Ductless mini-split systems combine the flexibility of room air conditioners with the whole-house cooling of central systems. Although some systems provide heating and cooling, ductless mini-split heat pumps are usually installed primarily for cooling.
Conventional heat pumps operate with a single indoor unit and single outdoor unit. In cooling mode, the outdoor unit serves as the condenser while the inside unit serves as the cooling coil (evaporator). Air is cooled at the evaporator coil and distributed through ducts to different rooms. In ductless systems, there is (usually only) one outdoor unit serving multiple indoor units. Again, in cooling mode, the outdoor unit is the condenser while multiple individual evaporators are located indoors in rooms or zones. Refrigerant is piped from the outdoor unit through small-diameter insulated refrigerant lines directly to individual rooms or zones. Cooled air is blown into the room by a fan in the individual evaporator units. The term "mini" is used to describe the small indoor units located in each room or zone.
While distribution energy losses in conventional systems have been estimated at 25 percent, distribution losses for ductless systems are about 1 to 5 percent.
Ductless systems are relatively easy to install. It takes two installers about a day to install a system having up to three zones. Wiring for power and controls is easier than with a conventional unit since wires can be run along with the refrigerant lines. Lines from outdoor units can span up to one hundred feet to indoor units.
Indoor units are about six to eight inches deep and are mounted flush on a wall or ceiling, or recessed in a drop ceiling. A three-inch hole is cut through the wall. Wiring, refrigerant lines, control cables, and the condensate drain all pass through this hole.
Ductless system benefits include ease of installation-air ducts are bulky and require special structural attention, while split system piping can often be routed through walls and joists. Further, split systems allow zone control for increased comfort and efficiency. System energy losses are reduced because distribution takes place through insulated refrigeration lines rather than ductwork. Aesthetics are improved over window units and no windows need to be blocked. Each zone has its own thermostat, so occupants can modify temperatures in each zone.
From a 1994 NAHB Research Center study, costs to the installer ranged from $2100 for a two-zone system, 1.5 ton system to $4200 for a four-zone, 3-ton system. Installed costs ranged from $3800 for a two-zone system to $7500 for a four-zone system. By comparison, the same study found a 1.5 ton conventional heat pump to cost $1800 plus $800 for ductwork and associated equipment (for a new home).
Ductless mini-split HVAC systems are not cost effective over conventional systems for most new home installations. They are generally cost effective or the only acceptable option in retrofit situations. Because they are not common in the U.S., there may be some resistance to the look of the systems.
Few, if any, code or regulatory barriers limit ductless technology. The National Appliance Energy Conservation Act of 1992 requires that split systems have a minimum SEER of 10.0 and HSPF of 6.8. The Air-Conditioning and Refrigeration Institute provides a list of air conditioners and heat pumps and their rated efficiency.
Residential ductless systems are available through several manufacturers. Typical compressor sizes range up to 5-tons with a maximum of four zones.
Do you have a specific question about this technology and/or its 'real life' applications? Try the contacts listed below:
Air Conditioning and Refrigeration Institute
4301 North Fairfax Drive
Arlington, VA 22203
Energy Efficiency and Renewable Energy Network
NAHB Research Center, Inc.
Aitons' Equipment, Inc.
United Technologies-Carrier Corporation.
800-CAR-RIER (800-227-7437) .
HVAC SALES DIVISION .
P.O. Box 1540 .
San Antonio, TX 78295.
Klimaire Products, Inc. .
7909 Northwest 54th Street.
Miami, FL 33166.
HVAC Products Division.
3100 Avalon Ridge Place.
Norcross, GA 30071.
Sanyo Air Conditioning Products.
21605 Plummer Street.
Chatsworth, CA 91311.