Sequence of operation
VVT Bypass II Controller
CARRIER CORPORATION ©2019
Installation and Start-up Guide
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27
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.
Supply Air Temperature Alarm
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.
Airside linkage
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.
Summary of Contents for VVT Bypass II
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