Section 3: Modes Of Operation; Introduction; Indoor/Outdoor Reset Mode; Reset Ratio - Aerco Benchmark BMK 750 User Manual

Benchmark 750-3000 Boiler Operation, Service, Maintenance Guide - KOREA
SECTION 3 – MODES OF OPERATION

SECTION 3: MODES OF OPERATION

3.1 INTRODUCTION

The boiler is capable of being operated in any one of six different modes. The following sections
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. After
reading this section, parameters can be customized to suit the needs of the specific application.
A complete listing and descriptions of the temperature related parameters are included in
Appendix A, while factory defaults are listed in Sections 2.4 – 2.10, above.

3.2 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.

3.2.1 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.

3.2.2 Building Reference Temperature

This is a temperature from 40°F to 230°F (4.4°C to 110°C). 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 (21.1°C), then at an outside
temperature of 69°F (20.6°C), the supply header temperature will increase by 1.6° to 71.6°F
(0.9°C to 22°C).

3.2.3 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 200 feet (61m) 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 Section 2.10: AC Electrical Power Wiring of the
Benchmark 750 – 3000 Boiler Installation and Startup Guide Guide, OMM-0127 (GF-205-K) for
additional information on wiring.
OMM-0128_0C
GF-206-K
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Ph.: 800-526-0288
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11/29/2017