Startup
RT-SVX34F-EN
41
sequences for each system in heating and cooling. The
RTRM provides different timing sequences for Gas
Heat units and Cooling only units.
4. Low ambient cooling to 0°F with Frostat™.
5. Built in electric heat staging, provides a 10 second
“ON” delay between resistance heat stages.
6. Economizer preferred cooling allows fully integrated
economizer operation with mechanical cooling if
actually needed.
On Constant Volume and Single Zone VAV
applications, a 3 minute delay allows the RTRM to
evaluate the rate of change in the zone. If the zone
temperature is dropping faster than acceptable
parameters, the compressor(s) will not be required to
operate.
7.
Free night setback allows the unit to enter an
unoccupied mode by simply shorting across terminals
RTRM J6-11 and J6-12. The short can be achieved by a
set of dry contacts or a time clock. Once this short has
been made the unit will close the economizer dampers,
go from continuous fan to auto fan operation, and:
CV or SZ VAV Unit w/Mechanical ZSM
If the unit has a valid cooling and heating setpoint, the
setup/setback is a minimum of 7°F.
If the unit does not have both setpoints, the setup/
setback is 0°.
If the unit has neither setpoint, the unoccupied cooling/
heating setpoints will be 74°F/71°F.
If the unit is configured as a Constant Volume unit and
a conventional thermostat is used, this input is ignored
and the unit will respond to thermostat requests as
during normal occupied mode.
VAV unit w/o ICS or NSB energizes heating if the space
temperature drops to 10°F below the MWU setpoint
but not less than 50°F
This option can not be used with programmable ZSM
or with an ICSTM system.
8. Low pressure cutouts on all compressors have been
added to insure compressor reliability in low
refrigerant flow situations. The compressor(s) will
lockout after four consecutive low pressure control
trips during the compressor minimum 3 minute “on”
time. The lockout will have to be manual reset as
explained in this document.
Economizer Operation with CV Controls
The control point for the economizer is designed to control
at least 1.5°F below the cooling setpoint or 1.5°F above the
heating setpoint, whichever produces the highest
economizer control setpoint.
Example:
Heating Setpoint = 68°F
Cooling Setpoint = 70°F
The control temperature for the economizer will be 1.5°F
above the heating setpoint
due to it producing the least amount of offset.
Heating Setpoint = 55°F
Cooling Setpoint = 75°F
Because of the spread between the heating and cooling
setpoints, the control will choose to control the
economizer at an offset temperature of 1.5°F below the
cooling setpoint. This will be the highest resulting control
setpoint temperature while maintaining the least amount
of offset.
The percentage that the economizer dampers open is
based on two factors:
1.
The zone temperature minus the economizer setpoint,
and
2. The zone temperature minus the outdoor air
temperature.
Note:
Table 20
lists the percentages the dampers will
open based on these conditions.
While economizing, if the supply air temperature falls
below 50°F, the damper will not be allowed to open any
further until the supply air temperature rises above 50°F. If
the supply air temperature falls below 45°F, the dampers
will be driven to minimum position and held there until the
supply air temperature rises above 50°F.
The mechanical cooling is disabled while in an
economizing state until two conditions are met:
1.
The economizer dampers have been fully open for
three minutes, and;
2. The calculated rate of change in the zone temperature
is less than 12°F per hour.
If the economizer is disabled due to unsuitable conditions,
the economizer is at the selected minimum position when
the supply fan is “On”, and is closed when the supply fan
is “Off”. The mechanical cooling will cycle as though the
unit had no economizer.
Modulating Power Exhaust
If the unit is equipped with the modulating power exhaust
option, the power exhaust actuator will follow the position
of the economizer actuator.
Table 20. Percent of damper travel
Zone Temp - Econ Setpoint °F
Zone - ODT
0.0-0.5 0.5-1.0 1.0-2.0 2.0-3.0 3.0-5.0 >5.0
0 - 7 F
0%
3%
9%
30%
90%
100%
7 - 14 F
0%
2%
6%
20%
60%
100%
> 14 F
0%
1%
3%
10%
30%
100%
