Technical manual
Page 33 of 72
ST0133 – A 02/09
SOLAR
The expansion volume of the system Vep can be calculated using Equation 7.
β
⋅=
sysep
VV [7]
Where: V
ep
[l] system expansion volume
V
sys
[l] total system volume
β [-] heat transfer medium expansion coefficient (0.00085)
The pressure relief valve pressure p
rv
can as first approximation be used as 6 bar. How-
ever, to allow for some tolerance it is recommended to calculate the pressure relief
valve pressure p
rv
in accordance with Equation 8.
)1.01( −⋅=
oprv
pp [8]
Where: p
rv
[bar] relief valve pressure
p
op
[l] opening pressure of relief valve (6 bar)
The last parameter to be calculated for use in Equation 5 is the cold fill pressure p
pc
of
the system. The cold fill pressure p
pc
depends on the static height h
stat
of the solar
thermal system and the required pressure in the highest system point p
min
. The defini-
tion of the static height h
stat
is depicted in Figure 33.
Figure 33 – Definition of static height of solar system
The pressure in the highest system point p
min
should be between 1 and 1.5 bar. The
cold fill pressure p
pc
can therefore be calculated as shown in Equation 9.
stat
m
bar
pc
hpp ⋅+= 1.0
min
[9]
Where: p
pc
[bar] cold fill pressure
p
min
[bar] pressure in highest system point
h
stat
[m] static height of system
Equation 9 concludes the calculation of parameters required for Equation 4 to calculate
the expansion vessel volume V
EV
. To be able to commission the expansion vessel, the
membrane pre-charge pressure p
mp
has to be calculated as shown in Equation 10.
h
stat
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