The Break Down
The exterior environment of a building envelope is subject
to ever-changing environmental conditions such as wind, humidity, rain,
sun and ambient temperature. One of the most significant influences on
the building envelope design is the sun. The sun is composed of ultraviolet
(UV), visible and infrared light that is dynamic and constantly changing
relative to the building. Designs that do not take the sun’s influence
into account can subject building occupants to conditions such as uncomfortable
glare, solar heat gain, variable temperatures and the early decay of fabrics,
and surfaces that fade over time.
A dynamic glazing product is a fenestration product that
has the fully reversible ability to change its optical performance properties,
such as visible light and near infrared transmission and solar heat gain
coefficient. These properties can be changed in different ways; some change
in response to electrical stimuli, others change in response to absorbed
sunlight, and some respond to ambient temperature. The ability to modulate
these properties provides for a building envelope that adapts to the outside
environmental conditions (or user requirements) and provides higher energy
performance by capturing useful daylight while controlling glare and unwanted
solar heat gain.
Types of Dynamic
Electrochromic (EC) Glazing
An electrical stimulus is used to change the visible light transmission
(VT) and solar heat gain coefficient (SHGC) of electrochromic glazings.
Tinting occurs with the application of a low voltage DC (<5V) current,
which causes lithium ions to move from an ion-storage layer through an
ion-conducting layer, into an electrochromic layer. The presence of ions
causes this electrochromic layer to absorb visible light, in proportion
to the number of ions transferred, thus making the glass appear tinted.
This glazing can be switched from a highly transparent state to a highly
tinted state stopping anywhere in between.
EC glazing can be configured to respond to manual control
through a simple switch on the wall, or can be controlled automatically
using, for example, sensors (e.g. for light, temperature, occupancy),
or by time of day with manual override as necessary. The VT range for
EC glazing can range from 3 to 62 percent and the SHGC can range from
0.09 to 0.48 in a dual-pane insulating glass unit.
EC glazing can be produced in dual-glazed insulating glass
units as well as triple-glazed units to provide good thermal insulation
performance or used as part of a laminated construction for safety. The
SHGC and VT can be varied to let as much light and heat into a building
as desired based on environmental conditions such as glare, daylight levels
or temperature and the needs of the building occupants, without loss of
view to the outside.
There are two main configurations for EC glazing: all ceramic
monolithic or organic laminated.
All ceramic monolithic glazing is made by depositing a
series of very thin coatings on glass, generally using large area sputter
(vacuum deposition) coating, the same process which is used to make millions
of square feet of low-E coatings annually. All layers in the coating are
applied to one lite of glass and all materials are durable ceramic, inorganic
materials. The resulting coated lite is fabricated like low-E coated glass
into insulating glass units which fit into fenestration framing systems.
The monolithic coating stack also has low-E properties, so additional
low-E coatings are not generally required in the finished insulating glass
With organic laminated glazings, some of the layers are
applied to one lite of glass and some to a second lite, which are then
laminated together in a non-structural laminate. In these products the
laminating material is a polymer ion conductor and forms part of the functionality
of the EC. This laminated unit can be made into an insulating glass unit
incorporating a low-E coating added for insulation performance.
Photochromic materials change their transparency in response
to UV light. This glazing can be glass with integral photochromic compounds
or a photochromic film that is laminated between or applied to glass.
The main application of photochromic materials is in eyeglasses that change
from clear in the dim indoor light to dark in the bright outdoors. Currently
there are no cost-effective, large, durable photochromic products on the
market for architectural glazing applications.
Photochromic –Electrochromic Hybrid
Lawrence Berkeley National Laboratories (LBNL) and others have
conducted research on a UV-activated photochromic glazing that is electrically
reversible. Currently there are no cost-effective, large, durable, hybrid
photochromic products on the market for architectural glazing applications.
Polymer Dispersed Liquid Crystal (PDLC)
This glazing is made by encapsulating a liquid-like layer in
which organic particles are suspended between two sheets of polyethylene
terephthalate (PET) plastic, coated with a transparent conducting oxide,
then laminated between two lites of glass using two adhesive layers. Liquid
crystal technology has been used for more than 20 years as privacy glazing
because it transitions from an opaque to transparent state. When power
is off, the liquid crystals are in a random and unaligned state. They
scatter light, which makes the glass appear translucent, thus obscuring
direct views and providing privacy. When the voltage is applied the crystals
align, allowing light to pass through and thus appearing transparent.
The light transmission and the solar heat gain coefficient
are not modulated in this product (the light is scattered, not blocked),
so it provides little energy or glare control performance. As a result,
this type of dynamic glazing is used most often for privacy in interior
applications, such as bathrooms, conference rooms, and changing rooms
in retail stores.
This type of dynamic glazing changes its VT and SHGC properties
based on absorbed sunlight. These products continuously change their tint
level based on the amount of the sun’s energy incident to the window.
A sunlight-activated glazing is constructed with an extruded
thermochromic polyvinyl butyral (PVB) film utilizing existing PVB film
lamination equipment used worldwide. Additives in the film respond to
increasing temperature to slowly vary the VT and SHGC, as well as fading
factors when laminated be ween two lites of glass and exposed to the sun.
The change in glass characteristics is based on the directness of the
sunlight on the window and thus responds based on sun angle. The absorbed
sunlight warms the glass and causes the change in light transmission (proportional
to the temperature), the warmer the window gets the darker it gets, the
cooler the window gets, the more transparent it gets. In an insulating
glass unit with a double silver low-E, for good thermal performance, the
VT ranges from 60 percent down to less than 10 percent based on absorbed
sunlight and window construction. Tinted glass can be used on the outboard
of an insulating glass unit. The outboard lite of the laminated unit can
be tinted. Tinted glass and a variety of low-E coatings can be used in
this laminated glass product.
Suspended Particle Device (SPD) Glazing
In a similar way to PDLC glazings, SPD’s are constructed utilizing
two electrically conductive coated plastic layers with an emulsion containing
suspended particles placed between the plastic layers forming a film or
sheet. This is then laminated between two lites of glass utilizing two
adhesive interlayers, one on either side of the plastic-film. SPDs are
electronically controlled to provide variable tinting. When a voltage
(~80V) is applied to the SPD, the suspended particles align and allow
light to flow through unhindered (the clear state). Once the electricity
is turned off, the particles revert to a random pattern and block light
(the tinted state). SPD can be in the form of a monolithic glass-plastic
laminate or this laminate can be incorporated into insuating glass units
with the addition of a low-E glass for improved insulation value.
This type is constructed with the active thermal component
between lites of glass or plastic. If it is between plastic, it then has
an adhesive applied to the glass. If it is between two lites of glass
it can be a monolithic laminate or combined into an insulating glass unit.
There are three types of thermotropic glazing: reflective, absorbing and
light scattering. The visible light transmission of a thermotropic glazing
changes when the ambient temperature exceeds a fixed activating temperature
set point. The VT changes from a highly transparent state to a tinted
reflective or light scattering state (depending on the type) when this
temperature threshold is exceeded.
Benefits of Dynamic Glazing
The US Department of Energy (DOE) states that dynamic solar
control on the building envelope is a critical component in achieving
net zero commercial buildings. In combination with two other key façade
related technologies, low U-factor fenestration (to reduce thermal energy
losses), and addressable, dimmable lighting controls, an integrated solution
can be provided to maximize energy efficiency and provide a clear path
to achieving net zero1.
The Windows and Daylighting Group at LBNL has studied the
performance of electrochromic glass. Its studies have shown that electrochromic
windows can save up to 60 percent of daily lighting energy and predicted
that commercial build ings relying on electrochromic window systems could
save up to 28 percent in energy costs when compared to buildings with
static, spectrally selective, low-E windows2. Additional studies by LBNL3
show that electrochromic glass can help achieve:
• 10-20 percent operating cost savings;
• 15-24 percent peak demand reduction; and
• Up to 25 percent decrease in HVAC system size.
Natural daylight through glass benefits peoples’ health and
well-being. However, glazing can also cause thermal and visual discomfort.
Indeed, interior building temperature is a primary occupant complaint.
Perimeter offices have a tendency to be cold in the winter and hot in
the summer. In addition, occupants may be affected by significant glare
on their computer screens. Dynamic glazing can improve thermal and visual
comfort significantly while preserving the view and connection to the
outside. Studies4 have shown productivity increasing by 0.5-5 percent
annually with increased daylight and better control of office temperatures.
Because they do not become opaque, these glazing products do
not provide complete privacy. However, they do give some measure of it
in that the more tinted the glass is, the harder it is to see through
from the exterior of the building. It should be understood that, when
light levels are substantially higher on one side of the dynamic glazing
than the other side, one will still be able to see through them. PDLC
glazing is the only switchable glazing that
provides strict privacy by switching from clear to opaque, by scattering
the light, but it does not provide light and heat attenuation. Dynamic
glazing for use on the building envelope generally switches from a highly
transparent state to a more tinted state, preserving a clear view to the
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