The direct multizone system unit is roof mounted and can be used for cooling and heating. See Fig. 16-6. It can use chilled water for cooling up to 550,000 Btu/h.
Air distribution is 12- or 16-zone multizone control at the unit or double duct with independent mixing dampers at each zone. Figure 16-7 shows the typical applications of such a unit with a zone distribution system using mixing dampers located at the unit. A double duct distribution system with zone damper boxes can be used. Mixing dampers are remote from the unit. The net weight of the unit is 2525 lb or 11/4 tons.
Figure 16-8 shows the location of the parts inside the unit. Figure 16-9 shows how the refrigerant piping is laid out for the unit when two compressors are used for cooling purposes. Note that this unit uses an accumulator. There are certain conditions under which the capacity of such a unit must be rated. These conditions are the temperature of the evaporator air, the condenser coil air temperature, the speed of the blower motor, and its volume of air delivered.
