0503RHC8RJLGBEN
11/34
3.5 M
AXIMUM AIRFLOW CONDITION
Special attention must be given to ensure that the
temperature rise of the air, passing through the enclosure
(duct channel) around the heat exchanger tubes, is high
enough to avoid condensation forming within the tubes. This
condensation forming could occur by super cooling of the
products of combustion. Such condensation can be the
source of severe corrosion and damage to tubes or part of
the tubes.
The chart below indicates the probability of condensation
forming within the tubes reference :
-
the temperature rise of the air through the enclosure
(around the tubes) (see figure 4)
-
the inlet air temperature passing over the heat
exchanger
In function of the expected minimum inlet air temperature,
the minimum required temperature rise (to avoid
condensation) must be derived from the chart below (figure
5).
Example
•
expected minimum inlet temperature = -5°C
•
minimum required temperature rise shown on the chart
= +13°K
Table 1 indicates the heat output (kW) of the different
models.
The maximum allowable airflow
[
through the enclosure
(duct channel) around the tubes
]
can be calculated as
follows :
0.3423
minimum
T
1000
(kW)
output
heat
(m³/h)
max
V
×
×
=
∆
Example :
△
Tmin = 13K (with min. inlet temp. = -5°C)
model 8075 09 at 100% heat output : 75.00kW results into
Vmax = 16850m³/h
Remark
:
For air heaters with the option 2 stage gas valve (50%
minimum heat input) or the option modulating gas valve
(30% minimum heat input) attention must be given to
determine the maximum allowable airflow in function of the
appropriate heat input
Example :
△
Tmin = 13K (with min. inlet temp. = -5°C)
model 8075 09 at 30% modulation (see table 1 ‘output’) :
21.200kW
results into :
h
/
³
m
4764
0.3423
13
1000
(kW)
21.200
max
V
=
×
×
=
Figure 5 : Dew-point occurrence chart (condensation zone)
░
░
░