Every building has an ambient temperature within it. However, it is possible that this temperature increases beyond the comfort zone. When this happens, any additional heating will lead to discomfort. This used to be a big problem until architects came up with a concept to prevent additional heating, called solar shading devices.
Sun control and shading devices are fast becoming integral aspects of several energy-efficient building design systems. It is more common among buildings that depend on daylighting or passive solar heating.
Solar Radiation and the resulting thermal effects
Either from your windows or the rooftop, sun rays will always find a way into your interiors. When solar radiation hits the surfaces of any space, it results in a couple of things, notably a rise in air temperature and the mean radiant temperature. Likewise, if such radiations hit an occupant directly, such an individual will experience a higher mean radiant temperature.
Let’s not forget the discomfort glare that also comes with radiations of high intensities, either from the diffuse sky or the sun. If not efficiently controlled, such radiations can also lead to impaired visual performance of the affected occupant.
The only way to prevent or eliminate these effects is to ensure adequate shading. Shading, over time, has proven to be a difficult concept to perfect; it is associated with a few constraints. For instance, buildings without air-condition require proper airflow maintenance, especially during the day’s cooler hours. There is also the need to admit regulated levels of diffused daylight, and sometimes, a unique arrangement for views out of the window.
Considering these diverse challenges, it is clear why a one-cap-fits-all approach will not work for shading devices. Architects have had to come up with different shading devices to achieve different shading functions. Let’s get to know them.
Types of Solar Shading Devices
There are three types of solar shading devices:
- Movable opaque shading devices;
- Louvers – fixed, adjustable, or removable;
- Fixed overhangs
The movable opaque shading devices are ideal for reducing solar gains. However, the downside here is that they block air movement and block views. Examples of movable opaque shading devices include curtains and roller blinds, among others.
Louvers are usually of three types – the removable louvers, adjustable louvers, and fixed louvers. They are excellent in blocking radiations that contribute to unwanted solar gains but impede air movement and views to an extent.
Fixed overhangs – the third class of solar shading devices – are great for overhanging roofs and balcony. They are also suitable for protecting openings and walls from the rain. Unlike other types of shading devices, they hardly block air movement or impede views.
Solar Shading Devices – Applications
The application of solar shading devices is an interesting one. Sometimes, they are used individually, and other times, devices of different types are combined to achieve the desired results.
Moveable Curtains or Blinds
They are suited for air-conditioned buildings where their airflow impediment will not constitute a problem. The case in most air-conditioned buildings is a higher outside air temperature compared to room temperature. Therefore, glazing the windows with translucent or opaque blinds does not lead to inadequate airflow. If done well, such an application reduces cooling load, glare, and relieves the effects of direct solar radiation on individuals in the building.
While it is possible to use reflective or light-colored fabrics to reflect the radiated energy out of the building, they tend to transmit a considerable amount of these radiations – up to 15%. The colorful nature of the blinds on application makes them a secondary source of daylight. To avoid this unwanted transmission, some designers opt for dark colors of blinds. But this, again, does more harm than good. Dark blinds are good absorbers and inadequate reflectors, thus raising the heat levels in the building.
Fabrics with aluminized finishing work best for this purpose since they are highly opaque and retain a light color when illuminated from inside.
Louvers and Overhangs – Geometric Shading
Both overhangs and louvers are designed to block the parts of the sky where the sun passes into the building. Another way to put this is that they block the parts of the sky with brightness levels high enough to cause issues.
The principle here is simple – ensure that the low angle view is free, so air ingress or flow is not impeded. Like the natural shading technique in the tropics, fixed overhangs can be combined in the right orientation to achieve the same results.
Do solar shading devices really work?
Curious about how solar shading devices achieve the desired results, here are some heads up:
Reduce heat/solar gains
When properly designed for the building in question, a sun control or shading device will considerably reduce the rate at which a building gains heat, thus reducing discomfort. It also comes handy in improving natural lighting quality that gets into the interiors of the building.
Reduce cooling loads
We all want to have a slight heating effect during winter, considering how cool this period can be. Depending on the nature of the shading device – geometrically selective or moveable – they also help optimize heat gain or block excess heat gain in the winter and summer.
Less energy consumption
Shading devices have been repeatedly used to significantly reduce the annual cooling energy consumption, although this depends on the location and amount of fenestration. Since your lamps are generating less heat, you have reasons to expend energy on air conditioning.
Excellent UV protection
Not every building can withstand direct exposure to solar radiation. This is why museums, libraries, and exhibition spaces have solar shading devices installed to prevent such exposure and complement their designs.
Improved lighting quality with no glare
These pieces of tech also come handy in improving user visual comfort. They do this by reducing contrast ratios and regulating glare. So, if you want to up the productivity and satisfaction you get from your workspace, installing the right shading devices is the way to go.
Efficient lighting control
Shading devices ensure a consistent delivery of luminance, which, in turn, prevents the problem of excessive brightness at the windows. In some cases, it is possible to set the desired amount of illumination in some regions of the building.
Improved external vision
With shading devices, you can safely and conveniently see the outside from the comfort of your interiors. They also offer excellent solar protection for this purpose.
What happens when you shade on daylighting?
Recall that we mentioned how shading devices tend to affect both the daylight, which is needed, and the solar gains, which are unneeded. So, how do we fix this? The fix is multi-step and revolves around adequate evaluation and optimization of the adopted shading design.
Step 1 – Understand that there is no coincidence in time between the shading and the limiting daylight conditions. This means that the need for shading comes with an excess amount of radiant energy – up to 10x higher than the minimum illumination requirements. Relying on sky luminance for daylight, on the other hand, requires no shading to achieve glare or thermal control.
Consequently, a moveable shading will constitute no problem, provided that such shading can illuminate the room sufficiently by transmitting the right amount of light in the right direction.
As useful as solar radiation is, especially in providing heat and natural light and reducing energy use and emissions, it becomes a problem when it is in excess. The overheating that comes with excessive solar radiation requires energy-intensive cooling techniques to correct. It can cause glare in some cases.
Solar shading devices are proven solutions to excessive solar radiation. The right type of shading device does not only fix these anomalies but also do so efficiently and without adversely affecting the design or the integrity of the building.
Post by HL Architects North East