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BRADFORD WHITE CORP.
Page 26
tank is drawing down, the heater will react to sustain
a minimum tank temperature. Boilers generally have
higher differentials than water heaters, to minimize
short cycling (see throttling range). The differential
is set by removing the cover of the A350 control
and adjusting the potentiometer marked “DIFF” (see
Figure 13).
5.5.3 Offset
The offset determines the temperature below the
controller’s setpoint where the throttling range begins.
It offsets the throttling range.
For instance, if the setpoint is 120°F (49°C) and
the offset is 5°F (3°C), then the unit’s throttling range
will begin at 115°F (46°C). Between 115°F (46°C) and
120°F (49°C), the Brute Magnum will be in low fire.
The offset can be adjusted between 0°F and 30°F
(0°C and 17°C) by removing the cover of the S350P
control and adjusting the Offset dial (see Figure 14).
5.5.4 Throttling Range
The throttling range allows the Brute Magnum
to match the BTU demands of varying systems, by
allowing the user to choose the temperature range
through which the unit will modulate. This will tell
the controller how fast to respond to a change in
temperature. A small throttling range keeps the unit
in high fire more, and quickens the response of the
system. A larger throttling range allows the Brute
Magnum to spread its modulating range over a larger
temperature range.
Example, Imperial units: Using a temperature
setpoint of 120°F, with a 20°F differential, a 5°F
offset, and a throttling range of 10°F, the unit will
come on at 100°F and shut off at 120°F. The offset
will set the top of the throttling range 5°F under the
setpoint, which is 115°F in this example. Therefore,
the throttling range will cause the Brute Magnum to
modulate between 25% and 100% of full fire between
115°F and 105°F. Between 115°F and 120°F, the unit
will remain at low fire. Between 100°F and 105°F, the
unit will be at full fire.
Example, Metric units: Using a temperature
setpoint of 49°C, with a 11°C differential, a 3°C offset,
and a throttling range of 5°C, the unit will come on at
38°C and shut off at 49°C. The offset will set the top
of the throttling range 3°C under the setpoint, which is
46°C in this example. Therefore, the throttling range
will cause the Brute Magnum to modulate between
Figure 14. Control Parameter Graph.