Comparing the Results of Static and Dynamic Daylight Simulations

to Support Architectural Decision-Making in the Context of Dhaka

Abstract

The evaluation processes of indoor daylighting by computer simulation are at crossroads between static and dynamic methods. Now-a-days, both the methods are used, yet static method is more widely practiced and perceived by architects, designers and researchers in Bangladesh due to its simplicity. Static method concentrates generally on daylight factor (DF) approach. Under DF approach, overcast sky is usually considered as reference sky and by definition; DF is unable to account for the contribution of direct sunlight. In reality, the sun's position and sky conditions change rapidly; DF is unable to predict the dynamic variations in interior illuminance. Therefore, an alternative concept of dynamic simulation has been developed that can calculate indoor lighting levels considering the annual variances of the outdoor available natural light simultaneously with time. A common argument for the DF approach is that, as the reference overcast sky is the worst sky condition, any other sky will lead to better daylight in the space and additional lighting information obtained from a more detail analysis based on a series of sky models under dynamic simulation often not change the design decisions significantly to justify their inclusion in the early design phase. Using two simulation methods, this paper compares the significance of static and dynamic simulations by demonstrating a case of decision-making among six skylight configurations available for the industrial roof in Bangladesh. ECOTECT is used for static simulation and as the modelling interface to launch DAYSIM - a program used for dynamic simulation. The results show, as the dynamic method considers the contribution of the sun to the overall illumination of the building, it can indicate potentiality of glare resulting from direct sun and/or skylight, therefore, can explain a situation in more detail and accurately, compared to a static method. This paper also presents a general methodology for decision making regarding daylight design elements with both static and dynamic daylight methods.