The overall efficiency for the condensing unit, comprising the gas boiler
and the Vitotrans 300 flue gas/water heat exchanger results from add-
ing the boiler efficiency and the increase in efficiency as a result of the
heat exchanger, which has been calculated for the respective system
temperature.
Example:
Efficiency Vitoplex 300 = 96 %
The increase in efficiency resulting from the Vitotrans 300 at 75/60 ºC =
9 % leads to a total efficiency for the condensing unit of
96 % + 9 % = 105 %.
A
C
D
20
40
60
80
+15 +10 +5 0 -5 -10 -15
Heating water temperature in °C
Outside temperature in °C
B
A
Flow temperature for heating systems 75/60 ºC
B
Return temperature for heating systems 75/60 ºC
C
Flow temperature for heating systems 40/30 ºC
D
Return temperature for heating systems 40/30 ºC
Calculation of possible energy savings (B
E
)
■ Annual heating load Q
a
of a boiler system with ²
k
= 500 kW and 1650
full utilisation hours (b
a
) p.a.:
Q
a
= b
a
· Q
k
= 1650 h/a · 500 kW
= 825000 kWh/a
■ Annual consumption B
N
of natural gas LL (calorific value H
u
=
8.83 kWh/m
3
) when using a Vitoplex 300 low temperature boiler with
a standard seasonal efficiency [to DIN] of η
N
= 96 %:
Q
a
B
N
=
η
N
· H
u
825000 kWh/a
0.96 · 8.83 kWh/m³
=
= 97320 m³/a
■ Increase in efficiency η
AWT
through the downstream installation of a
Vitotrans 300 flue gas/water heat exchanger. The design tempera-
ture of the heating system routed through the heat exchanger is
75/60 ºC.
η
AWT
= 9 % (according to table on page 47)
η
ttl
= η
N
+ η
AWT
= 96 % + 9 % = 105 %
■ Annual consumption B
B
of natural gas LL (net calorific value H
u
=
8.83 kWh/m
3
) when using a Vitoplex 300 with a Vitotrans 300 flue
gas/water heat exchanger installed downstream of the boiler:
Q
a
B
B
=
η
ges
· H
u
825000 kWh/a
1.05 · 8.83 kWh/m³
=
= 88980 m³/a
■
Savings in natural gas LL in m
3
/p.a.:
B
E
= B
N
– B
B
= 97320 m³/a – 88980 m³/a
= 8340 m³/a
Using a downstream Vitotrans 300 flue gas/water heat exchanger can
achieve fuel savings of approx. 8.5 %. Substantially higher savings are
realised when modernising an out-dated boiler system with low effi-
ciency rates.
Hydraulic connection
The entire heating water flow rate, relative to the rated boiler output
and a minimum temperature differential of 20 K can be routed through
the Vitotrans 300 flue gas/water heat exchanger.
If a partial volume flow is directed via the Vitotrans 300, e.g. in order
to use a heating circuit with lower return temperatures, the rated vol-
ume flow should be selected so that the temperature range in the
Vitotrans 300 is relative to the upper output of max. 10 K.
Design information
(cont.)
48
VIESMANN
OIL/GAS BOILERS
10
5822 426 GB
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