Sizing 4.1 Sizing According To Peak Draw-Off Rate And Din 4708-2; Calculating The Heat Demand For Dhw Heating In Residential Buildings - Viessmann Vitocell 100-H Technical Manual

Sizing
4.1 Sizing according to peak draw-off rate and DIN 4708-2
For residential buildings, the DHW demand is calculated based on the
demand factor N. The calculations are set out in DIN 4708-2 and
described below. Based on the demand factor N, a DHW cylinder with
a corresponding performance factor N
The performance factor N of a DHW cylinder can also be expressed
L
as the peak output over 10 minutes. Systems for DHW heating are
sized according to this "peak draw-off rate" if a specific volume of DHW
has to be provided for a short period of time, after which a longer period
of time is available to reheat the cylinder again. This may occur, e.g.
in commercial enterprises or schools (intermittent operation). The 10-
minute peak output is determined almost exclusively by the volume of
water stored (cylinder capacity).

Calculating the heat demand for DHW heating in residential buildings

This calculation is based on DIN 4708 (central DHW heating systems)
Part 2.
DIN 4708 is the basis for the standard calculation of the heat demand
for central DHW heating systems in residential buildings.
For the purposes of calculating the heat demand, a standard residen-
tial unit is defined as follows:
The standard residential unit is a dwelling based on statistical values,
for which the demand factor N = 1 is as follows:
■ Room factor r = 4 rooms
■ Occupancy factor p = 3.5 people
■ Draw-off demand w = 5820 Wh/draw-off volume for a bath
v
The following information is required to calculate the demand
a) All sanitary equipment on all floors (from building design drawings
or details supplied by architect or client)
b) Number of occupied rooms (room factor) excluding ancillary
rooms, such as kitchen, entrance, hall, bathroom and storage area
(from building design drawings or details supplied by architect or
client)
c) Number of people per residential unit (occupancy factor).
If the number of occupants for each residential unit cannot be
ascertained, a statistical occupancy factor p can be calculated on
the basis of the room factor r for the residential unit concerned
using table 1.
Calculating the occupancy factor p
If the number of people per residential unit cannot be ascertained, this
table can be used to calculate the occupancy factor p.
Table 2 – Accommodation with standard equipment level
Existing amenities per residential unit
Room Equipment
Bathroom 1 bath 140 l (according to table 4, no. 1, on page 14)
or
1 shower cubicle with/without mixer tap and standard shower
head
1 washbasin
Kitchen 1 kitchen sink
*3 If the residential building concerned mainly comprises residential units with 1 and/or 2 main rooms, increase the occupancy factor p by a
factor of 0.5.
DHW heating
is then selected (N ≥ N).
L L
Calculation program EDIS/DIN 4708-2
DHW cylinders can also be sized with the aid of the EDIS calculation
program. The program sizes DHW cylinders on the basis of
DIN 4708 for residential units and includes various calculation pro-
cesses for hotels, catering businesses, hospitals, residential homes,
campsites, sports halls, etc.
You can obtain the Viessmann "EDIS" calculation program by con-
tacting one of our sales offices.
The performance factor N and the maximum continuous output of the
L
DHW cylinders is given in the tables from page 9. The detailed spec-
ification and performance parameters, including the continuous output
diagrams can be found in the datasheet for the relevant DHW cylin-
der.
Table 1
Room factor r Occupancy factor p
1.0
2.0
1.5
2.0
2.0
2.0
2.5 2.3
3.0 2.7
3.5 3.1
4.0 3.5
4.5 3.9
5.0 4.3
5.5 4.6
6.0 5.0
6.5 5.4
7.0 5.6
Establishing the number of draw-off points to be taken into
account when calculating the demand
The number of draw-off points must be taken into account when cal-
culating the overall demand. This varies according to the specifications
of the residential unit (basic or deluxe) and can be derived from tables
2 or 3.
To be taken into account for calculating the demand
1 bath 140 l (according to table 4, no. 1, on page 14)
Not taken into account
Not taken into account
*3
*3
*3
VIESMANN
4
13