Calculating the demand of residential units with centralised supply
systems
Project no:
Part no:
5 5.0 5 4.3 21.5 1 NB2 6510 6510 139965
(0.5) NB1 5820 5820 62565 50 % w
v
as
per Tab. 3
on page 15
Σ n
i
= 25
Σ (n · p · v · w
v
) = 676710 Wh
Σ(n · p · v · w
v
)
N =
3.5 · 5820
676710
20370
= = 33.2
Now use the calculated demand factor N = 33.2 to select the
required DHW cylinder from the tables in the relevant datasheets at
the available heating water flow temperature (e.g. 80 °C) and a cylin-
der storage temperature of 60 °C. Select a DHW cylinder with an N
L
factor at least equal to 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 the Vitocell 300-H datasheet:
Vitocell 300-H with 700 l capacity (N
L
= 35) as cylinder bank com-
prising 2 x Vitocell 300-H, each with 350 l capacity
■ From the Vitocell 300-V datasheet:
Vitocell 300-V with 600 l capacity (N
L
= 34.8) as cylinder bank
comprising 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 3 main demands for the rated heating output
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
performance 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
as well as the standard heat load
Φ
HL buil.
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 utilisation of building heating (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,
including supplement Z
K
, is sufficient for the selected performance
factor. It may be necessary to select a larger DHW cylinder.
Sizing
(cont.)
DHW heating
VIESMANN
17
5414646
4
To Next Page
Loading...
Need help?
General