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chart shown in
Table 12, p.
what DC voltage corresponds to CFM per ton of unit
cooling.
Note: If 1200 cfm is required from a 3 ton unit
(037) the R136 potentiometer should be
adjusted so that the DC voltage measured
atTP1 to ground reads 1.65 volts DC.
3. To increase theTP1 voltage, turn the R136
potentiometer clockwise.
4. To decrease theTP1 voltage, turn the R136
potentiometer counter-clockwise.
Note: With the indoor fan access panel removed, the fan
will operate at a lower RPM because static pressure
is reduced with the door open. Once the panel is
returned the RPM of the indoor fan will increase.
Table 12.
Cfm vs. vdc
Potentiometer
PWM% value
Voltage (vdc)
70
<0.1
75
0.7
80
1.25
85
1.65
90
1.95
95
2.17
100
>2.4
Variable Air Volume Applications
(Traditional VAV)
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° 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° deadband. 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.
Note: The RTRM is designed to maintain a selectable
supply air temperature of 40°F to 90°F with a +/-
3.5°F deadband. However, to reduce the risk of
evaporator coil freeze-up in Precedent andVoyager
Light Commercial applications, supply air
temperature should not be set below 50° F .
RT-SVX21N-EN
49.
Table 12, p. 49
shows
CFM/Ton
320
347
373
400
427
453
480
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.To reduce the risk of evaporator coil freeze-up
supply air temperature should not be set below 50° F .
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.
Note: The RTRM is designed to maintain a selectable
supply air temperature of 40°F to 90°F with a +/-
3.5°F deadband. However, to reduce the risk of
evaporator coil freeze-up in Precedent andVoyager
Light Commercial applications, supply air
temperature should not be set below 50°F .
VHR Relay Output
During unoccupied mode, daytime warm-up (DWU),
morning warm-up (MWU) and heating mode the Supply
Fan will operate at 100% of user set maximum airflow. 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
10°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
MorningWarm-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.
Unit Start-Up
49
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