144
RT-SVD03L-EN
Setpoint, but is not yet 50 ppm below the setpoint, the
OA damper will stop modulating (holding its current
position). If the space CO
2
level drops below the CO
2
setpoint minus 50 ppm, the OA damper will close to the
DCV min position setpoint. If there is a call for
economizer cooling, the outdoor air damper may be
opened further to satisfy the cooling request.
Supply Fan Mode = AUTO (from Zone Sensor
or all T-stat Inputs Inactive)
When the supply fan is energized (commanded ON by
another function, such as comfort heating or cooling
control), DCV control will operate as described above
("Supply Fan Mode = ON").
When the supply fan is de-energized, if the space CO
2
level rises above the CO
2
setpoint, DCV control will
energize the supply fan and open the OA damper to the
design min position setpoint. When the space CO
2
level drops below the CO
2
setpoint, the supply fan will
be de-energized and the OA damper will close to 0%.
Failure and Override Conditions
•
If the CO
2
value goes invalid while DCV is enabled:
•
A CO
2
sensor failure diagnostic is called out.
•
DCV is disabled.
•
Design min position setpoint will be used for the
damper min position
•
After power is cycled to the unit, the CO
2
sensor
failure diagnostic is cleared and DCV is disabled.
•
For all configurations, (RTEM, RTRM 8.0,
Honeywell, etc.) if a CO
2
sensor value becomes
valid at any point during unit operation the unit will
utilize the value and perform demand controlled
ventilation.
•
If a ventilation override mode goes active it will take
priority over DCV.
•
If an emergency override mode goes active it will
take priority over DCV.
•
Any BAS economizer minimum position request
takes priority over DCV.
•
The remote minimum position input will be used as
the design minimum position setpoint when
connected.
Honeywell Operation
N
No
otte
e:: Obsolete - Honeywell only.
When the indoor CO
2
level rises above the DCV
setpoint (upper limit), the supply fan will energize, and
a PID control loop modulates the position of the
outdoor-air damper to bring in more outdoor air to
maintain indoor CO
2
level at this upper limit (the
operation of compressors or heat are not affected; they
still operate to maintain space or discharge air
temperature at setpoint). When the indoor CO
2
level
drops back below this limit minus 50 PPM, the outdoor-
air damper is allowed to return to its minimum position
and the supply fan is allowed to de-energize if no
longer requested.
N
No
otte
e:: When using CO
2
-based demand controlled
ventilation with the ReliaTel
™
controller, the
minimum OA damper position should be set to
be less then the code required design ventilation
rate for the system. See HVAC Knowledge Center
case #4144 for guidance on determining the
indoor CO
2
setpoint and minimum OA damper
position for a given application.
As a safety precaution, if the mixed air temperature
drops to 40º F, the mixed air sensor overrides DCV
control and closes the outdoor-air damper to its
minimum position to protect the gas heat exchanger
(or to prevent water coils, if installed, from freezing).
When the mixed air temperature rises to 43º F, DCV
control reverts to normal.
N
No
otte
e:: Since it is possible for the outdoor air damper to
drive wide open, it is also recommended to
install an evaporative defrost control to prevent
the evaporator coil from freezing (Frostat
™
is a
standard feature on the Voyager
™
Commercial
27.5 to 50 ton units).
Voyager
™
™
27.5 to 50 Tons VAV
Notes
•
During morning warm-up (MWU), the DCV setpoint
is ignored.
•
During unoccupied mode, the DCV setpoint is
ignored.
•
During occupied cooling or daytime warm-up
(DWU) mode, DCV control is allowed.
Figure 92.
Wiring connections using CO
2
accessory
(v)
INSET A - DUCT MOUNT
- WALL MOUNT
ECA
DCV
Setpoint
DCV
0%
10 0%
Demand Controlled Ventilation
(CO
2
) Setup for Single Zone
VAV, Multi-Speed and 17 Plus
units
Because of the need to maintain the same outdoor cfm
during different fan speeds, set up of demand
Summary of Contents for ReliaTel
Page 174: ...174 RT SVD03L EN N No ot te es s...
Page 175: ...RT SVD03L EN 175 N No ot te es s...