effectively a filter captures dust, germs, and odors. The higher the MERV, the more airborne particles the filter removes.

Zoned central air conditioning systems distribute cool air to individual rooms and floors controlled with their own individual thermostats. Single-zoned systems often are inadequate if a single thermostat in the living room “thinks” everything is the desired temperature when upper floors and rooms with a lot of windows are actually still hot. Zoned systems are more energy efficient, as well as better equipped to keep all rooms in the house comfortable. However, whether your house is better off with a multi- or single-zoned system depends on a number of factors best assessed by a professional HVAC contractor. 

Ongaro & Sons—Your Air Conditioning Experts 

Ongaro & Sons is a family-owned business in its fourth generation of operation, providing complete home central air conditioning services, including installation, maintenance, and repair. We are a licensed state contractor with fully insured, qualified, and professional technicians dedicated to industry-leading home cooling solutions tailored to your specific requirements and budget. Our 100% guarantee ensures your complete satisfaction. No A/C? We have some great information on adding A/C to your existing HVAC system.

Contact Ongaro & Sons here or call us at 707-419-3135 today to have us answer your questions about air conditioning and keeping your home cool.