Ductless, Split-System Air-Conditioners

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++CTA++Ductless split-system air-conditioners are relatively new to North America, although the Japanese manufactured and used them in their country for many years.

They have numerous residential and commercial applications. The most common residential applications are in multifamily housing or as retrofitted add-ons to houses with hydronic or other non-ducted distribution systems (radiant panels, wood stoves, etc.).

Installation in new additions, where extending or installing ductwork is not feasible, is also a popular application. Commercial uses are also numerous. Some applications include schools, perimeter cooling for office buildings, additional cooling for restaurant kitchens, and cooling for small offices within larger spaces, such as arenas, warehouses, and auditoriums.

Ductless split-system air-conditioners combine the zoning flexibility of a conventional room unit (a single air-conditioner installed through a wall or a window frame) with the whole-house cooling potential of central systems. Like central systems, they have two main components: a compressor/condenser, as well as an air handling unit, which contains an evaporator and a fan. Some units operate as heat pumps and provide both summer cooling and winter heating.

The noisy compressor and condenser are housed as one unit and located outdoors. The quiet fan/evaporator unit is indoors, located in the area to be cooled. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and condensate drain, links the outdoor and indoor units.

The term, "split-system," also describes some central air-conditioners and heat pumps. If you ask about ductless, split-system air-conditioners, make sure the dealer understands which system you are talking about. Another common term for ductless split-systems is "mini-splits."


The advantages of ductless split-systems over room and central air-conditioners are: easy installation, quiet operation, versatility in zoning and design, and security. The split systems also eliminate the loss of cool air as it passes through the ductwork.

A key advantage of split systems is their ease of installation. Hook-up requires only a three-inch hole (7.62 centimeters) in the wall for the conduit. Unlike with central air conditioning, you do not need ductwork. Since the compressor in most ductless split-systems is as much as 50 feet (15.24 meters) away from the indoor evaporator, it is usually possible to cool rooms on the front side of the house, while still hiding the compressor in a less conspicuous area. The compressor units also fit well on flat commercial building rooftops.

Ductless split-system air-conditioners operate relatively quietly, since the compressor is outside and the evaporator unit's fan generally runs at a low speed. Variable speed high efficiency fans are also available.

By providing zone cooling, ductless split-system air-conditioners save energy, since only the rooms that are occupied need to be cooled. A thermostat independently controls each zone. Therefore, operating costs are often lower than those of central systems that cool every room, whether it is in use or not.

If you cannot afford to purchase an air conditioner for the whole house, you can also buy the system one zone at a time. A single outdoor unit controls from one to four zones, depending on the size of the unit. Commercial buildings tend to use larger units. Typically, the Btu per hour rating (Btu/h) of these units ranges from 8,700 to 60,000, and the Seasonal Energy Efficiency Ratio (SEER) ratings are between 10.0 and 11.5. Since January 1, 1992, the National Appliance Energy Conservation Act of 1987 (NAECA) has required a minimum SEER of 10.0 for newly manufactured or imported single phase (the type of power normally supplied to residences), split-system air conditioning units.

When compared to other add-on systems, split-systems also provide better interior design options. The air handlers can be suspended from a ceiling, mounted flush into a drop ceiling, or hung on a wall. Floor-standing models are also widely available. Most indoor units are low-profile models, no more than seven inches (17.78 centimeters) deep, and come with decorative jackets. Most newer models come with a remote control unit as standard equipment. This allows the positioning of air-handling units high on a wall or suspended from a ceiling, without compromising convenience.

Unsecured room air-conditioners provide an easy entrance for intruders. Split- systems are more secure than window units since there is only a small hole in the wall.


The primary disadvantage of split-system units is their cost. Split-system air- conditioners cost about $1,500-$2,000 per ton (12,000 Btu/h) of cooling capacity. This is about 30% more than central systems, and may cost twice as much as window units of similar capacity.

The installer must judge the best location for the air handling unit. It also needs to be the correct size for the area it cools. The air handler blows air up to 30 or 40 feet. If the system is improperly positioned and/or sized, the air can bounce off a wall or another obstruction. This results in short-cycling, which wastes energy and does not provide the desired temperature control. An oversized unit also costs more than a correctly sized unit.

Some people may also not like the appearance of the air handling unit. While less obtrusive than a window unit, they seldom have the built-in look of a central system. There must also be drainage for condensate outside the building. If the drainage is not well placed, the condensate can stain concrete or building materials.

Qualified service centers may not be easy to find until the systems become more widespread.


The following articles provide additional information about split-system air- conditioners. This bibliography was reviewed in August 1996.

"The Benefits of Radiant Ceiling Panels," B. Sullivan, Journal of Light Construction, (13:10) pp. 59-60, July 1995.

"Decentralized Air Conditioning," A. Cala, Home Mechanix, (87:756) pp. 43-45, June 1991.

"Ductless Heating and Cooling&151;Zoning with the Minisplits," Energy Design Update, (11:9) pp. 6-14, September 1991.

"Ductless HVAC Simplifies Installation," J. Nisson, Journal of Light Construction, (10:51) pp. 40-41, February 1992.

"Ductless, Multizone Split-System Provides New Design Options," R. Esparza, Heating/Piping/Air Conditioning, (59:7) pp. 63-65, July 1987.

"Here Are Six Ways Ductless Systems Can Provide Comfort," Air-Conditioning, Heating, & Refrigeration News, (195:7) pp. 20, 22, June 12, 1995.

"The Marketing Puzzle of Residential Ductless Splits," B. Checket-Hanks, Air Conditioning, Heating & Refrigeration News, (197:7) pp. 5, 8, February 12, 1996.

"Multi-Zoning with Ductless Split-Systems," T. Tollinger, Western HVACR News, (8:11) pp. 24, 26, November 1988.

"Split Coolers," V. Gilmore, Popular Science, (233:2) pp. 76-77, July 1988.

Source of Story: The U.S. Department of Energy's Energy Efficiency and Renewable Energy Clearinghouse

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