Re-examining Glass Building Design: Exploring the Myths of Achieved Energy Savings

Climate change is not something that will happen in a far, distant future. Unbeknownst to many, the phenomenon is already having severe implications on the City of Boston, which is particularly vulnerable to its future impacts. We've seen multiple storms with near-record high tides flooding the Seaport as recently as the Winter of 2018.

So, what exactly have we been doing to combat these adverse effects?

One of the primary focuses is on building energy consumption, a major contributor to climate change emissions. In 2007, Boston set goals of reducing emissions 25% by 2020 and 80% by 2050, relative to the baseline emissions from 2005. In an effort to meet those targets, Boston adopted both the Stretch Code and Article 37, which require energy savings relative to the American Society of Heating, and Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 90.1. By 2014, the goal was elevated to achieving carbon neutrality by 2050. In order for Boston to reach its ambitious 2050 goal, urban office buildings (new construction or major renovation) need to achieve a measured Energy Use Intensity (EUI) of around 25 Btu/sf-yr2.

To aid Boston in reaching its goal, SMMA's Sustainability Group wants to turn their sights towards an unlikely source – the prevalence of glass enclosures among newly constructed buildings. Let's explore the myths and realities surrounding them to inspire the building community to prioritize performance, and to leverage the metric of EUI to define a new urban architecture that is both beautiful and responsible. 

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Relative vs. Absolute Metrics

Consider the following example to understand the impact of different performance metrics:

Two LEED core and shell office buildings are designed in Massachusetts by the same firm. Both are approximately 250,000 gsf and 8 stories in height. When modeled relative to ASHRAE 90.1-2007, Building A demonstrated a 25% energy cost savings and Building B demonstrated a 14% energy cost savings. Based on the LEED rating system, Building A would be considered a higher performing building with respect to energy use. However, Building A actually has a higher EUI, at 40 kBtu/sf-yr, while Building B has a modeled EUI of 34 kBtu/sf-yr.

In respect to EUI, the energy cost savings data skewed the analysis of the buildings’ design performance.

Energy Cost Savings diagram for Glass building design.

Comparison of Heat Loss Through a Window & Well-Insulated Wall on a Winter Day

Because the assembly u-factor is approximately ten times that of an insulated wall assembly, so is the heat loss. The overall enclosure heat loss is determined by a weighted average based on the area of each enclosure element.

Heat loss diagram for Glass Building Design.


Glazing diagram for Glass Building design.

View Glazing Provided Below a Typical Desk Height Does Not Contribute to Quality Daylighting or Views

In a typical office building, vision glazing below desk height does not provide useful daylight. Views through this glazing are generally blocked by furniture.

Do Occupants Really Want All That Glass?

While the marketability of space is primarily cited as the driver behind highly glazed buildings, in practice, the answer is no.  A recent study presented at the Living Future Conference found that regardless of time of day, orientation, and building type, over 75% of the highly glazed commercial and residential buildings surveyed had more than half of their window area covered by blinds.  Since the high levels of shading make much of the glazing functionally opaque, developers and designers need to consider whether they should prioritize thermal performance over the supposed marketability of all-glass buildings.

Image: Clean and consistent look of automated shades versus the disjointed appearance of manual blinds


Glass buildings example.

"The comprehensiveness of EUI explains why the industry relies on it to best understand building’s energy use […] If we are serious about our sustainability goals, we too need to adopt this metric and move towards a proactive approach to sustainable design."

Contact Us!

Access the full whitepaper here.

If you have any questions, email us or Martine Dion, Director of Sustainable Design.

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