I love a good debate. That’s one of the reasons watching the latest discussion in our “Architectural Solar Shading” Group on LinkedIn has been so fascinating (and another reason you should join right now!).
Three months ago, I asked this simple question on our discussion board: “Is solar shading better suited for the interior or exterior of a building?”
21 comments, many paragraphs, and a lot of great insights later, here are some of the comments which stood out the most. I’m interested in what our readers think. Do you agree? Have you used shading on a project before? How have you decided to shade that building and where to place shading devices? What’s missing from the conversation?
So, without further ado, here are some of what I feel are the best points made (but be sure to check them all out). I’ve credited and linked to each person’s respective LinkedIn profile. With almost 200 members from a cross-section of companies within the industry, and more joining every day, there are some smart & talented people here worth connecting with!
If the goal of the shading is reducing the SHGC then an exterior mounted shade is typically more than 5 times more effective. This is greatly simplified though as there are many more choices for interior shades, but if performance is what you are looking for go for exterior. – Dan Fogarty
My understanding of the physics is that if you let the solar radiation through the insulating barrier of the glass then block it with a shade, you have already let much of the energy into the building. Thus, exterior blinds are better than interior. – Michael Ludvik
At this point, Charles Kramer stepped in, asking us to rethink our definition of ‘shading’:
With respect to the shades labeled as solar shades, generally, the views expressed are correct. However, that is simply because such shades are not really solar controlling (ie shearweave, ecoshade etc). They are merely shading devices which, as noted, absorb solar radiation and other heat transmitting spectrum waves. However, there are interior products available which use science, rather than mere shade, to actually reflect out the heat rather than absorb it – Charles Kramer
The problem with that is that all glass itself has some amount of absorption and some of the heat is absorbed as it passes through on its way to your shade and then if your shade is say 80% reflective 20% is left at the shade and then it tries to go back outside and must make another trip through the glass dumping even more of it into the glass. – Dan Fogarty
That being said, if the application is truly one where the driving force is the need to reduce the heat virtually in total, such that cost, cosmetic and ease of use are mnimal or nonissues, then you are absolutely correct that an exterior shade can be designed to get superior results. - Charles Kramer
To get an idea I just calculated the total solar transmittance (g-value) for
1- standard double glazing 6 12 6 (without coating) -> 0.76
2- same glazing with indoor shading with a reflectivity of 0.8 -> 0.23
3- same glazing with same outdoor shading -> 0.17
And, finally, Leo Bakker stepped up and was the first (which was shocking to me) to mention the idea of both of these shades working together! One for thermal control (exterior) the other for glare and managing light (interior):
Ideally, both indoor and outdoor shading are there.
In summer (warmer periods):
+ Outdoor shading to avoid overheating / minimizing energy for cooling.
+ Indoor shading to control daylight.
In winter (colder periods):
+ Outdoor shading stays opened.
+ Indoor shading is used to control the daylight.
More solar radiation enters the room, minimizing energy for heating.
So, with this in mind, why are exterior solar shading systems only just starting to leave their mark in the building industry? Dan Fogarty says one of the most intelligent points in all of this discussion:
Now while green is still the color of money almost no one would have imagined that buying a Hybrid car in 1996 was a good Idea because very few people understood them. Today 10s of thousands are sold and they continue to get better and better. In our world interior shades window films and glazing options have a much greater degree of implementation within the US (outside the US many areas of the world have begun to adopt them). I believe this is due to a lack of options of high quality dynamic exterior products. The more we develop them the more they will get adopted and then costs and acceptance will come down.
In my opinion, Dan nailed it. Big kudos to him! It’s an important reminder that it’s up to all of us in the industry to work together to push the mandate of effective solar external shading, to innovate and develop new products, and to position ourselves in the market as the most effective way of conserving energy and managing daylight in a building.
And that’s only HALF of the information found within this discussion thread. Are you in the shading, daylighting, facade, or building envelope sector? You owe it to yourself to be connecting with the best of the best in the industry in this group and learning from one other. Signing up takes only 10 seconds if you are already on LinkedIn. You can get started here.