Discomfort glare is an underutilized parameter in contemporary architectural design due to uncertainties about the meaning of existing metrics, how they should be applied and what the benefits of such analysis are. Glare is position and view direction-dependent within a space, rendering it difficult to assess compared to conventional illuminance-based metrics. This paper compares simulation results for five glare metrics under 144 clear sky conditions in three spaces in order to investigate the ability of these metrics to predict the occurrence of discomfort glare and to hence support the design of comfortable spaces. The metrics analyzed are Daylight Glare Index, CIE Glare Index, Visual Comfort Probability, Unified Glare Rating and Daylight Glare Probability. It is found that Daylight Glare Probability yields the most plausible results. In an attempt to deal with multiple positions and view directions simultaneously, the concept of an 'adaptive zone' is introduced within which building occupants may freely adjust their position and view in order to minimise the effect of glare. The spatial and directional extents of the adaptive zone depend on furniture layout and the freedom of occupants' tasks. It is found that applying the adaptive zone concept to a sidelit office with manually operated venetian blinds reduces the predicted hours of intolerable discomfort glare from 735 to 18 occupied hours per year and increases the annual mean daylight availability from 40% to 72%. Nomenclature L s luminance of the glare source (cd/m 2 ) ! solid angle of the glare source (sr) ! pos the solid angle of the glare source modified for its position in the field of view (sr) P weight factor based on position in a viewing hemisphere, the position index E v total vertical eye illuminance (lux) V solid angle of a viewing hemisphere subtended by glare sources (sr) L b background luminance determined by taking the average luminance of areas not identified as glare sources (cd/m 2 ) L adapt adaptation luminance (cd/m 2 ) L exterior average exterior luminance (cd/m 2 ) L window average window luminance (cd/m 2 ) E d direct vertical illumination (lux) E i diffuse vertical illumination (lux) E ave average illuminance for a viewing solid angle of 5 steradians

In this paper we present, demonstrate and validate a method for predicting city-wide electricity gains from photovoltaic panels based on detailed geometric urban massing models combined with Daysim-based hourly irradiation simulations, typical meteorological year climactic data and hourly calculated rooftop temperatures. The resulting data can be combined with online mapping technologies and search engines as well as a financial module that provides building owners interested in installing a photovoltaic system on their rooftop with meaningful data regarding spatial placement, system size, installation costs and financial payback. As a proof of concept, a photovoltaic potential map for the city of Cambridge, Massachusetts, USA, consisting of over 17,000 rooftops has been implemented as of September 2012. The new method constitutes the first linking of increasingly available GIS and LiDAR urban datasets with the validated building performance simulation engine Daysim, thus-far used primarily at the scale of individual buildings or small urban neighborhoods. A comparison of the new method with its predecessors reveals significant benefits as it produces hourly point irradiation data, supports better geometric accuracy, considers reflections from neareby urban context and uses predicted rooftop temperatures to calculate hourly PV efficiency. A validation study of measured and simulated electricity yields from two rooftop PV installations in Cambridge shows that the new method is able to predict annual electricity gains within 3.6 to 5.3% of measured production when calibrating for measured weather data. This predicted annual error using the new method is shown to be less than the variance which can be expected from climactic variation between years. Furthermore, because the new method generates hourly data, it can be applied to peak load mitigation studies at the urban level. This study also compares predicted monthly energy yields using the new method to those of preceding methods for the two validated test installations and on an annual basis for ten buildings selected randomly from the Cambridge dataset.

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In this paper, we present a post-occupancy study of 326 participants in 10 daylit office buildings in Singapore and correlate the results with climate-based daylighting metrics and electric lighting simulations using calibrated simulation models of the 10 buildings. For the first time, this study tests the climate-based daylighting metrics which are used in building design against their impact on occupant perception within buildings. We find significant correlations between climate-based daylighting metrics and reported occupant satisfaction with access to daylight, view interest, perception of ‘too low’ lighting levels and visual comfort. Overall, climate-based daylighting metrics which account for lower illuminance thresholds such as continuous daylight autonomy and useful daylight illuminance combined (100–3000 lx) correlate more strongly with subjective results than do electric lighting sufficiency metrics such as daylight autonomy at 300 and 500 lx thresholds. Simple descriptive statistical representations of annual daylight distributions, mean and median annual daylight illuminance values, outperform climate-based daylighting metrics in correlation strength and p-value. Based upon these results, new metrics are proposed for occupant satisfaction with daylight access and views. In addition, increased daylight levels are shown to decrease reporting of lighting levels being ‘often too low’ even when adequate electric lighting is provided, and contrast is likely to be beneficial to space perception at non-glaring thresholds.

Disability glare, or visual impairment due to extreme brightness or contrast, can be caused by intense reflections from new constructions onto existing transportation or building infrastructure located nearby. A case study analyzed a disability glare hazard at an airport created by the installation of a large array of photovoltaic panels between an air traffic control tower and the aircraft taxiway. The panels reflected blinding quantities of daylight into the control tower, produced temporary afterimages, and dangerously obscured taxiing aircraft. The existing FAA guidelines for installation of solar technologies are discussed relative to their shortcomings in identifying the glare hazard. High dynamic range photography was used to analyze the glaring situation at the airport. The authors proposed a maximum brightness threshold of 30,000 cd/m2 based on the physiology of human vision and the brightness of tasks necessary for air traffic controllers at the case study airport. Detailed reflectivity and three-dimensional models of the photovoltaic panels and the airport were created and validated against measured data. These models were used to perform an annual analysis of the glare hazard. This analysis is displayed temporally by graphs and spatially by images that indicate where the glaring reflections originate. Such information is useful in identifying potential for disability glare before new constructions are built. Finally, the authors used the new method to analyze designs for remediation of the glare hazard.