Watts AERCO Benchmark 2.0, User Manual

Page: 39 / 97

MODE OF OPERATION
5-1
CHAPTER 5 MODE OF OPERATION
5.1 INTRODUCTION
The Benchmark 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 unit 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. 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 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 2.7.1 for
additional wiring information.
5.2.4 Indoor/ Outdoor Startup
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.
NOTE
A design engineer typically provides
design outdoor air temperature and
supply
header
temperature data
4. Once the design outdoor air temperature is
chosen, go across the chart to the desired
supply header temperature for the design
temperature chosen in step 3.
5. Next, go up that column to the Reset Ratio
row to find the corresponding reset ratio.
6. Access the Configuration Menu and scroll
through it until the display shows Bldg Ref
Temp . (Building Reference Temperature).