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humidity sensors for determining economizer mode. Before
allowing economizer mode, unit must be in cooling or
dehumidification mode. economizer mode is enabled
whenever the outdoor air enthalpy falls below the return air
enthalpy (1.5 btu/lb. deadband).
During economizer mode with mechanical cooling, the outdoor
air damper position opens to the maximum setpoint, and
mechanical cooling is allowed to operate to achieve the
discharge air temperature setpoint.
Economizer without Mechanical Cooling (Free
Cooling)
Enthalpy (Comparative) Economizer
Units equipped with modulating outdoor/return air dampers
have factory installed outdoor and return air temperature/
humidity sensors for determining economizer mode. Before
allowing economizer mode, unit must be in cooling or
dehumidification mode.
Economizer mode is enabled whenever the outdoor air
enthalpy falls below the return air enthalpy (1.5 btu/lb.
deadband).
Free cooling mode (without mechanical cooling) is enabled
during economizer mode and when the outdoor air
temperature active is 5° below the discharge setpoint active
but is locked out during dehumidification mode. During free
cooling, mechanical cooling is locked out, and the outdoor air
damper position is modulated to maintain the discharge
setpoint active.
If during free cooling mode, the damper control request
reaches the minimum damper position, heating may be
allowed to operate to maintain a 35° discharge air temperature
to prevent supply freezing temperatures.
Ventilation Mode
Ventilation mode is used during neutral outdoor air conditions
when there isn't a need for heating, cooling, or
dehumidification. A demand for dehumidification locks out
ventilation mode.
Space Control
Ventilation mode is enabled when the outdoor air temperature
is between the high and low ventilation setpoints active (adj.),
and the space temperature is within 2° of setpoint. During
ventilation mode, all forms of heating, cooling, and energy
recovery are disabled.
Single Zone VAV
Ventilation mode is enabled when the outdoor air temperature
is between the high and low ventilation setpoints active (adj.),
and the space temperature is within 2° of setpoint. During
ventilation mode, all forms of heating, cooling, and energy
recovery are disabled, and the supply fan runs at minimum
airflow.
OAU-SVX007A-EN
Sequence of Operation v12.0
Discharge Air Control
Ventilation mode is enabled when the outdoor air temperature
is between the high and low ventilation setpoints active (adj.).
During ventilation mode, all forms of heating, cooling, and
energy recovery are disabled.
Multi-Zone VAV
Ventilation mode is enabled when the outdoor air temperature
is between the high and low ventilation setpoints active (adj.).
During ventilation mode, all forms of heating, cooling, and
energy recovery are disabled.
Dehumidification Mode
The following sections describe the standard sequence of
operation based on ordered options. Additional options are
available for enabling and controlling dehumidification.
Contact the factory for additional information.
Space Control (Lab/Critical Application) with
Outdoor Air Damper
A space dewpoint setpoint is calculated using space
temperature setpoint active and space dehumidification
setpoint (relative humidity). Dehumidification mode is enabled
when the space dewpoint rises above the space dewpoint
calculated enable setpoint (2° deadband) or when the outdoor
air dewpoint rises above 53° (3° deadband). Dehumidification
mode is terminated based on the setpoint deadbands or if the
space becomes significantly overcooled.
During dehumidification mode, cooling is controlled to the
dehumidification temperature setpoint active, and hot gas
reheat (if installed) controls to the discharge air temperature
setpoint active.
Dehumidification temperature setpoint active is reset by
comparing the space dewpoint to the space dewpoint
calculated enable setpoint but is limited to not rise above the
discharge air temperature setpoint active. Discharge air
temperature setpoint active is reset by comparing the space
temperature to the space temperature setpoint active. If the hot
gas reheat remains at 100% and there is insufficient reheat to
meet the discharge temperature setpoint, and primary electric
heat is installed, the heater may be energized to provide
additional reheat.
Space Control (Lab/Critical Application)
without Outdoor Air Damper
A space dewpoint setpoint is calculated using space
temperature setpoint active and space dehumidification
setpoint (relative humidity). Dehumidification mode is enabled
when the space dewpoint rises above the space dewpoint
calculated enable setpoint (2° deadband). Dehumidification
mode is terminated if the space dewpoint falls below the
deadband.
During dehumidification mode, cooling is controlled to the
dehumidification temperature setpoint active, and hot gas
reheat (if installed) controls to the discharge air temperature
setpoint active. Dehumidification temperature setpoint active
is reset by comparing the space dewpoint to the space
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