|
|
Home  About
Western Power
Marketing Transmission Jobs EPTC Energy
Services |
Technology Spotlight:
|
||||||
 |
Mounted on the outside of a building and connected to multiple indoor fan coils, the multi-split ductless air conditioner is a good option for retrofitting homes with electric resistance heating. (Photo by Washington State University) |
Ductless split system air conditioners and heat pumps consist of an outdoor compressor unit and one or more indoor fan coil units. Instead of distributing conditioned air through ducts, refrigerant is circulated between the outdoor and indoor units through standard, insulated refrigerant lines. Indoor units heat or cool the room in which they are located and may be installed on walls, ceilings or floors. "Mini-split" systems have only one indoor fan coil unit. "Multi-split" systems have two or more indoor fan coil units connected to a single outdoor unit and use some method of achieving independent zone control. Different manufacturers of residential multi-split systems accomplish this in different ways, such as having a dedicated compressor for each indoor unit or using a variable speed inverter compressor.
The United States is one of the few countries in the world where ducted systems are more popular than ductless systems. Ductless systems have long been manufactured by Asian and European companies. Popularity has been growing rapidly here, however. Several U.S. companies have entered the market in recent years.
Energy savings are largely due to elimination of duct leakage, which often accounts for 20 percent of a ducted system's energy consumption. The ductless system's inherent zoning capability can also result in significant savings as heating and cooling can be provided only where it is needed. Some models incorporate advanced control systems and variable speed compressors, which improve part-load efficiency and the unit's seasonal energy efficiency ratio (SEER). On the other hand, losses in refrigerant lines (approximately 0.7 to 0.9 percent reduction per 10 feet) are greater than in a conventional system, but these losses are small in comparison to typical duct losses. Ductless split systems do not take advantage of economy cooling during cooler weather, reducing air conditioning savings potential in climates with mild summers.
Ductless split systems are easy to retrofit in existing homes, requiring a single 2- to 4-inch diameter hole through the outside wall through which pre-charged refrigerant tubing, condensate waste line, power and control wiring is routed. Ductless heat pumps can be used with an existing electric resistance heating system, with the heat pump supplying the bulk of the heating requirement and electric resistance heat supplying supplemental heat during very cold weather and morning warm-up.
As with any technology, there are downsides, too. Although most units are generally quiet, they are not as quiet as a properly designed ducted system because the fan coil is located in the room it serves. Also, some homeowners object to the aesthetics of the units—the fan coil is fairly large and is impossible to hide, requiring sensitivity on the part of the system designer. Effective cooling depends on proper placement of indoor coils to avoid recirculation of already-conditioned air (short-circuiting). Also, ductless systems have long refrigerant runs, increasing the potential for refrigerant leakage and the volume of refrigerant lost when a leak occurs.
Ductless units are usually more expensive than an equivalent-sized conventional system partly because they are not considered typical practice in the United States. The ease of retrofitting the system somewhat mitigates cost. Equipment costs are difficult to estimate, since price depends on unit size and features, which, in turn, depend on the particular application. Contractors who have installed small ductless, split-system air conditioners note that these units are as much as 50 percent more expensive than an equivalent ducted split system on a capacity basis. Ductless split systems are most cost effective in new installations or where there is no existing ductwork.
"Ductless (Mini-Split) Heat Pumps" is an overview from Toolbase Services of the National Association of Home Builders Research Center.
"Ductless, Mini-Split Heat Pumps," from U.S. DOE's Office of Energy Efficiency and Renewable Energy, covers the pros and cons of the system.
"Emerging technologies: Ductless split systems," ASHRAE Journal, v 48, n 7, July 2006, p 115-117, can be downloaded free from the ASHRAE Web site.
"Mini-splits Are Moving Into The Mainstream," Air Conditioning, Heating, Refrigeration News, January 2002; discusses installation issues.
| December 2008 |
Previous issues
Ductless (Mini-Split) Heat Pumps
Ductless, Mini-Split Heat Pumps
Emerging technologies: Ductless split systems