Emerson MultiFlex RTU, Installation And Operation Manual

Page: 27 / 36

Curtailment Software Overview • 21
Zone applications. For as long as the ENABLE
signal lasts, AHU Zone applications treat the
economization dampers as if they are
preliminary cool stages; if cooling is needed, the
dampers will open and economization will
begin. If more cooling is needed, the cooling
stages would then cycle on as normal.
6.5.1. Analog Economizers
Certain HVAC rooftop units have
variable-position economizers which are
controlled by analog output points. When
economization is enabled, the RTU varies the
position of the analog economizers to maintain a
constant mixed air temperature.
6.6. Curtailment
Some power companies offer curtailment
programs that allow participating stores to
disable user-defined loads during peak power
times in return for discounts on utility rates.
If you are participating in a curtailment program,
the power company will supply you with a
digital curtailment device that closes to signal
the beginning of curtailment. This input must be
connected to the CURTAILMENT IN input in
Einstein Global Data, or to an Input Sensor
Module set up as a “Curtail” input type for BCU.
To set up curtailment in the RTU, you must
designate which specific heating and cooling
stages will be subject to curtailment. When the
power company sends a curtail command, all
stages that are set up to be curtailed will be shut
off and locked out.
Fan control is not directly affected by a call for
curtailment. The rooftop unit fan will still run at
a speed based on the number of active, non-
curtailed stages (or, if using modulated outputs,
the curtailed modulating percentage). If this
causes the fan to slow down or shut off during
curtailment, there will be energy savings from
the fans.
6.7. Reversing Valve Control
The RTU supports the control of a heat reversing
valve and a cool reversing valve. These valves
may be wired to any auxiliary output on an RTU.
The output is controlled as follows:
1. When no heat or cool stages are active, the
coil is de-energized (N.C. contacts closed,
N.O. contacts open).
2. When a cool stage comes on, the coil will be
energized (N.C. contacts open, N.O. contacts
closed).
3. When a heat stage comes on, the coil will be
de-energized (N.C. contacts closed, N.O.
contacts open).
Therefore, in order for the output to control the
valve properly, heat reversing valves must be
wired to the Normally Closed (N.C.) contacts,
and cool reversing valves must be wired to the
Normally Open (N.O.) contacts. This causes the
heat valves to activate when heat stages are ON,
and cool stages to activate when cool stages are
ON.
6.8. Stand-Alone Operation
If for some reason an RTU board loses
communications with its parent Einstein unit for
longer than five minutes, the board will go into
Stand-Alone Mode.
In Stand-Alone Mode, the RTU will continue
Temperature Control as normal using the space
temperature as a control input. Since an RTU has
its own stored fallback setpoints and a fallback
occupancy schedule, the RTU will continue
operating using its occupied or unoccupied
heating and cooling setpoints.
If reversing valves are used, the AHU Zone
application will not be allowed to bring on stages of heat
to compensate for cool stage activation during
dehumidification.