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6 | Basic principles
2.2
Making optimal use of condensing
technology
2.2.1
Matching to the heating system
Condensing boilers or boilers with condensing heat
exchangers can be installed in any heating system.
However, the available proportion of condensation heat
and the efficiency resulting from this type of operating
mode depend on the design of the heating system.
To be able to use the condensation heat of the water
vapour in the hot gas, the hot gas must be cooled to
below the dew point. The utilisation rate of the
condensation heat is therefore necessarily subject to the
system design temperatures and the hours run in the
condensation range. This is shown by the graphs in
Fig. 4 and Fig. 5. The dew point is approx. 56° C for
natural gas and approx. 47° C for low-sulphur fuel oil.
Heating system 40/30 °C
In this heating system, the benefits of the performance
capacity of condensing technology can be seen
throughout the heating season. The low return
temperatures are always below the dew point, so
condensation heat is always created ( Fig. 4). This is
achieved with low temperature area heaters or
underfloor heating systems, which are ideal for
condensing boilers or boilers with condensing heat
exchangers.
Targeted utilisation of the condensing effect is possible
with the condensing heat exchanger (ECO 6) connected
separately to a low temperature heating circuit.
W
[%]
Ha
100
A
a
80
60
b
40
c
20
0
– 15 – 10
– 5
± 0
Fig. 4
Condensation heat utilisation at 40/30 °C
(example with natural gas)
A
Proportion of operation with condensation heat
utilisation
a
Annual heat load curve
b
Dew point temperature curve (example with
natural gas)
c
System temperatures
ϑ
Outside temperature
A
ϑ
Heating water temperature
HW
W
Annual heat load
Ha
6 720 807 794 (2013/04)
100
80
60
56
40
20
0
5
10
15
20
6 720 803 977-30.1itl
Heating system 75/60 °C
Even with a design temperature of 75/60 °C, it is
possible to make above average utilisation of the
condensation heat for around 95 % of the annual heat
load. This applies for outside temperatures of –7 °C to
+20 °C ( Fig. 5).
Due to the safety supplements in the former DIN 4701
from 1959, older heating systems designed with 90/
70 °C are nowadays to all intents and purposes operated
as systems with 75/60 °C. Even if these systems were
run with system temperatures of 90/70 °C and
modulating, weather-compensated heating circuit
temperatures, they would still use the condensation
heat for 80 % of the annual heating load.
W
[%]
Ha
95
a
A
80
60
40
20
0
– 15 – 10
– 5
± 0
Fig. 5
Condensation heat utilisation at 75/60 °C
(example with natural gas)
A
Proportion of operation with condensation heat
utilisation
a
Annual heat load curve
b
Dew point temperature curve
c
System temperatures
ϑ
Outside temperature
A
ϑ
Heating water temperature
HW
W
Annual heat load
Ha
100
80
60
b
56
40
c
20
0
5
10
15
20
6 720 803 977-31.1itl
UNIMAT
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