Installation and Maintenance Manual

SCXG-SVX01H-EN 63
Operating Principals
Control Sequences of Operation
Occupied/Unoccupied Switching
There are four ways to switch occupied/unoccupied:
1. Night setback zone sensor
2. Field-supplied contact closure (hard wired binary input
to RTM)
3. Tracer Summit
4. Factory-mounted time clock
Field Supplied Occupied/Unoccupied Input on
the RTM
This input accepts a field supplied switch or contacts
closure, such as a time clock, with a rating of 12 mA at 24
VDC minimum.
Tracer Summit System
TheTracer Summit system can control the occupied/
unoccupied status of the self-contained unit.
Factory Mounted Time Clock
A time clock can control the occupied/unoccupied status of
the self-contained unit.
Unoccupied Sequence of
Operation
The unoccupied mode helps conserve energy during
times when a building is usually unoccupied. When in
unoccupied mode, the unit will control to the unoccupied
setpoints (usually a lower heating setpoint and higher
cooling setpoint). Setpoints can be programmed at the HI,
Tracer Summit, or the night setback zone sensor.
The unit enters the unoccupied mode when the RTM
receives a closed signal on the unoccupied input for more
than five seconds. For units with supply air temperature
control entering unoccupied mode, the following
sequence will occur:
• Heating/cooling functions cease and the economizer
option closes fully.The supply fan shuts down for
proper cool-down time of the heat exchanger.
However, the supply fan may remain on for a short
period of time.
• After the supply fan shuts down, the occupied/
unoccupied relay energizes. Also, the VAV box stroke
time begins.The VAV box stroke time is field
adjustable to allow time for VAV boxes to go to the full
open airflow position.
• After the max VAV box stroke time expires, the supply
fan, economizer (if enabled), compressors, and heat
are enabled to satisfy the unoccupied zone
temperature setpoints.
Note: Unoccupied economizer operation can be enabled
or disabled at the HI or usingTracer Summit.
For units without volume control entering unoccupied
mode, the following sequence will occur:
• The occupied/unoccupied relay energizes and the
economizer option fully closes.
• The fan mode is set to auto and the unit will control to
the unoccupied zone temperature setpoints.
With MWU enabled at the HI, if the zone temperature is
below the MWU setpoint, the unit enters the MWU mode.
Morning Warmup
This feature can be enabled at the HI, and can be used with
factory or field-installed heat. If MWU is not required
disable the function in the setup menu at the HI. MWU
transitions the zone from unoccupied to occupied. It will
heat until the MWU setpoint is met.The unit is then
released to occupied mode. Supply duct static pressure is
maintained during this sequence. MWU can be set (at the
HI) to function as either full or cycling capacity.
Full Capacity Morning Warmup (MWU)
Full capacity morning warmup uses full heating capacity
to heat the zone as quickly as possible. Full heating
capacity is provided until the morning warmup setpoint is
met. At this point, the unit is released to daytime mode.
Cycling Capacity Morning Warmup (MWU)
Cycling capacity morning warmup provides a more
gradual heating to overcome “building sink” as the zone is
heated. Normal zone temperature control with varying
capacity is used to raise the zone temperature to the MWU
zone temperature setpoint.This method of warmup is
used to overcome the “building sink” effect.
See Figure 55, p. 63 for a pictorial explanation of the
cycling MWU sequence. Cycling capacity MWU will heat
until MWU temperature setpoint is reached. Next a 60
minute timer begins. If the building load reaches the MWU
ventilation setpoint, or the 60 minutes expire, whichever is
first, the airside economizer will control to the minimum
position. MWU will end when the zone temperature rises
above the MWU terminate setpoint.
Figure 55. Typical cycling morning warmup cycle