How High Performance, Energy-Saving Glass and the LEED Certification Process
Can Maximize the Potential of Green Construction & Renovation
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Facilities managers understand that by making buildings more energy efficient
and environmentally friendly they can reduce operational costs and increase
building occupant productivity and health. That's the good news.
The bad news - it isn't obvious how to produce an all green facility. As stake
holders desire to save energy and make facilities more environmentally benign,
property managers need not become versed in the often confusing language of
sustainability to define realistic green construction and renovation project
objectives and management requirements. Fortunately, there is plenty of help
Surprisingly, the promise of green design, as exemplified in the Leadership in
Energy and Environmental Design (LEED) certification process of the United
States Green Building Council, is very straightforward. Despite this simplicity,
it is quite powerful and effective at delivering desired energy-saving
performance within budgets often comparable to those for traditional
So, what do facilities managers need to know when planning a green construction
or renovation project?
Embrace an integrated and holistic approach to building design. The LEED
certification process is a practical realization of the vision expressed by
the celebrated environmentalist John Muir, who believed that "everything in
the universe is connected to everything else." In the universe of green
building and renovation, this means that a project's ultimate energy
efficiency and synergy with the environment is a function of the many
building components, design elements, equipment and appliances working
together as a fully- integrated system. The many choices among these
components that need to be made by the architect, builder and facility
manager will invariably impact the outcome of the project's final
incarnation as a green facility.
Use LEED to guide you through the process. It may seem as if design choices
reflect far too many variables for decision makers to understand, let alone
measure. Rest assured that the power and practicality of the LEED process
simplifies and prioritizes the decision-making for achieving your green
Understand and accept that there are tradeoffs. The objective of "greenifying"
is not just to earn a particular LEED rating (Silver, Gold or Platinum
signifying increasing levels of energy efficiency and eco-friendliness).
Rather, the key is use the LEED certification process to more easily achieve
the level of efficiency that the project budget will allow.
This integrated systems approach to green design inherent in the LEED
certification process is best demonstrated by evaluating the role of high
performance window glass as a key component in determining the energy efficiency
of an entire facility. Why is that so?
The building envelope - foundation, roof, walls and windows -is the interface
between the building and its environment and a structure's first line of defense
against the elements. Design choices regarding building envelope components
affect a project's ultimate energy efficiency more than the internal systems and
components (lighting, heating and cooling, etc.).
In an era of R-19 walls and ceilings (R being a measure of insulating
performance), window glass has been the weak link in conservation performance.
From 25% to 35% of the energy used in American buildings is wasted due to
inefficient windows and glass, which themselves account for 10% of all CO2
Improving the performance of windows represents a significant savings
opportunity both for the nation and for individual green building and renovation
projects. Glass options alone will have a disproportionate impact on overall
building energy efficiency compared to other building components. In that regard
let us evaluate those glass options in terms of their impact on energy
efficiency and achieving a project's green objectives.
Single pane glass does not adequately prevent heat transfer and is no longer
acceptable for buildings in most of the US.
Standard insulating glass, providing an insulating performance of R-2 as
compared to an R-19 wall, is obviously unacceptable although still
code-compliant in many locations. Selection of standard insulating glass
will necessitate the use of much larger and expensive HVAC systems than
would otherwise be the case.
Insulating glass with low-e coatings, providing twice the insulating
performance of standard insulating glass, simultaneously reflects radiant
solar and ambient heat and is the de facto energy efficient standard for
buildings in which both summer cooling and winter warming are important. The
"e" in low-e, which stands for "emissivity", is the ability of a surface to
Many might think that this is where the story ends, because generic low-e
insulating glass, consisting of two pieces of coated glass separated by a
sealed, gas-filled air space (or cavity), achieves a maximum R value of 4.
However, this level of performance is not nearly enough to achieve what green
building promises in terms of energy savings and CO2 reduction. Fortunately,
much of the success of green construction is due to higher performing glass
technology that provides powerful energy-conserving alternatives to generic
low-e glass and about which facility managers need to become familiar.
Understanding these superior glass options in relationship to LEED accreditation
(see sidebar below) will help optimize design choices and achieve desired green
Alternatives to single-cavity low-e insulating glass are available that can
narrow the energy conservation performance gap between windows and walls. One is
triple pane glass, consisting of three panes of glass and two low-e coatings. By
using a third pane of glass to create a second insulating cavity, triple pane
low-e glass doubles the performance of low-e insulating glass from R- 4 to R-9.
Unfortunately, triple pane glass is 50% heavier than standard insulating glass,
imposing size constraints and requiring stronger window framing at increased
A superior multi-cavity alternative consists of suspending a very thin, low
emissivity and solar reflective coated film inside of an insulating glass unit.
Without the weight disadvantages of a third pane of glass, suspended film can
create two, three or even four insulating cavities that maximize light
transmission and provide conservation performance ranging from R-6 to an amazing
R-20. Such internally-mounted films do not replace low-e glass. Rather, they
leverage the benefits of film-based and glass-based technologies to create a
lightweight, multi-cavity insulating glass that offers a level of performance
that enables designers to downsize or eliminate other building components (AC
systems, perimeter heating, etc) to cost-effectively achieve maximum energy
Calculating the energy-conserving value of a particular glass option is more
meaningful when it is evaluated as part of an integrated approach to a
building's energy conservation design as exemplified by the LEED certification
process. The selection of suspended film insulating glass at Manheim Township
High School in Lancaster County, Pennsylvania, played a key role in the school's
ability to qualify for a LEED Silver designation. This high school facility
consists of renovated and newly constructed buildings totaling 432,000 square
feet. The use of suspended film insulating glass enabled project engineers to
specify a smaller HVAC system, which provided considerable up-front cost savings
that made the ROI of the high performance insulating glass much more attractive
than otherwise would have been the case.
Consider the numbers. Specifying suspended film insulating glass cost Manheim
about 3X that of generic low-e glass, saving 40% in annual energy costs. The
payback: 11.5 years. However, factoring in a $90K up-front savings by being able
to specify a smaller HVAC system reduced the payback to 6.5 years. This
"holistic" approach to green design, in which building components are selected
as part of an integrated system to achieve the greatest cost savings and total
energy performance, is precisely how LEED architects are designing the
"greenest" buildings today.
When facility managers are assessing such issues as energy efficiency,
greenhouse gas emissions, occupant comfort and well being, window glass
specifically, and the building envelope more generally, must be viewed together
with all other building components by as an integrated system to maximize
desired conservation results at the most affordable cost. Understanding the
potential of film-based, multi-cavity insulating glass to reduce costs while
achieving desired efficiencies will make the choices of decision makers that
much more effective in the greening of facilities.
Bruce Lang is Vice President of Marketing & Business Development at Southwall
Technologies, Inc., in Palo Alto, CA. He can be reached at firstname.lastname@example.org.
Southwall's Heat MirrorÆ suspended film insulating glass units are available
from over 50 window and insulating glass manufacturers world wide.
LEEDing the Way
With its energy-saving performance capabilities,
multi-cavity suspended film insulating glass offers an
opportunity for a project to flexibly achieve certification
under the LEED program.
The thermal and solar shading performance of suspended film
insulating glass as part of an integrated construction or
renovation strategy can help project manager's earn up to 21
LEED credits, or 54 percent and 40 percent of the total
required credits for Gold and Platinum certification,
respectively. Superior glass performance can help achieve
LEED credits in the following categories:
Sustainable Sites (SS) Credit 1, Site Selection
Energy and Atmosphere (EA) Credit 1, Optimize Energy
Materials and Resources (MR) Credit 1, Building Reuse;
MR Credit 5, Regional Materials;
Indoor Environmental Quality (EQ) Credit 2, Increased
EQ Credit 7, Thermal Comfort; and
EQ Credit 8, Daylight & Views.