Float
Glass
Viracon uses clear and tinted float glass from
all the major U.S. float glass manufacturing companies.
In the float glass process, the molten glass is
introduced to a molten tin bath.
The glass floats on the tin and spreads, seeking
a controlled level. Controlled heating allows
the glass to flow, forming a flat ribbon of uniform
thickness while on the tin bath. After the tin
bath, the glass is slowly cooled; then, it is
fed off the molten tin into the annealing lehr
for further cooling. The glass thickness varies
by changing the speed at which the glass ribbon
moves into the annealing lehr.
The float glass process was developed in the early
1900s. Due to technical problems, its development
was delayed. In 1959, Pilkington Brothers Ltd.,
England, introduced float glass for commercial
uses. Today, there are three types of flat glass
manufactured in the U.S.: sheet, float and rolled.
Float glass accounts for over 98 percent of the
flat glass currently being produced in the U.S.
It is the fundamental building block in the world
of fabricating architectural glass.
Solar Spectrum
The
solar spectrum, commonly referred to as sunlight,
consists of ultraviolet light (UV), visible light
and infrared (IR). The energy distribution within
the solar spectrum is approximately 2 percent
UV, 47 percent visible light and 51 percent IR.
One aspect of the solar spectrum is its wavelength
in which nanometer (nm) is the unit of length
[1 nm = 10-9 m].
UV is invisible to the human eye and has a wavelength
range of ~300 - 380 nm. The damaging effects on
long-term UV exposure results in fabric fading
and plastic deterioration.
Visible light is the only portion of the solar
spectrum visible to the human eye. It has a wavelength
band of ~380 - 780 nm.
IR is invisible to the human eye, has a wavelength
range of ~790 - 3000 nm and has a penetrating
heat effect. Short-wave IR converts to heat when
it is absorbed by an object.
Heat Transfer Methods
Heat
transfers from one place to another via convection,
conduction or radiation. Convection occurs from
the upward movement of warm, light air currents.
Conduction occurs when energy passes from one
object to another. Radiation occurs when heat
is sent through space and is capable of traveling
to a distant object where it can be reflected,
absorbed or transmitted (see Figure 1).
Solar
Energy
When solar energy meets glass, portions of it
are reflected, absorbed or transmitted—giving
you the RAT equation (see Figure 1).
RAT Equation
The RAT equation accounts for 100 percent of solar
energy, which is equal to the sum of solar reflectance,
absorption and transmittance. For example, with
a single pane of 1/8" (3 mm) clear glass,
83 percent of solar energy is transmitted, 8 percent
is reflected and 9 percent is absorbed by the
glass (see Figure 2).
Solar Control
The visible light and IR portions of solar energy
are an essential part of sunlight, since they
represent nearly 100 percent of the solar spectrum.
As a result, each plays an important role when
glass is selected as a glazing material for commercial
building applications. To enhance thermal performance,
thin metallic films are applied to one or more
glass surfaces.
Solar Reflective
Coatings
Solar reflective coatings reduce solar heat gain
through higher reflection and absorption with
the glass appearing mirror like. Typically, the
coating reflects and absorbs high amounts of visible
and IR portions of the solar spectrum. As a result,
heat gain is dramatically reduced, but the trade
off is lower light transmission through the glass.
Monolithic Glass
Today, glass is used for building construction
to fulfill many design and performance requirements.
Some of these include allowing natural daylight
into the building while reducing unwanted heat
gain.
Viracon's
Solarscreen™ High-Performance
Reflective Monolithic Glass
This type of glass combines the thermal advantages
of insulating glass with the superior control
characteristics of Solarscreen reflective coatings.
