# How to dimension the filling vessel for a DualSun installation?

The filling vessel is only recommended for installations of more than 12 DualSun SPRING hybrid panels in a pressurized system.

The filling vessel is used to store heat transfer fluid during hydraulic commissioning and to improve the filling quality of the system.

After numerous tests, the DualSun engineering team has defined the following calculation formula to determine the volume of the tank to be connected to a system equipped with DualSun SPRING panels.

Panels in portrait mode
Vvessel = [Vexpansion_fluid + (Number_SPRING_panels x 0,33)] / Acceptance_factot

Panels in landscape mode
Vvessel = [Vexpansion_fluid + (Number_SPRING_panels x 0,93)] / Acceptance_factor

Vvessel = Total volume of vessel in Liters [L]
Number_SPRING_pannels = Total number of SPRING panels connected to the installation

The choice of vessel volume must be rounded to the superior standard vessel volume

• Vexpansion_fluid = Vinstallation x Cexpansion_fluid
• Vinstallation = Total volume of installation
Vinstallation = Transfer lines volume + Panels volume + Heat exchanger volume

• Cexpansion_fluid = Expansion coefficient of heat transfer fluid

 Expansion coefficient of heat transfer fluid  (%) Glycol content (%) Temperature (°C) -20 -10 0 10 20 30 40 50 60 70 80 90 0 0 0,1 0,2 0,4 0,8 1,2 1,7 2,3 2,9 3,6 10 0,1 0,3 0,5 0,7 1,1 1,5 2 2,6 3,2 3,9 20 0,2 0,5 0,8 1,1 1,4 1,8 2,3 2,9 3,5 4,2 30 0,1 0,4 0,7 1 1,3 1,6 2,1 2,6 3,1 3,8 4,4 40 0,4 0,7 1 1,3 1,5 1,7 2,1 2,5 3 3,6 4,2 4,9 50 0,6 0,9 1,2 1,5 1,8 2 2,4 2,8 3,3 3,9 4,5 5,2

• Acceptance_factor = [(Pfilling + 1) - (Pvessel_inflation + 1)] / (Pfilling + 1)
• Pfilling = Hydraulic commissioning pressure of the installation at the level of the solar station
Pfilling = 1,5 + H/10 [bar]

• Pvessel_inflation = Inflation pressure of the filling vessel before hydraulic filling of the installation
Pvessel_inflation = 0,1 + H/10 [bar]

H = Height of the installation in meters [m] (distance between filling vessel and panels)