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How Ductless Air Conditioning Systems Work

How Ductless Air Conditioning Systems Work

April 02, 2022

Ductless Mini-Split in Norcross, GA

Ductless air conditioning systems, often called mini-splits, were originally innovated in Japan. Air conditioning was becoming increasingly prevalent in homes in post-World War II America, but the systems designed at the time for American homes were unsuitable for most Japanese homes. Due to the way Japanese homes were constructed, AC systems at the time were too loud and had impractical ductwork requirements. But Japan as a society was enamored with the idea of air conditioning, and Mitsubishi got to work and reimagined the air conditioner as the mini-split. The design was so clever that demand for it extended beyond Japan to much of the world.

Understanding Split Systems

As the name suggests, mini-splits are split systems. A split system is a type of HVAC system and an alternative to what is known as a packaged system. There are four core components to an air conditioning unit: an evaporator coil, condenser, compressor and blower. In a packaged HVAC unit, all four of those components are contained within a single metal cabinet that is installed outside the home. In a split HVAC system, an outdoor metal cabinet houses the condenser and compressor while an indoor cabinet houses the evaporator coil and blower.

Split AC systems are generally preferred because they provide better energy efficiency and the evaporator coil and blower have a longer lifespan. Nevertheless, traditional split systems are not practical in all homes, which is why packaged units were developed. The “mini” in mini-split refers to the size of the indoor unit. With a mini-split, the indoor unit can usually be installed on the wall, and that eliminates the concerns with a traditional split system, which typically needs an attic, basement or crawlspace.

Understanding Heat Pumps

A mini-split is a type of heat pump. A heat pump can both cool and warm a home. That means that if you have a mini-split, you have a single system that provides both cooling and heating. This differs from the traditional American home, which has an air conditioner that is separate from the furnace or boiler. When it comes to cooling, there is little difference between a heat pump and an air conditioner. They both cool the air in the same way by using refrigerant and transferring heat energy.

What differentiates a heat pump from an air conditioner is that it can essentially run in reverse in order to provide heat. This approach is quite different from a furnace or boiler, which both generate heat. A heat pump does not generate heat. It transfers heat energy into the home. That makes it incredibly efficient compared to other home heating equipment but also introduces a potential shortcoming, which is that the heat pump is limited by the heat energy available as opposed to a fuel source.

Air Source

The main distinction between a heat pump and a mini-split is that a heat pump forces air through ductwork whereas a mini-split blows air directly into the living space. Traditional heat pumps and mini-split systems are air sourced. We have previously mentioned that these systems heat and cool by transferring heat energy. In the case of an air-sourced unit, that heat energy is transferred to and from the ambient air. In the summer, your mini-split will transfer heat energy from inside the home to the outside. In the winter, it will transfer heat energy from outside the home to the inside, and this is where the limitation comes in. When it is cold outside, there is only so much heat energy available.


An alternative air source is a geothermal heat pump or mini-split, which can either be ground or water sourced. Rather than transfer heat energy to and from the air, these systems have pipes that transfer heat energy to and from the earth or a large body of water. It is notable that geothermal mini-splits are not yet commonplace for residential applications. However, that is likely to change in the years ahead as there is wider demand for mini-splits and geothermal heat pump technologies are becoming more affordable.

The Outdoor Unit

The average home with a mini-split system only needs a single outdoor unit. That unit contains the condenser and compressor and is housed in a metal cabinet. The metal cabinet also houses one or more fans that draw air into the system. The compressor is the heart of the system as this is the component that employs condensation to alter low-pressure gas into high-pressure gas. The condensing coil then converts the high-pressure gas back into the liquid refrigerant.

The Indoor Unit

The indoor unit houses the evaporator coil and blower. This unit is small enough to mount on the wall, and there are slim designs available that can be installed on the ceiling and in other areas. Based on the temperature setting, the indoor unit draws cooled or heated air into the home from the outdoor unit and blows it out directly into the living space. The indoor unit may have temperature controls, but it is more common for modern systems to be controlled via a dedicated thermostat. While these units do blow air directly, noise is usually not a factor as the average noise level is just 32 decibels.

Multiple Indoor Units and Zoned HVAC

The reason most homes only need a single outdoor unit is that most modern systems can support up to four indoor units. That allows you to have four distinct zones. In other words, you can set the living room temperature to a different temperature than the bedrooms and so forth. In the U.S., the use of mini-splits was once limited to older homes that lacked ducts and to home additions and the like. Recent innovations that have allowed for zoning in addition to providing heat at colder temperatures have made them a popular option even in newer homes.

Are Mini-Splits Viable in Cold Temperatures?

The technologies used in air-sourced mini-splits have advanced greatly in recent years. Most systems can maintain peak efficiency down to 30° F, and they will not cut off as a protective measure until they reach 20 degrees Fahrenheit. That makes them quite suitable for our service area. If you live in a colder area, there are low-ambient mini-splits available than can operate down to 0° F, or you may want to consider a geothermal system.

Your Ductless AC Experts Serving Greater Atlanta

Bardi Heating, Cooling & Plumbing has served the Greater Atlanta area since 1989. That means that we have more than three decades of experience meeting the needs of area homeowners. Our company installs, services, and repairs mini-split systems. We also install, service, and repair furnaces, boilers, heat pumps, air conditioners and all other manner of home heating and cooling equipment. You can also count on us as your local plumbing pros, and we clean drains, install tank and tankless water heaters, detect and repair leaks, install fixtures, and specialize in whole-house water filtration and softening. Call Bardi today or contact us online with any questions or to schedule an appointment!