Combination Control System Field Wiring; Combination Control System Setup And Startup - Watts Aerco Benchmark BMK750 Operation And Service Manual

Benchmark with Edge [I]: Operation-Maintenance Manual
SECTION 6 – STANDALONE MODES OF OPERATION
between constant setpoint and ACS control.
For a typical CCS, 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 as well.
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.
Only the AERCO Control System (ACS) is necessary to configure this system if only a single
valve is used to switch from space heating to domestic hot water. However, the ACS Relay
Panel is required in combination with the ACS when there are up to two isolation valves, boiler
interlocks, and/or a Domestic Hot Water (DHW) pump in a Combination heating plant where
AERCO boilers are being used for both Building Heat and Domestic Hot Water heating.
The following two options are available for using a combination system; one that uses only the
ACS, and one that requires the optional ACS Relay Box:
•
OPTION 1 - This option is selected when the ACS controls a boiler plant containing up to
eight combination boilers that are Domestic Hot Water Priority (DHW PRIORITY) boilers,
along with building heat (BLDG HEAT) boilers, and one hydronic isolation valve in the main
header between the BLDG HEAT boilers and the DHW PRIORITY boilers.
•
OPTION 2 – When this option is selected, the ACS Relay Panel must be used in conjunction
with the ACS. For this option, the ACS controls a boiler plant containing up to eight
combination boilers that are divided up into Building Priority (BLDG PRIORITY) boilers and
Domestic Hot Water Priority (DHW PRIORITY) boilers, along with building heat (BLDG
HEAT) boilers, and using two hydronic isolation valves in the main header, one between the
BLDG HEAT and BLDG PRIORITY boilers, and the other between the BLDG PRIORITY
and the DHW PRIORITY boilers.
In Option 2, when the space-heating load is such that when all the space-heating boilers are at
the 100% valve position, the ACS will then ask the ACS Relay Box 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 ACS Relay Box switches
the combo units back to the domestic load. The ACS in combination with the ACS Relay Box
will ask the BLDG PRIORITY boilers to help with domestic hot water heating if the DHW
PRIORITY boilers are not able to satisfy the domestic hot water demand.
When the combo units are satisfying the domestic load, they are in the Constant Setpoint
mode of operation. When the combo units switch over to space heating, their mode of operation
changes to follow the ACS command. For more information concerning the operation of the
ACS, consult the AERCO Control System Manual (OMM-0081, GF-131); for information on
mounting and wiring the ACS Relay Box, see section 2.14 in that manual.

Combination Control System Field Wiring

6.6.1
Wiring for this system is between the ACS, the ACS Relay Box, and the 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.

Combination Control System Setup and Startup

6.6.2
To setup a boiler for Combination mode:
OMM-0145_D • GF-218 •
11/2/2020
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