By Smita Chandra Thomas
Imagine a man standing outdoors on a blustery cold day, wrapped in nothing but a flimsy sheet of plastic, trying to warm himself up with cup after cup of hot coffee. The same principle is at work in a building being pumped with hot air while clad in walls made of glass and steel, chugging away to keep the inside warm. Buildings encased in glass and steel are poor insulators, yet they are ubiquitous.
Top U.S. architectural firms have risen to the occasion and signed up for the Architecture 2030 Challenge to design new buildings with ‘zero’ fossil-fuel consumption by 2030. Zero-energy buildings are no futuristic dream either; while the exact definition of zero-energy is being hashed out, thousands of zero-energy units exist in the U.S. today.
The first opportunity to reduce energy use in buildings lies in the building skin, which can impact the total energy use of a building by 10 to 50 percent. And yet we continue to see buildings being encased in glass. Here are five myths surrounding glass skins that explain why this is cause for concern.
|Single-pane window||Less than R-1 (close to metal)|
|‘Efficient’ Double-pane and triple-pane window||R-2 to R-3|
|‘Top-of-the-line’ Electrochromic glass window||R-6 at center; R-5 or less including frame|
|Fiberglass batt insulation 3.5” thick||R-11|
|Foam insulation- expanded polystyrene 3” thick||R-10|
|Fiberglass batt insulation 6” thick||R-19|
|Foam insulation - extruded polystyrene 6” thick||R-30|
Glass is also at a disadvantage because it allows more radiant heat gain by allowing sunlight to pass through – a significant problem in hot climates – even with Low-E glass. It is mildly helpful in cold climates during the short daytime hours with direct sunlight exposure, but not significant enough to make up for the heat loss through low resistance.
Some creative and high-tech solutions to combat heat transfer in glass walls include double-walled systems (which take up valuable urban space) and double-glazed ventilated wall systems whose thermal performance is only marginally better.
Smart design strategies include smaller windows with features that help daylight penetrate deeper into the space.
Besides, views to the inside of an all-glass office building from an opposite building can be messy! Optimal window sizing and positioning, on the other hand, can provide strategically-framed views.
Building designers who understand the basics of the path to 'zero' energy – designing passive design solutions before leaning on mechanical systems and renewable energy – can lead us away from all-glass to more sophisticated solutions. Will you do your part to spread awareness about this?
Image credits: 1. Wikimedia Commons 2. Guy Marsden (used with permission) 3. The Building Science Group (used with permission)
Smita Chandra Thomas is a U.S.-based sustainability consultant and a LEED AP with an undergraduate degree in Architecture, and a Master's in Building Science from the University of California (LA and Berkeley). For nearly two decades, Ms. Thomas has been focused on enabling energy efficiency in buildings through building science for lesser waste, greater economy, better health, and a sustainable environment for future generations. Ms. Thomas runs her private consulting practice Energy Shrink in Washington DC. She can be reached at <firstname.lastname@example.org>.
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