Estimation of outdoor illuminance for passive solar architecture in Malaysia

Illuminance and daylight availability are important parametersin daylighting design for passive, low energy architecture. In Malaysia, the only climatic parameter that can be used for determining daylight availability is global solar irradiation, which is measured at major meteorologicalstations around the country. However, it is possible to estimate the global illuminance from global solar irradiation data if the global luminous efficacy is known. Several attempts have been made to determine the mean and hourly global luminous efficacy values for the sky at Shah Alam in the Klang Valley, Malaysia, which is about 15 km away from Malaysias capital city, Kuala Lumpur. Global solar irradiation data is available from this station and global illuminance may be derived from solar irradiation data using global luminous efficacy,KG. Past studies in the determination of KG involved the measurement of global illuminance using simple outdoor luxmeters and simultaneous data collection of global solar irradiance using a pyranometer. The present study used a sky scanner to measure both parameters simultaneously from the sky dome. The results of the present study were then compared with the results of previous work for the same location. The mean global luminous efficacy was calculated for each set of data using the General Illuminance Model. The monthly average illuminance was then estimated using the obtainedKG while the irradiance data used were from the Model Year Climate (MYC) data. The illuminance was also calculated using the Du Mortier-Perraudeau-Page (DPP) Model recommended for intermediate or averagesky types. The results of KG obtained from the 2 periods of measurements were then compared with that produced by the DPP Model. This paper shows that the sky scanner results are closer to the data produced from the DPP model than those obtained from the separate luxmeter-pyranometer experimental set-up.