Daylighting through unshaded and shaded windows | |
| Author | Lerdlekha Tanachaikhan |
| Call Number | AIT Diss. no.ET-10-02 |
| Subject(s) | Daylighting Energy conservation |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Energy Technology, School of Environment, Resoruces and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ET-10-02 |
| Abstract | Electric lighting is a second largest energy consuming sector in air-conditioned buildings and, in turn, also raises cooling load for air conditioning system. Daylighting using skylight has been shown to have a high potential in reducing electrical lighting energy, and could also provide a more pleasant atmosphere of daylit space and allowing people to have visual contact with the exterior view. Howeve r, in hot climates, the main constraint of daylighting is the solar heat gain that contributes to major heat load for air-conditioning system. Therefore, daylighting strategies for energy conservation aim to control heat gain especially in air conditioned buildings wh ile still benefiting from light gain. Recently, appropriate designs for daylighting as well as the effective daylighting system installation have not yet been fully defined. Also, no standard methods for design of daylighting system are available. The main objective of this research is to evaluate the potential of daylighting for energy conservation and analyze suitable window conf igurations that allow beneficial gain of daylight while allowing minimal gain of heat under the tropical climate conditions through experiments and analysis. The two specific objectives are the studies on windows with and without shading device to assess the influences of window and shading designs on daylighting. A detailed procedure for calculating daylight illuminance, heat gain, and energy consumption due to daylighting in a typical office building was carried out. The window and shading design parameters, such as, window size, orientation, glazing, shading type and dimension, and lighting control method were chosen for theoretical analysis based on literature review, reference building configur ation, and also tropical climate conditions. Moreover, the calculation model developed was validated by comparing the results obtained for the case of Bangkok climate and a typical office building to those from previous results and from experimental observations. The results of the simulation study for uns haded windows indicated that, at Bangkok the potential for daylighting is high, as more than 90% of occupancy period can be sufficiently illuminated by daylight alone compared to 70% in Montreal, Canada. The possible savings in lighting are in the ranges of 63% to 99%, and the overall savings from daylighting is up to 65% compared to no daylight applied condition. The influences of shading devices on daylighting were also studied by choosing exterior shading devices commonly used in tropical buildings, namely, vertical fins and ve rtical louvers to assess the performance for east-facing window and horizontal shelf and horizontal louvers in analysis of south-facing window. Shading devices are therefore appr opriate only for window with large opening areas as beneficial light gain and heat gain control are well balance and up to 50% of saving in cooling can be expected. The influences of shading designs were analyzed by choosing four variables for shading dimension of vertical fins and horizontal shelf and for tilted angle of vertical and horizontal louvers. Vertical fins would be less influenced by variation of shading size while the significa nt influences of shading dimension can be observed for horizontal shelf due to considerable reduction of daylight availability. Louvers are also notably influenced by tilted an gles which contribute to variation of total electric power. The optimum power demand is relatively identical for five considered tilted angles of vertical louvers while the minimum power required for window facing south is fully-open horizontal louvers. Experiments were set up for measurement of interior illuminance and heat gain through glazing under the variation of tropical climate c onditions to evaluate the accuracy of light and heat calculation models. Interior daylight illuminance was measured at three distances from window. The measurement of heat gain through glazing was performed separately for short wavelength (solar transmission) and l ong wavelength heat components (convection and radiation) by measuring composition parame ters and then calculating for experimental results. For unshaded window, Relative Root Me an Square Difference (RRMSD) values of point illuminance and heat gain through glaz ing from calculation and measurement were within 50% and 25%, respectively. The influences of sky variation were also analyzed for unshaded window on south façade during work hours. Point illuminance and solar heat gain were found to be influenced by sky va riation especially under clear sky condition while heat convection and thermal radiation were insignificantly varied under tropical sky condition. Window with shading devices (horiz ontal shelf and louvers) can exhibit lower variations of light gain and heat gain through glazing with 48% of RRMSD for point illuminances and up to 37% of RRMSD for total heat gain through window system. Uncertainties of measurement were estimated using error propagation analysis and found up to 2.3% and 18% of uncertainties for poin t illuminance and heat gain through glazing, respectively. In conclusion, the potential of daylighting in the tropics was assessed in this study by using the calculation model developed and then validated by experimental study. It can be indicated that the beneficial light gain and reduction of heat gain due to daylighting can be obtained by use of appropriate window designs and shading devices. Many parameters such as window area, window height, glazing, and shading configuration, were also found to have significant influences on daylighting performance in terms of daylight availability and energy demand for lighting and cooling that should be taken into consideration to achieve the optimal potential of daylighting. |
| Year | 2010 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ET-10-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Chairperson(s) | Kumar, Sivanappan; |
| Examination Committee(s) | Honda, Kiyoshi ;Salam, Abdul; |
| Scholarship Donor(s) | Queen Sirikit Scholarships (Queen HRD) ;Energy Policy and Planning Office (EPPO) ;Ministry of Energy, Royal Thai Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2010 |