Space Heating Mode; Domestic Hot Water Supply; Electronic Combustion Control; Dhw Boost Heating / Additional Heating Function - Viessmann VITODENS 200-W WB2B Start-Up/Service Instructions

Outdoor Reset Programming Unit
Functional description

Space heating mode

The control unit calculates a boiler
water setpoint temperature based on
the outdoor or room temperature
(where a room temperature dependent
remote control is connected) and on
the slope/shift of the heating curve.
The computed boiler water setpoint
temperature is transmitted to the
burner control unit.
From the boiler water setpoint and the
actual temperature the burner control
calculates the degree of modulation
required, and regulates the burner
accordingly. The maximum operating
boiler water temperature is limited in
the burner control unit to 165 ºF/74 ºC
by the electronic temperature
control.The maximum adjustable high
limit of the boiler is 190 ºF/88 ºC.
The fixed high limits of the safety chain
interlock the burner control unit at
210 ºF/99 ºC boiler water temperature.

Electronic combustion control

Air factor λ λ λ λ - CO /O content
2 2
Air factor λ
1.24
1.27
1.30
1.34
1.37
1.40
1.44
(continued)

Domestic hot water supply

with gas-fired space heating boiler
Domestic hot water heating is
activated when the tank temperature is
4.5 ºF/2.5 ºC below the tank
temperature setpoint value. The burner
and the tank DHW pump are switched
on. In the factory default setting, the
desired boiler water temperature is set
at 36 ºF/20 ºC above the tank
temperature setpoint value. When the
actual tank temperature rises 4.5
ºF/2.5 ºC above the tank temperature
setpoint value, the burner is switched
off and the time delay function of the
tank DHW pump is activated.
The temperature differential of 4.5
ºF/2.5 ºC can be adjusted in coding
level 2, address "59".
The electronic combustion control utilizes the physical correlation between the
level of the ionization current and the air factor λ. For all gas qualities, the
maximum ionization current results in air factor 1.
The ionization signal is evaluated by the combustion control unit, and the air
factor is adjusted to between λ=1.24 and 1.44. This range provides for an
optimum combustion quality. Thereafter, the electronic gas valve regulates the
required gas volume subject to the prevailing gas quality.
To check the combustion quality, the CO
gas is measured. The actual values enable the prevailing air factor to be
determined. The relationship between the CO
illustrated in the table below.
To achieve an optimum combustion control, the system regularly carries out an
automatic self-calibration; also after a power failure (shutdown). For this, the
combustion is briefly regulated to the max. ionization current (equals air factor
λ=1). The automatic calibration is performed shortly after the burner starts and
lasts approx. 5 sec. During the calibration, higher than normal CO emissions may
occur briefly. The combustion control unit can also be calibrated manually, e.g.
after maintenance or service work (see coding address "85").
O content (%)
2
4.4
4.9
5.3
5.7
6.1
6.5
6.9
Control Technology
DHW boost heating / additional heating
function
This function will heat your DHW tank
to a second DHW setpoint temperature
within the fourth time phase. It can act
as an "Anti-Legionnaire-Function" if the
DHW supply is not heated to 140 ºF/
60 ºC during the regular time schedule.
You can activate this function by
selecting a switching period for the
fourth time phase. (See Vitodens
200-W, WB2B Operating Instructions.)
The temperature setpoint for this
function is adjustable in coding
address "58".
content or the O content of the flue
2 2
or O content and air factor λ is
2 2
CO content (%) for natural gas
2
9.2
9.0
8.7
8.5
8.3
8.1
7.8
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