The ultimate tool for the correct

choice of solar shading

The problem

In a modern homeretrofit, the building is transformed into a highly insulated and air-tight environment,the risk of overheating duringsummer tremendously increases (as the risk of condenstaion and molds during winter). Hence a window maker should be able to accurately find the correct orientation of windows and to suggest the correct solar protectoon accordingly.

The solution

The company glassAdvisor, specializing in advanced energy simulation of the window, has developed and patented a tool designed specifically for the window makers to be used during site inspections. With a few simple steps you can immediately identify the criticality of a specific window and suggest to the customer a shading solution that considers not only the thermal comfort but also the wellbeing inside the room.

All the energy studies and dynamic simulations necessary to find the solution proposed by the solarScanner were performed prior by the most advanced algorithms, leaving only the easy part to the window maker, finding the orientation, and the proposing the best shading solution to the customer within a complete digital library.

Why the Solar Factor is so essential

What is the Solar Factor (g-value)

The solar factor is a very useful indicator to understand how much solar energy passes through a window at a given time. The Solar Factor of a glazing unit is often indicated by the letter “g” (always lowercase) without any subscript. Whereas the Solar Factor of a glazing + shading composition is indicated by the letter “gtot” (with a subscript “tot)”. Moreover it can be indicated as a percentage (%) from 0% to 100%, or with decimal values from 0 to 1 (so talking about a 35% g-value os equivalent to 0.35).

The Solar Factor is the sum of two components:

Te: it’s the Solar (energetic) Direct Transmittance that draws the shape of the window on the floor. It contains light, but is not made of light only, actually, according to the glass configuration half of this radiation can be invisible (but still energy carrying). The Solar Direct Transmission expresses a percentage value (%) of the incident energy, and consists of the portion of solar radiation that is neither reflected nor absorbed by the glass. It is difficult to estimate it without any special tool, so you must always refer to the Declaration of Performance of the Glazing Unit (or DOP), or for glass + shading compositions to calculations performed by a certified software.

qi: it’s the “secondary heat transfer factor towards the inside”, or in other words the “heated glass component”. This is the part of the sun radiation which after being absorbed by the glass is dispersed into the internal environment. It is possible to have a brief estimation of it byplacing your hand on the glass. It is important not to confuse the qi with the Solar Factor. A hot glass may mean that the solar radiation has been intercepted, hence greatly reducing the Solar Transmittance. Or the opposite, a very transparent glass might seem cool, but this means having a high Solar Transmittance hence a high g-vlaue.

Why the Solar Factor is so important

The Solar Factor until now has been considered especially for the solar heat gain it gives on winter, being old-fashioned buildings poorly insulated and with many ventilation leaks (draughts). However, in an energy efficient retrofit or a new constructions the amount of energy dispersed through the walls or draughts is decreased drastically, completely changing the energy behavior of the entire building. One typical evidence of this change is the considerable increase humidity indoors after the replacement of windows and doors and increased probability of condensation and mold.

Let’s make a brief comparison between U-value and g-value:

Many are already familiar with the concept behind Thermal Transmittance, a very important value for the calculation of heat loss of a building in the winter season, beside being regulated by norms. But let’s make a quick approximate comparison to understand how much energy is dissipated by a square meter of a glass pane in winter and how much energy can instead pass through with the solar radiation in the worst case during summer.

Winter: A double glass with a low-e coating has Ug value of 1.1 W/m2K, if we have 20°C inside and -5°C outside the house, the heat flow generated by the Thermal Transmittance is 25°C x 1 m2 x 1.1 , so  27,5W.

Summer: in the worst case during summer, the radiation on a vertical surface can get up to 765W/m2. This means that if a double-glazed with low-e  coating has a solar factor of 60% (or 0.60) the solar energy passing thourgh that window will be around 60% of 765W, or about 460W.

Basically, if during the worst case on summer we had an outside temperature of -5 ° C, the incoming energy would still be 17 times higher than the outgoing dispersion. It goes without saying that a well insulated and air-tight house becomes extremely sensitive to the Solar Factor and is at risk of overheating even on cold climates.

The sun changes depending on the orientation

We are used to think about the U-value of a windows, and use the same value on every façade of a building regardless of its orientation. The sun follow different rules because it is present in different ways for each window and it changes not only during a single day but also throughout the year.

The sunpath:

During a site inspections, a good window maker must be able to anticipate any criticality related to Solar Factor, without asking for indications to the customer but instead anticipating them. In fact, the customer does not know that the Solar factor (such as what happens for condensation) will become as delicate aspect.

In order to understand the criticality of a specific window we only need a compass and a bit of knowledge.

On the northern hemisphere during the winter the sun rises in the Southeast and sets in the Southwest. The trajectory is then very short and covers only one third of the horizon. The result is obvious, the day is short. In addition to this the sun path is very low, reaching less than 25° of elevation on the horizon.
In the northern hemisphere during summer we see a very different behavior. The sun rises in the Northeast and sets in the Northwest, with an overall trajectory that covers two-thirds of the horizon. Moreover the sun gets very high in the sky.
Often ignored in the building design, the middle season (spring and autunm) is a period where the building is likely to get overheated. The sun is already (or still) very strong, but the elevation is quite low having a more aggressive angle of incidence towards the window. This behavior is not compensated by the external temperature that in most cases is still not so cold to compensate that solar gain.

Window dimension

Finally the criticality of a window should also be identified by its size. Not in square meters (area) but from the proportion between transparent surface and the floor of a room. A 6m2 window can be small if it insists on a large conference room of 300m2, instead a 3m2 window can be large if for example insists on a bedroom of just 16m2.

Breaking the myths:

 The South orientation is not necessarely the most critical during summer

Sometimes North solar shading may be necessary

The East orientation is in many cases as critical as the West one



solarScanner has a high sensitivity compass to precisely find the orientation of a specific window

Weather based values

solarScanner have a specific version for each country and studies are carried considering weather data of many cities

One size fits all

solarScanner on its suggestion considers the dimension of the window suggesting a solr shading only when its necessary


solarScanner is portable and you can use it on every site inspection, it will keep good company to your measuring tape

Dyamic simulations for each country

Identified situations

Analyzed cities

Specialists involved

Buy now a solarScanner at one of our dealers

If you’ve already purchased a solarScanner, read below the User Instructions

#1 Place the solarScanner against the glass

Keeping the solarScanner horizontally, lay the blue edge against the glass

#2 Orient the compass

Turn the compass until the red needle overlays the letter N (North).

Note: The compass is very sensitive, keep it away from other metals. Sometimes friction or static electricity may cause the needle to be carried away by the movement of the compass, slightly knock on the compass itself to normalize the situation.

#3 Read the orientation

The blue arrow will indicate the orientation of the window. The North is indicated as 0 °, and clockwise you may find the East (90 °), the South (180 °), the west (270 °) and of course all intermediate orientations. It could be a good practice to record the orientation of a window (beside its dimensions), this may be useful a later further analysis.

#4 Window size

To understand how critical a window is we must also consider its size. But the size of a window frame is not only given by its square meters, what makes it large or small is the ratio between the surface of the room and the floor of the room itself. A very simple calculation can be performed by dividing the transparent surface in square meters by the floor area of a room. solarScanner identifies in this way three types of frames:

Very large windowsare those for which the glass surface divided by the area of the room takes on a value greater than 0.20. For example sliding door with a transparent area of 3,5m² which insists on a 16m² room belongs to this category because the ratio is 3.5 / 16 = 0.22
Large window (es. Porta-finestra): are those for which the glass surface divided by the area of the room takes on a value between 0.10 and 0.20. For example, a door with 2,1m² transparent surface which insists on a 14m² room belongs to this category because the ratio is 2.1 / 14 = 0.15
Medium to small windows: are those for which the glass surface divided by the area of the room takes on a value less than 0.10. For example, a window with 0,8m² glass surface which insists on a 16m² room belongs to this category because the ratio is 0.8 / 16 = 0.05

#5 Find the situation

solarScanner identifies 18 different situations created by the combination of orientation and size of the window frame. Once you find the situation, read the its number on the solarScanner and find the appropriate row of the table on the left. You will find below:

Recommended g-value: that is the Solar Factor recommended in order to avoid overheating and air conditioning during summer by simply having a well designed solar shading.

Type: the type of solar shading suggested (outside solar shading, integrated, indoor or coated glass)

Criticality: a brief explanation of the critical moments during the year and / or along the day of that specific situation

#6 Complete the advisory online

solarScanner will suggest a Solar Factor value to be reached during the most critical moments over the year so that avoid room overheating. If you want to learn what shading solution is preferable to offer for the recommended g-value, you can enter the link provided on solarScanner directly from your smartphone or tablet and browse the digital library side by side with the customer and choosing the solution or combination of technical solutions suits them the best.

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