Ingersoll-Rand ReliaTel, Manual, Page: 48 / 176

48 RT-SVD03L-EN
Single Zone VAV, Multi-Speed and 17 Plus
Features and Operation -
Voyager
™ ™ Light Commercial,
Precedent ™ ™ and Odyssey ™ ™
Single zone variable air volume (SZVAV) and multi-
speed evaporator fan operation was developed to meet
ASHRAE 90.1 and California Title 24 Requirements.
Both SZVAV and multi-speed units reduce energy
consumption by decreasing the indoor fan speed and
reducing the compressor cooling stage during part
load conditions. Efficiency at full load may not be
affected but part load efficiency and energy savings is
increased.
Single zone variable air volume (SZVAV) units must
have ZSM or ICS controls, and will not operate
correctly with 24 VAC thermostats. 17 Plus and multi-
speed units will work with 24 volt thermostats but 3
stages of cooling will not be available on 2 compressor
units.
Single zone VAV and multi-speed evaporator fan units
are neither designed to be discharge air controlled
(DAC) units nor used in a multi zone application (VAV
boxes).
Single zone VAV and multi-speed evaporator fan units
do have a discharge air setpoint limit that must be
adjusted at start up but this only acts as a discharge
temperature threshold. If the discharge air setpoint
limit is set too high it will limit the cooling capacity of
the unit. If the setpoint limit setting is unknown it is
recommended that it be set all the way counter
clockwise to the coolest setting. Precedent
™ and
Odyssey ™ SZVAV units have this potentiometer
remotely mounted but Voyager ™ units use the R-136
"DA Cool - Fan Spd" potentiometer on the RTOM circuit
board.
Different products use different methods to vary the
evaporator fan speed. Voyager
™ units use a variable
frequency drive (VFD) to control evaporator fan speed
but sheaves and pulleys are still used for maximum fan
speed adjustment. Odyssey
™ units also use a VFD in
the air handler but unlike Voyager ™ units, airflow is
adjusted directly on the VFD keypad and by adjusting
R-136 potentiometer on the RTOM circuit board.
Precedent
™ units do not use VFDs but instead use
direct drive variable speed motors. Maximum airflow
can be changed on both types of Precedent
™ units by
adjusting the R-136 potentiometer on the RTOM circuit
board. Each unit's IOM will have specific information
regarding verifying proper airflow.
Enhanced Dehumidification
All 17 Plus units have the additional standard feature of
enhanced dehumidification. Once the space humidity
value exceeds the dehumidification setpoint on the
RTOM (R 41) the unit will energize the first stage of
cooling and drive the evaporator fan to low speed.
Enhanced dehumidification is terminated once space
humidity falls below 2% of the humidity setpoint.
Enhanced dehumidification requires a field installed
humidity sensor or a BAS provided space humidity
value. A humidistat cannot be used with enhanced
dehumidification. Enhanced dehumidification does not
require the hot gas reheat (HGRH) option but will work
in conjunction with HGRH as the first stage of
dehumidification if present.
General Sequence of Evaporator Fan
Operation
The evaporator fan is energized approximately 1
second after a call for cooling or heating for all units
except for those equipped with gas heat. Gas heat units
energize the evaporator fan approximately 45 seconds
after gas heat ignition. The RTRM de-energizes the
evaporator fan approximately 160 seconds after a
cooling call is satisfied and 90 seconds after a heating
call is satisfied to enhance efficiency.
Precedent ™ multi-speed units maintain the evaporator
fan speed at approximately 50% (low speed) of
maximum during "fan on" and economizer operation.
After cooling stage 1 is energized the evaporator fan is
ramped up to approximately 82% (medium speed) of
maximum fan speed. If cooling stage 2, hot gas reheat
(if equipped) or any stage of heat is called, the
evaporator fan is ramped up to 100% (high speed) of
maximum. Voyager
™ and Odyssey ™ multi-speed units
will only have two speeds 100% high speed (used when
both compressors are running and any stage heating)
and approximately 50% on low speed (all other fan
operations).
SZVAV units work differently than multi-speed units.
SZVAV units modulate the evaporator fan based on the
cooling demand of the space. The ReliaTel
™ controller
monitors the space temperature, space temperature
deviation from setpoint, discharge air temperature, and
space temperature recovery rate to determine the best
airflow level. This control algorithm is not adjustable.
Only the maximum airflow of the unit is adjustable.
On all multi- speed and SZVAV products the evaporator
fan will operate at 100% (high speed) during any stage
of heating except for Voyager
™ units with modulating
gas heat.
Indoor Fan Control Description;
Precedent
™ ™ 17 SEER (17 Plus) - Unit
Identification
• The "7" in the 6th digit indicates the unit is a 17 Plus
unit.