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For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners. Like your refrigerator, heat pumps use electricity to move heat from a cool space into a warm, making the cool space cooler and the warm space warmer. During the heating season, heat pumps move heat from the cool outdoors into your warm house; during the cooling season, heat pumps move heat from your cool house into the warm outdoors. Because they move heat rather than generate heat, heat pumps can provide up to 4 times the amount of energy they consume.
The most common type of heat pump is the air-source heat pump, which transfers heat between your house and the outside air. If you heat with electricity, a heat pump can trim the amount of electricity you use for heating by as much as 30% - 40%. High-efficiency heat pumps also dehumidify better than standard central air conditioners, resulting in less energy usage and more cooling comfort in summer months. However, the efficiency of most air-source heat pumps as a heat source drops dramatically at low temperatures, generally making them unsuitable for cold climates, although there are systems that can overcome that problem.
For homes without ducts, air-source heat pumps are also available in a ductless version called a mini-split heat pump. In addition, a special type of air-source heat pump called a "reverse cycle chiller" generates hot and cold water rather than air, allowing it to be used with radiant floor heating systems in heating mode.
Higher efficiencies are achieved with geothermal (ground-source or water-source) heat pumps, which transfer heat between your house and the ground or a nearby water source. Although they cost more to install, geothermal heat pumps have low operating costs because they take advantage of relatively constant ground or water temperatures. However, the installation depends on the size of your lot, the subsoil and landscape. Ground-source or water-source heat pumps can be used in more extreme climatic conditions than air-source heat pumps, and customer satisfaction with the systems is very high.
A new type of heat pump for residential systems is the absorption heat pump, also called a gas-fired heat pump. Absorption heat pumps use heat as their energy source, and can be driven with a wide variety of heat sources.
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A heat pump is like a conventional air conditioner except it also can provide heat in winter. In the summer, the heat pump collects heat from the house and expels it outside. In the winter, the heat pump extracts heat from outside air and circulates it inside the house. The heat pump works best when the outdoor temperature is above freezing. Below that, supplementary heat often is needed. A heat pump can save 30 to 60 percent less energy to supply the same heat when compared to an electric furnace with a resistance heating element.
COOLING CYCLE - Refrigerant passes through the indoor coil, evaporating from a liquid to a vapor. As the liquid evaporates, it absorbs heat, cooling the air around the coil. An indoor fan pushes this cooled air through ducts inside the house. Meanwhile, the vaporized refrigerant laden with heat, passes through a compressor which compresses the vapor, raising its temperature and pressure. The reversing valve directs the flow of hot, high pressure vapor to the outdoor coil where the heat released during condensation is fanned into the outdoor air, and the cycle begins again.
HEATING CYCLE - Note that the slide inside the reversing valve has shifted, causing the refrigerant flow to reverse. Liquid refrigerant now flows to the outdoor coil picking up heat as it evaporates into a low pressure vapor. The vapor travels through the compressor where it is compressed into a hot, high pressure vapor, then is directed by the reversing valve to the indoor coil. The vapor turns into liquid as it passes through the indoor coil, releasing heat that is pushed through the ducts by the indoor fan.
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Ductless split air conditioning offer higher efficiency and reduced noise without a large hole in the wall or an open window. By separating compressor and condenser fan from indoor blower, the noisiest components are outside and away from the room. The indoor part of the ductless air conditioner has remote control capabilities and a timer to cycle the system only when needed.
Since mini split air conditioners have no ducts, they avoid energy losses associated with ductwork of central forced air AC systems. Duct losses can account for a significant portion of energy consumption for space conditioning, especially if the ducts are in a unconditioned space such as an attic.
Ductless air conditioning offers Higher Efficiency vs. window air conditioning, less noise, and no costly ductwork.
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