Ingersoll-Rand ReliaTel, Manual, Page: 66 / 176

66 RT-SVD03L-EN
Table 21. Minimum supply fan speeds (continued)
Unit Mode
VFD, BC
Plenum, non-17
SEER Minimum
Fan Speed
17 SEER
Minimum Fan
Speed
Stage 2
50% 82%
Stage 3 (if
available)
50% 82%
Mode Transitions
Auto-Changeover - The following auto-changeover
rules will be implemented:
• At power-up, when the local unit mode is set to
Auto, or after a unit reset, the active unit mode is
set to Heat if the active ZT < CSP, or Cool if the
active ZT > CSP.
• If the active unit mode is Cool, the active unit mode
is switched to Heat when both the active ZT < HSP
and it has been 5 minutes since last active call for
cooling was terminated.
• If the active unit mode is Heat, the active unit mode
is switched to Cool when both the active ZT >
greater of CSP and [HSP + 3 F] and it has been 5
minutes since last active call for heating was
terminated.
Occupied Heating Operation
Occupied heating operation on units configured with
SZVAV control will utilize two separate control
methodologies based on heating configurations.
Staged Heating Operation
For units configured with staged heat once a request
for active heating capacity has been determined and
the unit has met all auto-changeover requirements, the
unit will energize the supply fan and ramp up to full
speed. Heating stages will be energized/de-energized
to meet the zone heating demand.
Modulating Heat Operation with SZVAV
Heating
Units configured with a modulating heat type will
utilize true SZVAV control. DAHSP will be used in order
to determine heating capacity demand and a fan speed.
Heating Sequence
Once the unit has met all auto-changeover
requirements and the unit is requesting active heating
capacity (ZT < ZHSP) the unit will transition into zone
heating.
Once the DAHSP calculation has reached its Upper
Limit (UL) and the modulating heat output is being
utilized, the supply fan speed will begin to ramp up
toward 100%. Note that the supply fan speed will
remain at the minimum value until the DAHSP value is
calculated above the DAHSP UL.
As the heating load in the zone decreases the fan speed
will decrease down to minimum and the heat output
will modulate as necessary. As the load in the zone
continues to drop the fan speed will be maintained at
this minimum airflow and the algorithm will continue
to calculate the DASP down toward the zone neutral
state (ZHSP<DASP<ZCSP) and control the mod. heat
output accordingly. Once the modulating heat output
reaches 0% and the heating demand in the space is
satisfied, the unit will de-energize all heating outputs.
Modulating Heat Operation with
Traditional Constant Volume Fan
Operation
Units configured with a modulating heat type will also
support a user configurable input to select traditional
constant volume (TCV) heating control. The RTOM
modulating heat 1st input will be utilized for this
configuration.
If configured to utilize TCV, the unit will perform
normal heating control utilizing full airflow and a
modulating heat output.
Supply Air Tempering Operation
Supply air tempering operation on units configured
with SZVAV control will utilize two separate control
methodologies based on heating configurations.
For all staged heating types, the unit will utilize the
same supply air tempering scheme as is used on TCV
units.
For units configured with a modulating heat type and
for true SZVAV heating, tempering is an extension of
normal heating control which allows a transition from
Auto-Cool mode to heating based on discharge
temperature if the ZT is in control. The following
conditions must be true to allow the unit to enter
Supply Air Tempering:
• Supply Fan is ON
• Unit is in occupied mode
• Unit is operating in Auto-Cool mode
• Cooling has been inactive for 5 minutes
• Unoccupied cooling and heating operation
For SZVAV controlled units, the unit will control during
unoccupied periods using the heating and cooling
SZVAV algorithm. The following will be true during
unoccupied periods:
• Unit will utilize setback/modified zone setpoints.
• Minimum OA damper position will be overridden to
0.
• Fan mode will be overridden to Auto as on normal
CV units.
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