Expansion Vessels
Polysun enables users to design membrane expansion vessels according to EN 12828.
It is assumed that a system simulation has been completed. Then open the “Solar loop pump” dialogue box and click on the design wizard icon 
(in the upper portion of the box). The tool is intended for solar loops only.
Now, a new dialogue box opens prompting the user to enter various information. Hoovering with the mouse over an input field, a help text is shown explaining the meaning of the relevant entry. All values shown as “derived values” are directly imported from the Polysun simulation and are essentially based on pipe size, collectors and controller settings. All derived values must be checked for plausibility.
Click on the “Import” button to import all modified values. All changes in the “Solar loop pump” dialogue box must be confirmed by pressing “OK”. Now, you can make other changes and start the simulation. The dimensioning of membrane expansion vessels does not affect the simulation and its results. The values calculated for the membrane expansion vessel are, then, displayed in the professional report under the section dedicated to the relevant pump.
Calculation Basis for Membrane Expansion Vessels in Polysun
Minimum operating pressure (p0): \(p_{0} = p_{st} + d_{pp} + d_{p}\)
Final pressure (pe): \(p_{e} = p_{SV} – 0.5bar\) for pSV ≤ 5 bar
\(p_{e} = p_{SV} – 0.1bar\) for pSV > 5 bar
Nominal capacity (Vn): \(V_{n} = \left( V_{e} + V_{V} + V_{k} \right)*\frac{p_{e} + 1}{p_{e} – p_{0}}\)
where:
Collector capacity (Vk): Calculation through Polysun
Expansion volume (Ve): \(V_{e} = \frac{n}{100}*V_{A}\) where:
Degree of expansion (\(n\)): depending on the fluid in the loop
System volume (VA): \(V_{A} = \sum_{}^{}{Kollektorvolumen,\ Rohrleitungen\ etc.}\) \(V_{A} = \sum_{}^{}{Kollektorvolumen,Rohrleitungenetc.}\) \(V_{A} = \sum_{}^{}{collector\ volume,\ pipes,\ etc}\).
Water header (VV): \(V_{V} = 0.005*V_{A}\) for Vn > 15 l with VV ≥ 3 l
\(V_{V} = 0.2*V_{A}\) for Vn ≤ 15 l