Benchmark 2500 - 3000 Boilers
CHAPTER 5 – MODE OF OPERATION
OMM-0094_0E
AERCO International, Inc.
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100 Oritani Dr.
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Blauvelt, NY 10913
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GF-137
Ph.: 800-526-0288
03/20/2014
CHAPTER 5.
MODE OF OPERATION
5.1 INTRODUCTION
The boiler is capable of being operated in any one of six different modes. The following sections
in this Chapter provide descriptions of each of these operating modes. Each boiler is shipped
from the factory tested and configured for the ordered mode of operation. All temperature
related parameters are at their factory default values which work well in most applications.
However, it may be necessary to change certain parameters to customize the unit to the system
environment. A complete listing and descriptions of the temperature related parameters are
included in Appendix A. Factory defaults are listed in Appendix D. After reading this chapter,
parameters can be customized to suit the needs of the specific application.
5.2 INDOOR/OUTDOOR RESET MODE
This mode of operation is based on outside air temperatures. As the outside air temperature
decreases, the supply header temperature will increase and vice versa. For this mode, it is
necessary to install an outside air sensor as well as select a building reference temperature and
a reset ratio.
5.2.1 Reset Ratio
Reset ratio is an adjustable number from 0.1 to 9.9. Once adjusted, the supply header
temperature will increase by that number for each degree that the outside air temperature
decreases. For instance, if a reset ratio of 1.6 is used, for each degree that outside air
temperature decreases the supply header temperature will increase by 1.6 degrees.
5.2.2 Building Reference Temperature
This is a temperature from 40°F to 230°F. Once selected, it is the temperature that the system
references to begin increasing its temperature. For instance, if a reset ratio of 1.6 is used, and
we select a building reference temperature of 70°F, then at an outside temperature of 69°F, the
supply header temperature will increase by 1.6° to 71.6°F.
5.2.3 Outdoor Air Temperature Sensor Installation
The outdoor air temperature sensor must be mounted on the North side of the building in an
area where the average outside air temperature is expected. The sensor must be shielded from
the sun's direct rays, as well as direct impingement by the elements. If a cover or shield is used,
it must allow free air circulation. The sensor may be mounted up to two hundred feet from the
unit. Sensor connections are made at the Input/Output (I/O) Box on the front of the boiler.
Connections are made at the terminals labeled OUTDOOR AIR IN and AIR SENSOR COM
inside the I/O Box. Use shielded 18 to 22 AWG wire for connections. A wiring diagram is
provided on the cover of the I/O Box. Refer to Chapter 2, section 2.9.1 for additional wiring
information.
5.2.4 Indoor/Outdoor Startup
Startup in the Indoor/Outdoor Reset Mode is accomplished as follows:
NOTE
A design engineer typically provides design outdoor air
temperature and supply header temperature data
