SENV 7006
Case Study
Qualitative analysis
Daylighting and control
Actually, in order to achieve good daylight and views in occupied spaces, designers make better use of optimized glazing in different direction elevations, especially in the south and north. However, normally western and eastern direction are installed with little openings because excessive solar radiation. Shown in the figure 1 is the optimum orientation in Des Moines of Iowa, where the IUB/OCA building located. It is clear that the best orientation is southeast so that the key strategy should be taken orientation into account. On the one hand, the building has take advantage of daylighting. On the other hand, unnecessary glare must be minimal.
Figure 1 optimum orientation in Des Moines of Iowa (Eco-tect)
In IUB/OCA building, each side of façade is determined by sun exposure, running the two-wing structure along an east-west axis with a shallow north-south depthprovided optimum solar orientation. This orientation, along with a proper footprint depth, allowed the building to take advantage of the more appropriate and controllable north and south daylight and natural ventilation opportunities. What’s more, in the south direction, where fenestration is supported by daylight-harvesting, and visible light transmittance is maximized at this area to work in concert.
For example, figure 2 indicates that main work area is placed in the south, making for decreasing the need of artificial lighting and intensely maximized daylighting. Even the workstation furniture―based on daylight modeling―was optimized. Light color furniture panels with translucent upper panels were selected for the open office spaces; the translucent panels contribute to daylight harvesting for high reflection. More importantly, light tube skylights installed in the building deliver additional daylighting in other sides. On the northern exposure the interior windows are also installed to maximize daylighting by increasing the diffuse north side light.
Figure 2 open space workstations on the south[3]
Figure 3 northern elevation daylighting design[3]
As a result, at the innermost space of the building, daylighting proved that the selected spaces allowed for the required footcandles at the work surface but without artificial lighting for 70% of the time[2]. Above all, the design team also uses various daylighting control strategies with dimming the fluorescent lighting in the interior spaces. The dimming is either stepped or continuous and is examined for the open offices, private offices, conference room, and lobby/corridor areas. Daylighting photo sensors are investigated for continuous dimming control in the open and private offices.
Lighting and control
Along with natural daylighting, artificial lighting including proper lamps, ballasts and lighting control by switch on or off are used to achieve energy saving and great visual experience. According to ASHRAE 90.1-2004, there is different allowable lighting power in different space function or typical building usage. To be more specific, the standard minimum code lighting power density is about 1.30 W/sf, while the design team selects 3 different densities: 1.00, 0.75 and 0.50 W/sf, respectively, in terms of various functions[3].
Figure 4 artificial lighting[5]
As for specific lighting type, super T8 lamps, extra efficient ballasts, high Kelvin lamps are chosen for highly reflective innermost spaces. Further speaking, due to different working time and function use, the design team determined in certain zones a lower than code lighting system allowed for power density equal to 0.75 W/sf and occupancy sensor controlled lighting provided sufficient energy cost savings to be included in the building design strategies. Dual level switching and manual dimming of electric lights were also designed into the conference room.Occupancy sensors are used throughout the building, even in the open office, where at night and on weekends lighting is only allowed if staff is working.
Figure 5 lighting system [1]
Shading and control
On the one hand, louvered sunscreens, along with horizontal blades and vertical fabric panels (figure 6) at the south elevation of each wing, reflect daylight during all seasons, on the other hand, they can well block unwanted heat gain in summertime, but allow passive winter heating. The parabolic profile (figure 5) reflect high elevation sunshine off of the curved portion to give daylighting in the innermost spaces and low winter sun angles maintly from the flat portion of the louvers[4].
The sunscreens, combined with an optimal building footprint depth, allow daylight to penetrate deeply into the building during all seasons. Furthermore, Zinc-clad office enclosures on the north take advantage of diffusing northern light. As for west and east direction, each wing with glazing strategically located to outside views. These windows were placed for key views at circulation minimized; they have additional fritting to minimize glare and provide more shading.
Figure 6 Sunscreens with parabolic louver blades are an integral part of the
daylighting strategy at IUB/OCA building [2]
Figure 7 Occupied Hour Average Lighting Power Densities by Building Zones[2]
Quantitative analysis
Dayligting metrics
Daylighting at levels that allow lights to be off during daylight hours: 98%
Views to the Outdoors: 98%
Within 15 feet of an operable window: 53%[1]
Lighting system
Shown in the figure 7 is how much the occupied hour average lighting power densities in different building spaces. We can see that south level 1 area has lower average lighting power densities than that of north level area. It is should be mentioned that south zone is used for working section, which seems to be half less than north area. Compared to north area and south area normally used for office area, link area use more lighting energy, which almost comprised of public spaces. Overall the lighting energy use is quite low in this building, and the lighting availability in main working area is high.
Monthly lighting energy consumption is indicated in Figure 8. The building employees make better use both lighting control and natural daylighting features to help reduce lighting energy consumption. Analysis of data collected demonstrates that automatic daylighting controls have helped the building maintain a near uniform electricity consumption for total building lighting at approximately 4,300 kWh/month.
Figure 8 Monthly Energy Consumption of Lighting System[2]
Note:The overall energy performance of IUB/OCA office building was analyzed based on the data collected in one full operating year starting in April 2012 through March 2013.