RT-SVX34C-EN 61
Startup
Variable Air Volume Applications
Supply Air Temperature Control - Occupied Cooling and Heating
The RTRM is designed to maintain a selectable supply air temperature of 40° F to 90° F with a +/-
3.5° F deadband. In cooling, if supply air temperature is more than 3.5 degrees warmer than the
selected temperature, a stage of cooling will be turned "On" (if available). Then if the supply air
temperature is more than 3.5 degrees cooler than the selected temperature, a stage of cooling will
be turned "Off".
At very low airflows the unit may cycle stages "On" and "Off" to maintain an average discharge air
temperature outside the 7 degree deadband.
If the unit has modulating heat, the unit can be made to do discharge heating with VAV control. This
is done by placing a contact closure across the "Changeover Input" on the RTAM. During this mode,
the unit will heat to the Supply Air Heating Setpoint +- 3.5F. During low load or low airflow
conditions the actual temperature swing of the discharge air will likely be greater.
The RTRM utilizes a proportional and integral control scheme with the integration occurring when
the supply air temperature is outside the deadband. As long as the supply air temperature is within
the setpoint deadband, the system is considered to be satisfied and no staging up or down will
occur.
Supply Air Temperature Control with an Economizer
The economizer is utilized to control the supply air cooling at +1.5° F around the supply air
temperature setpoint range of 40° F and 90° F providing the outside air conditions are suitable.
While economizing, the mechanical cooling is disabled until the economizer dampers have been
fully open for three minutes. If the economizer is disabled due to unsuitable conditions, the
mechanical cooling will cycle as though the unit had no economizer.
VHR Relay Output
During unoccupied mode, daytime warm-up (DWU) and morning warm-up (MWU) the IGV's or
VFD's will open to 100%. All VAV boxes must be opened through an ICS program or by the VHR
wired to the VAV boxes. The RTRM will delay 100% fan operation approximately 6.5 minutes when
switching from occupied cooling mode to a heating mode.
Zone Temperature Control without a Night Setback Panel or ICS - Unoccupied
Cooling
When a field supplied occupied/unoccupied switching device is connected between RTRM J6-11
and RTRM J6-12, both the economizer and the mechanical cooling will be disabled.
Zone Temperature Control without a Night setback Panel or ICS - Unoccupied
Heating
When a field supplied occupied/unoccupied switching device is connected between RTRM J6-11
and J6-12 and DWU is enabled, the zone temperature will be controlled at 10o F below the Morning
Warm-up setpoint, but not less than 50° F, by cycling one or two stages of either gas or electric heat,
whichever is applicable.
Morning Warm-up (MWU) Control
Morning Warm-up is activated if the zone temperature is at least 1.5° F below the MWU setpoint
whenever the system switches from Unoccupied to Occupied status. The MWU setpoint may be
set from the unit mounted potentiometer or a remotely mounted potentiometer. The setpoint
ranges are from 50° F to 90° F. When the zone temperature meets or exceeds the MWU setpoint,
the unit will switch to the "Cooling" mode. The economizer will be held closed during the morning
warm-up cycle.
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