# How does the temperature gradient of the SPRING panel change according to outdoor conditions?

As with all thermal solar panels, the thermal behavior of our DualSun SPRING panels varies according to several parameters.

 In order to analyse in more detail the parameters that influence the thermal behaviour (DT) of a solar panel, let's recall the calculation formula: DT = [2.G.A.a0/(2.⍴.Q.Cp+a1.A)]-[2.A.a1/(2.⍴.Q.Cp+a1.A)].(Tin-Ta)

• DT = Tout-Tin = Heat input to the fluid by the solar panel [°C]
• a0 = Panel optical efficiency [%]
• a1 = Loss coefficient [W/K/m²]
• A = Panel area [m²]
• G = Solar irradiation [W/m²]
• = Volumic mass of fluid [kg/m3]
• Q = flow rate [m3 /s]
• Cp = Calorific capacity of the fluid [kJ/K/kg]
• Tout = Panel outlet temperature [°C]
• Tin = Panel inlet temperature [°C]
• Ta = Ambient air temperature [°C]

The panel data a0, a1 and A are available in the data sheets accessible in the online documentation area.

These values come from the EN 9806:2017 certification tests for unglazed solar collectors carried out with a wind speed u = 1 m/s.

You can also find the above details in the installation manual of the DualSun SPRING panel.

## Thermal behaviour curves

As a function of the water temperature at the panel inlet and the ambient air temperature at various flow rates.

### SPRING INSULATED - ISWH with variable speed circulator

Fluid: 40% Glycolated water (Cp = 3800 J/K/kg - ⍴ = 1000 kg/m​​3​​)

 Panel temperature gradient as a function of (Tin-Ta) for a flow rate of 30 L/h/panel

### SPRING INSULATED - ISWH / CSWH / Technical water storage

Fluid: 40% Glycolated water (Cp = 3800 J/K/kg - ⍴ = 1000 kg/m​​3​​)

 Panel temperature gradient as a function of (Tin-Ta) for a flow rate of 60 L/h/panel

### SPRING INSULATED - ISWH with pool discharge / Swimming pool heating Pressurized

Fluid: 40% Glycolated water (Cp = 3800 J/K/kg - ⍴ = 1000 kg/m​​3​​)

 Panel temperature gradient as a function of (Tin-Ta) for a flow rate of 100 L/h/panel

### SPRING NON-INSULATED - Swimming pool heating Pressurized / Heat pump

Fluid: 40% Glycolated water (Cp = 3800 J/K/kg - ⍴ = 1000 kg/m​​3​​)

 Panel temperature gradient as a function of (Tin-Ta) for a flow rate of 100 L/h/panel

### SPRING NON-INSULATED - Heat pump

Fluid: 40% Glycolated water (Cp = 3800 J/K/kg - ⍴ = 1000 kg/m​​3​​)

 Panel temperature gradient as a function of (Tin-Ta) for a flow rate of 200 L/h/panel

### SPRING NON-INSULATED - Swimming pool heating - Direct

Fluid: Water (Cp = 4180 J/K/kg - ⍴ = 1000 kg/m​​3​​)

 Panel temperature gradient as a function of (Tin-Ta) for a flow rate of 200 L/h/panel