Switching Method - REMEHA Celcia MC4 Manuel D'installation Et D'utilisation

Remeha Celcia MC4
Required output
Data are exchanged between the regulator and the boilers via
the OpenTherm connections. The Celcia MC4 receives the
flow temperature demand from an Celcia 15 or 20 regulator.
In the case of a room thermostat the flow temperature demand
is determined on the basis of the ambient temperature. In the
case of a weather-dependent regulator the flow temperature
demand is determined on the basis of the heat curve and the
outside temperature. The Celcia MC4 transmits the measured
outside temperature to the controlling Celcia 15 or 20 regula-
tor. The required output is determined according to the differ-
ence between the measured flow temperature and the flow
temperature demanded.
The Celcia MC4 distributes this capacity over the (OpenTherm
controlled) boilers connected. A set switching method deter-
mines the distribution.

5.1.3 Switching method

By way of a set switching method the Celcia MC4 deter-
mines when the boiler is switched on and the required output.
The regulator ensures that the boilers are equally loaded by
recording the number of hours each boiler is in operation. The
switching method is such that as the required output increas-
es, the regulator will wait as long as possible (the first boiler
will then operate at 95% of its own capacity) before switching
the second boiler on (after a time delay of 5 minutes). As the
required output decreases, the regulator will wait as long as
possible before switching the first boiler off.
Operating sequence
The sequence in which the boilers are to be switched on and
off, is set during the configuration. It is determined on the
basis on the number of operating hours. The boiler with the
least operating hours is switched on first and the boiler with
the most operating hours is switched on last. The boilers are
switched off in reverse order, so the boiler that was switched
on first is switched off last.
P = required output
Kt = total output
K1 = output boiler 1
K2 = output boiler 2
* This is a global description of the operation. The effect of
part load time, individual power differences etc. are not shown
in this graph.
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