Smart Windows

1
Smart Windows

• Presented by John Helme
• 2/27/07

2
What are Smart Windows?

• Smart Windows are windows which use a glazing
  material to control the amount of light that is
  allowed to pass through the glass panes.
• The glazing material is often called switchable
  glazing.

3
Types of Smart Windows

• Non-Electrical
• Photochromatic
• Thermochromatic
• Electrical
• Phase Dispersed Liquid Crystal (PDLC)
• Electrochromatic
• Suspended Particle Device (SPD) or Dispersed
  Particle System (DPS)

4
Non Electrical

• Thermochromatic dependent on temperature
• Photochormatic dependent on ultraviolet light
  intensity
• Both technologies automatically adjust. There is
  no user control.
• Both processes were discovered in about 1870.

5
Thermochromatic Transmittance
Visible light spectrum 380nm to 720nm
6
PhotochromaticTransmission
7
Electrical Systems
Liquid Crystal Electrochromatic Suspended Particle
Power off White Slight yellow or green tint Dark Blue or Black
Power applied Clear (slight haze) Dark Blue Light Blue
Variable State No Yes Yes
Memory No Yes (for a few days) No
Power 1.44 watt/sq.ft 0.32 watt/sq.ft .06 watt/sq.ft
Response time .1 sec on, 4 sec off 1 to 40 min .5 sec on, 1 sec off
Tv when off 58 (diffused) 60 .5 to 10
Tv when on 77 .05 35 to 55
Temperature -4F to 158F 14F to 204F -22F to 194F
Tv Transmission of visible light
8
Liquid CrystalDevice

• Two layers of electrically conductive film
  enclose a layer of tiny liquid crystals.
• When the power is off, the liquid crystals are
  randomly scattered. Light entering the glazing
  does not have a clear path out, and the window is
  a translucent milky white.
• When an electric current is applied between the
  two conductive coatings, the liquid crystals
  align and you can see through the window.

9
Electrochromatic Device

• A bipolar potential is applied to the outer
  transparent conductors.
• Lithium ions migrate across the ion-conducting
  layer from the counter-electrode layer to the
  electrochromic layer.
• A reversible electrochemical reaction takes place
  causing a tinted Prussian blue appearance.
• Reversing the potential causes the ions to
  migrate back, causing a bleached clear
  appearance.

10
Suspended Particle Device

• Microscopic light-absorbing particles are
  dispersed in droplets within a film.
• In the "off" state when no voltage is applied,
  the particles are suspended randomly throughout
  the film and absorb light, making the window
  dark.
• When moderate voltage is applied to the glass or
  plastic wall coatings on both sides of the SPD
  film, the particles align and permit light to
  pass through.
• By varying the amount of voltage, the user can
  adjust the level of light transmission.

11
Modified Smart Windows
A metal hydride switchable mirror which becomes
reflective when injected with hydrogen
12
Conclusion

• Smart Windows should not be used to control the
  maximum temperature of a solar panel because they
  transmit a maximum of 80 of the light, reducing
  the solar panel efficiency by at least 20.
• Smart Windows may work very well for applications
  where transmitting the maximum amount of light
  possible is not important.