100 RT-SVD03G-EN
ReliaTel Economizer Operation
Economizer Operation with Zone Sensor,
Programmable Zone Sensor or ICS
When economizing is enabled and the unit is operating in the cooling mode with a zone sensor,
the economizer damper is modulated between its minimum position and 100% to maintain the
zone temperature at the economizer setpoint.
When the unit is applied with a zone sensor, programmable sensor or ICS, the economizer setpoint
(ESP) is derived from the Cooling and Heating setpoints (CSP and HSP) so that ESP is the higher
of 1) CSP – 1.5°F or 2) HSP + 1.5°F.
When enabled, the economizer will modulate between minimum position and 100% to maintain
the mixed air temperature to the calculated mixed air setpoint (53°F minimum). If the mixed air
temperature starts to fall below the mixed air setpoint, the economizer starts closing. If the mixed
air temperature falls to 50°F or below, the damper will close to the minimum position.
If the economizer is not able to satisfy the cooling setpoint, 1
st
stage cooling will be energized.
Should the cooling setpoint not be satisfied with 1
st
stage cooling, 2
nd
stage cooling will be
energized. Most often, the economizer and 1
st
stage cooling will be adequate to satisfy the load. 1
st
stage cooling will not start until the economizer has been full open for five minutes on a non-V3
(3 minutes if the unit is a V3) and the zone temperature error has not been reduced quickly enough.
Economizer Operation with Conventional Thermostat (CV only)
When the unit is operating from a conventional thermostat or other binary input, the economizer
setpoint feature, relative to the cooling and heating setpoints, is lost.
The economizer control is based strictly on a signal from the thermostat, but still maintains mixed
air temperature control of 53°±3°F when in the economizer mode. The economizer enable and
disable function is still determined by the outside air sensor through the RTRM.
If a single-stage thermostat is used, only the economizer (if enabled) or the compressor (if
economizer is disabled) will operate on a call for cooling. A two-stage thermostat is required to
achieve economizer operation and compressor operation at the same time.
With economizer enabled, a Y1 call for 1
st
stage cooling will be the economizer. The damper will
modulate between minimum position and 100% to maintain mixed air temperature at 53°±3°. At
50°F the damper will be at minimum position. If the economizer is enabled, a Y2 call for 2nd stage
cooling will start the first compressor only if the economizer damper is at 100% open continuously
for 5 minutes on a non-V3 (3 minutes if the unit is a V3).
If the economizer is disabled, 1st stage (Y1) will be the first compressor. If the unit has two
compressors, a call for 2
nd
stage cooling (Y2) will start the second compressor.
When using a conventional thermostat, or other binary input, the ReliaTel controls will only allow
two stages of cooling.
Barometric Relief
Units with economizers bring in outside air for ventilation and/or economizer cooling. Because the
economizer contains a return air damper that operates inversely to the outdoor air damper, the
outdoor air will tend to pressurize the conditioned space. This can cause exterior doors to open or
audible noise from air escaping through various building openings.
Units without exhaust fans rely on barometric dampers to vent the pressure that builds up in the
space due to outdoor airflow.
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