Sun and solar protection

Definition and explication


Objects covered in large glass surfaces are one of key features of modern day architectural design. Glass surfaces allow maximum usage of natural light, and that is one of the reasons why they easily and naturally blend in with the surrounding landscapes. Despite their attractive and modern looks, these objects have their downsides, mainly because of the huge amount of sunlight and solar radiation penetrating the facilities.


Normally glazed surfaces without protection leak 88% of sunlight, 80% of which penetrates directly into the interior of the building.

The solar radiation, which has a certain wavelength, passes through the glass, after which the walls and room furniture absorb it and convert that energy into a long heat wave.

These waves (the heat) can not pass through the glass and so they remain inside. It is this phenomenon that causes the "greenhouse effect," causing heat build up in the premises and increasement in the temperature.

Unless the outside temperature falls below the temperature inside the building, the accumulated heat remains inside and it cannot be lowered simply by ventilation or air circulation. With all of this, double or triple glazed windows transmit internal heat to the outside even more slowly.

For example, in buildings with 50 or more and percent of single glazed window surfaces and in the case the windows are closed and exposed to the sun, the temperature of the interior can be 10 to 15% higher than the outside temperature. That means that when the outside temperature is 25°C, the room temperature can be 35°C or 40°C.

Significant amounts of energy can be saved by using fiberglass screen shades.


The size of glass surfaces on buildings is an important factor that affects power consumption. Air-conditioners and other cooling devices are neccessary for maintaining pleasant temperatures in the premises, especially during summer months. But in order to achieve a comfortable temperature without a cooling device, it is necessary to use external blinds that can provide quality protection and are easy to maintain.


Studies conducted by CEBRT have shown that, with the use of MERMET Sunscreen protective curtains, the maximum room temperature in different building types can be reduced by 6°C. The experiment lasted for three ordinary, sunny days in France. The difference between the high and medium thermal inertia (isolation) of the room was minimal.


In rooms where air temperature was maintained at a level of 25°C with air-conditioners, it has been shown how much electricity can be saved by using the MERMET sunscreen protective fabric:


• for a room with high inertia, with protective fabrics installed on the outside of the glass surfaces, the cooling devices must have a maximum power of 2000 W, while in a room without protective curtains the devices should have a power of 3800 W;
• for a medium inertia room, the following values can be compared: 2000 W with, and 4100 W without protective curtains.


In both examples, the installation of external protective covers reduced power consumption by 62% (15 kWh per day).

Outside shades are a necessity and an important piece of modern architecture. They contribute to a buildings look, its living comfort, and they are significant energy savers.


A large selection of MERMET protective shades provides a perfect protection against strong sunlight and other unplesant factors such as rain, wind, hail, dust and insects.

Besides from thermal protection, MERMET shades are translucent – you see through them but at the same time but protect you from the prying eyes from the outside.

By filtering the natural light they protect you from the sun's glare. The effectiveness of the curtain is based on the sun's factor Fs and the coefficient of shading Sc.


The sun's factor is the part of the energy that passes through the glass:

  1. Sun’s rays that hit the glass window (100%)
  2. Reflection/reflected sun's rays energy
  3. Absorbed energy inside the glass exiting towards the outside.
  4. Solar energy penetrating the interior.
  5. Absorbed energy inside the glass penetrating the interior.

Fs = Total amount of energy passing through the glass / Total amount of energy hitting the glass

Coefficient of shading is the ratio between the sun's factor, in the case of a protected glass (glass + curtain) and sunlight, in the case of unshaded glass.

Sc= Fs (glass + curtain) / Fs (glass)

Sun protection factor (SPF) is the procentage of solar radiation reflected by the fiberglass screen.


PS= (1 – Sc)
The values by which the effectiveness of the shades is determined must be given in precise measures for a particular type of glass and only in the case of closed windows. These values are also conditioned by other favorable and unfavorable factors.

In addition to the thickness and nature of the glass, other things that must be taken into account are the position and direction of the facade, the difference in the outside and the inside temperature and the gap between the shades and the window.

The following diagram is based on CEBTP studies, and it shows the effectiveness of MERMET Sunscreen window blinds on single and double glazed windows.

Chart 3 shows that 82% of the solar radiation is reflected (80% for single glazed windows). Only 14% of total solar energy and radiation coming through windows penetrates the interior ( 18% in the case with ordinary, one glass windows). When used from the inside, the sun's factor is reduced by 64%.