Re ECF Project: 2011-23

Project Title: Green features for sustainable daylighting design in buildings

Applicant: Prof. Mak Cheuk Ming of The Hong Kong Polytechnic University

Total Approved Grant: $426,240.00 (ECF & WWGF: 50/50)

Duration: 7/2/2013 to 6/2/2015

Project Status/Remarks: Completed

The objectives of the project are to study, demonstrate and promote the usefulness of two types of building green features, namely sunshades & reflectors and balconies to optimize the daylighting performance so as to eliminate unnecessary energy use in lighting and air-conditioning system with a view to achieving a sustainable development and arousing public awareness of sustainable building lighting design.

Summary of the Findings/Outcomes:
Questionnaire survey and numerical simulation were conducted to demonstrate the effects of green features, including sunshades, reflectors and balconies, on residents’ subjective luminous comfort, daylighting performance and energy use in Hong Kong housing units. Luminous comfort was firstly found to be most affected by satisfaction with daylighting. External obstructions are the major physical factors affecting luminous comfort, and uniformity is the major factor of residents’ feelings toward daylight. Green features affect luminous comfort indirectly by affecting residents’ feelings and behaviour patterns stealthily. A cumulative metric, Daylight Autonomy, was chosen by adopting the climate-based simulation to quantify luminous comfort. Based on this metric, Energy Daylight Ratio was proposed to optimize the green features by considering the balance of daylighting performance and energy consumption. The best reflector structure was found to be a meniscus section which was wide at the top and narrow at the bottom with a curvature angle ranging from 44.3° to 90°. Balconies provided unexpected poor condition of privacy, which enforced residents to use internal shading and artificial lighting more often. Lengthening the overhang is an efficient way for shading but many public housing units need to open a second window to meet comfort requirements. Design guideline was produced to provide suggestions to the design of green features used in buildings and disseminate the knowledge to engineers and stakeholders in building industry. Two research seminars were conducted and two research papers based on the findings were published.