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Startup

RT-SVX34F-EN

Controlled Ventilation, if the Design Minimum Position at
Middle fan speed command is set to a point that would be
higher than the calculated linear line between the Design
Minimum Position setpoints at Minimum and Maximum
fan speed command, the minimum position will be limited
to the point that would make the Design Minimum Position
schedule linear.

Provisions have been made in Service Test Mode to allow
for proper damper minimum position setup:

To set the Design Minimum Position setpoint at
Minimum Fan Speed, set the unit to operate at Step 1
(Fan ON) or Step 2 (Economizer Open) and make the
proper adjustment.

2. To set the Design Minimum Position setpoint at Middle

Fan Speed, set the unit to operate at Step 3 (Cool 1) and
make the proper adjustment.

3. To set the Design Minimum Position setpoint at Full

Fan Speed, set the unit to operate at Step 4 (Cool 2) and
make the proper adjustment.

Space Pressure Control

For units configured with an exhaust fan, with or without
Statitrac, the control described previously for economizer
minimum position handling requires additional changes
to the existing Space Pressure Control scheme. The overall
scheme will remain very similar to non-Single Zone VAV
units with Space Pressure Control with the exception of a
dynamic Exhaust Enable Setpoint.

For Single Zone VAV the user will select an Exhaust Enable
Setpoint during the Maximum Fan Speed Command.
Once selected, the difference between the Exhaust Enable
Setpoint and Design OA Damper Minimum Position at
Maximum Fan Speed Command will be calculated. The
difference calculated will be used as an offset to be added
to the Active Building Design OA Minimum Position Target
to calculate the dynamic Exhaust Enable Target to be used
throughout the Supply Fan Speed/OA Damper Position
range

The Exhaust Enable Target could be above or below the
Active Bldg Design OA Min Position Target Setpoint based
on the Active Exhaust Enable Setpoint being set above or
below the Bldg Design Min Position at Full Fan Speed
Command. Note that an Exhaust Enable Setpoint of 0%
will result in the same effect on Exhaust Fan control as on
non-Single Zone VAV applications with and without
Statitrac.

Supply Air Temperature Control - Heating
and Cooling

For Cooling, Heating (Modulating Heat Only), and
Dehumidification operation the unit will control the active
capacity outputs to meet a varying, calculated Discharge
Air Setpoint that is calculated based on zone conditions in
order to maintain the Zone Temperature to the active Zone
Setpoint. Note that this setpoint will be clamped between
the user selected DA Heat and DA Cool - Fan Speed
setpoints that are set on the RTOM for compressor and
economizer control. In general, as the zone temperature
rises above the ZCSP, the Active Discharge Air Setpoint will
be calculated down and as the zone temperature falls
below the ZHSP Tset will be calculated upward. This
calculated setpoint is a direct indication of space demand
and is also used to determine the proper supply fan speed
to meet the space requirements. During active capacity
control, the unit will utilize a +/- 3.5°F deadband around the
active Discharge Air Setpoint to determine when to
request additional heating or cooling capacity similarly to
traditional VAV control, as described below. If the unit is
maintaining the discharge air temperature within the +/-
3.5°F deadband around the calculated discharge air
setpoint requirements, no additional capacity will be
requested.

The calculated setpoint will also be used for active
economizer control, but the economizer will utilize a
tighter control deadband (+/- 1.5°F) than that is used for

Figure 41.

SZVAV OA damper min position w/ OA CFM
compensation

Maximum Fan Speed

Minimum Fan Speed

Middle Fan Speed

OAD

Posion

Setpoints

Design @ Minimum Fan Speed

Design @ Maximum Fan Speed

Design @ Middle Fan Speed

Figure 42.