VCB-X Controller Field Technical Guide
SEQUENCE OF OPERATIONS
65
Heating Mode
Available heating options are Staged Gas, Modulating Gas, Staged
Electric, On/Off Hot Water, Modulating Hot Water, and Modulating
SCR Electric.
Heating is enabled when the temperature at the Mode Enable Sensor
falls one deadband below the Heating Setpoint. Heating is disabled
when the Mode Enable temperature raises one deadband above the
Heating Setpoint.
In the Heating Mode, as the Supply Air Temperature falls below the
Active Supply Air Heating Setpoint (see Supply Air Temperature
Setpoint Reset section for explanation), the heating will begin to
stage on or to modulate. Each stage must meet its Minimum Off
Time (adj.) before it is allowed to energize, and successive stages
are subject to a Heating Stage Up Delay (adj).
Heating stages will continue to run until the Supply Air Temperature
rises above the Active Supply Air Temperature Setpoint plus the
Heating Stage Control Window at which point the heating will begin
to stage off. Each stage must meet its Minimum Run Time (adj.)
before it is allowed to stage off, and successive stages are subject
to a Heating Stage Down Delay (adj.).
Mechanical heating is disabled if the Outdoor Air Temperature (OAT)
rises 1° above the Heating Lockout Setpoint and will remain disabled
until the OAT falls 1° below the Heating Lockout Setpoint. If the
OAT disables mechanical heating while it is currently operating,
mechanical heating will stage off as minimum run times and stage
down delays are satis
fi
ed.
Modulating Heating
The VCB-X supports various forms of Modulating Heat such as
SCR Electric Heat, Modulating Hot Water Heat, and Modulating
Steam Heat. This references Modulating Heat that is controlled from
AOUT3 on the VCB-X Controller with a user-adjustable voltage
range between 0-10 VDC. Modulating Gas, which is controlled by
the ModGas-X Controller, is not included in this section. Whichever
form of Modulating Heating is used, the VCB-X will modulate the
Heat Source to achieve the Active Supply Air Temperature Setpoint.
The Modulating Heating Proportional Window is used to determine
the signal to the Modulating Heating Source and is user-adjustable.
The Modulating Heating Signal is calculated by the differential
between the Supply Air Temperature and the Active Supply Air
Temperature Setpoint based on the Modulating Heating Proportional
Window. The maximum signal adjustment per Time Period is 10%
and is not user- adjustable. The minimum signal adjustment per Time
Period is based on the Modulating Heating Proportional Window.
The larger the Modulating Heating Proportional Window, the smaller
the signal adjustment will be per Time Period. The Time Period is
the delay between another increase or decrease in the Modulating
Heating source signal and is user-adjustable.
For example, if the Modulating Heating Proportional Window is
5°F, the signal will be adjusted 2% per °F each Time Period above
or below the Active Supply Air Temperature Setpoint. When the
Supply Air Temperature is above or below the Active Supply Air
Temperature Setpoint by 5°F or more, the signal will adjust 10%
each Time Period.
Primary and Secondary Heating
The VCB-X can activate two forms of Heating, which are classi
fi
ed
as Primary and Secondary Heat Sources. The following section
describes that operation.
Primary Modulating Heat with Secondary Staged Heat
The Modulating Heat source can be ModGas, Modulating Hot Water,
Modulating Steam, or SCR Electric Heat. In this case the modulating
heat will be the
fi
rst form of heat used and will operate as described
above to attempt to achieve the Active Supply Air Heating Setpoint.
If the modulating heat reaches 100%, the Heating Stage Up Delay
begins. If the Primary Heat Source is still at 100% after the Heating
Stage Up Delay expires, the Secondary Heat Source will activate. The
Primary Heat Source can then modulate as necessary to achieve the
Active Supply Air Heating Setpoint. If there are additional stages of
heat, they will stage up as described, with the Primary Heat Source
modulating as necessary.
If the Secondary Heat Source is activated and the Primary Heat
Source has modulated to 0%, the Heating Stage Down Delay will
begin. If the Primary Heat Source is still at 0% after the Heating Stage
Down Delay expires, the Secondary Heat Source will deactivate. If
there are multiple stages of Secondary Heat, they will stage off in the
same manner. Then, if the Supply Air Temperature rises above the
Active Supply Air Heating Setpoint plus the Heating Stage Control
Window, the Primary Heat Source will modulate to 0% to allow the
Supply Air Temperature to cool off.
Ventilation Mode
This mode is only available in the Occupied Mode of operation
on units con
fi
gured for continuous Supply Fan operation and is
generated anytime there is no demand for heating or cooling. The
fan will operate at the con
fi
gured Minimum Vent speed.
Off Mode
Off Mode occurs in the Unoccupied Mode when there is no heating
or cooling demand. The Supply Fan is off and the outside air damper
is closed.
Off Mode can only occur in the Occupied Mode if the fan is
con
fi
gured to cycle with heating and cooling and there is no call for
heating or cooling. Space Sensor Operation
Heating Mode, Ventilation Mode & Off Mode
