ALUTHERM
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Boilers 11
ALUTERM A 170 - 300
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Installation, user and service manual
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instructions for user
Heating
Alutherm A 170 - 300
4.2.5
Slow start
The boiler uses a “slow start” procedure to prevent the boiler from supplying excessive power in low load situations.
After “zero check” APS and closure APS with pre purge ignition starts. Following a stabilization period, the boiler modulates down to low capacity
and maintains this capacity for 1 minute. Subsequently the boiler power increases at a rate of 4 °C/min until maximum capacity or set temperature
has been reached. Once heat demand has finished the burner will turn off following a set post purge period.
The graph below illustrates this;
4.2.6
Protection against insufficient flow through boiler
If the requirements of 6.3.2 are fulfilled the boiler will protect itself against insufficient flow. This is done by checking the difference in temperature
between flow and return (so called ΔT).
In a low flow scenario the ΔT will rise rapidly. The ΔT safe-guarding principle is as follows;
At ΔT > 22 the boiler starts modulating
At ΔT between 22 and 27 the boiler continues modulating
At ΔT > 27 boiler the fan speed will reduce until ΔT < 25
5000
4000
3000
2000
1000
0
Fa
nsp
ee
d r
pm
APS
Pre purge
Pre ignition
Ignition
Slope 4°C/min
High
Post purge
Off
Low
Time
Zero check APS
End off heat demand
Slow start sequence
Start heat demand
