Viessmann VITOCAL 160-A - Page 31

Whereby:
V
N
= Rated volume of the diaphragm expansion vessel in
litres
V
V
= Safety water seal (here heat transfer medium) in litres
V
V
= V
A
· 0.005 in litres (min. 3 litres)
V
A
= Liquid content of the entire system
V
2
= Increase in volume during system heat-up
V
2
= V
A
· β
β = Expansion factor (β = 0.13 for Viessmann heat
transfer medium from –20 to 120 °C)
p
e
= Permissible final pressure in bar (ü)
p
e
= p
si
– 0.1 · p
si
p
si
= Safety valve blow-off pressure
p
st
= Nitrogen pre-charge pressure of expansion vessel in bar
(ü)
p
st
= 1 bar + 0.1 bar/m · h [m]
h = Height differential between the Vitocal 160-A
and the highest point of the solar thermal sys-
tem
z = Number of collectors
V
k
= Collector capacity in litres
Example:
System comprising:
1 Vitosol 200 type 5DI with 4.2 l capacity
Total liquid content of the system:
V
A
= 22 litres
Static head: h = 4 m
Permissible final pressure: pe = 5.4 bar (ü)
(Safety valve blow-off pressure: 6 bar)
p - p
e
(p + 1)(V + V + z · V )
V =
N
v 2 k
·
e st
V = V · 0.005
v A
= 0.11 litres, selected 3 litres
V = V · β
2 A
= 2.86 litres
p = 1 bar + 0.1 · 4
st
5.4 - 1.4
(5.4 + 1)(3 + 2.86 + 1 · 4.2)
V =
N
·
= 16.1 litres
= 1.4 bar
Due to the risk of vapour also being created in the solar circuit pipe-
work, we recommend the multiplication of the calculated value for V
N
by a safety factor of 1.5.
In this case, 24.15 litres would result.
Select the next largest expansion vessel (25 l).
Sizing
(cont.)
VITOCAL 160-A
VIESMANN
31
5822 485 GB
7