Orion System VCM Controller - Manual (Page 41)

VCM Controller
Technical Guide
41
MODGAS II Controller
The MODGAS II Controller is treated as a single stage of gas Heating
when connected to the VCM’s expansion port. The Supply Air Tem-
perature is broadcast from the MODGAS II Controller to the VCM.
The Supply Air Temperature Setpoint is broadcast from the VCM to the
MODGAS II Controller. When the VCM enters the Heating Mode, it
broadcasts a command to activate the MODGAS II Controller. The
MODGAS II Controller modulates the Natural Gas Valve to maintain
the Supply Air Temperature Setpoint. See the MODGAS II Controller
Technical Guide for detailed operation information of the MODGAS II
Controller.
MODGAS II Controller
with Additional Stages of Heat
The VCM can activate the MODGAS II Controller and additional stages
of heating if needed. If this configuration is needed, a heating relay
must be configured on the VCM for the MODGAS II Controller, but it
will not be connected to anything. The MODGAS II Controller will
always be the first stage of heating in this configuration. Additional
heating relays can be configured and connected to Staged Heating
sources, such as Natural Gas or Electric Heat. In order for the addi-
tional stages to activate, the MODGAS II Controller must be at 100%
and then the Stage Up Delay begins. Once the Stage Up Delay expires
and the Gas Valve is still at 100%, another Fixed Stage of Heating will
activate. This will be the VCM’s second stage of heat. The MODGAS
II Controller will modulate to achieve the Active Supply Air Tempera-
ture Setpoint. If the MODGAS II Controller modulates to 0% and the
Supply Air Temperature is above the Active Supply Air Setpoint plus
the Heating Stage Control Window, the Stage Down Delay begins. Once
the Stage Down Delay expires and the Supply Air Temperature has
remained above the Active Supply Air Setpoint plus the Heating Stage
Control Window, the Fixed Stage of Heating will be deactivated. The
MODGAS II will remain active, even at the minimum valve position
unless the Supply Air Temperature remains above the Active Supply
Air Setpoint plus the Heating Stage Control Window. The MODGAS II
controller will be the last stage of heating to be deactivated.
Modulating Heating
The VCM supports various forms of Modulating Heat such as SCR
Electric Heat, Modulating Hot Water Heat and Modulating Steam Heat.
Whichever form of Modulating Heating is used, the VCM will modu-
late the Heat Source to achieve the Active Supply Air Temperature
Setpoint. Modulating Natural Gas is a form of Modulating Heat, but is
controlled by the MODGAS II Controller. The VCM only activates the
MODGAS II as a stage of heat, therefore, the Modulating Heating Pro-
portional Window does not apply when the VCM is connected to the
MODGAS II Controller and is the only form of Heating activated by
the VCM.
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 Modu-
lating Heating Proportional Window. The larger the Modulating Heat-
ing 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 adjust-
able. For example, if the Modulating Heating Proportional Window is
5°F, the signal would 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 would adjust 10% each Time Pe-
riod.
The VCM can activate two forms of Heating that are classified as Pri-
mary and Secondary Heat Sources. The Primary Heat Source used can
be SCR Electric Heat, Modulating Hot Water Heat or Modulating Steam
Heat. The Secondary Heat Source used can be Modulating Natural Gas
(MODGAS II Controller), Staged Gas Heat or Staged Electric Heat.
Primary Modulating Heat and
Secondary Heat with MODGAS II Controller
The Modulating Heating Proportional Window is used to determine the
signal to the Primary Heat Source and is user adjustable. The Heating
Stage Control Window is used to determine stage up and stage down of
the Secondary Heat Source. In the Heating Mode, the Primary Heat
Source will modulate to achieve the Active Supply Air Temperature
Setpoint. When the Primary Heat Source 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, which is controlled by the MODGAS II Controller. The Pri-
mary Heat Source will then be forced to 0%, allowing the MODGAS II
Controller to modulate the gas valve to achieve the Active Supply Air
Temperature Setpoint. When the Secondary Heat Source reaches 100%,
the Heating Stage Up Delay begins. If the Secondary Heat Source is
still at 100% after the Heating Stage Up Delay expires, the Primary
Heat Source will be forced to 100%. The Primary Heat Source will
remain at 100% to allow the Secondary Heat Source to modulate to
achieve the Active Supply Air Temperature Setpoint. If the Supply Air
Temperature rises above the Active Supply Air Temperature Setpoint
plus the Heating Stage Control Window, the Heating Stage Down De-
lay begins. If the Supply Air Temperature is still above the Active Sup-
ply Air Temperature Setpoint plus the Heating Stage Control Window
and the Heating Stage Down Delay expires, the Primary Heat Source
will forced to 0%. If the Secondary Heat Source modulates to 0%, the
Heating Stage Down Delay begins. If the Secondary Heat Source re-
mains at 0% and the Heating Stage Down Delay expires, the Secondary
Heat Source will be deactivated, and the Primary Heat Source will
modulate to achieve the Active Supply Air Temperature Setpoint. If the
Supply Air Temperature rises above the Active Supply Air Temperature
Setpoint plus the Heating Stage Control Window, the Primary Heat
Source modulates as needed to allow the Supply Air Temperature to
cool off.