Expansion Vessel Sizing according to EN 12828
Polysun offers an assistant for the quick and standard-compliant design of membrane expansion vessels in accordance with EN 12828 in the context of solar thermal systems.
What is an expansion vessel, and why is it necessary for solar thermal systems?
An expansion vessel absorbs volume changes in the heat transfer medium (e.g. due to temperature fluctuations), thereby preventing pressure peaks. Without an expansion vessel, excess pressure could damage pipes, collectors or components.
How to proceed with Expansion Vessel Sizing in Polysun?
With Polysun, the design of the expansion vessel is carried out directly after a system simulation: First, the dialogue window for the solar circuit pump must be opened.
symbol for the design assistant (at the top of the window). The Expansion Vessel Sizing is only possible for solar circuits.Another dialogue box opens and asks for various user inputs.
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 for Membrane Expansion Vessel Sizing 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
Why is an expansion vessel necessary for solar thermal systems?
An expansion vessel absorbs volume changes in the heat transfer medium due to temperature fluctuations, preventing pressure peaks that could damage pipes, collectors, or other components in solar thermal systems.
How does Polysun assist with expansion vessel sizing?
Polysun’s design assistant guides users through sizing membrane expansion vessels per EN 12828. After system simulation, users input data in the solar circuit pump dialogue, import derived values, and view results in the professional report.