With the aid of the calculated demand factor N = 33.2, the tables in the
relevant datasheets enable the selection of the required DHW cylinder
at the available heating water flow temperature (z. B. 80 ºC) and a
cylinder storage temperature of 60 ºC:
For this, select a DHW cylinder with an N
L
factor at least equal to the
calculated demand factor N.
Note
The performance factor N
L
varies subject to the following variables:
■ Flow temperature
■ Storage temperature
■ Available or transferable output
For deviating operating conditions, modify the performance factor N
L
from the values shown in the tables in the relevant datasheets.
Possible DHW cylinders:
■ From selection diagram from page 10 and the Vitocell 300-H data-
sheet:
Vitocell 300-H with 700 l capacity (N
L
= 35) as cylinder bank com-
prising 2 × Vitocell 300-H, each with 350 l capacity
■ From selection diagram from page 10 and the Vitocell 300-V data-
sheet:
Vitocell 300-V with 600 l capacity (N
L
= 38) as cylinder bank com-
prising 2 × Vitocell 300-V, each with 300 l capacity
Selected DHW cylinder:
2 × Vitocell 300-V, each with 300 l capacity.
Boiler supplement Z
K
According to DIN 4708-2 and VDI 3815, the rated heating output of a
boiler must be increased by the boiler supplement Z
K
to cover the DHW
heating demand (see table 6).
Observe the explanations in DIN/VDI [or local regulations].
DIN 4708 specifies three main demands for the rated heating out-
put of the heat source:
Demand 1
The performance factor must be at least equal to or greater than the
demand factor:
N
L
≥ N
Demand 2
Only if the rated boiler heating output
²
K
or Φ
K
is higher or at least
equal to the continuous output can the DHW cylinder deliver the per-
formance factor N
L
stated by the manufacturer:
²
K
≥
²
D
or Φ
K
≥ Φ
D
Demand 3
Heat generating systems used for both DHW and central heating must
cover the additional output Z
K
for heating systems in buildings, as well
as the standard heat load Φ
HL buil.
calculated to EN 12831 (previously
DIN 4701):
Φ
K
≥ Φ
HL buil.
+ Z
K
On the basis of DIN 4708-2, VDI 3815 is used for calculating a sup-
plement to the rated boiler heating output as a function of the demand
factor N and a minimum cylinder capacity (see table 6).
It has proved successful in practice to take the boiler supplement into
account according to the following relations:
Φ
K
≥ Φ
HL buil.
· ϕ + Z
K
ϕ = Factor for the capacity utilisation of the building heating system (all
rooms heated)
Number of residential units per building ϕ
up to 20 1
21 to 50 0.9
> 50 0.8
Table 6 – Boiler supplement Z
K
Demand factor N Boiler supplement Z
K
in kW
1 3.1
2 4.7
3 6.2
4 7.7
5 8.9
6 10.2
7 11.4
8 12.6
9 13.8
10 15.1
12 17.3
14 19.5
16 21.7
18 23.9
20 26.1
22 28.2
24 30.4
26 32.4
28 34.6
30 36.6
40 46.7
50 56.7
60 66.6
80 85.9
100 104.9
120 124.0
150 152.0
200 198.4
240 235.2
300 290.0
Note
In buildings with an extremely low heat load Φ
HL buil.
, a check must be
carried out to determine whether the output of the heat source, includ-
ing supplement Z
K
, is sufficient for the selected performance factor. It
may be necessary to select a larger DHW cylinder.
Sizing
(cont.)
16
VIESMANN
DHW heating
4
5414 646 GB
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