Result
Preliminary calculation: This tool is for quick sizing and information. In real projects, load calculation, selection and commissioning require engineering calculations and a site survey. Results are approximate values.
Formulas
e = ρ(T_fill) / ρ(T_max) − 1V_tank = ( e × V_system + V_reserve ) / ( 1 − (p0 + 1) / (p_max + 1) )p0 is the tank pre-charge pressure and system static pressure; p_max is the safety valve opening pressure (bar-g). The reserve volume is taken as 3 liters or 0.5% of the system volume.
- Check the tank pre-charge pressure when the system is cold
- If glycol is used, the expansion ratio increases
- Selecting a tank that is too small causes the safety valve to open
- A membrane failure shows up as falling pressure and frequent water top-ups
Frequently asked questions
Why is an expansion tank necessary?
Water expands when heated. In a closed circuit, if there is no volume to take up this excess, pressure rises and the safety valve opens.
What changes in a glycol system?
A glycol mixture expands more; the tank volume must be increased accordingly.
How is the tank pre-charge pressure set?
With the system empty and the tank isolated from the water, the air side of the tank is set according to the static pressure of the system.