Orion System VCM-X Modular E-BUS - Manual (Page 54)

Zone
Zone
SEQUENCE OF OPERATIONS
VCM-X Modular E-BUS Controller Technical Guide 54
Stage Control Window
The Cooling Stage Control Window Setpoint determines when the
compressors start to stage up and stage down. In the Cooling Mode,
as the Supply Air Temperature rises above the Active Supply Air Tem-
perature Setpoint, the Cooling Stages will begin to stage on based on
the Cooling Stage Up Delay setting. The Cooling Stages will continue
to run until the Supply Air Temperature drops below the Active Supply
Air Temperature Setpoint minus the Cooling Stage Control Window. For
example, if the Supply Air Temperature Setpoint is 55° and the Cooling
Stage Control Window is 5°, as the Supply Air Temperature drops below
50°, the Cooling Stages will begin to stage off based on the Cooling
Stage Down Delay setting.
Cooling Staging Delay
Minimum Off Time
A Cooling Stage cannot be activated unless it has been off for this
amount of time.
Minimum Run Time
After a Cooling Stage has been activated, it must remain on for
this amount of time.
Staging Up Delay
After the fi rst Cooling Stage has been activated, this delay pre-
vents additional stages from activating too quickly before they are
needed to achieve the Active Supply Air Temperature Setpoint.
Staging Down Delay
After a Cooling Stage has met its Minimum Run Time and is not
needed, this delay prevents additional stages from deactivating too
quickly in case they are needed to maintain the Active Supply Air
Temperature Setpoint Temperature.
Modulating Cooling
The Modulating Cooling Proportional Window is used to determine the
signal to the Modulating Cooling Source and is user-adjustable. The
Modulating Cooling signal is calculated based on the differential between
the Supply Air Temperature and the Active Supply Air Temperature
Setpoint based on the Modulating Cooling 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 Cooling Proportional Window. The larger
the Modulating Cooling Proportional Window, the smaller the signal
adjustment will be per Time Period. The Time Period is the delay be-
tween another increase or decrease in the Modulating Cooling Source
Signal and is user-adjustable. For example, if the Modulating Cooling
Proportional Window is 5
F, the signal would adjust 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 Period.
The VCM-X E-BUS can control one of two Modulating Cooling
sources, such as a Chilled Water Valve or a Copeland Digital Scroll™
Compressor. Whichever source is used, the VCM-X E-BUS will con-
trol the Modulating Cooling source to maintain the Active Supply Air
Temperature Setpoint.
A Copeland Digital Scroll™ Compressor is a Variable Capacity Com-
pressor that has a 10-to-1 turn down ratio. The VCM-X E-BUS is ca-
pable of handling a single-stage Cooling unit with a Copeland Digital
Scroll™ Compressor as its only stage. It is also capable of handling
multistage Cooling units with a Copeland Digital Scroll™ Compressor.
The Copeland Digital Scroll™ Compressor is always the fi rst stage of
Cooling. On multistage Cooling units with a Copeland Digital Scroll™
Compressor, Fixed Capacity Compressors will stage up while the Co-
peland Digital Scroll™ Compressor modulates to achieve the Active
Supply Air Temperature Setpoint.
To stage up the extra compressor(s), the SAT needs to be above the Active
Supply Air Cooling Setpoint and the Digital Compressor needs to be
at 100% for a period of time equal to the Stage Up Delay. Once a fi xed
compressor is enabled, the digital compressor signal will go to 50% and
modulate up as needed. This will repeat as additional fi xed compressors
are staged up. For compressors to stage on, Minimum Off Times (adj.)
must be satisfi ed as well as Stage Up Delays (adj.).
To stage down the extra compressor(s), the SAT needs to be below the
Active Supply Air Cooling Setpoint minus the Cooling Stage Control
Window, the Digital Compressor needs to be below 30%, and the Stage
Down Delay requirement met. Once a fi xed compressor stages off, the
digital compressor will go to 50% and modulate down as needed. This
will repeat as additional fi xed compressors stage off.
For compressors to stage down, Minimum Run Times (adj.) must be
satisfi ed as well as Stage Down Delays (adj.). The digital compressor
is always the last compressor to be deactivated.
Economizer Operation
This section assumes you have confi gured your HVAC unit to control
the Outdoor Air Dampers in an Economizer Mode of operation.
The Economizer is used as the fi rst stage of Cooling if the Outdoor Air
or Wetbulb Temperature is below the Economizer Enable Setpoint. For
Wetbulb control of the Economizer, an Outdoor Air Humidity Sensor
must be installed. If the unit is equipped with a Return Air Temperature
Sensor, the Outdoor Air or Wetbulb temperature must be at least 5°F
colder than the Return Air Temperature to allow the Economizer to
modulate. By using the Return Air Temperature reference, it allows
the VCM-X E-BUS to calculate whether the Outdoor Air Temperature
will assist in Free Cooling. The Return Air Temperature and Space
Temperature must be above 50°F for the Economizer operation to occur.
The VCM-X E-BUS Controller can monitor an Outdoor Air Humidity
Sensor and combine that reading with the Outdoor Air Temperature
reading to calculate a Wetbulb Temperature. If this Wetbulb Tempera-
ture is not available, only the Outdoor Air Temperature will be used.
Whichever temperature is available, it must be below the Economizer
Enable Setpoint by 1°F to enable the Economizer during the Cooling
Mode of operation. When the temperature rises 1°F above the Econo-
mizer Enable Setpoint, the Economizer will be disabled and return to
the Minimum Position.
As soon as the Cooling Mode is started, the Economizer will calculate a
starting damper position based on the Outdoor Air Temperature and the
differential between the Supply Air Temperature and the Active Supply
Air Temperature Setpoint. After it moves to this initial Setpoint, further
adjustments will be made in small increments to fi ne tune the damper
Cooling Mode