Equipment Fan Off Detection; Supply Air Temperature Alarm; Airside Linkage - Carrier VVT Bypass II Installation And Startup Manual

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The Bypass does not resume normal control to the Duct Static Pressure Setpoint until the SAT drops 15 °F

(8.3 °C) below the Maximum Heating Sat or rises 7 °F (3.9 °C) above the Minimum Cooing Setpoint.

If the supply air temperature exceeds the configured limits, a Supply Air Temperature Alarm is generated. If

Linkage is active, the controller monitors the supply air temperature from the equipment rather than its own

temperature input for faster response.

Equipment fan off detection

The VVT Bypass II continuously monitors its damper's position and the supply duct static pressure. If the

pressure drops below 10% of the nominal setpoint and the bypass damper is fully closed (or VFD is

commanded to maximum speed), after 1 minute the controller assumes that the equipment fan turned off.

The bypass damper then modulates to 65% open and the VFD speed is commanded to 35% (3.5 volts) to

facilitate a fan restart. The controller monitors the static pressure to determine when the equipment fan

restarts. If it rises above 10% of the nominal pressure setpoint, the controller assumes the fan restarted and

controls to maintain the duct static pressure setpoint. If Linkage is active, the air source mode is provided to

the VVT Bypass II.

The VVT Bypass II generates an alarm if the supply air temperature remains above the configured Maximum

Heating SAT or below the configured Minimum Cooling SAT for more than 5 minutes.

When the VVT Bypass II is part of a linked system, it uses data received through Linkage (equipment SAT and

mode) to detect excessive leaving air temperature (LAT) conditions at the equipment and equipment

operating mode.

VVT Bypass II Controller

Installation and Start-up Guide

Sequence of operation

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