60
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Wöhler DC 100
PRO
The conversion formula for determining the ventilation loss according to
equation 4.1 is stored by the measuring instrument. This value is directly indi-
cated on the display after the measurement.
The ventilation loss qLSNorm (according to equation 4.1) can, however, be
calculated easily with the help of a simple pocket calculator. Only the flow
velocity and the temperature in the exhaust-gas outlet are required for this:
with:
q
LSNorm
ventilation loss, in %
A
v
cross-section area of the exhaust-gas line, in m
2
v(30 sec)
flow velocity in the exhaust-gas line, in m/s
ρ
Air
density of air, standard: 1.2 kg/m
3
c
pL
specific thermal capacity: 0.279 Wh/kg°C
ϑ
Air
air temperature in the exhaust-gas outlet after 30
seconds, in °C
ϑ
Room
air temp. in the heating equipment room, in
°
C
ϑ
ext ACTUAL
outside temperature, actual value, in °C
ϑ
extREF
reference outside temperature, 15°C
Q
load
set firing performance or boiler output, in W
The last term in equation 4.1 reduces the effect of the outside temperature on
the result. Without this standardization to a reference temperature of 15 °C, a
low outside temperature
ϑ
extACTUAL
would inevitably lead to higher ventilation
losses, since the thermal lift is increased.
The following example describes the procedure with the help of a pocket
calculator.
Example: Diameter of the exhaust-gas line = 0.15 m
(cross-section area 0.0177 m2), 30 sec. after burn-out:
Residual flow = 0.61 m/s, residual temperature = 85 °C, outside temperature
= 0 °C, type of boiler: Viessmann 13211, year of construction: 1981, 26 kW,
with burner: Brötje 0-110, 1976, performance = 26 kW.
(Equation 4.1)
(Equation 4.2)
4. Menu Q vent.
A
v
· v (30 sec)·
ρ
air
·
c
pl
·
(
ϑ
air
-
ϑ
room
) 273 +
ϑ
extACTUAL
q
LSNorm
=
273 +
ϑ
extREF
Q
load
