THE IMPACT OF ROOFING CONFIGURATION ON THE DAYLIGHTING PERFORMANCE OF SKYLIGHTS IN OFFICES

Transcription

1 THE IMPACT OF ROOFING CONFIGURATION ON THE DAYLIGHTING PERFORMANCE OF SKYLIGHTS IN OFFICES LADAN GHOBAD DR. WAYNE PLACE DR. JIANXIN HU NORTH CAROLINA STATE UNIVERSITY, COLLEGE OF DESIGN

2 Introduction Daylighting has great benefits Psychological and physiological effects on body Energy saving 70% of total ELECTRICITY used by BUILDINGS Figure 1. An office with daylight is preferred more than an office without daylight.

3 What is Toplighting? Toplighting: strategy that permits daylight to enter a space from above, through a glazed opening in the roof that protects the interior from wind and weather (Phillips, 2004). Typology Toplighting has great potentials Figure 2. CIBSE Rooflights Typology Reduce 90% of electric use in DL hours Installed on 50% area of nonresidential buildings Figure 3. Phoenix, Arizona

4 Why Toplighting? Toplighting advantages over sidelighting: It creates greater illuminance than sidelights on horizontal surfaces (Tregenza 2011, Place) Depth of plan is no longer a limitation Figure 4. Incident light and admitted light are at a more favorable angle in toplit room. Figure 5. Polytechnic University of Catalunya- Services Building, Barcelona, Spain

5 Problem Statement Toplighting has not been extensively used in commercial buildings (Lawrance & Roth, 2008) Concerns about performance Initial costs Failures of skylights, most widely experienced system Special structural design required Failures of electric lighting controls Figure 6. A skylight at a Walmart Store, Northern Illinois

6 Research Goals 1. Investigate the problems with toplighting systems. 2. Define a range of promising rooflighting configurations, including construction details structural sizing selective construction cost assessments for a range of climates. 3. Simulate and evaluate Daylighting effectiveness Thermal performance 4. Optimize the daylighting parameters and refine the details of all the crucial elements in the systems. 5. Suggest guidelines making recommendations regarding applicability of the systems to various building types and climates.

7 Research Questions Q1: How much electric light could be saved by implementing skylights and linear apertures in flat roofs? Q2: How does daylight quantity and variability differ by changing the construction type in skylights and linear apertures? How much illuminance levels vary with changing the construction type from unintegrated to integrated structure and ductwork? How much illuminance levels vary by splaying the light-well from right angle to 45 in each daylighting configuration? How much illuminance levels change by changing the area and spacing between apertures in case of square apertures (skylights) and linear apertures?

8 Independent Variables Buildings location: Boston Toplighting configurations: Skylights Linear apertures Spacing between apertures Array of 2x2 skylights Array of 3x3 skylights 2 linear apertures 3 linear apertures The glazing to floor area 5% 7% Transmissivity of the glazing 40% 54% Figure 7. Plans and sections for the two skylight roofing schemes, showing the aperture arrangements and aperture dimensions corresponding to SFR = 0.07.

9 Independent Variables Construction type Un-integrated structure and ductwork Integrated structure and ductwork 5'-7" 2' (0.61m) (1.70m) (0.71m) 2'-4" Roof is lowered 2' (0.61m) by 2' integrating the systems. (0.38m) 1'-3" Bottom of light well is raised 2'-4" (0.71m) by splaying ceiling. 2'-4" Figure 8. Two skylight roofing schemes: A. No integration & No Ceiling Splay B. Integration & Ceiling Splay. Light-well configuration Straight light-wells with no splay Splayed light-well with 45 Figure 9. 3D perspective of systems components: A: No integration & No Ceiling Splay B. Integration & Ceiling Splay.

10 Dependent Variables Dependent Variables: Light Quantity Average Daylight Factor Average illuminance Useful Daylight Illuminance (UDI) Figure 10 : Daylight Factor defined as internal/external illuminance in standard overcast condition Figure 11: UDI map shows useful daylight in 80.25% of occupied time, for a room with four skylights

11 Dependent Variables Dependent Variables: Light Quantity Light Distribution Variation on horizontal planes Max-to-Min illuminance at task level Max-to-Min illuminance at eye level

12 Dependent Variables Dependent Variables: Light Quantity Light Distribution Electric Light Savings during Operation, however: 1. Reduced internal heat gains by electric lighting Metrics: 2. Increased solar heat gains 3. Increased thermal transmittance of roof Annual Electric Use (kwh/ft 2 ) Annual Savings ($/ft 2 )

13 Modeling Modeling in Rhino Building Parameters Building function: Office Dimensions: 30ft x 30ft Surrounded by eight other identical spaces No interior partitions or walls Height: 9 ft Lighting Target: Desk-based workplace with Ambient light: 300 lx Desk-lights where needed

14 Results Illumination Variation A: 2 x 2 Array of Square Apertures. B: 3 x 3 Array of Square Apertures. C: 2 Linear Apertures. D: 3 Linear Apertures. Figure 12. Illuminance on the Work Plane for Various Roofing System configurations.

15 Results- Daylight Factor, Average Illuminances Fig. 13: Average illuminance on task surface with various levels of SFR for integrated, splayed systems Fig. 14: Illuminance variations in spaces with various levels of SFR, for integrated, splayed systems.

16 Ladan Ghobad, Ph.D. Proposal NC State University, College of Design Results- UDI Fig. 15: Annual daylight performance for 2 x 2 and 3 x 3 arrays of square apertures, with systems integration and splayed ceilings (SFR=7%, T=54%) Fig. 16: Annual daylight performance for 2 and 3 linear apertures, with systems integration and splayed ceilings (SFR=7%, T=54%)

17 Kwh/ft 2 /yr Kwh/m 2 /yr Ladan Ghobad, NC State University, College of Design Results- Electricity Use, Savings from electricity SFR7% T=54% Office Area = 900ft 2 = 83.6m 2 Electricity Use (LPD=1.0 W/ft 2 ) (LPD=10.76 W/m2) Annual Lighting Electricity Use Annual Lighting Electricity Costs ($/900ft 2 /yr) (electric cost = $0.15 per kwh in Boston) Base Case No Skylight Uninteg 2x2Array Square Apertures Integ 2x2Array Square Apertures Integ 3x3Array Square Apertures Uninteg 2 Linear Apertures Integ 2 Linear Apertures Integ 3 Linear Apertures Fig. 17: Electricity use for no skylights and six skylight schemes (Kwh/ft 2 /yr), SFR=7%, T=54% Fig. 18: Annual monetary savings from lighting electricity reductions (Dollars / 83.6m 2 module / yr.).

18 Conclusions Splaying the ceiling and integrating the subsystems substantially benefits the daylighting system in terms of: Increasing the quantity of useful illuminance on the task surface. Decreasing the variations of the illuminance on the task surface. Increasing the potential lighting electricity savings from the daylighting. Integrating the ducts into the structural volume allows the roof to be lowered, reducing the cost of the building and wall surface area through which unwanted thermal gains and losses will occur. A product that would assist in the design and construction of sloped ceilings around the light wells would be very helpful in improving the performance and market penetration of skylights for low spaces with hung ceilings.

19 Future Work Add other locations in different climate zones Energy analysis accounted for electricity use reduction; not heating/cooling loads Modification of UDI Change of occupancy schedule from the default 9am-5pm weekdays Provide options for electric light controls (default control in Diva is dimming), account for power drawn by dimmers Define locations of electric lights Adjust location of grid points in models based on the real location of luminaires in the spaces Account for the limitations of the sensors that performs based on the minimum light levels Figure 19. Suggested revision of UDI Lighting Schedule Weekdays 0:00-8: :00-12: :00-13: :00-17: :00-18: :00-20: :00-24: Figure 20. New Lighting Schedule for next step of the research

20 Thank You!

21 References Ander, G. D. (2003). Daylighting performance and design. Hoboken, N.J.: John Wiley. Retrieved from Baker, N., & Steemers, K. (2002). Daylight design of buildings. London: James & James. CIBSE. Code for Interior Lighting. London: Chartered Institution of Building Services Engineers, Citation: Veitch, J. A. (2001). Psychological processes influencing lighting quality. Journal of the Illuminating Engineering Society, 30(1), IESNA Lighting Handbook: Reference and Application, 9th Edition. New York: Illuminating Engineering Society of North America (IESNA), 2000; 1 7: Lagios, K., Jakubiec, A., Niemasz, J., & Reinhart, C. F. (2010). Quick Start Guide for the DIVA-FOR-RHINO Toolbar, Harvard University, graduate School of Design. Lagios, K., Niemasz, J., & Reinhart, C. F. (2010). Animated Building Performance Simulation (Abps) Linking Rhinoceros/ Grasshopper With Radiance/ Daysim. Conference Proceedings of SimBuild 2010, New York City. Larson, G. W. (1998). Rendering with radiance : The art and science of lighting visualization. Lawrence, T., Roth, K. W. (2008). Commercial Building Toplighting: Energy Saving Potential and Potential Paths Forward, Final Report for the U.S. Department of Energy. Lawrence, T., Roth, K., Crawley, D. B., & Brodrick, J. (2008). Toplighting & lighting controls for commercial buildings. ASHRAE Journal, 50(9), Retrieved from Mardaljevic, J., Heschong, L., & Lee, E. (2009). Daylight metrics and energy savings. Lighting Research & Technology, 41(3), doi: /

22 References McHugh, J, Manglani, P, Dee, R, & Heschong, L. (2003). Modular Skylight Wells:Design Guidelines for Nabil A., & Mardaljevic J. (2005). Useful Daylight Illuminances: A Replacement for Daylight Factors. Energy and Buildings, 38(7). McHugh, J. Heschong, L. Heshong Mahone Group. Skycalc Guideline. Chapter 6. Available at Nabil, A., Mardaljevic, J. (2005). Useful Daylight Illuminance: A New Paradigm to Access Daylight in Buildings. Lighting Research & Technology, 37(1), Phillips, D., (2004). Daylighting : Natural light in architecture. Amsterdam ; Boston: Elsevier, Architectural Press. Retrieved from Place, W., Coutier, P., Fontoynont, M., Kammerud, R., Andersson, B., Bauman, F., Carroll, W. L., Wahlig, M., & Thomas L. W. (1987). The Impact of Glazing Orientation, Tilt, and Area on the Energy Performance of Roof Apertures, ASHRAE Transactions, Vol. 93, Part 1A, New York, January Place, W. (2009). Fundamentals of Daylighting. Class lecture notes. Reinhart, C. F., Andersen, M. (2006). Development and Validation of a Radiance Model for a Translucent Panel, Building and Environment, (38) Reinhart, C. F., Mardaljevic, J., & Rogers, Z. (2006). Dynamic daylight performance metrics for sustainable building design. Leukos, 3(1-4), doi: /leukos Slater, A. I., & Boyce, P. R. (1990). Illuminance uniformity on desks: Where is the limit? Lighting Research and Technology, 22, Szokolay, S. V. (2008). Introduction to architectural science : The basis of sustainable design. Amsterdam ; Boston ; London: Elsevier/Architectural Press. Retrieved from Tregenza, P. (2011). In Wilson M. (. P. (Ed.), Daylighting : Architecture and lighting design. New York: Routledge. Retrieved from