Heat pumps and central air conditioners are split systems, which means that there is an outdoor unit (condenser) and an indoor unit (coil). The job of the heat pump or air conditioner is to transport heat from one station to the other. The vehicle your system uses to carry the heat is called refrigerant.
In air conditioning operation, the compressor in your outdoor unit pushes the liquid refrigerant through copper tubing into the evaporator coil located in your fan coil unit or attached to your furnace. As the refrigerant is compressed, it turns into a gas. When it moves through the evaporator coil, the refrigerant takes on heat from the air circulating over the coil. The cooler air is then recirculated into your home. Meanwhile, the heat absorbed by the refrigerant is carried outside through the copper tubing and given off to the outside air as a fan pulls the air over the condensing coil in your outdoor unit.
While its keeping you cool, your air conditioner or heat pump also works as an effective dehumidifier. As warm air passes over the indoor evaporator coil, it can no longer hold as much moisture as it carried at its higher temperatures. The extra moisture condenses on the outside of the coils and is carried away through a drain. The process is similar to what happens when moisture condenses on the outside of a glass of ice water on a hot, humid day.
A heat pump basically reverses that process in cold weather. It takes heat out of the outside air (or the ground, if you have a ground-source heat pump) and moves it inside, where it is transferred from the evaporator coil to the air circulating through your home.
Where does a heat pump get the heat to warm your home when its cold outside? Well, to a heat pump, cold is a relative term. Even though 35 F air may feel cold to humans, it actually contains a great deal of heat. The temperature at which air no longer has any heat is well below -200 F. A heat pumps heat exchanger can squeeze heat out of cold air, then transfer that heat into your home with the help of a fan coil or a furnace, which circulates the warm air through your ducts.
Heat pumps are often installed with back-up electric resistance heat or a furnace to handle heating requirements when more heat is needed than the heat pump can efficiently extract from the air. Carrier also offers a Smart Heat accessory package that provides back-up electrical heat in stages. This option allows homeowners to enjoy the energy-saving benefits of a heat pump and still maintain comfortable indoor temperatures as outdoor temperatures gradually drop.
If youd like more details on heat pump and air conditioner efficiency ratings, go to What should I look for in a new heat pump or air conditioner? For information on matching indoor and outdoor units, go to Why do I need to match my condensing unit and indoor coil?
Comfort Features
Some air conditioners and heat pumps offer additional features that provide greater comfort (as well as additional energy savings). Two-speed units can run on low speed (using 50% of the energy) up to 80% of the time, so they operate more quietly and run for longer periods of time than single-speed models. Longer operating periods translate into fewer on/off cycles, fewer drafts and much smaller temperature swings -- only two or three degrees instead of the four-degree swings common with single-speed units. Plus, better air circulation helps prevent air stratification warm air rising to the ceiling and cold air settling on the floor. In short, you get consistent, even cooling throughout your home.
If you purchase a multi-speed or variable-capacity furnace or fan coil with your unit, you will enhance both the comfort and the efficiency of your air conditioning or heat pump system even further.
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