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Likewise, the RTU will determine the current
season from its parent Einstein if associated with
a zone, or it will use its own methods if a zone
association is not present or not available. You
may choose to have the RTU use specific dates
in the year for summer/winter switch overs, or
you may switch summer/winter mode based on
outdoor air temperature (note: the RTU must
have an auxiliary input set up as "Outdoor
Temp" to use this method of summer/winter
switch over).
6.3. Fan Control
The RTU boards support control of one
single-speed fan stage, a low- and a high-speed
fan stage (i.e., two-speed fan control), or a
variable-speed fan. The fans may be controlled
in one of three ways:
• Continuous - The fan is always on, even when the
AHU Zone application is not in heating, cooling, or
dehumidification mode.
• Auto - The fan is only on when the AHU Zone
application is in heating, cooling, or
dehumidification mode.
• Summer ON, Winter Auto - This mode allows the
fan to operate in Continuous mode during the
summer months and in Auto mode during the winter
months.
If desired, activation and deactivation delays
may be set up for the AHU Zone application for
both heating and cooling mode.
6.4. Dehumidification and
Humidification Control
Unlike Temperature Control, Dehumidification
Control and Humidification Control is handled
entirely by zones. A zone typically has a single
humidity sensor, humidistat, or dewpoint probe
input connected to the central building controller
that measures relative humidity or dewpoint for
20 • MultiFlex RTU Operator's Guide
the entire zone. If the zone determines that
dehumidification or humidification is necessary,
it notifies all RTUs in the zone to begin
dehumidification.
6.4.1. Dehumidification Control
RTUs dehumidify by using cool stages or
auxiliary outputs that are configured on the RTU
as dehumidification devices. When the
command to begin dehumidification is received,
the RTUs begin by cycling on the
dehumidification output (if available), and then a
cool stage. After a programmed delay, if
dehumidification is still necessary, a new stage
of cool will cycle ON. The RTUs will continue
cycling cool stages ON in this manner until
100% of its dehumidifying capacity is active (or
until the setpoint is met). Once the setpoint is
met, the dehumidifier will switch OFF and
stages will cycle OFF.
You may choose the number of cool stages that
will be made available for dehumidification.
6.4.2. Humidification Control
RTUs humidify by activating and deactivating a
humidifier output. Humidification, like
dehumidification, is controlled by the RTU's
zone. If a zone is not available, the RTU may
control humidity in stand-alone mode if a
humidity input is available on one of its
auxiliary inputs.
When operating in stand-alone mode, the RTU
uses cut-in and cut-out setpoints to control the
humidifier.
6.5. Economization
Economizer dampers on rooftop HVAC units are
used to bring outside air into the building for use
in cooling.
Before economization may occur, the zone must
determine when the outside air conditions are
favorable for economization. If economization is
OK, it sends an ENABLE signal to its AHU
026-1706 Rev 3
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