HAMWORTHY HEATING LTD
27
PUREWELL VariHeat he
500001155/F
8.5.7.3 Step
Modulation
This function is particularly effective in avoiding too many firing cycles where the boiler power is relatively high
compared to the minimum heat load. By setting the relevant parameters, as soon as the CH demand is active,
step modulation begins. When in operation, the step is increased over time. The duration of each step, as well as
the power corresponding with each step, determines the rate of increase / decrease in the boiler power.
Note:-
the sum of all individual time steps may not exceed 109 minutes.
Figure 8.5.7.3 - Step modulation control
8.5.7.4
Monitoring On/Off ratio remote control On/Off input
This monitoring function provides information about the number of On/Off cycles of the Remote On/Off input. This
can indicate a poor controls philosophy. By setting the relevant parameters, the details will be logged and the
message “BLR: Min CH Cycl” will be shown on the display. This message will be removed automatically as soon
as the time between successive heat demands, within the last time frame, is higher than the minimum cycle time.
8.5.7.5 Blocking
Inputs
The BIC 930 control is designed with the ability to programme each input function, open or closed circuit.
Operation of the device on the input (combustion chamber pressure switch or low gas pressure switch), will result
in a block on all heat demands, with corresponding message on the display screen.
8.5.7.6 Fan
Speed
Control
The fan will modulate to the setpoint determined by the PI—regulation based on the actual flow temperature.
Proportional bandwidth as well as Integration time can be altered together with fan speed settings, by setting the
relevant parameters.
The modulation is limited by the maximum and minimum fan speed settings.
During pre-purge and ignition, the fan speed is fixed at different levels according to the specific boiler. During post
purge, the fan speed is set to the last fan speed achieved with the boiler firing. When no flame is sensed after
ignition, the fan speed is set to the flue gas purge time.
If the desired fan speed is not reached within a specific time period, the control will block the heat demand with a
corresponding message on the display. The fan speed is considered acceptable as soon as the actual speed is
within 30% of its setpoint.
To avoid problems with flame ionisation during the increase/decrease of fan speed, the slope of the increase/
decrease can be limited. During boiler firing, these limits are more important than non firing fan functions (pre-
purge etc).
8.6
DATA LOGGING FUNCTIONALITY
8.6.1
Gas Consumption
Gas consumption based on fan speed and gas valve opening is logged from two points. The start point is cleared
just before leaving the factory. The second start point can be cleared by the User or Service Engineer, in both
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