Characteristics of a Ductless Air Conditioning Unit

Posted on January 2nd, 2011 by

Ductless-split systems have existed for more than 50 years, and have been available in the United States HVAC residential and/or light commercial market for more than 30 years. Most American consumers, however, are unaware of these products. Currently, the U.S. market primarily consists of traditional unitary equipment, with ductless-split systems contributing only 3 percent to 4 percent of total HVAC sales. Compare the U.S. heating and cooling market to other world markets: ductless systems make up 90 percent of Japan HVAC sales, and 81 percent of HVAC systems sold in Europe are ductless.

What Makes a Ductless-split System?

A ductless-split system isn’t a window unit; it’s a permanent fixture in a home or small commercial building. There are two different types of ductless-split systems—cooling-only or heat pump—but the basic structure is the same. In ductless-split systems, the major HVAC components are housed in separate chassis, a feature that permits ductless-split systems to operate at low sound levels. The outdoor unit, also called the compressor unit, contains the compressor, condenser, propeller fan(s), circuit board, and a heat exchange coil. The indoor unit, or air handler, contains a heat exchange coil, air filter(s), remote signal receiver, and fan.

The outdoor and indoor unit components are connected by electrical wiring, control wiring, and a refrigerant piping system—one pipe for the refrigerant in its liquid state and one pipe for the refrigerant in its gas state—requiring only a small three-inch opening in the wall or ceiling. This refrigerant piping configuration makes ductless-split systems distinct from traditional unitary systems; instead of using a central air distribution system for the whole building, the outdoor compressor unit supports one (or more) indoor unit air handlers to condition the air within a specific area or zone. Because no ductwork is involved, extensive building renovation isn’t required. The design of ductless-split systems makes the equipment easy to install, and flexible enough to be included in any floor plan.

Ductless-split systems save energy—the consumer can cool or heat only the spaces that are occupied and doesn’t have to waste energy to condition a whole building. No ductwork means ductless-split systems don’t have the maximum 30 percent energy loss amount associated with central forced-air systems. Advancements in compressor technology further add to ductless-split system efficiency. Most systems now incorporate inverter-driven compressors, which allow for system ramp-up until the desired set temperature is met, then permit the system to modulate its operation so that a comfortable temperature is maintained. This operation avoids the abrupt and energy-consuming start and stop exhibited by traditional HVAC systems.

Past, Present, and Future of Ductless-split Systems

When first introduced to the market, ductless-split systems were offered in a one-to-one (or mini-split) configuration with one wall-mounted indoor unit connected to one outdoor unit. These products were installed in home additions, renovations, or used to transform a hot or cold area into a comfortable living space.

Split-system technology has continued to advance. Manufacturers eventually developed mini-splits with higher capacity sizes, and multi-split systems that could connect two, three, or more indoor units to one outdoor unit. They added ceiling-suspended, cassette, concealed, and floor-mounted indoor unit styles to their product offering. Current split-systems achieve higher energy efficiencies than before, and some heat pump models can even provide heating at extremely low temperatures.

The HVAC industry, private and public energy groups and U.S. government agencies have taken notice, recognizing ductless-split systems in certification programs, product standards, and federal, state, and local major-appliance rebate offers. With continuing education, the U.S. consumer and HVAC contractor may learn to look beyond the unique configuration and unfamiliar installation procedure of ductless-split systems, and embrace what these products offer—high comfort with high energy savings.

Written by Heather Tullis, Mitsubishi Electric

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