Cooling: Perimeter Zone Vav Diffuser

Cooling

1. On an increase in temperature above the cooling set point of the primary zone control thermostat, the hot supply air control damper will close (a minimum can be set for fresh air requirements).
2. The cold supply air control damper will begin to open and will adjust to maintain a constant down stream static pressure. The recommended static pressure is .25"w.g. The static pressure is field adjustable.
3. Cold supply air (<65 degrees F.) will flow to the Vari-Flow diffusers. A cooling / heating change over sensor in the neck of the Vari-Flow diffusers will change the Vari-Flow diffusers to the VAV cooling mode of operation. Upon change over from heating to VAV cooling the individual Vari-Flow diffuser dampers will position themselves from full open to closed as needed to reach their VAV cooling temperature set point. A field adjustable minimum airflow / damper position can be set. The Vari-Flow diffusers will then modulate between full open and the minimum airflow / damper position to maintain their individual set-point temperatures.
4. The control thermostat is placed in the area of extreme for the exposure. This is typically the area that requires heating and cooling first and is satisfied last. The area with the zone control thermostat is called the "control zone". The "control zone" and the diffusers that supply air to it will be constant volume diffuser(s). As the exposure starts to approach the control thermostat cooling set point, the cold supply air control damper will begin to modulate the volume of cold air to maintain the set-point temperature.

NEXT: Interior Zone sequence of operation.