Ductless (Mini-Split) Heat Pumps
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Summary
An increasing number of homeowners expect central air conditioning
in their homes-more than twice the number of new homes were built with central
air in 1996 (81 percent) than in 1971 (36 percent). Most central air
conditioning systems rely on ductwork to distribute cool air to rooms
throughout the house. So, what about homes that don't have ducts, like those
with hydronic or electric baseboard heat? Ductless
electric heat pumps are one solution to cooling or heating a home
without the need for ductwork.
Details
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.
Installation
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.
Benefits/Costs
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.
Limitations
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.
Code/Regulatory
Few, if any, code or regulatory barriers limit duct
less 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.
Availability
Residential ductless systems are available through several
manufacturers. Typical compressor sizes range up to 5-tons with a maximum of
four zones.
Contacts
If you have any specific questions about this technology and/or
its applications please contact the following resources.
Air Conditioning and Refrigeration Institute
4301 North Fairfax Drive
Suite 425
Arlington, VA 22203
703-524-8800
Energy Efficiency and Renewable Energy Network
800-363-3732
NAHB Research Center, Inc.
HOMEBASE Hotline
800-898-2842
Aitons' Equipment, Inc.
Ontario, Canada.
905-542-0588.
United Technologies-Carrier Corporation.
800-CAR-RIER (800-227-7437) .
EnviroMaster.
315-336-3716.
http://www.enviromaster.com/emiframe.shtml
Friedrich.
HVAC SALES DIVISION .
P.O. Box 1540 .
San Antonio, TX 78295.
210-357-4400.
http://hometown.aol.com/fredihvac/index.html
Klimaire Products, Inc. .
7909 Northwest 54th Street.
Miami, FL 33166.
305-593-8358.
Mitsubishi Electronics.
HVAC Products Division.
3100 Avalon Ridge Place.
Suite 200.
Norcross, GA 30071.
770-613-5840.
Sanyo Air Conditioning Products.
21605 Plummer Street.
Chatsworth, CA 91311.
818-998-7322.
Fact Sheet Source
The material provided in this section is used with permission by
the National Association of Home Builders Research Center and the Partnership
for Advancing Technology in Housing (PATH).
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