Watts AERCO Benchmark 2.0, User Manual

Page: 43 / 97

MODE OF OPERATION
5-5
5.7 COMBINATION CONTROL SYSTEM
(CCS)
NOTE
Only BMS Model 168 can be utilized for
the Combination Mode, not the BMS II
(Model 5R5-384).
A Combination Control System (CCS) is one
that uses multiple boilers to cover both space-
heating and domestic hot water needs. An
AERCO Boiler Management System (BMS)
Model 168 and a Combination Control Panel
(CCP) are necessary to configure this system.
Typically, an adequate number of boilers are
installed to cover the space-heating load on the
design day, however one or more units are used
for the domestic hot water load.
The theory behind this type of system is that the
maximum space-heating load and the maximum
domestic hot water load do not occur simul-
taneously. Therefore, boilers used for the
domestic hot water are capable of switching
between constant setpoint and BMS modes of
operation. These boilers are the combination
units and are referred to as the combo boilers.
The combo boilers heat water to a constant
setpoint temperature. That water is then
circulated through a heat exchanger in a
domestic hot water storage tank.
When the space-heating load is such that all the
space-heating boilers are at 100% firing rate, the
BMS will then ask the Combination Control
Panel for the domestic boilers to become space-
heating boilers. Provided the domestic hot
water load is satisfied, the combo (hot water)
boilers will then become space-heating boilers.
If the domestic hot water load is not satisfied,
the combo boiler(s) remain on the domestic hot
water load. If the combo boilers switch over to
space heating, but there is a call for domestic
hot water, the CCP switches the combo units
back to the domestic load.
When the combo units are satisfying the
domestic load they are in constant setpoint
mode of operation. When the combo units
switch over to space heating, their mode of
operation changes to the BMS mode. For more
information concerning the operation of the
Combination Control Panel see the AERCO
CCP-1 literature.
5.7.1 Combination Control System Field
Wiring
Wiring for this system is between the BMS
Model 168 panel, the CCP and the B.M.S.
(PWM) IN terminals in the I/O Box. Wire the
units using a shielded twisted pair of 18 to 22
AWG wire. When wiring multiple units, each
unit’s wiring must conform to the above. For a
complete CCP system-wiring diagram see the
AERCO CCP-1 literature.
5.7.2 Combination Control System Setup
and Startup
Setup for the Combination Mode requires entries
to be made in the Configuration Menu for boiler
mode, remote signal type and setpoint. The
setpoint is adjustable from 40°F to 240°F.
Enter the following settings in the Configuration
Menu:
MENU OPTION SETTING
Boiler Mode Combination
Remote Signal BMS (PWM Input)
Internal Setpt 40°F to 240°F
Refer to paragraph 3.3 for instructions on
changing menu options.
While it is possible to change other temperature-
related functions for combination mode, thes
functions are preset to their factory default
values. These default settings work well in most
applications. It is suggested that AERCO be
contacted prior to changing settings other than
the unit’s setpoint. For a complete listing of
temperature related function defaults, see
Appendix E.
To set the unit to the manual mode, press the
AUTO/MAN switch. The MANUAL LED will
light.
To set the unit back to the auto mode, press the
AUTO/MAN switch. The MANUAL LED will go
off and the REMOTE LED will light.
When the boiler is switched to BMS mode, the
AERCO BMS controls the firing rate. There are
no setup requirements to the boiler(s) in this
mode.