Table of Contents
Advertisement
Benchmark 2500DF-3000DF Installation, Operation & Maintenance Manual
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
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.
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.
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:
A design engineer typically provides design outdoor air
temperature and supply header temperature data
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.
OMM-0099_0A
GF-145
CHAPTER 5 – MODE OF OPERATION
Once selected, it is the temperature that the system
NOTE
Indoor/Outdoor Startup
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Ph.: 800-526-0288
Page 69 of 234
PR1: 05/21/2014
Advertisement
Table of Contents
