Multi Zone Systems
Zone requirements are direct indications of system load conditions and they are also used for supply air temperature reset. normally, the supply air temperature set point is set at the highest value that will keep the zone requiring the most cooling at its set points and zone humidity within acceptable limits. The drawback of this reset scheme is that it can potentially have one or two hot spots dictating the supply air temperature set point. This scheme can be seen as one variation of return air temperature based reset.
A multi-zone unit uses a single fan to produce both cold and hot air. Cooling and heating coils are both used to produce either cold air, hot air, or a mixture of both when the space temperature has been satisfied. Actuators are used to move mixing dampers in the discharge of the unit to achieve the correct position to meet space temperature requirements. The unit can maintain a designed discharge air temperature on both the cooling and heating sides of the unit by modulating the chilled and hot water valves. The unit is made up of 2 or more zones serving various spaces. Each zone duct will have a manual balancing damper that MUST be installed to balance out the airflow on each zone duct. Design airflow should be set first by pitot tube traverse through the zones before any grille balancing is started.