The theory that placing dark objects behind sun-struck glass increases their temperature has been explored for well over 100 years – yet most building designers still seem unfamiliar with this phenomenon.
The American Naturalist, Edward Morse, was awarded a patent by the US Patent Office in 1881 for this discovery and then in the 1960‘s French Engineer Felix Trombe fully developed Morse’s observation into an architectural element of design that became widely known as a “Trombe Wall.” Trombe Wall and Attached Sunspace | Sustainability Workshop
A Trombe Wall utilizes the basic concept of the greenhouse effect where incoming solar energy that passes through glass is converted to heat on the room side of the glass and it remains inside the building as heat energy. In the case of a Trombe Wall, the heat is collected in the mass of a dark colored wall and distributed into the building at a time when heat is desirable. Glass is transparent to short wave energy (sunlight) but opaque to long wave energy (heat), therefore the light energy that passes through the glass and is absorbed remains inside the building envelope as trapped heat. It is the greenhouse phenomenon that allows us to grow orchids in cold climates and is causing the earth’s temperature to rise; when thinking of trapped solar energy, glass and our atmosphere are analogous. Improving Fenestration Performance
Leaving Messrs. Morse and Trombe back in the 1800’s and 1900‘s, fast forward to an AIA Educational Workshop in 2016 that I attended in California. I am listening to a presenter who represents one of the worlds leading motorized shade manufacturers, he is instructing a room full of Designers and Architects how to properly specify shade materials when solar heat gain is a concern. He explains to the class that the most important consideration in selecting a material is the “openness factor” and that the tighter the weave, the greater the solar control – all the while holding up a piece of black shade material. Looking around the room I expect to see the Architects and Interior Designers squirming in their chairs while listening to the nonsensical premise that putting a piece of solid black material behind glass would somehow reduce heat gain – no one flinched. Certainly someone in this room who is LEED certified would understand enough about building science, the greenhouse effect or thermal dynamics to know that the presenter was in effect suggesting that they build Trombe Walls to control heat gain – but everyone just nodded along in agreement. After class I had a private conversation with the presenter about what he was suggesting and he clearly did not understand that the information he was providing through this AIA Continuing Education class was inaccurate. He was merely repeating what he had been told to present. Sadly, the information gathered by the design professionals attending this class was wrong, and if applied as directed, will negatively affect their building designs – the presenter is probably still teaching the same class somewhere else this week.
When I observe the fenestration on buildings where we work (the greater Phoenix and Los Angeles areas) clearly, many people who make decisions regarding glass and window treatments do not understand how to design an efficient fenestration system