Sizing According To Peak Flow Rate With Reference To Din 1988-300; Application; Calculating The Dhw Demand - Viessmann Vitocell 300-H Technical Manual

Sizing
(cont.)

4.2 Sizing according to peak flow rate with reference to DIN 1988-300

Application

For DHW heating systems operating according to the instantaneous
water heater principle, e.g. freshwater modules, the DHW demand
can be determined according to the peak flow rate principle.
For this, the assumption is made that the peak flow rate to DIN
1988-300 determined for calculating the pipe dimensions for the
DHW pipework will also have to be heated by the DHW heating sys-
tem.
The peak flow rate is the sum of all connected individual consumers
(total flow rate), reduced by a simultaneity factor. This is subject to
the type of building.

Calculating the DHW demand

This is based on determining the peak flow rate ´
= a (Σ ´ ) b - c
´
S R
(Valid for ´ max. = 500 l/s)
R
= Peak flow rate
´
S
= Total flow rate (sum of calculation flow rate of all con-
´
R
sumers)
a, b, c = Constants subject to building and its type of use (see ta-
ble 11)
Table 11
4
Building type
Residential buildings
Hospital ward
Hotel
School
Administration building
Facility for supported living, retirement
home
Care home
describes the total flow rate of all consumers. The values of the
´
R
DHW calculation flow rate of individual consumers is added to this.
For details of the DHW calculation flow rate, see consumer manufac-
turers, e.g. tap manufacturer. If no details are available, use values
from DIN 1988-300:
Table 12 - Calculation flow rate for the connections on the cold
and warm water sides
Mixer taps for type of draw-off point
Shower tray
Bath
Kitchen sink
Washbasin
Bidet
Example:
Detached house with 2 bathrooms, 1 kitchen with kitchen sink, 1
guest toilet with washbasin.
Equipment, bathroom 1: Shower, washbasin
Equipment, bathroom 2: Bath, shower with body showers, 2 washba-
sins
VIESMANN
22
However, to avoid oversizing, the calculated peak flow rate must not
be higher than the sum of the two largest individual consumers that
may be operating simultaneously. For systems with several inde-
pendent consumers, e.g. in apartment buildings, also carry out this
check with the total flow rate of the respective largest consumer, e.g.
of all apartments.
Assumptions:
to DIN 1988-300.
S
A manufacturer datasheet is available for the shower with body
shower.
The calculated DHW flow rate is: 20 l/min = 0.33 l/s.
Standard values from Table 12 are used for the remaining consum-
ers.
The total flow rate of the detached house is:
´
R
Constants
To calculate the peak flow rate, factors a, b, c for a residential build-
a b c
ing are selected from Table 11:
1.48 0.19 0.94
0.75 0.44 0.18
a
0.70 0.48 0.13
b
0.91 0.31 0.38
c
0.91 0.31 0.38
1.48 0.19 0.94 Peak flow rate:
1.40 0.14 0.92
´
S
The calculated peak flow rate of 0.53 l/s is greater than the sum of
the two simultaneously operating consumers (shower in bathroom 1
= 0.15 l/s and shower with body shower in bathroom 2 = 0.33 l/s) =
0.48 l/s. Therefore, the value of 0.48 l/s is taken as the peak flow
rate.
The DHW heating system must heat 0.48 l/s = approx. 29 l/min of
DHW from 10 to 60 °C. This results in a transfer rate of approx.
DN Calculation
101 kW. Subject to the heating water temperature or heating water
flow rate ´
R
storage temperature in the heating water buffer cylinder (assump-
15 0.15 l/s
tion: 70 °C) select a Vitotrans 353 freshwater module from the data-
15 0.15 l/s
sheet.
15 0.07 l/s
Example: Vitotrans 353, type PZMA for installation on a
15 0.07 l/s
Vitocell 100-E buffer cylinder (see Table 13).
15 0.07 l/s
The values for Vitotrans 353, type PBMA (for wall mounting) are the
same as those for the Vitotrans 353, type PZMA (for installation on a
cylinder).
= Shower 0.15 l/s + washbasin 0.07 l/s + bath 0.15 l/s + show-
er with body shower 0.33 l/s + 2 washbasins 0.07 l/s + kitch-
en sink 0.07 l/s + washbasin 0.07 l/s
= 0.98 l/s
= 1.48
= 0.19
= 0.94
= a (Σ ´ b
) - c
R
= 1.48 x 0.98 0.19 – 0.94
= 0.53 l/s
DHW heating