High-Performance Glass for High-Performance Schools
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By Glenn Miner, Director, Construction PPG Industries
Daylighting strategies can have a significant impact on energy consumption
in educational facilities, particularly those that incorporate advanced
solar control, low-e glasses such as double-silver-coated Solarban 60 glass
and triple-silver-coated Solarban 70XL glass by PPG, both of which were
specified for CY Middle School (featured on page 36 of this issue).
To quantify the energy-saving capability of these products, which are
designed to maximize light transmittance while blocking the sun’s radiant
heat energy, PPG commissioned an independent energy and environmental
analysis firm to conduct energy modeling studies on a prototypical 200,000
square-foot middle school.
To ensure accurate and objective results, the testing corporation used the
U.S. Department of Energy’s (DOE) 2.2 Building Analysis Tool, which is
regarded as the most accurate and well- documented energy modeling software
in the U.S.
The DOE 2.2 tool calculates hour-by-hour energy consumption at prototype
buildings over an entire year. Input includes hourly climate data for the
building’s location as well as local utility costs, heating and air
conditioning systems and controls, interior and exterior building mass,
shading and fenestration, hourly scheduling of occupants, lighting
equipment, thermostat settings and numerous other variables.
For comparative purposes, the testing firm modeled three glazing types:
Solarban 70XL glass
Solarban 60 glass
Dual-pane, spectrally selective, tinted glass (light-green)
Relevant performance data for each glazing type is included in the
The three architectural glasses were glazed on the prototype school: one
with punched windows on each façade and another with complete window
walls on each exposure. It was equipped with a packaged VAV air-handling
system, DX coils for cooling, an economizer, hot-water boilers for the
heating plant, and a gas water heater.
Operating hours were from 7:00 a.m. to 9:00 p.m. on weekdays from
September to June, and from 10:00 a.m. to 3:00 p.m. on weekends during
July and August. The heating and cooling temperatures were 72oF and
Internal peak load assumptions were 125 square-feet per-occupant, and
1.1 watts of lighting and .45 watts of equipment per-square-foot.
To provide a representative sample, the prototype school was tested with
climate data from 10 major U.S. cities. In addition to representing a
range of weather conditions, the cities had widely fluctuating prices
for natural gas and electricity, which were obtained and factored into
In the end, 120 energy-modeling simulations generated precise
calculations for building load, cooling equipment size, energy costs and
HVAC cooling costs.
The following chart compares the performance of Solarban 60 and Solarban
70XL glasses to more commonly specified spectrally selective, dual-pane
tinted glass in the prototype, window-walled middle school.
Single-story middle school, four window walls, Total Floor Area: 200,000
ft2; Total Glass Area: 45,027 ft2
Annual Energy Cost Savings
The study showed that schools constructed with Solarban 60 glass instead
of dual-pane tinted glass can expect annual energy savings that range
from 5 percent ($7,204) in St. Louis to 8 percent ($13,510) in Seattle
and Chicago ($19,395). Average annual energy savings with Solarban 60
glass across the 10 U.S. cities was 7 percent ($18,992).
While the energy savings from Solarban 60 glass were impressive, they
were significantly less those realized with Solarban 70XL glass.
When substituted for dual-pane tinted glass in the same middle school
building, Solarban 70XL glass generated energy savings of 8 percent
($23,137) in Philadelphia to 12 percent in Phoenix ($26,967) and Houston
($42,727). The 10-city average for energy cost reductions was more than
10 percent ($27,726).
HVAC Equipment Cost Savings
Because of their ability to block heat and transmit light, schools with
Solarban 60 and Solarban 70XL glasses require less cooling capacity than
those glazed with less-advanced products, which enables architects and
school administrators to spend less on HVAC equipment for their
With Solarban 60 glass in place of dual-pane tinted glass, initial HVAC
equipment cost savings for the prototype middle school averaged 9
percent ($111,947), including 10 percent reductions in such
climactically diverse cities as Phoenix ($134,171), St. Louis ($125,090)
and Boston ($122,169).
In schools modeled with Solarban 70XL glass, HVAC equipment costs were
slashed by 14 percent in Chicago ($182,603) and Philadelphia ($174,383),
and 19 percent ($229,919) in Los Angeles. The average equipment cost
savings for all 10 cities was nearly 17 percent ($207,613).
Lower Operational Costs. More Educational Resources.
Energy modeling demonstrates that schools equipped with advanced
architectural glass can reap the rewards of an investment that pays for
itself many times over.
Over the 40-year lifetime of a typical middle school, annual energy
savings of $25,000 can total $1 million, enough to pay for 2,000
computers or 50,000 textbooks. What’s more, the value of that investment
continues to grow with the escalation of energy prices, a trend that
will accelerate well into the future.
Even more important, however, is the investment in our country’s
schoolchildren. It has never been clearer that schools with abundant
daylight, fresh air and a strong visual connection to the outdoors help
provide the best possible environments for learning and growth. By
investing in the latest solar control, low-e glasses, architects and
school administrators can get energy savings they need while promoting
the academic performance they demand. In the end, that makes them a
winner for students, parents and taxpayers.