The drive towards sustainable, low-energy buildings has increased the need for simple, yet accurate methods to evaluate whether a "daylit" building meets minimum standards for energy and human comfort performance. Current metrics do not account for the temporal and spatial aspects of daylight, nor of occupants comfort or interventions. This paper reviews the historical basis of current compliance methods for achieving daylit buildings, proposes a technical basis for development of better metrics, and provides two case study examples to stimulate dialogue on how metrics can be applied in a practical, real-world context.

a b s t r a c tThis paper presents a simulation study of the energy and CO 2 benefits of a transparent, near-infrared switching electrochromic (NEC) glazing for building applications. NEC glazings are an emerging dynamic window technology that can modulate the transmission of NIR heat without affecting transmission of visible light. In this study, a hypothetical NEC glazing is simulated on clear and tinted glass in six building type models in 16 U.S. climate regions using Energy Plus 7.1. The total annual energy consumption for lighting, heating, cooling, and ventilation for the NEC glazings are compared with high performance static windows and conventional tungsten-oxide EC glazings. Using regional CO 2 intensities and building stock totals, the results from individual building model simulations are scaled up to national totals. The U.S. national savings from NEC deployment is found to be 167 TWh/yr (600 PJ/yr) compared to the existing building stock, but only 8 TWh/yr (29 PJ/yr) or 1.56 million tonnes of CO 2 per year when compared to high performance static glazings with lighting controls installed. NEC performance varied significantly by building type and location. This analysis reveals that 50% of the total energy savings can be realized by deploying NEC glazings in only 18% of the total window stock, and 75% of the savings in only 39% of the stock. The best performing locations include medium offices and midrise residential buildings in northern climates, where energy savings per unit window area range from 50 to 200 kWh/m 2 -yr.

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Forty-three subjects worked in a private office with switchable electrochromic windows, manuallyoperated Venetian blinds, and dimmable fluorescent lights. The electrochromic window had a visible transmittance range of approximately 3-60%. Analysis of subject responses and physical data collected during the work sessions showed that the electrochromic windows reduced the incidence of glare compared to working under a fixed transmittance (60%) condition. Subjects used the Venetian blinds less often and preferred the variable transmittance condition, but used slightly more electric lighting with it than they did when window transmittance was fixed.

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