DE DIETRICH INNOVENS MCA 15 - MCA 25 - MCA 25_28 MI - Manual (Page 10)

3 Description
3.1 Operating principle
3.1.1. Gas/air setting
The casing fitted to the boiler is also used as an air box. Air is sucked
in by the fan and gas injected into the venturi by the fan intake. The
fan rotation speed is set according to the settings parameters, the
thermal energy requirement and the temperatures measured by the
temperature sensors. The gas and air are mixed in the venturi. The
gas/air ratio ensures that the quantities of gas and air are adjusted to
each other. This provides optimum combustion on the entire output
range. The gas/air mixture is fed into the burner on top of the
exchanger.
3.1.2. Combustion
The burner heats the heating water circulating in the heat
exchanger. At a return temperature lower than around 55°C, the flue
gases cool down to a temperature lower than the dew point, thus
causing the condensation of the water vapour contained in the flue
gases in the back side of the heat exchanger. The heat released
during this condensation process (the latent heat or condensing heat)
is also transferred to the heating water. The cooled combustion gases
are evacuated via the combustion gas outlet flue. The condensation
water is evacuated via a siphon.
3.1.3. Heating and domestic hot water production
On heating and domestic hot water production type boilers, an
integrated plate exchanger heats the domestic water. A 3-way valve
determines whether the heated water is fed into the heating system
or the plate exchanger. A pick-up sensor signals that a hot water tap
is being opened. This signal is transmitted to the control panel, which
then switches the 3-way valve to the hot water position and trips the
heating pump. The 3-way valve is spring-loaded but only consumes
electricity when it switches to another position.
The heating water reheats the domestic water in the plate
exchanger. In comfort mode, if there is no hot water draw-off, the
boiler handles the periodic reheating of the plate exchanger. Any
limescale particles are kept out of the plate exchanger by a self-
cleaning water filter (self-cleans once every 76 hours).
3. Description MCA 15 - MCA 25 MCA 25/28 MI
9 23/08/2011 - 300024159-001-B