I&O Manual - ECCS Control System - Categories On Thermal ...

Section 2: Principles of Operation
2.1 SYSTEM DESCRIPTION
The ECCS (Electronic Controls and Communication
System) is a Lead Lag sequencer for modulating and
on/off boilers capable of auto rotation, Outdoor reset,
and communication using a Modbus protocol.
All the control signals between the boiler and the ECCS
panel are transmitted over a 3 wire shielded cable using
the Modbus protocol. This includes the enable/disable
signal, the modulating signal, and the local/remote
signal.
System water temperature is continuously monitored
through the header water temperature sensor. The
system compares this temperature to the setpoint which
is fixed or generated from the outdoor reset curve. If
the system water temperature falls below the adjustable
system ON POINT set on the screen (refer to Figure
5.3) the lead boiler will turn on via a signal from the
ECCS system. For a modulating boiler, The PID
control will generate a signal and send it to the boilers
via the MODBUS. If the firing rate goes above the
START TRIGGER Point set on the screen for the
amount of time set in the START DELAY, the first lag
boiler will start. Once the lag boiler starts it will drive
to the same firing rate as the lead boiler. Both boilers
will fire in tandem, at the same firing rate. Additional
lag boilers will start by the same criteria in the order
that set as the LEAD LAG SEQUENCE. Boilers will
be shed in the reverse order of which they came on
(AKA: First On, Last Off). As load is shed the boilers
will use the STOP TRIGGER point and the STOP
DELAY parameters set on the screen.
For On/Off boilers, additional boilers will be added
when the system water temperature drops below the
system ON POINT for the time set in the boiler START
DELAY. Boilers will be shed in reverse order using
the OFF POINT and STOP DELAY parameters.
The Lead Lag (LL) system will be capable of running a
maximum number of 6 boilers. Parameters in the
temperature controller and flame safeguard are
transmitted via the Modbus connection to the PLC and
Touch screen.
2.2 LEAD LAG
2.2.1. In a Lead Lag (LL) system (refer to Figure 5.4),
one boiler is designated as a lead boiler. The lead
boiler will always be the first boiler to come on and the
last boiler to shut off. The lag boilers will always
come on after the lead in order of their number. The
first lag (lag#1) will always be the second boiler to
come on, the second lag (lag#2) will always be the
third to come on, etc. They will turn off in reverse
order.
6
2.2.2. There is a sequence preprogrammed from the
factory as a default of: Lead = boiler 1, Lag #1 =
boiler 2, Lag #2 = boiler 3, etc., in sequential order.
Sequence can be changed to any order that is
desired. Numbers cannot be duplicated or out of
range.
2.2.3. To change the lead lag sequence go to the
SEQUENCE AND ROTATION SCREEN
(Figure 5.5). From the main screen press the system
setup button, then the Enter Lead Lag Sequence
button.
2.2.4. The system will turn on the lead boiler when the
temperature drops below the System ON POINT. The
boiler will turn the lead off only if it is the only
boiler running and the temperature is above the
System OFF POINT.
The ECCS system turns on additional boilers when the
firing rate of the lead boiler rises above the START
TRIGGER (See Figure 5.4: Lead Lag Trigger Setup
Screen) point for the length of time in the BOILER
START DELAY box. The START TRIGGER is the
percentage of the firing rate that a modulating boiler
must reach in order to start the delay timer. Once the
delay timer finishes timing, the next boiler in the
sequence will start. If the firing rate drops below the
START TRIGGER before the timer is complete, the
timer will reset.
ON/OFF boilers will sequence in accordance with the
System ON and OFF POINTS. See Figure 5.4 under
Setpoint differential.
2.3. UNAVAILABLE BOILERS
2.3.1. If a boiler is unavailable for any one of the
following reasons the LL sequence will remove them
and adjust the sequence until they become available
again. The purpose of this is to save time between
stages if there is an unavailable boiler. If the
desired lead boiler is unavailable, Lag #1 will
become the lead and other boilers will shift
accordingly. The program will rotate based on the
sequence that has been entered onto the screen.
Flame fail – If the boiler has a flame failure the boiler
will be removed from the LL sequence until the unit
has been reset.
Boiler in Local mode – If the Local/Remote switch is
in Local the boiler will be removed from the LL
sequence until the unit has been placed back in
Remote.