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What’s the Difference Between Ductless Air Conditioning and a Central A/C?

Your HVAC technician can help you decided between a ductless or ducted system.Home improvement and new construction projects involve special considerations for comfort and air quality, energy expenditures, design costs and interior design specifications. Such projects include converting attic or garage space to usable living space, a new family room or new energy-efficient home design. Traditionally, projects on the drawing board, or kitchen table, would include designs and space accommodations for air ducts. Before you install or extend a central A/C system in your home or project, find out how it measures up to ductless A/C systems.

Familiar Principles

Like their bigger air-source central A/C cousins, ductless A/C systems provide energy-efficient cooling by transferring heat energy between the air inside and outside the home. This is efficiently accomplished by manipulating high-efficiency refrigerant under pressure and temperature changes. Here’s how:

  • Refrigerant enters the indoor coil (evaporator) under low pressure.
  • The refrigerant evaporates with the help of airflow across the coil.
  • During the vaporization phase, the refrigerant becomes extremely cold.
  • The cold refrigerant draws heat energy from the warmer airflow, which cools the air.
  • The cooled air returns to the living space to cool the home (central A/C system) or the zone (ductless A/C system).
  • The refrigerant flows to the compressor where it is squeezed and prepped to release the heat energy at the condenser coil outside the home.
  • Under high pressure, the refrigerant condenses to a liquid phase in the condenser, and becomes extremely hot, releasing heat energy to the air outside.

This heat exchange process repeats to maintain the temperature in the home or zone in relation to the thermostat setting. However, while the heat exchange processes -- refrigeration principles -- are essentially the same for ducted or ductless systems, the distribution method of cooled air is different.

Central Ducted Vs. Ductless Point-of-Use

One of the great advantages of ductless systems is the fact ductless A/Cs are refrigerant distribution systems, where ducted central systems are air distribution systems. As the name indicates, ductless systems do not use ducts to transport cooled air to the living spaces. This engineering and home comfort feat is made possible by the following ductless components:

  • Piping system -- Mitsubishi Electric, the inventor of ductless systems four decades ago, ductless systems incorporate a piping system that houses refrigerant lines, power source and condensate lines connected to the outside unit and each indoor air-handling unit (AHU).
  • Smaller footprint -- The outside unit of ductless systems contains the compressor and condenser just like central A/C systems, but ductless systems are generally smaller than large central systems, which offers installation advantages with less cumbersome units to install. The outside unit of a ductless system may be mounted to the outer wall of the home or installed on a small concrete square. The unit may be strategically tucked away and obscured by vegetation, for instance, for more pleasing aesthetics. The piping system may extend 200 feet, so place the outside unit anywhere you like.
  • Indoor AHU -- The indoor AHUs (single or multiple AHUs) of ductless systems are installed in the immediate zone (room or area) which requires air conditioning. Therefore, indoor air is cooled and monitored for precise temperature for continuous comfort independently from other cooling systems in the home. 

In contrast, a ducted central system has one large centrally located outside unit, one large centrally located indoor AHU and a network of air ducts to channel cooled air to all the living spaces at the same time, regardless of cooling demand from room to room.

In this way, ductless systems offer the advantage of meeting the cooling load of a zone as needed, rather than expending considerably more electricity to meet the cooling load of the entire home -- like it, need it or not.

Ductless Systems Redefine Efficiency

The cooling efficiency of any air-source A/C is designated as Seasonal Energy Efficiency Ratio, or SEER. The SEER rating is basically a factor of the amount of electricity consumed to the cooling output during the course of the cooling season. A higher SEER number, such as 26 SEER, means greater cooling efficiency.

Several Mitsubishi Electric ductless systems are Energy Star-qualified and Energy Star Most Efficient, which means these systems have met stringent efficiency and performance criteria, and offer a nice return on investment (ROI). While central A/C systems are certainly available with high SEER ratings and Energy Star-qualified, few are able to match the cooling efficiency of high-efficiency ductless systems. Those that do are typically geothermal systems, which draw and exchange heat energy from the ground or a water source. They are excellent systems, but well above the installation costs of ductless and ducted systems.

Accommodating Interior Designs

Ductless systems were originally designed to provide home and business owners a practical and energy efficient cooling solution and alternative to ducted central A/C systems and noisy window A/Cs. While the popularity of ductless systems exploded in Japan, Asia and through Europe beginning in the 1970s, ductless applications in the U.S. were primarily limited to commercial uses -- until recent years.

More than ever, homeowners are concerned with maintaining healthful indoor air quality and maximum home comfort in an energy efficient manner. Ductless systems offer all these benefits, and more, in low-profile mounting options that are specifically sized and tailor-made, so to speak, to accommodate practically any interior design.

  • Concealed cassette -- The AHU is concealed above the ceiling, below the floor or in wall cavities.
  • Universal mounting -- The AHU is mounted to the surface of the ceiling or wall.
  • Recessed cassette -- The AHU is partially recessed into the ceiling or wall, offering nicer aesthetics than Universal.
  • Floor console -- With special mounting brackets and airflow enhancements, floor mounted console is another nice option, and may be concealed by furnishings as long as airflow to the unit is not restricted.
  • Slim duct -- This installation is excellent for large rooms, areas and hallways. A short duct run is used to offer an air supply outlet and return grille. Like the concealed installation (which this is), the grilles are installed flush to the ceiling, wall or floor surface.

Central A/C systems offer the smooth look with the supply outlets and return grilles installed flush to interior surfaces. The drawback to central systems is the amount of square footage the ductwork occupies, which is why ductless systems were first designed. In older homes, duct space was not given much consideration. However, savvy homeowners who want to leverage every inch of square footage, particularly for new home design, are finding out that ductless is the way to go.

Zoned Temperature Control

Zoned temperature control is the ability of a cooling (and heating) system to condition the living spaces room by room, or a combination of rooms and areas (zones), independently of one another. While a zoning system is an add-on feature to ducted central A/C systems, zoned temperature control is inherent in ductless system design. Each indoor AHU comprises a zone, and offers independent temperature control from any other system in the home.

A central A/C zoning system consists of modulating motorized duct doors installed inside the air ducts, and a network of thermostats for each zone to control the duct doors. If you ultimately decide upon a central A/C system, or are just adding one or two ductless AHUs to augment your central system, then in fact ducted zoning systems are exceptional upgrades which to consider any time.

Indoor Air Quality

With super viruses, bacteria and other harmful contaminants in the air these days, healthful indoor air quality (IAQ) is a concern for many homeowners. Mitsubishi Electric has great news for concerned homeowners, and those that suffer from respiratory issues, such as asthma and allergies. Mitsubishi ductless systems come standard with a multi-phase filtration system installed in each AHU.

The multi-phase filtration system removes odors, viruses, germs and a host of other airborne contaminants in each zone an AHU is installed. The filters may be easily removed and cleaned, and they last up to 10 years. That saves a lot of money otherwise spent on disposable filters. With such a high quality onboard air-filtration system, ductless systems are virtually room air cleaners.

Ducted central A/C systems have an air filter, of course, and filters are critical to the protection HVAC components, such as the evaporator coil and air ducts, from contaminant accumulation. An important difference in IAQ with ductless and ducted systems is cross contamination.

Ductless AHUs do not circulate airflow through the entire home as do central systems. This can help reduce the spread of some contaminants, and it can help keep specific zones cleaner, such as a home office, media room or a room with an occupant that requires separate temperature and IAQ control.

Noise or Lack Thereof

Ductless systems beat central A/Cs hands down for operational noise. Many ductless systems literally operate at whisper-quiet decibels -- about twice as quiet as low-noise central systems. Enjoy your conversations, favorite shows or book in quiet comfort.

For more details about the benefits of ductless A/C systems for supplemental or whole-home cooling, contact us to speak with a licensed Mitsubishi Electric Contractor near your Virginia home today.

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