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Chapter Overview
This chapter describes the sequence of
operation of the available unit types.
Unit operation during the available
override commands will also be
described. This chapter contains
sequence of operations pertaining to
the following:
— Single Duct Units
— Parallel Fan-Powered Units
— Series Fan-Powered Units
— Zone sensor functions
— Flow Sensor
— Failure Modes
24
Sequence Of
Operations
CHAPTER 5: SEQUENCE OF OPERATIONS
Single Duct Units
When the UCM control action is COOL,
the UCM controls the modulation of the
air valve as a cooling source to main-
tain 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.
Stage
ON Switch point
Off Switch point
1
At the heating
0.5°F above the
set point
heating set point
2
1°F below the
0.5°F below the
heating set point
heating set point
3
2°F below the
1.5°F below the
heating set point
heating set point
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.
Heating
If the control action is edited to HEAT ,
the UCM controls the air valve as a
heating source rather than cooling.
Electric reheat is available the supply air
temperature (or auxiliary temperature)
o
is below 70
F . Local hot water reheat is
always available to keep the zone above
the heating set point. The "Heating
Minimum Flow Set Point" will set the
minimum flow.
Flow Control Override
Flow control may be overridden by any
of the following commands:
— Drive Air Valve Fully Open
The air valve will be fully open and heat
outputs disabled.
— Drive Air Valve Fully Closed
The air valve is driven fully closed and
heat outputs disabled.
— Drive Air Valve to Minimum Flow
The air valve is driven to the minimum
airflow set point. The heat outputs
remain operational.
— Drive Air Valve to Maximum Flow
The air valve is driven to the maximum
airflow set point. The heat outputs
remain operational.
Heat Control Override
Heat control can be disabled, locking
out heat outputs.
Control Offset
Control offset may be enabled, which
adjusts the edited cooling and heating
set points.
Recalibrate (Reset)
The recalibrate function can be enabled.
If enabled, the unit will perform a
recalibration.
VAV-SVX01B-EN
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