Today homeowners can choose from a variety of air conditioning and cooling options, ranging from compact window-mounted units to whole-house systems that distribute conditioned air through a ductwork system. All of these refrigerant-based units don't just cool the air; they also dehumidify it. When warm, moist air is blown over the cold evaporator coils in an AC unit, condensation occurs, producing water (condensate) that is drained away.
Types of air conditioners and coolers
Window-mounted and through-wall units: These may be installed in a window or hole in the wall. Various sizes and shapes are available for all types of windows. Low-profile units are designed to obscure less window area. The advantage to window and wall AC is primarily cost. You can cool a house with 3 or 4 units for much less than a central system. Disadvantages, however, are numerous. They include noise, off-season storage, security issues, and loss of the use of the window while the unit is installed.
Portable air conditioners: Freestanding units that reside inside a room but that must be ducted to a window or hole in the wall. The most efficient portables have two hoses, similar to dryer vent hoses, to expel warm air. Capacities range up to 14,000 BTUs. With hoses, the units take up considerable space, so think twice about putting one of these units in a small room. Also, customer reviews for portables are mixed. Many feel they do not perform as well as window units.
Split-system: Half the system (the evaporator coil) is located inside the home, typically in a plenum above the furnace or in a separate air handler located in the attic. The other half (condenser, compressor coil, and a large cooling fan) are stationed outside in a metal cabinet. Insulated copper tubing carries the refrigerant between the outdoor and indoor components. Split systems are the preferred approach to air conditioning to homes that already have a forced-air heating system and the associated air ducts.
Packaged system: With a packaged system, all components are located outside the house, typically on the roof or mounted to a concrete slab next to the foundation. Cool air is moved via insulated ducts into the home and is then circulated to rooms in the home via additional ductwork.
Mini-split or ductless systems: A mini-split air conditioning system, also called a ductless system is a smart alterative to central air conditioning and heating for homes that have hydronic (water-based) heating, or for homes that rely on space heaters. They are ideal for homes where installing ducts would be expensive or infeasible. Like central air conditioning, a ductless system’s compressor/condenser components are located outside the living space. Air handlers, each of which includes an evaporative coil and blower, are typically mounted on interior walls near the ceiling.
Sizing and rating air conditioners
Window, portable, and mini-split air conditioners are typically rated by the number of BTUs they can remove. A BTU, or British Thermal Unit, is a unit of energy about equal to the energy produced by a single match. Large central air conditioning systems utilize a different sizing convention called the "ton." A "ton" of cooling capacity equals the amount of heat absorbed by one ton of ice melting over a 24-hour period. One ton of cooling capacity is equal to 12,000 BTUs.
The capacity of an air conditioner should be carefully sized according to the space it is intended to cool. That’s because a big part of an air conditioner’s effectiveness is its ability to dehumidify the interior air – and drier air feels significantly cooler than humid air. If you install an oversized unit, such as a 10,000 BTU model in a 150 sq. ft. room, it will cool the room quickly and turn off before it has removed moisture in the air. The result is a damp, uncomfortable feeling. Use the energystar.gov chart below for finding the right size air conditioner for you.
While BTUs and tons describe cooling capacity, EER and SEER ratings are used to describe an air conditioner's efficiency. The Energy Efficiency Ratio (EER) denotes the efficiency of a cooling system at a specific outdoor temperature (usually 95 degrees Fahrenheit). Seasonal Energy Efficiency Ratio (SEER) is used to measure the efficiency of a cooling system over an entire cooling season. With both EER and SEER, the higher the rating the more efficient the unit.
Window, portable, and central air conditioning units should have EER and SEER ratings. SEER ratings will always be slightly higher than EER ratings. More efficient air conditioners are also likely to have an ENERGY STAR® rating, which means that they are at least 10% more efficient than the minimum standard established by the federal government.