9 of 36
© 2010 D 265 - 07/10
MIN Segment On
Med (2)
The Med setting is selected if the boiler that is used has a medium thermal mass. This means that the boiler either has a large
water content and a low metal content or a low water content and a high metal content. This is typical of many modern residential
cast iron boilers or steel tube boilers.
The Med mass setting provides a moderate response to the heating system.
Hi (3)
The Hi setting is selected if the boiler that is used has a high thermal mass. This means that the boiler has both a large water
content and a large metal content. A boiler that has a high thermal mass is relatively slow in coming up to temperature. This is
typical of many commercial cast iron and steel tube boilers.
The Hi mass setting provides a slow response to the heating system.
DIFFERENTIAL
A modulating boiler must be operated with a differential while operating in low fire. The boiler differential is divided around the boiler
target temperature. The boiler starts at low fire when the supply water temperature is ½ of the differential setting below the boiler
target temperature. The boiler is shut off in low fire as the supply temperature reaches at least ½ of the differential above the boiler
target temperature. With the control, either a fixed or an auto differential may be selected.
When the boiler is modulating above low fire, the differential does not apply. Instead, the modulation output signal is determined
using Proportional, Integral and Derivative (PID) logic in order to satisfy the boiler target temperature.
Fixed Differential
If the user desires to have a fixed differential, this is set using the
boiler differential setting in the ADJUST menu.
Auto Differential
If the Auto Differential is selected, the control automatically determines
the best differential as the load changes. This reduces potential short
cycling during light load conditions.
BOILER MINIMUM
The boiler minimum is the lowest temperature that the control is allowed
to use as a boiler target temperature. During mild conditions, if the control
calculates a boiler target temperature that is below the boiler minimum
setting, the boiler target temperature is adjusted to at least the boiler
minimum setting. During this condition, if the boiler(s) is operating, the
minimum segment is turned on in the display when viewing either the
boiler supply temperature or the boiler target temperature. Set the boiler
minimum setting to the boiler manufacturer’s recommended temperature.
BOILER MAXIMUM
The boiler maximum is the highest temperature that the control is
allowed to use as a boiler target temperature. If the control does target
the boiler maximum setting, and the boiler temperature is near the boiler
maximum temperature, the maximum segment will be turned on in the
display while either the boiler target temperature or the boiler supply
temperature is being viewed. At no time does the control operate the
boiler(s) above 248°F (120°C).
MAX Segment
On
MAX Segment
On
T
em
p
e
ratu
re
f
al
l
T
e
m
pe
ra
tu
re
ri
s
e
Time
Desired temperature
160
°
F (71
°
C)
Differential
10
°
F (6
°
C)
Boiler Off
Boiler On
155
°
F (68
°
C)
165
°
F (74
°
C)
Increasing Load
Time
Differential
On
Off
