Room A/C’s

A room air conditioner is an encased assembly intended to be mounted as a single unit in a window, through a wall, or as a console. It is designed primarily to provide free delivery of conditioned air to an enclosed space, room, or zone. A room air conditioner must include a source of refrigeration for cooling and dehumidification, and a means of circulating and cleaning air. It may also include a means of ventilating and heating.

The process of selecting a room air conditioner can be oversimplified. All too often, selection is based solely on the floor area of the room. You may  hear the figure “400 square feet per ton” used as the rule of thumb for this selection method. The thinking is that “one horsepower is roughly equivalent to one ton,” so a 1-hp unit is selected for a room with a floor area of 400 ft2, a 3/4-hp unit is chosen for a room with a floor area of 300 ft2, and so on.

But room area is only one factor in the heat load imposed on an air conditioner. Selection on the basis of floor area alone ignores many other important factors, including:

• which side of the house the room is on

• the number and size of the windows, whether they are shaded, and which direction they face

• whether the walls and ceiling are insulated

• the number of people normally expected in the room at one time

• the presence of lights, radios, television sets, and other equipment used in the room

• whether or not the conditioned room can be entirely closed off from adjacent rooms

• the normal dry-bulb and wet-bulb outside temperatures of the locality.

Excerpt from TECHNICAL INSTITUTE MANUAL #2, available at the online store of the Refrigeration Service Engineers Society, the HVAC/R Training Authority.

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