Viessmann VITOCELL 100-W - Page 25

Conversion of continuous output from l/h to kW
²
req.
or Φ
req.
= Continuous output in kW
µ
WW
= Continuous output in l/h
c = Spec. thermal capacity
1 kWh
860 l · K
ΔT
WW
= Temperature differential between DHW outlet
temperature and cold water inlet temperature in
K
²
req.
or Φ
req.
=
µ
DHW
· c · ΔT
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 = 1700 l/h
Heating water flow temperature = 80 °C
Heating water return temperature = 60 °C
Heating water temperature differ-
ential
= 80 °C – 60 °C = 20 K
Cold water inlet temperature = 10 °C
DHW outlet temperature = 45 °C
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
²
req.
or Φ
req.
= µ
WW
· c · ΔT
WW
1
860
= 69 kW
= 1700 · · (45 – 10)
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
0 5 40 453025201510 35
Heating water temperature differential (ΔT)
in K
40
45
0
5
10
15
20
25
30
35
50
55
60
65
70
0
Continuous output in kW
45
50
45
60
60
45
45
60
70
80
90
5.0 m³/h
3.0 m³/h
2.0 m³/h
Heating water flow rate in m³/h
Pressure drop on heating water side
in mbar (kPa)
45
60
1
2
3
410 mbar (41 kPa)
125 mbar (12.5 kPa)
45 mbar (4.5 kPa)
10 mbar (1.0 kPa)
1.0 m³/h
Calculating the required number of DHW cylinders of a given
size
n = Required number of DHW cylinders
²
req.
or Φ
req.
= Required continuous output in kW
²
cyl
or Φ
cyl
= Continuous output of the selected DHW cylinders
in kW
Q
req.
²
cyl.
n = =
Φ
req.
Φ
cyl.
69 kW
37.5 kW
=
= 1.84
Required number of DHW cylinders = 2
Sizing
(cont.)
DHW heating
VIESMANN
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