Viessmann Vitocell 300-H Technical Manual page 25

Sizing
(cont.)
Conversion of continuous output from l/h to kW
= Continuous output in kW
or Φ
²
req. req.
= Continuous output in l/h
µ
WW
c = Spec. thermal capacity
1 kWh
860 l · K
ΔT = Temperature differential between DHW outlet
WW
temperature and cold water inlet temperature in
K
= µ
or Φ · c · ΔT
²
req. req. DHW
The number of DHW cylinders required and their required size can
be determined using the diagrams for the continuous output of the
DHW cylinders concerned.
Example:
Required continuous output
Heating water flow temperature
Heating water return temperature = 60 °C
Heating water temperature differ-
ential
Cold water inlet temperature
DHW outlet temperature
A vertical DHW cylinder has to be used on account of the structural
characteristics of the building.
Conversion of continuous output from l/h to kW
or Φ = · c · ΔT
² µ
req. req. WW WW
1
= 1700 · · (45 – 10)
860
= 69 kW
Calculating the continuous output of the various cylinder sizes
As the method of calculation is the same for all cylinder sizes, the
process for calculating the continuous output of the Vitocell 300-V
DHW cylinder with 300 l capacity is shown as an example.
From point 1 (20 K) via point 2 (required DHW heating from
10 °C to 45 °C at heating water flow temperature 80 °C) read at
point 3: Continuous output of the DHW cylinder 37.5 kW
DHW heating
DHW
= 1700 l/h
= 80 °C
= 80 °C – 60 °C = 20 K
= 10 °C
= 45 °C
70
65
60
55
90
50
45
40
80
2
35
3
30 70
60
25
45
45
20
60
15
45
10
5
1
0 0
0 5 10 15 20 25
Heating water temperature differential (ΔT)
in K
Calculating the required number of DHW cylinders of a given
size
n = Required number of DHW cylinders
= Required continuous output in kW
or Φ
²
req. req.
= Continuous output of the selected DHW cylinders
or Φ
²
cyl cyl
in kW
Q Φ
req. req.
n = =
Φ
²
cyl. cyl.
69 kW
= = 1.84
37.5 kW
Required number of DHW cylinders = 2
45
60
45
60
30 35 40 45
VIESMANN
4
25