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Visual discomfort in a day-lit interior environment is usually represented by the degree of discomfort glare perceived by the user. The paper reports on the evaluation of several models for the prediction of discomfort glare from daylighting, using data collected over a 10-month period, in a purpose built test cell. The Daylight Glare Index (DGI) was evaluated according to different interpretations of the background luminance (L b ). The evaluation of the models led to a better understanding of the effect of the adaptation function and a modi ed DGI is explored in light of these ndings. The Uni ed Glare Rating (UGR), which is the CIE model for the prediction of discomfort glare from arti cial lighting, was also evaluated to identify the differences between the two approaches and to test the potential for the development of a general UGR that would include both lighting environments. List of symbolsL s source luminance (cd/m 2 ) L b background luminance (cd/m 2 ) L a average luminance (cd/m 2 ) L w window luminance (cd/m 2 ) E un average vertical illuminance from surroundings (lux) E s average vertical shielded illuminance from source (lux) v solid angular subtense of source at the eye of the observer (sr) V solid angular subtense of source modi ed for the effect of the position of the observer in relation to the source 1 (sr) pGuth Position Index 2 f con guration factor of source in respect to the measurement point 3 n number of glare sources

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a b s t r a c tCool roofs are most effective in reducing cooling loads and alleviating overheating in locations with high solar radiation and external air temperature. This paper presents results of an experimental study of a low income house in Jamaica and a computational study in three countries around the equator: Jamaica, Northeast Brazil (Recife) and Ghana. A case-study typical of single storey houses in Jamaica was monitored before and after the installation of a cool paint on the roof; on days with average solar radiation intensity of ∼420 W/m 2 and ambient air temperature of ∼28 °C, internal ceiling surface temperature is reduced by an average of 6.8 °C and internal air temperature by 2.3 °C. Monitoring results were used to calibrate successfully an EnergyPlus model; similar models were developed for Ghana and Brazil differing in size and/or construction to reflect country specific practices. Annual simulations indicate that internal ceiling surface temperatures are reduced on average by 3.2-5.5 o C and internal air temperatures by 0.75-1.2 °C. Cooling demand simulations (setpoint 24 °C) indicate similar annual potential savings in the three locations ( ∼190 kWh/m 2 /year) although estimated CO 2 emissions reduction differ reflecting electricity generation fuels. Aging of the cool roof has an impact reducing load savings by 22-26 kWh/m 2 /year.

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