STOBAG Österreich is a full member of the Austrian Association for Sun Protection Technology, and as part of this we work together with other market players to constantly improve the sun protection industry.  

Since the beginning of this year, the effectiveness of sun protection has now been defined in up-to-date terms by means of a new standard. An interesting report by the Association describes safe, simple dimensioning of sun protection.

The shading factor used previously, Fc, has been replaced by the gtot factor,and the whole method of calculation has been radically simplified. The aim is that, by using this new standard, even end users will now be able to correctly classify the effectiveness of sun protection according to the total energy transmission.


Report Federal Association for Sun Protection Technology:

Effectiveness of sun protection defined in up-to-date terms

Proper sun protection, simply planned

Vienna, April 2019 – Experts agree: Shading windows is the best protection against overheating in summer. But how effective is shading if you still want to have daylight and see outside? From now on, all that’s needed is for the planner or energy consultant to input the required gtot factor from the standards table – the architect or end user can then get advice on all the various types of sun protection under consideration very easily and make their selection according to personal preference.

Since the turn of the century, the number of days when overheating threatens has more than doubled. On the one hand, this is in connection with more hot days and longer periods of heat. But at the same time, well insulated, airtight building envelopes combined with larger glass surfaces are also responsible. This is because the result of avoiding heat loss in the cooler half of the year is that, in the summer months, the solar energy radiated through the windows remains inside the building and can only be removed by ventilation at suitably low temperatures during the night.

‘On hot summer days the supply of direct sunlight must be restricted to maintain proper indoor comfort. An unshaded window with an area of 2 m2 gives out between 1 and 1.5 kW of heat – and in summer at that! Just as an energy-efficient wall needs good heat insultation, windows need good insulation against overheating in the form of variable shading,’ explains engineer Johann Gerstmann, spokesperson for the Austrian Association for Sun Protection Technology.

Sustainable protection against overheating

The best possible sun protection during the day and efficient cooling at night have always formed the basis for making buildings fit for summer use and guarantee that residential buildings (newly built or refurbished) basically work even without active cooling systems. As Gerstmann says, ‘The key to building sustainable residential buildings that are fit for summer is therefore to be found in the planning stage of construction. Creating a comfortable indoor climate by means of active cooling is not very sustainable, because the energy saved on heating is then used again for active cooling in summer!’ Since state-of-the-art residential buildings are supposed to be fit for summer without cooling, the energy consumed by cooling is not yet recorded at present. And that falsifies the published results for energy saving!
The most important passive method to restrict the daytime warming of buildings to a minimum has always been external, intelligently used sun protection.
Shading is above all else a building technology system for prevention by cooling, and so it must also be possible to plan roller shutters, venetian blinds and canvas awnings like any other technological system. As Gerstmann says, ‘Effective sun protection is installed outside the window! If the shading is in the room, the sun’s energy is already in the room as well, and can scarcely be radiated back outside again – because modern windows are constructed so as to keep as much heat in the room as possible.’ Sun protection is at its most effective when it’s completely closed – but is that always desirable? Gerstmann’s reply to that is: ‘No, of course that’s not always desirable or necessary. Because on a bright, sunny day, it’s counterproductive to switch on artificial light and lose contact with the outside world completely. And it’s not necessary, because rooms can easily tolerate a moderate intake of warmth. For example, in order to guarantee a supply of daylight and an outside view while simultaneously protecting against heat, it’s enough to adjust the slats in such a way that the glass surface doesn’t get any direct sunlight. In the case of façade awnings, you choose a perforated material, and with roller blinds, it can be enough to pull them three-quarters of the way down.’  

Dimensioning sun protection, easily and safely  

In the same way that the U-factor is used to measure a window’s heat insulation properties, when it’s a question of protection against overheating, the gtot factor is used. This factor provides information about the total energy transmission of the window and shading system. If the value is 0.10, then 10% of the irradiated solar energy is effective in the room, and 90% is not admitted into the building at all. Therefore, it is not necessary to cool down the solar heat either. Depending on the type of hanging and its colour, a good shading system combined with a heat protection glass (U ≤ 1.5 W/m2K) allows 3% to 20% of the energy through.
Standards document the state of the art and are therefore adjusted accordingly every few years. At the beginning of this year, the Austrian standard ÖNORM B8110-6-1 was updated to reflect technological improvements in glazing and shading systems, and at the same time the previous, highly complex calculation of the energy input according to ÖNORM B 8110-3 was quite radically simplified. The shading factor used previously, Fc, was abolished, because the gtot factor is easily understood even by those who are not building physicists. The aim of the new standard is, on the one hand, to enable the end user to classify the effectiveness of the sun protection correctly and, on the other, to model the way in which it is typically used – i.e. as shading which allows use of daylight and a view outside. As Gerstmann says, ‘Until now a basic rule has applied: because of their higher reflection values, light hangings are more effective than dark ones. That’s certainly still true for interior shading systems, but not for exterior ones. By their very nature, dark hangings warm up more than light ones, but heat protection windows not only prevent loss of valuable heat during winter, but also reduce the flow of heat from the sun protection into the cooler interior during the summer. Today, dark-coloured surfaces combined with heat protection glass are at least just as effective as light ones!’

Sun protection planning made simple

In Austria, 85% of planning applications are for private residential buildings. In order to demonstrate a building’s fitness for summer use in the energy performance certificate, up to now one of the requirements has been to stipulate the glass/shading system fairly precisely even in the planning phase. Now all that’s needed is for the planner or energy consultant to input the required gtot factor from the standards table – the end user can then get advice on all the various sun protection systems under consideration very easily and make their selection according to personal preference.

This simplification was based on a fundamental interrogation of the method used to date. The essential point is that the energy input, gtot, is a combination of the light and heat inputs, where the light input is determined by the light transparency of the shading, and the heat input by the U-factor of the glazing. By this means, it was possible to develop very clearly set out tables for exterior and interior sun protection in ÖNORM B 8110-6-1.

As Gerstmann says, ‘Throwing the dice to get the correct shading value for venetian blinds, roller awnings and façade awnings is now a thing of the past! Less is often more – and better!’

The room matters

In the end, what matters when choosing the right sun protection is the function it is supposed to fulfil. As Gerstmann says, ‘Sun protection plays a different role in every room. In the bedroom, it should be possible to darken the room as much as possible, because that’s the basic requirement for sleeping soundly. In the living room, you want to have as much daylight as possible and see the surroundings, while in the evening you don’t want to be exposed to curious eyes – so it’s also a question of security and privacy.’ And, last but not least, shading systems contribute to the way a building looks.  

About the Austrian Association for Sun Protection Technology

The Austrian Association for Sun Protection Technology is the umbrella association for the Austrian sun protection industry. Its cooperation partners include klima:aktiv, IBO, ÖGUT and Bau.Energie.Umwelt.Cluster NÖ.
The Association represents 21 member organisations with a total of over 1,700 staff. With a value creation of approx. 800 million euros, it safeguards around 10,000 domestic jobs, mainly in the industrial sector.
The Association is a founding member of the European umbrella organisation ES-SO (European Solar-Shading Organisation), to which 28 member associations belong. In the area covered by this association as a whole, the total of services connected with sun protection (including assembly and servicing) support jobs for 400,000 salaried staff and workers, who generate a total turnover of around 35 billion euros.

Bundesverband Sonnenschutztechnik, www.bvst.at