Window air conditioners (air-cooled room conditioners) and through-the-wall room air conditioners with supplemental heating are designed to cool or heat individual room spaces. Window units are used where low initial cost, quick installation, and other operating or performance criteria outweigh the advantages of more sophisticated systems.

Room units are also available in through-the wall sleeve mountings. Sleeve-installed units are popular in low cost apartments, motels, and homes. Ventilation can be through operable windows or limited outside air ventilation introduced through the self-contained room HVAC unit.

Window units may be used as auxiliaries to a central heating or cooling system or to condition selected spaces when the central system is shut down. These units usually serve only part of the spaces conditioned by the basic system. Both the basic system and window units should be sized to cool the space adequately without the other operating.

A through-the-wall air-cooled room air conditioner is designed to cool or heat individual room spaces. Design and manufacturing parameters vary widely. Specifications range from appliance grade through heavy duty commercial grade, the latter known as packaged terminal air conditioners (PTACs) or packaged terminal heat pumps (PTHPs) (ARI Standard 310/380). With proper maintenance, manufacturers project an equipment life of 10 to 15 years for these units.

Air-cooled heat pumps located on roofs or adjacent to buildings are another type of package equipment with most of the features noted here, with the additional benefit of supply air distribution and equipment outside the occupied space.

This improved ductwork arrangement makes equipment accessible for servicing out the occupied space, unlike in-room units.

• Installation of in-room unit is simple. It usually only requires an opening in the wall or displacement of a window to mount the unit, and connection to electrical power.

• Installation of outside heat pumps is simple with rigging onto concrete pad at grade level or on the roof.

• Generally, the system is well-suited to spaces requiring many zones of individual temperature control.
• Designers can specify electric, hydronic, or steam heat or use an
air-to-air heat pump design.

• Service of in-room equipment can be quickly restored by replacing a defective chassis.

• Equipment life may be less than for large central equipment, typically10 to 15 years, and units are built to appliance standards, rather than building equipment standards.

• Energy use may be relatively high.

• Direct access to outside air is needed for condenser heat rejection; thus, these units cannot be used for interior rooms.

• The louver and wall box must stop wind-driven rain from collecting in the wall box and leaking into the building.

• The wall box should drain to the outside, which may cause dripping on walls, balconies, or sidewalks.

• Temperature control is usually two-position, which causes swings in room temperature.

• Ventilation and economy cycle capabilities are fixed by equipment design.

• Humidification, when required, must be provided by separate equipment.

• Noise and vibration levels vary considerably and are not generally suitable for sound-critical applications.

• Routine maintenance is required to maintain capacity. Condenser and cooling coils must be cleaned, and filters must be changed regularly.

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