AERCO BMK 1.5 LN July 2011 - Manual (Page 53)

PR2: 05/01/11 Page 53 of 152
Benchmark 1.5LN Low NOx Boiler
Operation and Maintenance Manual
OMM-0041_0D
GF-120
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913 • Ph: 800-526-0288
CHAPTER 5: MODE OF OPERATION
5.1 INTRODUCTION
The boiler is capable of being operated in any one of six different modes. The following
paragraphs 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 E. 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.
Reset Ratio 5.2.1
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.
Building Reference Temperature 5.2.2
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.
Outdoor Air Temperature Sensor Installation 5.2.3
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 SENSOR IN and SENSOR
COMMON 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, paragraph 2.9.1 for
additional wiring information.
Indoor/ Outdoor Startup 5.2.4
Startup in the Indoor/Outdoor Reset Mode is accomplished as follows:
1. Refer to the Indoor/Outdoor reset ratio charts in Appendix D.
2. Choose the chart corresponding to the desired Building Reference Temperature.
3. Go down the left column of the chart to the coldest design outdoor air temperature expected
in your area.