Σ(n · p · v · w
v
)
N =
3.5 · 5820
Σ(n · p · v · w
v
)
20370
=
n = Number of similar residential units
p = Occupancy factor per similar residential unit
v = Number of similar draw-off points per similar residential unit
w
v
= Draw-off demand in Wh
(n · p · v · w
v
) must be calculated for each relevant draw-off point per
similar residential unit.
Now use the calculated demand factor N to select the required DHW
cylinder at the appropriate heating water flow temperature from the
tables on pages 8 and 11. Select a DHW cylinder with an N
L
factor at
least equal to N.
The demand factor N is identical to the number of standard residen-
tial units in the building project.
It does not necessarily correspond to the actual number of residen-
tial units.
Example:
For a residential building project, design the DHW system on the
basis of demand factor N.
The numbers of similar residential units, the room factor and the
equipment level listed in table 5 have been taken from the building
plans.
The occupancy factor p was determined using the room factor r and
table 1 on page 14.
The number of draw-off points to be used in the design was calcula-
ted using table 2 on page 14 and table 3 on page 15.
Table 5
No. of residen-
tial units
Room factor Occupancy
factor
Amenities in the residential unit Apply for the demand calculation
n r p Number, description No. of draw-off points, description
4 1.5 2.0 1 shower cubicle with standard shower
head
1 washbasin in the bathroom
1 sink in the kitchen
As per table 2 on page 14
1 shower cubicle (BRN)
10 3 2.7 1 bath 140 l
1 washbasin in the bathroom
1 sink in the kitchen
As per table 2 on page 14
1 bath (NB1)
2 4 3.5 1 shower cubicle with mixer tap and de-
luxe shower head
1 shower cubicle with standard shower
head (in a physically separate location)
1 washbasin in the bathroom
1 sink in the kitchen
As per table 3 on page 15
1 shower cubicle (BRL)
4 4 3.5 1 bath 160 l
1 shower cubicle with deluxe shower
head in a separate room
1 washbasin in the bathroom
1 bidet
1 sink in the kitchen
As per table 3 on page 15
1 bath (NB2)
1 shower cubicle (BRL)
5 5 4.3 1 bath 160 l
1 washbasin in the bathroom
1 bidet
1 bath 140 l, in the guest room
1 washbasin in the guest room
1 sink in the kitchen
As per table 3 on page 15
1 bath (NB2)
1 bath (NB1) with 50 % of the draw-off
demand w
v
1 washbasin (WT)
1 bidet (BD)
Form for calculating the heat demand for DHW heating in residential buildings
Calculating the demand of residential units with centralised supply
systems
Project no:
Part no:
Calculating the demand factor N for determining the required DHW cylinder size
Project
Occupancy factor p based on statistical values as per table 5, page 16
1 2 3 4 5 6 7 8 9 10 11
Sequential
number of
residential
unit
groups
Room fac-
tor
No. of resi-
dential
units
Occupancy
factor
No. of draw-off points to consider
(per residential unit)
Comments
r n p n · p No. of
draw-off
points
v
Short
code
Draw-off
demand
w
v
in Wh
v · w
v
in Wh
n · p · v · w
v
in Wh
1 1.5 4 2.0 8.0 1 NB1 5820 5820 46560 NB1 for
BRN
2 3.0 10 2.7 27.0 1 NB1 5820 5820 157140
3 4.0 2 3.5 7.0 1 BRL 7320 7320 51240
1 BRN 3660 3660 25620
4 4.0 4 3.5 4.0 1 NB2 6510 6510 91140
1 BRL 7320 7320 102480
Sizing
(cont.)
16
VIESMANN
DHW heating
4
5414646
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