Emerson MultiFlex RTU, Installation And Operation Manual

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Introduction to Zone Control Software Overview • 19
6 Software Overview
6.1. Introduction to Zone
Control
RTUs are designed to be grouped together in
zones . Zones are groups of ARTC/RTUs and/or
AHU (air handling unit) applications that share
the same heating, cooling, and dehumidification
setpoints, as well as other control parameters.
The primary purpose of zone control is to
maintain a specific temperature and humidity
level throughout a wide area using multiple
rooftop units.
In general terms, it is best to think of the
relationship between an RTU and its parent
controller (Einstein or BCU) as a master-slave
arrangement. Each RTU does most of the work
to keep its own environmental conditions within
the range specified by its master. The “master”
tells each slave what conditions must be met.
Because zone control is already covered in the
Einstein BX manual ( P/N 026-1602) and
REFLECS BCU manual ( P/N 026-1102), this
manual will only cover how the RTU itself
performs its control functions. Refer to the
controller’s user manual for instructions on how
to set up zone control.
6.2. Temperature Control
In its most basic form, temperature control in an
RTU reads the space temperature input value,
compares it to the active heating or cooling
setpoint, and activates or deactivates heating or
cooling stages in an effort to satisfy the setpoint.
The majority of user setup that must be done in
Temperature Control involves defining different
setpoints in the RTU’s parent zone for use in
occupied, unoccupied, summer, and winter
modes, and setting up the operating
characteristics of the heating and cooling stages.
6.2.1. Setpoints
There are two active setpoints in an RTU: a
cooling setpoint and a heating setpoint (both of
which are supplied by the zone from the Einstein
or BCU). When the input rises above the cooling
setpoint, cooling mode begins, and when the
input falls below the heating setpoint, heating
mode begins.
RTUs activate stages in sequence, starting with
stage #1 and continuing on to the last stage, until
the space temperature meets the setpoint. When
the setpoint is satisfied, stages are deactivated in
reverse order, beginning with the highest
numbered active stage, and ending with stage 1.
6.2.1.1. Setpoint Deadbands
Both the currently active heating setpoint and
cooling setpoint have deadbands. A deadband is
a range of values around the setpoint where the
space temperature is considered to be “OK.” If
the temperature is within this deadband, the RTU
will not activate new stages or deactivate any
stages that are currently ON.
6.2.1.2. Stage ON and OFF Delays
Heating and cooling stages may be also be set up
with on and off delays as well as minimum ON
and OFF times.
6.2.1.3. Summer/Winter and Occupied/
Unoccupied Setpoints
The RTU may be programmed with different
setpoints that are used during occupied and
unoccupied building times, and summer and
winter seasons.
The RTU has two ways of determining whether
to use occupied or unoccupied setpoints. If the
RTU is associated with a zone in an Einstein or
BCU, it will use whatever occupied state the
zone says to operate in (i.e., the zone controls the
schedule). If the RTU is not connected to a zone,
or if the RTU loses communications with its
parent controller, the RTU uses a fallback
schedule that is saved in its own memory.