An air-handling unit consists of a fan, heat transfer surface, and casing.

A remote air-handling unit or a remote air-conditioning unit is a unit located outside of the conditioned space that it serves.

SELF-CONTAINED AIR-CONDITIONING

UNITS Self-contained air-conditioning units may be divided into two types: window-mounted and floor - mounted units. Window - mounted air-conditioning units usually range from 4,000 to 36,000 Btu per hour in capacity (fig. 7-5). The use of windows to install these units is not a necessity. They may be installed in transoms or directly in the outside walls (commonly called a "through-the-wall" installation). A package type of room air conditioner, showing airflow patterns for cooling, ventilating, and exhausting services, is shown in figure 7-6.

In construction and operating principles, the window unit is a small and simplified version of much larger systems. As shown in figures 7-7 and 7-8, the basic refrigeration components are present in the window unit. The outside air cools the condenser coils. The room air is circulated by a fan that blows across the evaporator coils. Moisture, condensed from the humid air by these coils, is collected in a pan at the bottom of the unit; it is usually drained to the back of the unit and discharged. Most window units are equipped with thermostats that maintain a fixed dry-bulb temperature and moisture content in an area within reasonable limits. These units are installed so there is a slight tilt of the unit towards the outside, toward the condenser, to assist in drainage of the condensate. It is a good idea to mount the unit on the eastside of the building to take advantage of the afternoon shade. These units require very little mechanical attention before they are put into operation. Window units are normally operated by the user who should be properly instructed on their use.

Floor-mounted air-conditioning units range in size from 24,000 to 360,000 Btu per hour and are also

Figure 7-5. - Window air conditioner.