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© 2010 D 270 - 08/10
To calculate the Maximum Modulation, use the following formula:
For 0 to 10 V (dc)
:
Maximum Modulation =
0 V (dc) – Boiler’s Maximum Input Signal
0 – 10 V (dc)
x 100%
For 2 to 10 V (dc):
Maximum Modulation =
2 V (dc) – Boiler’s Maximum Input Signal
2 – 10 V (dc)
x 100%
Example:
A boiler’s input signal range is 2 to 9 V (dc). The 270 control has an output signal range of 2 to 10 V (dc).
To make the two signal ranges the same, the Maximum Modulation required is:
Maximum Modulation =
2 V – 9 V
2 V – 10 V
x 100% = 88%
BOILER MASS
The
Boiler Mass
setting allows the installer to adjust the control to the thermal mass of the type of heat sources used in the
application. The modulation of the boiler can become unstable if the incorrect
Boiler Mass
setting is chosen. A key sign of the boiler
modulation being unstable is the flame will continue to increase and then decrease in short periods of time. By choosing a lower
Boiler Mass
setting, the boiler response will become more stable.
Lo (1)
The
Lo
setting is selected if the boiler that is used has a low thermal mass. This means that the boiler has a very small water
content and has very little metal in the heat exchanger. A boiler that has a low thermal mass comes up to temperature quite rapidly
when fired. This is typical of many copper fin-tube boilers. The
Lo Mass
setting provides a fast response to the heating system.
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 burner ignites at low fire when the supply water temperature is ½ of the
Boiler 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.
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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
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.