Daylighting designs and energy performance for air-conditioned commercial buildings
Student thesis: Doctoral Thesis
Daylighting is an important factor in interior design affecting the functional arrangement of spaces, occupant comfort (visual and thermal), structure and energy use in buildings. Good quality of daylight provides not only a more attractive and pleasing atmosphere in interiors, but also creates a better indoor environment to improve working performance. From the energy and cost-saving viewpoint, the arguments for daylight are also strong. However, very little research work focusing on its energy performance has been done systemically for high-rise building development. This thesis establishes systematic methods to evaluate daylighting and its energy performance for high-rise office buildings in a dense urban area. Building energy standards were studied and evaluated to identify salient features and useful experience. A performance-based building energy approach was adopted to evaluate daylighting and building energy performances using computer simulation techniques. A base-case office model was developed to serve as a baseline reference. To facilitate building energy analysis, a typical weather year for building energy analysis was developed and examined for Hong Kong. Sensitivity analysis was carried out to examine the important design parameters affecting daylighting schemes. Building envelope design parameters namely window-to-wall ratio and light transmittance of windows, and height of external shadings were found significantly for predicting the energy performances, for instances annual building energy expenditure and peak electrical demands. Detailed assessments of building energy performance due to various daylighting schemes and envelope designs were further conducted. Using regression analysis, it was found that the annual incremental electricity use, incremental peak electricity use and incremental peak cooling plant demand are a function of overall thermal transfer value and daylighting aperture. Sets of curves to indicate electricity usage and peak energy demands under different building envelope parameters were developed. Important features for daylighting schemes were highlighted and implications for OTTV designs were discussed. In Hong Kong, many buildings are constructed close to each other and hence the external environments play a significant role in daylighting designs. This thesis investigates the shading effects due to nearby obstructions when daylighting schemes are being employed. Analysis of electricity savings was carried out for the four perimeter zones (north, east, south and west) of the whole building and individual floors. Correlations of building energy savings and the angles of obstructions were developed. It was found that shading effects due to nearby obstructions strongly affect the building energy budget when daylighting designs are used. To extend the consideration of all the design variables together (i.e. building envelope parameters and external elements), multiple regression analysis was performed. A general form of energy equations was developed to help relate building energy performance to various daylighting schemes. Such an advanced technology can maximise the energy saving for daylighting schemes on existing commercial buildings. Recently, the thin film coatings for window glass products have been very suitable for installation of existing buildings for undertaking major refurbishment which provides a means of substantially reducing heat gain without proportionally reducing daylight transmittance. Measurements were undertaken for evaluation of the daylighting performance and energy issues (lighting and cooling) in a fully air-conditioned office using photoelectric dimming controls together with the solar control coating on the window glass. Thermal and visible properties for the window glass coupled with solar film were recorded and analysed. The findings showed that the solar film coating cut down the cooling load and decreased the energy expenditure for air-conditioning and artificial lighting systems. Energy analysis on the application of solar film coating in a reference office building using tinted glass windows with various glazing areas was demonstrated. The external obstructions together with the office building were also modelled based on a similar setting in one of the main business districts in Hong Kong. The findings can provide architects and building designers useful information for the energy saving potential of different daylighting schemes in a densely built urban city.
- Light in architecture, Hong Kong, Energy conservation, China, Daylighting, Design, Commercial buildings