Design and function of the expansion vessel
A
Heat transfer medium
B
Nitrogen filling
C
Nitrogen buffer
D
Safety water seal (min. 3 l)
E
Safety water seal
F
Delivered condition (3 bar pre-charge pressure)
G
Solar thermal system filled, without heat influence
H
Under maximum pressure with the highest heat transfer medium
temperature
The expansion vessel consists of a space containing liquid (heat trans-
fer medium) and a space containing gas (nitrogen filling), which are
separated from each other by a diaphragm. The appropriate pre-
charge pressure depends on the system head.
Note
Adjust the pre-charge pressure as follows: 1 bar + 0.1 bar/m × static
head in m (cold fill). The system fill level must be 0.3 to 0.5 bar higher
than the pre-charge pressure of the expansion vessel. The safety
water seal should be 0.005 x liquid content of the complete system,
but no less than 3 litres.
To safely prevent steam being created during the operating phase,
collectors in their cold state must be under at least 1 bar pressure. The
pre-charge pressure of the expansion vessel will then be 0.1 x higher
than static head h. In hot conditions, the system pressure rises by
approx. 1 to 2 bar.
Max. idle temperatures of the collectors
Vitosol 200-F, type SV2/SH2 221ºC
Vitosol 200-F, type 5DI 185ºC
Vitosol 200-T 300ºC
Vitosol 300-T 273ºC
The expansion vessel must be sufficiently large to accommodate the
collector content when steam forms (stagnation), to ensure that no
heat transfer medium can escape through the safety valve.
Specification of the expansion vessel
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