What is the FC value? Influence on solar shading & energy efficiency

The FC value helps to objectively assess the effectiveness of solar shading systems. It describes how much the solar heat input through window surfaces is reduced with the help of solar shading systems. The FC value is therefore crucial when it comes to protecting interiors from overheating. With shading systems such as Roller Shutters, External Venetian Blinds or Textile Screens, which have a particularly low FC value, energy efficiency can be optimized and a pleasant indoor climate created.

Let our ROMA specialist partners advise you on suitable sun shading systems.

The FC value - also known as the reduction factor - is a parameter for evaluating thermal insulation in summer. It shows how much the total energy transmittance (g-value) of a glazing is reduced by additional shading.

This means that it indicates how efficient solar shading systems are in reducing the solar heat from sunlight in the interior. The value is always in the range between zero and one, whereby the lower the FC value, the more effective the solar shading.

Two values are relevant for calculating the FC value of solar shading systems. One is the total energy transmittance (gtot) of the existing combination of solar shading and glazing, and the other is the pure g-value of the glazing. The reduction factor is calculated from the ratio of these two values.

This results in the simple FC value formula: FC value = gtot / g.

A low FC value means that only a small amount of heat enters the room through the glazing and solar shading. This prevents rooms from heating up unhindered in the warm summer months. This in turn means that no energy has to be used for subsequent cooling, which increases energy efficiency . In addition to energy savings in air conditioning, a low FC value also improves living comfort, as rooms remain at a pleasant temperature at all times.

As the FC value is determined by the energy transmittance of solar shading and glazing, the transmittance values of both components are relevant. High-quality solar control glazing with low g-values already improves thermal insulation without additional elements.

However, it should be borne in mind that a low g-value of the glazing can result in too little heat entering the building interior in winter, which increases heating costs. It is therefore essential that the g-value of windows is adapted to the climate zone of the building location. With efficient solar shading systems, a low FC value can be achieved even with a high g-value of the glazing, so that optimum thermal efficiency is ensured in summer and winter.

New buildings must meet certain minimum requirements for thermal insulation. This includes proof of thermal insulation in summer in accordance with DIN 4108-2. This mandatory proof is intended to ensure that the energy efficiency of buildings is already considered and optimized during the planning stage.

Efficient, external solar shading with a low FC value not only makes technical sense, but can also be financially attractive. BAFA funding is available as part of the federal subsidy for efficient buildings. ROMA provides you with a free subsidy assistant, which you can use to check quickly and easily whether your project is eligible for funding.

The FC value is determined by the glazing and the solar shading. However, the values of different blinds can vary greatly. This is due to different materials and the position of the solar shading - either internal or external.

External systems in particular are effective in reducing the heat input in the long term, as they stop the sun's rays before they reach the glazing. However, the values of external systems also differ greatly from one another:

The values show that external systems - Roller Shutters, External Venetian Blinds and Textile Screens - achieve a significantly lower FC value than internal roller blinds. This means that they can intercept a greater proportion of solar radiation, contribute more effectively to solar shading and increase energy efficiency.

A sound understanding of the FC value helps to find the right solar shading solution for every project. External sun shading systems offer clear advantages in terms of thermal insulation and energy efficiency. Systems such as Roller Shutters, External Venetian Blinds and Textile Screens from ROMA are ideal for improving sun protection all year round.

ROMA specialist partners can advise you on all questions relating to the selection, planning and installation of the most efficient sun shading possible.