Sizing According To Peak Flow Rate With Reference To Din 1988-300 - Viessmann Vitocell 100-H Technical Manual

Sizing
(cont.)
Example:
Heat load of the building
or Φ :
²
NW HL buil. W
DHW demand factor N:
Heating water flow/return tempera-
ture
– in winter:
– in summer:
Selected DHW cylinder:
1. Calculating the required district heating water volume
= District heating water volume in winter in l/h
µ
W
or Φ = Connected load in winter in kW
²
NW HL buil. W
c = Spec. thermal capacity
1 kWh
860 l · K
ΔT = Temperature differential in winter between district
W
heating water flow and return temperature in K
²
NW
=
µ
W
c · ΔT
W
Φ
HL buil. W
=
c · ΔT
W
860 · 20
=
4
110 – 50
= 287 l/h
Table 10 – Performance data with return temperature limit
Vitocell 100-V on request.
Vitocell 300-V (type EVI)
Cylinder capacity
Continuous output at
Heating water flow and return temperature 65/40 ºC and
DHW heating from 10 to 45 ºC
Performance factor N
L
at a heating water flow and return temperature 65/40 ºC and
DHW storage temperature T
10-minute peak output
Note
The performance data for DHW cylinders when there is a return tem-
perature limit can be found in the continuous output diagrams in the
relevant datasheets.
Note: When return temperatures are restricted, a check must be car-
ried out to determine whether the hygiene requirements in accordance
with TRWI/DVGW are met. A transfer pump may have to be provi-
ded.

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

For DHW heating systems operating according to the instantaneous
water heater principle, such as 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 system.
The peak flow rate is the sum of all connected individual consumers
(total flow rate), reduced by a simultaneity facto. This is subject to the
type of building.
With return temperature limit.
*15
VIESMANN
20
20 kW
1.3
110/50 ºC
65/40 ºC
1 Vitocell 300-V
(type EVI), 200 l capacity with
N = 1.4
L
*15
= 50 °ºC
cyl
2. Calculating the connected load in summer with a constant dis-
trict heating water volume (µ
= District heating water volume in summer in l/h
µ
S
o Φ = Connected load in summer in kW
²
NS HL buil. S
ΔT = Temperature differential in summer between the
S
district heating water flow and return temperature in
K
= Φ =
²
NS HL buil. S
with (
= 287 ·
= 8.33 kW
l 200
kW 15
l/h 375
1.4
l 164
However, to avoid oversizing, ensure that the calculated peak flow rate
is not higher than the sum of the two largest individual consumers that
may be operating simultaneously. For systems with several independ-
ent consumers, e.g. in apartment buildings, this check will also have
to be carried out with the total flow rate of the respective largest con-
sumer, e.g. of all apartments.
= µ )
S W
· c · ΔT
µ
S S
= )
µ µ
S W
1
· (65 – 40)
860
300
16
393
3.0
230
500
19
467
6.0
319
DHW heating