19
E2
Series Controller Operation Manual
4.6.4 Suction Pressure Fan
Speed Control (Optional)
Suction pressure may be controlled for DX based units by
modulating fan speed if optional suction pressure transducers
(sensors) are used. If suction pressure is normal (between 57.5
psi to 127.0 psi for R407C, between 112.5 psi to 185.0 psi for
R410A), the fan speed is controlled by the normal fan speed
algorithm based on static pressure, return temperature, or
dehumidification fan speed. If suction pressure rises above the
high suction pressure limit, the fan speed decreases, reducing
airflow to the evaporator coil to decrease the suction pressure. If
the suction pressure falls below the low suction pressure limit, the
fan speed increases to increase suction pressure. A message
Suct Press Limit Active will appear in the Info>Fans
and CW menu screen.
On dual compressor systems, a suction pressure transducer is
used for each circuit. In this case the controller will respond to the
lower suction pressure value to increase fan speed and to the
higher suction pressure value to decrease fan speed.
4.7 Communication With the Controller
It is possible for the controller to communicate in a variety of ways.
Multiple A/C unit controllers may be connected together using a
pLAN. This enables the operation of multiple A/C units to be
managed from a lead controller's interface display panel (see
Section 7.0).
Using a comm card, the controller(s) may also be connected to a
BMS for monitoring and control of data points using a choice of
available serial communication protocols.
In the event of a BMS monitoring/control signal failure, the E²
controller will default to local operation at the current setpoints for
the fan, external economizer damper and chilled water control
valve. The local sensors have priority over the BMS system.
4.8 Remote On/Off
Terminal positions are provided to connect a remotely located,
On/Off switching control device for Remote On/Off operation. If
the A/C unit is turned on and the E² controller receives a remote
24V input signal via the remote switching device, the system will
operate. If the switching device opens, removing the 24V input to
turn off the A/C unit, the controller disables all control outputs and
a message Off by Remote Shutdown appears in the main display
screen. The A/C system will automatically be re-enabled when the
24V Remote On/Off signal is restored for the A/C unit to turn back
on.
As an example, the control device may be an On/Off switch,
thermostat or a humidistat. If customer provided, the remote
On/Off control contacts must be sized appropriately. The Remote
On/Off contacts must have a rating of 15 mA @24 VAC. Refer to
the electrical drawing included with the A/C unit for the wiring
details.
4.9 Weekly Timer
The weekly timer may be used to set up an operating schedule
to automatically scale back or shut down the air conditioner
during low demand or unoccupied periods. This is an energy
saving feature offering the ability to create up to seven operating
schedules tailored to the needs of the building. For example, a
five day (Monday-Friday) weekday and two-day (Saturday and
Sunday) weekend operating schedule may be set-up. Each
operating schedule may be set-up with its own setpoints for
temperature and humidity and offsets which will replace the
current temperature and humidity setpoints during that
operating schedule's time period. An evening (night-setback)
schedule may also be set allowing the A/C unit to operate at
night with relaxed temperature/humidity setpoints and
offsets.
4.10 Dual Power Transfer Switching
Dual power transfer switching is optionally available for critical
operations. With this option, two power service disconnect
switches are provided to connect two independent power
sources. Each power source is monitored by a phase
monitoring relay. If the user selectable primary power source is
interrupted or, if a phase loss or imbalance occurs, the power
transfer circuitry switches operation of the A/C system to a
secondary power source. Switching is accomplished using
open transition, break-before-make contactors.
The dual power transfer switching sequence may be
controlled by one of two methods: 1) The phase monitor
relays in the air conditioner manage the power transfer
sequence and provide input signals to the system controller
for monitoring purposes or, 2) the phase monitor relays
provide input signals to the system controller which manages
the power transfer sequence and sends control signals to the
switching relays in the air conditioner.
4.10.1 Power Transfer Performed
by Phase Monitors
Each power source is monitored by a phase monitor relay, one
output of which goes to the power switching circuit and the
other output sent to the system controller for monitoring
purposes. Upon an interruption to the user selectable primary
power source, the system controller de-energizes along with
the fans and compressor and/or chilled water valve, and the
alternate power phase monitor relay starts a built-in timer
(adjustable). After an auto transfer sequence delay period
which ensures the switch to power source is stable, the air
conditioner is switched to the alternate power source.
When power is transferred, the system controller re-boots and
after approximately 30 seconds, it provides an alarm signal.
The controller also displays an alarm message indicating which
power source failed. This alarm message may be conveyed
through an optional BMS serial communications link. When the
controller reboots, it re-establishes the control sensor inputs
and restarts the operating sequence it was in at the time of the
switch over as described in Section 3.3. If the AC system uses
a compressor, and it was running at the time power is