Functional description
86
Boiler temperature control
Brief description
The boiler water temperature is
controlled by switching the burner
stages or modulation on and off.
The desired boiler water temperature
value is determined by the set-point
supply temperature value of the boiler
circuit (A1), the mixing valve circuits
or the heating circuits connected via
the LON BUS, through the external
request facility and the desired
domestic hot water temperature, and
is dependent on the boiler and the
heating and control facilities installed.
In conjunction with Therm-Control:
The desired boiler water temperature
is increased when the temperature
falls below the set-point value on
the sensor of the Therm-Control.
When the domestic hot water tank
is heated up, a desired boiler water
temperature is selected which is
20°C / 36°F higher than the desired
DHW tank water temperature (this
value can be changed via coding
address ”60”).
Coding addresses which influence
the boiler temperature control
02 to 06, 08 to 0b, 13 to 1C
See page 114 onwards for
description.
Functions
The boiler water temperature is
measured via a multiple sensor well by
three sensors separately:
Fixed high limit FHL (liquid
expansion)
Adjustable high limit AHL (liquid
expansion)
Boiler temperature sensor BTS
(change in resistance PT 500)
Upper limits of control range
Fixed high limit FHL 110°C / 230°F,
can be adjusted to 99°C / 210°F
Adjustable high limit AHL 95°C, can
be adjusted to 100°C / 212°F
Electronic maximum limit
Setting range: 20 to 127°C / 68 to
261°F
The maximum limit for the boiler
water temperature is defined in
coding address ”06”.
Lower limit of control range
The control unit regulates the
boiler water temperature in
normal operation and in the
frost protection mode according
to the boiler concerned (boiler
coding card).
Control sequence
Boiler temperature falls
The burner switch-on signal is set for
a boiler water temperature set-point
value of –2°C / -4°F, and the burner
starts its own monitoring program.
Depending on the range of additional
control facilities and the method of
firing, burner override can be delayed
by a few minutes.
Boiler temperature rises
The switch-off point of the burner is
defined by the switch-off differential
(coding address ”13”).
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