Heating expansion vessel calculator: inputs, result and limits
Which inputs are required?
VSystem is the complete water content of pipes, heat emitters, generators, and auxiliary circuits. Water densities correspond to the lowest and highest system temperatures; obtain verified fluid data when additives are present. p0 is minimum operating and gas pre-charge pressure, pfin the highest operating pressure; both are gauge pressures at the vessel connection. Selected nominal volume comes from a specific product.
What is returned?
Results include expansion coefficient e, expansion volume Vex, minimum water reserve, minimum nominal volume VN,min, and selected-size margin. Initial pressure pini is calculated to equation (D.6) and checked against the minimum p0 + 0.3 bar.
Method and interpretation
EN 12828 Annex D uses e = 1−ρmax/ρmin and Vex = VSystem·e. For VN ≤ 15 l, minimum water reserve is 20% of the vessel; above 15 l it is max(0.5% of VSystem, 3 l). VN,min = (Vex+Vwr,min)·(pfin+1)/(pfin−p0). The +1 terms approximately convert gauge to absolute bar.
Calculator limits
Annex D is informative. Separately verify the safety valve, pressure limiter, static and dynamic pressure differences, cavitation, membrane temperature, materials, water treatment, and manufacturer approval. Do not use pure-water densities for glycol or inhibited mixtures.
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Source: Locally held DIN EN 12828:2014-07, informative Annex D.1 and D.2, equations (D.1), (D.2), (D.4), (D.6), and (D.7).