American Standard UV05 manual Outdoor Air Damper Operation

Description of Operation

Unoccupied Operation

During unoccupied mode, the IA fan typically remains off and cycles with calls for heating and cooling.

Cycle Fan

The UVC is provided with a Fan Cycling Configuration variable that can be used to force the IA fan to cycle with calls for heating and cooling during the occupied, standby, and bypass occupancy modes. When the fan is off, the OA damper is closed. McQuay recommends using this feature only when it is acceptable that normal ventilation is not required.

When the IA fan is set to cycle, the UVC is configured to continue fan operation for a time period after heating or cooling is complete.

Off Delay

When the UVC is placed into off mode or shutdown mode, the UVC is configured to continue fan operation for a short time period and then shutdown.

Outdoor Air Damper Operation

The UVC is configured for an OA damper operated by a floating-point actuator. The OA damper actuator contains a spring that ensures the OA damper is closed upon loss of power. The floating-point actuator is driven by the UVC using two binary (Triac) outputs. The OA damper typically is open to the current minimum position during the occupied and bypass occupancy modes and closed during the unoccupied and standby occupancy modes.

A Triac output is best tested under load using a 24 V relay for verification. To verify:

1Put a relay across the Triac outputs.

2Cycle the power.

3Verify the relay’s closed contacts during calibration.

Minimum Position

The UVC is configured to maintain three OA damper minimum positions based on the operation of the IAF fan. This allows each unit to be field configured to provide the amount of fresh air required to the space at each of the three IA fan speeds.

Table 17: Default OA damper minimum positions

IAF speed	Without CO2	With CO2
High	20%	5%
Medium	25%	5%
Low	30%	5%

Note – If the CO2 Demand Controlled Ventilation (DCV) option is used, the UVC only uses the IA fan high speed OA damper minimum position regardless of fan speed. The DCV function adjusts the OA damper above this minimum as needed to maintain CO2 set point.

Economizer Operation

The economizer function is used by the UVC to determine if the OA is adequate for economizer (primary) cooling. When both the economizer and mechanical cooling are available, the economizer is used as primary cooling and the UVC adds mechanical cooling only if the economizer is not adequate to meet the current cooling load (e.g., the OA damper reaches 100% and cooling is still required).

The UVC supports three economizer functions:

•Basic (default)—Temperature Comparison Economizer

32 McQuay OM 751