General Information
20
RT-SVX24J-EN
prevent over/under pressurization. The overall scheme
will remain very similar to VAV units with Space Pressure
Control with the exception of the dynamic Exhaust Enable
Setpoint.
For SZVAV an Exhaust Enable Setpoint must be selected
during the 100% Fan Speed Command. Once selected, the
difference between the Exhaust Enable Setpoint and
Design OA Damper Minimum Position at 100% Fan Speed
Command will be calculated.The difference calculated will
be used as an offset and added to the Active Building
Design OA Minimum PositionTarget in order to calculate
the dynamic Exhaust Enable Target, which will be used
throughout the Supply Fan Speed/OA Damper Position
range.
The Exhaust Enable Target could be above or below the
Active Building Design OA Minimum Position Target
Setpoint, based on the Active Exhaust Enable Setpoint
being set above or below the Building Design Minimum
Position at 100% Fan Speed Command. Note that an
Exhaust Enable Setpoint of 0% will result in the same effect
on Exhaust Fan control as on VAV applications with and
without Statitrac.
Occupied Cooling Operation
For normal cooling operation, cooling capacity will be
staged or modulated in order to meet the calculated
discharge air target setpoint. If the current active cooling
capacity is controlling the discharge air within the
deadband, no additional cooling capacity change will be
requested. As the Discharge Air Temperature rises above
the deadband, the algorithm will request additional
capacity as required (additional compressors or
economizer). As the Discharge AirTemperature falls below
the deadband, the algorithm will request a reduction in
active capacity.
Default Economizer Operation
By default, the unit will be setup to optimize the minimum
supply fan speed capability during Economizer Only
operation. If the economizer is able to meet the demand
alone, due to desirable ambient conditions, the supply fan
speed will be allowed to increase above the minimum
prior to utilizing mechanical cooling if discharge air
setpoint falls below the discharge air Lower Limit
(Cooling) setpoint.
Unoccupied Mode
In Unoccupied mode the unit will utilize setback setpoints,
0% Minimum OA Damper position, and Auto Fan Mode
operation as on normal CV units. The Supply Fan speed,
and cooling and modulating types of heat, will be
controlled to the discharge air target setpoint as is done
during occupied periods. The Supply fan speed during
staged heat control will be forced to 100% as on normal CV
units.
Occupied Heating Operation
Occupied heating operation has two separate control
sequences; staged and modulated. All staged heating
types will drive the supply fan to maximum flow and stage
heating to control to the Zone Heating Setpoint. For units
with Hydronic and Gas heat, modulated SZVAV Heating.
On an initial call for heating, the supply fan will drive to the
minimum heating airflow.
On an additional call for heating, the heat will control in
order to meet the calculated discharge air target setpoint.
As the load in the zone continues to request heat
operation, the supply fan will ramp-up while the control
maintains the heating discharge air temperature. Heating
can be configured for either the energy saving SZVAV
Heating solution as described above, or the traditional,
less efficient CV Heating solution.
Compressor (DX) Cooling
Compressor control and protection schemes will function
identical to that of a traditional unit. Normal compressor
proving and disable input monitoring will remain in effect
as well as normal 3-minute minimum on, off, and inter-
stage timers. Also, all existing head pressure control
schemes will be in effect.
Cooling Sequence
If the control determines that there is a need for active
cooling capacity in order to meet the calculated discharge
air target setpoint, once supply fan proving has been
made, the unit will begin to stage compressors
accordingly. Note that the compressor staging order will
be based on unit configuration and compressor lead/lag
status.
Once the discharge air target setpoint calculation has
reached the Minimum Setpoint and compressors are
being utilized to meet the demand, as the discharge air
target setpoint value continues to calculate lower the
algorithm will begin to ramp the supply fan speed up
toward 100%. Note that the supply fan speed will remain
at the compressor stage’s associated minimum value (as
described below) until the discharge air target setpoint
value is calculated below the discharge air temperature
Minimum Setpoint (limited discharge air target setpoint).
As the cooling load in the zone decreases the zone cooling
algorithm will reduce the speed of the fan down to
minimum per compressor stage and control the
compressors accordingly. As the compressors begin to
de-energize, the supply fan speed will fall back to the
Cooling Stage’s associated minimum fan speed, but not
below. As the load in the zone continues to drop, cooling
capacity will be reduced in order to maintain the discharge
air within the ± ½ discharge air target deadband.
Содержание SEHJ090-162
Страница 40: ...Dimensional Data 40 RT SVX24J EN Figure 13 Evaporative condenser water connection locations RIGHT SIDE VIEW ...
Страница 48: ...Installation 48 RT SVX24J EN Figure 18 Ductwork conversion ...
Страница 58: ...Installation 58 RT SVX24J EN Figure 36 5 Connected tubes 6 install panels Connected tubes 5 6 ...
Страница 75: ...Installation RT SVX24J EN 75 Figure 51 Hot water coil piping Figure 52 Steam coil piping ...
Страница 87: ...Installation RT SVX24J EN 87 Figure 57 Typical field wiring diagram for 90 to 162 ton CV control options ...
Страница 89: ...Installation RT SVX24J EN 89 Figure 59 Typical field wiring diagram for 90 to 162 ton VAV control options ...