12
7.2
Calculation method for the expansion vessel volume
The volume for a closed diaphragm (membrane) expansion vessel for heating
system installation is calculated as follows:
where:
V = vessel's volume (l);
e = water expansion ratio. Calculated based on the maximum difference between the
water temperature when idle and the maximum working temperature.
Typically, for a
heating system, the standard value of 0,035 should be used
;
C = the total water contents of the installation (l);
Pi= initial absolute pressure (bar), at the vessel installation height, represented by the
hydrostatic pressure + 0,3 bar + atmospheric pressure (1 bar). Typically, this is the
pre-charge pressure of the vessel plus 1 bar;
Pf= final absolute pressure (bar) represented by the maximum working pressure of
the installation + atmospheric pressure (1 bar). Typically, this is the safety valve
setting plus 1 bar.
Table 2
– Water expansion rates
The expansion vessel should be sized for a heating system installation with the
following characteristics:
C =water content = 600 l
Phid = hydrostatic pressure at the installation location = 1 bar
Pseg= safety valve pressure setting = 3 bar
