Sequence Of Operations; Chapter Overview; Single Duct Units; Override Conditions (Single Duct) - Trane VAV-UCM 4.2 Installation & Maintenance Manual

Sequence of Operations

Chapter Overview

This chapter contains information about the following:
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Single Duct Units

When the UCM control action is COOL, the UCM controls the modulation of the air valve as a
cooling source to maintain the "active cooling set point" . Airflow is varied between the minimum
and maximum flow set points to maintain temperature set points. A PI control algorithm is utilized
to minimize the measured difference between the active zone set point and the actual zone
temperature.
It is possible for units to utilize electric or hot water heating coils to maintain temperature set points.
After the temperature loop calls for minimum cooling flow and the zone temperature is at or below
the heating set point, these units shall control to their respective "Minimum Heating Flow" . Once
this "Minimum Heating Flow" is established, heat is allowed to operate according to the "Heat
Control Type" specified for the controller. For electric heat units, this heating minimum flow set
point must be at or above 20% of the unit cataloged airflow. Electric heat may be pulse width
modulation or staged electric heat. Staging has the following ON and OFF switch points. UCM 3.3
and later allow hot water to turn on regardless of flow/position
Table 9.
Hot water heat control may be either ON/OFF or proportional. ON/OFF hot water is activated on the
same schedule as staged of electric heat.
Utilization of the "Heating Minimum Flow" set point allows separate minimum flows to be active
depending on whether or not the unit heat is active.

Override Conditions (Single Duct)

The UCM occupied controls can be overridden by the following override commands:
Unoccupied
If the control mode is unoccupied (either as edited by software or as determined by the binary
input), the unoccupied cooling and heating temperature set points are used for temperature
control. Heat outputs remain active.
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Single Duct Units
Override Conditions (Single Duct)
Fan-Powered Units
Parallel Fan-Powered Units
Override Conditions (Parallel Fans)
Series Fan-Powered Units
Override Conditions (Series Fan)
Zone Sensor Functions
Flow Sensor
Failure Modes
Set points
Stage
1
2 1°F below the heating set point
3 2°F below the heating set point
ON Switch point
At the heating set point
Off Switch point
0.5°F above the heating set point
0.5°F below the heating set point
1.5°F below the heating set point
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