GB-7
D
GB
F
NL
I
E
DANGER
Risk of explosion! Fill the gas line to the burner
carefully and correctly with gas and vent it safely
into the open air – do not discharge the test volume
into the furnace chamber.
Determining the gas and combustion air flow
rates
Q
Gas
= P
B
/H
u
Q
Luft
= Q
Gas
.
λ
. L
min
▷
Q
Gas
: Gas flow rate in m
3
/h (ft
3
/h)
▷
P
B
: Burner capacity in kW (BTU/h)
▷
H
u
: Gas calorific value in kWh/m
3
(BTU/ft
3
)
▷
Q
Luft
: Air flow rate in m
3
(n)/h (SCFH)
▷
λ
: Lambda, air index
▷
L
min
: Minimum air requirement in m
3
(n)/m
3
(n)
(SCF/SCF)
▷
Information on the gas quality supplied can be
obtained from the competent gas supply com-
pany.
Common gas qualities
Gas type
Lower calorific value
L
min
m
3
(n)/m
3
(n)
(SCF/SCF)
kWh/m
3
(n) (BTU/SCF)
Natural
gas H
11
1114
10.6
Natural
gas L
8.9
901
8.6
Propane
25.9
2568
24.4
Town gas
4.09
425
3.67
Butane
34.4
3406
32.3
▷
Data in kWh/m
3
(n) refer to the lower calorific
value H
u
and data in BTU/SCF refer to the upper
calorific value H
o
.
▷
A minimum air excess of 20% (lambda = 1.2)
should be set in a cold furnace for initial adjust-
ment since the air volume falls as the tempera-
ture rises.
▷
Fine adjustment should be carried out at max.
furnace temperature and at as high a capacity
demand as possible.
Notes on the flow rate curve
▷
If the gas density in the operating state differs
from that reflected in the flow rate curve, convert
the pressures according to the local operating
state.
p
B
= p
M
.
δ
B
δ
M
▷
δ
M
: Gas density reflected in the flow rate curve
[kg/m
3
(lb/ft
3
)]
▷
δ
B
: Gas density in operating state [kg/m
3
(lb/ft
3
)]
▷
p
M
: Gas pressure reflected in the flow rate curve
▷
p
B
: Gas pressure in operating state
Determining the gas and combustion air
settings
▷
Orifices are installed in the gas and combustion
air connections on the burner.
▷
Adjustment is made on the basis of the flow rate-
dependent pressure differential. The required
pressure differentials for gas and air are shown
in the burner diagram.
[mbar ("WC)]
[m
3
/h (ft
3
/h)]
Q
gas
∆p
air
∆p
gas
Q
air
∆p
gas
∆p
air
▷
Ensure an undisturbed flow to the orifice. We
recommend that a double nipple to ISO 65 with a
length of at least 5d be inserted into the connec-
tion. If pipe elbows and angles, reducing fittings,
couplings, etc. are used in the immediate vicinity
of the burner connection, differences from the
flow rate curves will occur which may result in
incorrect burner settings.
WARNING
Incorrect burner settings may result in substoichio-
metric burner operation.
Notes on motive air at the eductor
▷
The motive air is set at the eductor by measur-
ing the negative flue gas pressure p
FG
between
the burner and eductor. The required negative
pressure is shown in the eductor diagram, see
www.docuthek.com, on the basis of the maxi-
mum furnace temperature and burner capacity.
▷
With 80% flue gas extraction, a low furnace pres-
sure (0.1 to 0.3 mbar) can normally be main-
tained in direct heating systems. Initial adjust-
ment with a cold furnace should be made with
a reduced extraction rate. This avoids infiltrated
air caused by a negative pressure in the furnace
which would falsify the flue gas measurement.
▷
During the commissioning procedure, the motive
air setting must be optimized (maximize flue gas
extraction). The furnace pressure must remain
slightly positive in all operating states (0.1 to
0.3 mbar).
If the positive pressure exceeds approx. 0.3 mbar,
increase the flue gas extraction rate to prevent
the burner being damaged.
If there is a negative pressure in the furnace
chamber, reduce the flue gas extraction rate to
avoid infiltrated air.
