# What should be the diameter of the hydraulic lines between the DualSun panels and the technical room?

The choice of the diameter of the hydraulic lines between the DualSun panels and the technical room directly influences the hydraulic pressure drops.

We have defined charts for the different possible applications with DualSun Spring panels: flow rates per application are recommended to optimize heat exchange.

**1 - Individual Solar Water Heating Application (ISWH)**

The nominal flow rate is 32 L / h / panel, and we recommend to install multilayer pipes for their ease of implementation.

**2 - Individual Solar Water Heateing Application (ISWH) with Thermal Discharge**

The nominal flow rate is 100 L / h / panel, and we recommend to install multilayer pipes for their ease of implementation.

**3 - Direct solar pool heating application (without heat exchanger)**

The nominal flow rate is 200 L / h / panel and the pipes must be PVC pressure.

What piping is recommended between the solar panels and the hot water tank?

**Pressure drop theory:**

The formula for calculating linear pressure drops in a straight pipe is written as follows:

With:

Δp = Linear pressure loss in Pa

∧ = Pressure loss coefficient (value without dimension)

⍴ = Fluid density in kg/m3

V = Flow velocity in m/s

D = Internal diameter of hydraulic line in m

L = Length of hydraulic line in m

Thus the pressure losses are :

- linearly proportional to the length of the pipes
- inversely proportional to the pipe diameter
- proportional to the square of the fluid flow velocity

As the flow rate is calculated to optimise the heat exchange between the solar panels and the solar storage tank, to limit the pressure losses in the hydraulic lines it is then necessary to :

- bring the solar panels as close as possible to the technical room
- choose a sufficient pipe diameter

On the other hand, the viscosity of the fluid and its flow rate determine the pressure drop coefficient, as shown in the Moody diagram below:

Source: Wikipedia

The average roughness of the multilayer tube is 0.006 mm.

Its relative roughness varies between 1.4.10-4 and 5.10-4

The average roughness of the PVC pressure pipe is 0.0015 mm.

Its relative roughness varies between 2.3.10-5 and 4.4.10-5.

With the pipe diameters calculated in the charts above, the Reynolds number varies between 5000 and 60,000.

The average pressure drop coefficient to be used in the calculations, based on relative roughness and Reynolds number, is 0.025.