There are several types of cooling system technologies. Most air-conditioning systems work by transferring heat from inside the home to the outdoors rather than by creating cold air. However, cooling systems differ in how they remove and transfer heat, how they distribute cooled air throughout the home, and how much energy they require to operate.
Central air conditioners cool an entire home using a central cooling system connected to a network of ducts. Warm indoor air is pulled into the system, where heat and moisture are removed. The cooled air is then distributed throughout the home through supply ducts, while the heat removed from the indoor air is released outdoors.
Central air conditioners typically consist of an indoor unit and an outdoor unit. The indoor portion cools and dehumidifies the air, while the outdoor portion releases the heat that has been removed from the home.
Because central air conditioners rely on ductwork to distribute cooled air, the condition of the ducts can significantly affect system efficiency. Leaky or poorly insulated ducts can allow cooled air to escape or gain heat before reaching the rooms they are intended to cool.
Heat pumps operate similarly to central air conditioners when cooling a home: they transfer heat from inside the home to the outdoors. The primary difference is that heat pumps can reverse this process during cold weather, allowing the same system to provide both cooling and heating to the home. Because one system can provide both heating and cooling, heat pumps can replace separate air-conditioning and heating systems in many homes.
Heat pumps are often categorized by the medium they exchange heat with. Air-source heat pumps exchange heat with outdoor air. Ground-source heat pumps, also known as geothermal heat pumps, exchange heat with the ground. Water-source heat pumps exchange heat with water. Depending on the system, the water source or loop may be located above or below ground.
Heat pumps can distribute conditioned air through central ductwork, similar to a central air conditioner or furnace. Other heat pumps, such as ductless mini-splits, provide heating and cooling directly to individual rooms or zones without using central ductwork.
Ductless mini-splits are typically heat pumps that provide heating and cooling without using a central duct system. Instead, one outdoor unit is connected to one or more indoor units installed in individual rooms or areas of the home.
Each indoor unit conditions the space where it is located, allowing different areas of the home to be controlled independently. This approach, known as zoning, can reduce energy consumption by allowing occupants to condition only the areas that need cooling.
Because mini-splits do not require ducts, they also avoid the energy losses associated with leaky or poorly insulated ductwork. They can be particularly useful in homes without existing ducts, home additions, or areas that are difficult to adequately heat or cool with a central system.
Window air conditioners are self-contained systems designed to cool individual rooms or small areas. They are typically installed in a window or through an exterior wall, allowing the indoor side of the unit to cool and dehumidify room air while the outdoor side releases heat outside.
Because window units cool individual spaces rather than an entire home, they can use less energy when cooling is only needed in a small number of rooms. However, cooling many rooms with separate window units may be less efficient and convenient than using an appropriately sized central or ductless system.
Portable air conditioners are movable units designed to cool individual rooms. They draw warm air from the room, remove heat and moisture, and use an exhaust hose to release heat through a window or another opening to the outdoors.
Although their portability can make them convenient, portable air conditioners are generally less efficient than comparable window air conditioners. Some designs can also cause warm outdoor air to enter the home as they exhaust indoor air outside.
Evaporative coolers, sometimes called swamp coolers, cool air using water evaporation rather than a conventional refrigeration system. Warm outdoor air passes over water-saturated material, causing some of the water to evaporate. The evaporation removes heat from the air, lowering its temperature before the air enters the home.
Unlike conventional air conditioners, evaporative coolers add moisture to the air rather than remove it. As a result, they are most effective in hot, dry climates and are generally not appropriate for humid climates.
Evaporative coolers can use substantially less electricity than conventional air conditioners under suitable climate conditions.
Fans provide cooling differently from air conditioners. Rather than removing heat or moisture from the air, fans move air. Increased air movement helps sweat evaporate from the skin and increases heat transfer from the human body, making people feel cooler.
Therefore, fans cool people rather than rooms. Leaving a fan running in an unoccupied room does not lower the room's temperature and unnecessarily consumes electricity. However, when a room is occupied, using a fan can allow occupants to remain comfortable at a higher thermostat temperature, reducing the amount of energy required for air conditioning.