According to the experts, we lose up to 25% of the heat from our houses through the windows. Even the most energy-saving windows do not reduce the quantity to zero, although they may lessen it to the minimum. What happens if they also gain energy from the sun? Then we have to call these windows - active windows.

To make it clear, the active window is that one which never lets the heat out and, what is more, it heats up the room with sunlight.

Each energy-saving window can be active, no matter what type of construction and materials were used in its manufacture. It must meet two important standards, and it must have a certificate which confirms these characteristics:

• heat penetration rate for the window - Uw no more than 0,9W/m2K,
• windows which have a total light transmission factor of more than 45 %.

The analysis conducted by BuildDesk Energy Certyficate, to calculate the energy balance of buildings, shows that the use of active windows, instead of the standard ones, saves up to 16.1% of energy per annum. Replacing the old, leaking windows for the new active ones enables about 25.8% less energy consumption!

Energy-efficient construction, including active windows, is no longer much more expensive than the traditional one, and what is more, it has become the standard in the most European countries. German government is going to change regulations, and in 2012 every citizen of that country will be obliged to install windows with the heat penetration rate no less than 0,9W/m2K. Germany is a leader in the woodwork industry so in the next few years we can expect similar regulations in other EU countries.

In February 2010 a similar project was submitted by Polish Windows and Doors Association to the Ministry of Economy. If the provision is put into force, all the new windows will have to have heat penetration rate U less than 1,0W/m2K. It seems to be reasonable to invest in energy saving solutions to meet the highest standards in the future.

The most important factors

Heat penetration rate (Uw) - is the most important factor. The lower value is, the better it protects users from uncontrolled heat losses. Optimal heat penetration rate is 0,9 W/m2K, but it also may be lower when g - light transmission factor is not less than 45%. All the active windows meet such parameters.

Solar energy transmission factor(g) - Measures how much sunlight, falling through the glass, goes inside. The higher the solar energy transmission factor, the warmer is in the room.

Sound insulation value (Rw) - decisive factor of soundproofing windows. The higher the ratio, the quieter is in the room. Good noise-absorbing windows are those that achieve Rw from 30 dB.

Wind resistance - the most important factor for the windows on the high floors of the buildings and for the windows in houses which are not protected by any other buildings. The rates typically fall in a range between A 1-6, B 1-6 or C 1-6, where the weakest rate is marked A1 and C6 the strongest. In the average apartment windows with the rate C-3/C-4 are good enough.

Water resistance. - The decisive parameter of the wind load which measures how much water will leak into the window during the rainfall, and then into the room. The higher the ratio, the stronger the structure of the window is. In our climatic conditions, a sufficient rate is between 6A to 7A.

Air permeability. There are 4 classes of air permeability in widows, where class 4 means window completely airtight, which requires the use of ventilation. In Poland, since January 2009, all the windows in new buildings must be fully sealed, in class 3 or 4.

Operational forces is a factor that tells how much effort must be put into the opening of the window sash and turning the handle. In class 1 the value of this force is 10 kg, but in class 2 - 3 kg.

Mechanical durability - there are four classes of window mechanical durability. The higher the class of the window is, the safer is the user in case of unforeseen circumstances, such as hover on the wing.

Resistance to repeated opening and closing - specifies the method to be used to determine the mechanical durability of the opening parts of windows after a defined number of operating cycles. The windows are tested to show 5, 10 and 20 thousand cycles, which determine the strength of the hinges.

Light transmittance (Lt) - measures how much light comes through a product. The higher the light transmittance, the higher the potential for a day lighting is.