Nowadays, the need for conservation and rational use of energy as well as the improvement of energy efficiency of, for example, the end use of doors and windows is imperative. The proper management of energy requirements plays an important part in the economy and quality of life of the planet's population.
It is widely known that the burning of fossil fuels is a prime contributor to environmental pollution and the increase of the greenhouse effect. Global warming results in climate change with multiple consequences for both the natural and man-made environment. On the other hand, these specific natural resources are non-renewable, so there is also the problem of depleting their reserves.
The role of frames in saving energy
Improving the energy efficiency of buildings, contributes greatly to conserving the planet's energy. According to the new Regulation for Energy Performance in the Buildings Sector (KENAK), every new building and every existing one that is radically renovated, must compulsorily satisfy all the minimum requirements of the Regulation and the documented, via the Energy Performance Certificate, total primary energy consumption of the building, has to be within certain permissible limits.
Analysis of the structural elements' contribution to a building's heat losses, reveals the following conclusions:
• 20% of heat loss is due to the roof
• 25% of heat loss is due to the walls
• 20% of heat loss is due to the floor
• 35% of heat loss is due to the frames
So, the major source of energy leakage to the environment are the frames and glazing. Presenting this in numbers we have:
Heat loss through the frame (aluminium profile), which represents 31% of the total area of a frame, amounts to 74,87 Watts in the case of single - cold system vs. 44,92 Watts in the case of heat insulation. In other words, with common aluminium systems manufactured in previous decades, heat loss is increased by about 67% compared to the losses of heat insulating frames.
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Heat-insulating aluminium frames
Replacing a non thermal break with a thermal break frame has a dramatic effect on energy savings.
A thermal break frame substantially isolates the interior from the external environment, prohibiting the transfer of heat. In this way, the use of heating and cooling devices is limited.
How does an aluminium frame become a thermal break and what are its energy benefits?
A thermal break in the aluminium profile is defined as the insertion of a material called polyamide which is a poor conductor of heat between the inner and outer part of the profile. This material, thanks to its composition features thermal and chemical resistance properties.
The result of the polyamide insertion is the breaking of the heat bridge, created between the 2 metal parts which allows the transfer of heat from the exterior to the interior and vice versa.
Therefore the maximum possible reduction of heat loss through the aluminium is achieved.
The use of a heat-insulation or a plain aluminium system is connected to two basic parameters of a frame.
• the frame's heat insulation
• the probability of condensation of the interior's vapours from the interior forming on the surfaces of the frame and particularly on the frame itself
The use of a thermal insulating aluminium system improves the performance of the frame in both the above cases.
Heat loss is expressed by the thermal transmittance Uvalue index (W/ W/Km2). The use of a heat insulating aluminium system improves the final thermal transmittance Uw index of the frame by over 20%, compared to the thermal transmittance index of cold systems.
The heat-insulating aluminium frame's final thermal transmittance Uw index, in combination with energy glazing, provides us with the optimum energy efficiency and savings via the frames up to 40%.
The results are even more dramatic if appropriate low emissivity energy glazing is used.
The glazing, which takes up about 54% of the frame's total surface, significantly contributes to the overall performance of the frame.
Energy glazing & energy savings
In energy frames energy glazing is used, otherwise known as low-emissivity glazing, which is glass that allows light to pass through it while at the same time providing heat insulation.
With a special coating of microscopic metal oxides, on the inner side of one of the two panes (in double glazing), high reflectivity is achieved in the infrared portion of the spectrum and the transfer of heat from the exterior surroundings towards the house interior and vice versa is significantly slowed down.
These coatings are usually completely transparent or may have various colour tones, so the glazing in its final form has the desired hue (tinted, bronze, etc.).
Modern low-e soft coating energy glazing filter solar radiation, thereby blocking it a large degree, up to 70%, the transmittance of ultraviolet and infrared radiation that causes wear to carpets, curtains, furniture, etc.
Energy glazing on our aluminium doors and windows provides us the ability to control sunlight to our benefit and create a comfortable environment in our personal space with the minimum possible financial and energy costs.
Energy Coefficients
1. Uvalue or Ug (W/Km2): heat transmission rate, expresses the rate of loss of heat per square meter of glazing between the inner and the outer surface, and is determined by the ability of a surface to absorb or reflect heat.
The lower the Emissivity the lower the heat transmission rate K and therefore the more energy efficient is the glass.
2. Solar Factor - g: the solar factor expresses the percentage of the total solar energy-heat that passes through the glazing to the interior and its value ranges from 0-1.
As in Greece we have hot summers, it is very important to minimize its value (0), otherwise the glazing acts as passage for heat, resulting in an overheated interior and additionally burdened air conditioners.
3. Light Transmission - LT: light transmission, expresses the percentage of visible radiation passing through the glazing.
As the index increases the more light passes to the interior. A low light transmission rate increases consumption by the artificial lighting system. The ideal values for this index are 60% - 80%.
Therefore, for the optimum energy effect, we should choose glazing for aluminium frames with:
• Low Ug
• Low g
• High LT
which during the summer:
a) reflect the sun's infrared radiation
b) act as a shield to indirect heat from the surroundings - easier cooling
c) reduce the cooling cost (up to 35%)
d) reduce the cost of artificial lighting
and during the winter:
a) act as a shield to heat trying to escape from the interior - efficient heat insulation
b) reduce the cost of heating (up to 35%)
Installing new generation Low - E (Low-Emission) energy glazing in insulating aluminium systems significantly reduces heat losses and sunlight is filtered by preventing the permeation of ultraviolet and infrared radiation by up to 70%.