In closed hydronic systems expansion vessels must be placed in order to be able to cope with varying pressure and volume levels. Liquids are quasi incompressible fluids and volume changes of the system strongly affect the pressure levels.
It is important to adequately design the expansion vessels in order to avoid to air infiltration or to avoid too high pressure levels in the system.
Practically, in the Hysopt software, the expansion vessel blocks are also used to adapt the type of fluid used in the system. (e.g. glycol or ethanol mixtures)
Changing the Fluid type
The fluid type can be changed by pressing the Brine scroll down button. The mixture composition can be changed by the mixure pecentage setting. (E.g: 30% Mixture correlates to a mixture of 30% ethanol and 70% water). It is important to change your fluid type because brine mixtures have other heat transfer properties and will behave differently compared to pure water.
System volume
The system volume is equal to the sum of the pipe volumes in the hydronic system. Make sure to add the correct pipe lengths and diameters.
Based on the system volume, the expansion vessel design volume is calculated.