50 VAV-SVX01C-EN
Sequence of Operations
of unit airflow, must be set between 15% and 30% of the units cataloged airflow to assure proper
operation. A differential of 5% exists to avoid excessive fan cycling.
Note: The fan control offset is entered in CFM when used on a VariTrane unit.
Parallel Fan Temperature Type Control
When the fan control offset is in terms of a temperature above the heating set point, the fan shall
be energized whenever the zone temperature is below the heating set point plus the fan control
offset. A differential of 0.5°F (0.3°C) shall apply to this switch over to avoid fan cycling.
Heat stages are energized on the following schedule:
Whenever the fan is energized, the primary airflow is controlled at the “Heating Minimum Flow”
set point.
Override Conditions (Parallel Fans)
The UCM occupied controls can be overridden by the following override commands:
Unoccupied
If the control mode is unoccupied, the unoccupied cooling and heating temperature set points are
used for temperature control. Fan and heat outputs are activated at the unoccupied heating set
point.
Heating
If the control action is HEAT, the UCM controls the air valve as a heating source rather than cooling.
Fan and heat outputs are disabled for parallel units with electric heat. If the heat type is hot water
heat, then the fan will remain on if the heat is on during the heating control action.
Flow Control Override
Flow control may be overridden by any of the following commands:
• Drive Air Valve Fully Open. The air valve will be driven fully open. Fan and heat outputs are
disabled.
• Drive Air Valve Fully Closed. The air valve is driven fully closed. Fan and heat outputs are
disabled.
• Drive Air Valve to Minimum Flow. The air valve is driven to the minimum airflow set point. The
fan and heat outputs remain operational.
• Drive Air Valve to Maximum Flow. The air valve is driven to the maximum airflow set point. The
fan and electric heat outputs are disabled (hot water heat remains enabled).
Heat Control Override
Heat control can be disabled, locking out heat outputs.
Fan Control Override
Fan control can be disabled, locking out both fan and heat outputs. This affects only parallel fan-
powered units.
Control Offset
Control Offset may be enabled, which adjusts the edited cooling and heating set points.
Table 11. Heat stages
Stage point ON Switch point OFF Switch
1 At the heating set point 0.5°F above the heat set point
2 1°F below the heat set point 0.5°F below the heat set point
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