Page - 52 - in Water, Energy, and Environment - A Primer

technology– it also reflects thebehaviorof theoccupants. Inone illuminating example two families on Martha’s Vineyard in Massachusetts lived in identical zero-energy-designed homes and one family used half as much electricity in a year as the other. In the latter case, electricity for lighting and plug loads accounted for about half of total energy use. As one energy consultant noted: ‘There are no zero-energy houses, only zero- energy families.’ 5.5.7.2 Electrochromicwindows Athird example of an emerging energy efficiency technology is electrochromic (EC) windows. They have fascinated me since I first saw one demonstrated many years ago. It is part of the family of smart glass technologies that control the amount of light and heat that the glass transmits. This control can be activated by temperature (thermochromic), by light (photochromic), or voltage (electrochromic). This chapter will focus on the latter, which offers significant potential for reducing the energy consumed in buildings. They have other useful applications aswell. How do they work?When a voltage is applied between the transparent electrical conductors (usually less than 5 volts) an electric field is set up in thewindowmaterial. This fieldmoves ions reversibly through the ion storage film through the electrolyte and into the electrochromic film. Different ions (typically lithium or hydrogen) produce different colorations, and the window can be switched between a clear, highly transparent state and a transparent blue-gray tinted statewith no degradation in view (similar to that achieved in photochromic sunglasses) by reversingvoltage polarities. Critical aspects of designing and using electrochromic windows includematerials andmanufacturing costs, installation costs, electricity costs, durability, as well as functional features such as degree of transparency, possibilities for dimming, Water,Energy, andEnvironment–APrimer52