1、 Rob Guglielmetti and Jennifer Scheib are Daylighting Researchers at the National Renewable Energy Laboratory (NREL), in Golden, CO. Shanti D. Pless is a Senior Researcher at NREL. Paul A. Torcellini is the Group Manager of the Commercial Buildings Research Group at NREL. Rachel Petro is a Lighting
2、Designer at RNL Design, in Denver, CO. Energy Use Intensity and Its Influence on the Integrated Daylighting Design of a Large Net Zero Energy Office Building Rob Guglielmetti Jennifer Scheib Shanti D. Pless Paul A. Torcellini Rachel Petro IESNA, LEED AP IESNA, LEED AP ASHRAE, LEED AP Ph.D, P.E., ASH
3、RAE IALD, IESNA, LEED AP ABSTRACT Low energy or high-performance buildings form a vital component in the sustainable future of building design and construction. Rigorous integrated daylighting design and simulation will be critical to their success as energy efficiency becomes a requirement, because
4、 electric lighting usually represents a large fraction of the energy consumed. We present the process and tools used to design the lighting systems in the newest building at the National Renewable Energy Laboratory (NREL), the Research Support Facility (RSF). This 220,000-ft2 20,439-m2 office buildi
5、ng was turned over in June 2010. Employees began to move in almost immediately; their number will soon reach 820. The RSF will house a large data center, and is projected to eventually produce as much energy annually as it consumes. Its rapid construction schedule meant that the entire process had t
6、o be tightly integrated. Daylighting had to be integrated with the electric lighting, as low energy use (50% below ASHRAE 90.1-2004) and the LEED daylight credit were contractually required, with a reach goal of being a net-zero energy building (NZEB). The oft-ignored disconnect between lighting sim
7、ulation and whole-building energy use simulation had to be addressed, as ultimately all simulation efforts had to translate to energy use intensity predictions, design responses, and preconstruction substantiation of the design. We discuss how the lighting and building energy use simulation endeavor
8、s were married to inform the RSF design. During the coming year, the RSF will be thoroughly evaluated for its performance; we present preliminary data from the postoccupancy monitoring efforts with an eye toward the current efficacy of energy and lighting simulation methodologies. INTRODUCTION In 20
9、07, the National Renewable Energy Laboratory (NREL) began the procurement process for a new office building. NREL early on decided to create a building that would use one-half the energy of a typical large-scale office building. Building researchers used results from Griffith et al. (2006) to establ
10、ish the 50% savings level as achievable with no additional capital cost. This target is expressed as energy use intensity (EUI). In June 2010, NREL employees began to occupy the Research Support Facility (RSF). This 220,000-ft220,439-m2 office building in Golden, CO, USA, is projected to use 33.3 kB
11、tu/ft2/yr 0.38 GJ/m2/yr less than half the typical energy use for office buildings in the Denver Metro area. This was achieved by using a tightly integrated design-build construction process, and by keeping a sharp focus on the aggressive EUI distilling the buildings energy performance down to a sin
12、gle number that was part of the original Request for Proposals (RFP). We focus on how daylighting and thoughtful electric lighting systems and controls design and simulation can significantly reduce energy consumption, and on how approaching LV-11-C074610 ASHRAE Transactions2011. American Society of
13、 Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAES prior written permission
14、.the design from the standpoint of EUI gives designers and engineers more freedom to design an efficient building by rewarding integrated design, daylighting, and lighting controls. Daylighting the thoughtful introduction of natural light into a building is compelling not only for its many aesthetic
15、 and health benefits, but also for its energy savings opportunity. If a building admits sufficient daylight to the interior spaces, the electric lights can be dimmed or switched in response saving energy that otherwise would have been used to energize the light fixtures, and potentially addressing t
16、he added heat from the lamps. Daylighting means much more than letting light in, however. Windows and skylights allow natural light into a space, but can also hasten heat loss in winter and increase solar heat gain in summer; occupants can experience disabling glare from poorly shielded fenestration
17、. In essence, if one merely adds daylighting features such as windows and skylights without considering daylighting functionality such as lighting controls that respond to available daylight daylighting is likely to fail. But with lighting typically representing 30-40% of a commercial buildings tota
18、l energy use, an integrated daylighting design strategy that reduces the duration and intensity of electric lighting use should be considered a keystone strategy in any high performance/low energy building. To that end, Torcellini et al. (2006) classify daylighting as a best practice in high-perform
19、ance building designs, and list six keys to its successful implementation. These key aspects were integrated into the RFP for the RSF: Design daylighting into all occupied zones adjacent to an exterior wall or ceiling Provide for integral glare mitigation techniques in the initial design Provide aut
20、omatic, continuously dimming, daylighting controls for all daylit zones Design interiors to maximize daylighting distribution Integrate the electric lights with the daylighting system Commission and verify postoccupancy energy savings The RSF was procured as a high-performance building, and the ligh
21、ting design (which includes the daylighting) was critical for its success as a low energy building; still, all buildings can benefit from this lighting design concept. ENERGY USE INTENSITY AS A DAYLIGHTING DRIVER A primary goal of the RSF project was to create a low energy building; this was express
22、ed in the EUI goal that was central to the procurement process, and to the selection of a capable design-build contractor (the RFP and amendments are available at http:/www.nrel.gov/sustainable_nrel/rsf.html). The RFP mandated an EUI of no more than 25 kBtu/ft2/yr 0.28 GJ/m2, assuming a standard gov
23、ernment building occupant density of 650 employees, 220,000-ft220,439-m2 building area, and a data center large enough to serve the RSF occupants. As part of the RFP, a method to normalize for additional space efficiency and external data center use was established. As a result, the final as-built E
24、UI was normalized to 35 kBtu/ft2/yr 0.40 GJ/m2 for a building that accommodates 820 people, and includes a data center that can serve the entire NREL campus (at the time of project completion, this was approximately 1200 users). This ambitious energy target refocused the design team on total energy
25、consumption by the lighting systems in a way that current codes and building rating systems do not capture. Building codes generally approach lighting energy efficiency via ever-tighter lighting power densities (LPDs), but as these allowances continue to be revised downward, this approach has begun
26、to infringe on the lighting designers ability to meet other critical criteria such as minimum illumination levels and uniformity ratios, not to mention aesthetic creativity. Reliance on the connected load as the sole standard for lighting energy efficiency also prevents the design from taking credit
27、 for daylighting controls; daylighting a building will not save energy unless the electric lighting is used less often. By moving toward an energy use-based metric such as EUI to define building performance, the lighting designer is empowered to take advantage of daylight-responsive electric lightin
28、g controls, and in turn is incentivized to consider daylight as a core component of the lighting system. The entire team becomes motivated to work together toward an optimized, integrated lighting solution that saves energy. We believe this optimization is most efficiently discovered through simulat
29、ion. 2011 ASHRAE 611DAYLIGHTING A LEED Platinum rating was sought for the RSF; as such, every point that could reasonably be achieved was considered. The LEED iEQ8.1 “daylight credit,” which dictates that a large percentage of the occupied space receive illumination from daylight, was also mandated.
30、 As a result of this target and the aggressive EUI goal, the design-build team looked at daylighting as an energy efficiency strategy from a very early stage. Work to integrate and best take advantage of daylighting took place during the design competition phase. Daylighting simulation with Radiance
31、 (Ward 1994) was already being used during this phase. Based on Torcellini at al. (2006), the team sought to extend the daylight-illuminated zone as far north as possible, and optimized the fenestration by creating two discrete panes of glass with specific functions. The lower glazing was intended t
32、o provide shielded, glare-free views to the exterior; we call this the view glazing. The upper glazing was designed to provide maximum daylight penetration. This has a high visible light transmittance and is located high on the wall section to maximize the potential for daylight flux delivery to the
33、 interior; we call this the daylight glazing. The team selected an optical louver system to occupy the daylight glazing to provide glare control and to redirect the incoming solar radiation onto the ceiling and deeper into the space. To explore the systems ability to optimize the floor depth, a 3D b
34、uilding model of a typical office wing was created in AutoCAD and simulated in Radiance. With an eye toward the LEED iEQ8.1 goal, point-in-time simulations were conducted to determine how broadly an illuminance level of 25 footcandles 269 lux could be achieved at 30” 0.76 m above the finished floor
35、under clear skies, at noon, on the equinox one compliance demonstration method available under LEED iEQ 8.11. The building model was modified to study different fenestration options such as window head heights, window-to-wall area ratios (WWRs), and glazing visible light transmittances. This iterati
36、ve modeling process revealed 60-0” 18.3 m to be the maximum floor plan depth (north-south) that could be illuminated to the criteria set forth by the LEED compliance standards, given other optimization constraints such as floor to ceiling height and WWRs. Through the normal course of design developm
37、ent, Radiance was used to evaluate various changes to the design to determine their impact on the daylighting. A variety of interior finishes were studied, furniture options such as plan location, partition heights, and interior wall and ceiling configurations were investigated, and a series of chan
38、ges were recommended. Changes included increasing the size and lowering the mounting height of the optical louver units, and revised room surface finish reflectances. ELECTRIC LIGHTING The electric lighting design was influenced by best practices and lessons learned from other NREL campus buildings
39、again, informed through simulation. Design Process and Criteria The EUI is useful for a broad view of the designs progress toward the unifying team goal, but every energy-efficient building design must include smaller task, load, and aesthetic-specific subgoals. For quantity, the team first decided
40、on space-by-space design illuminance criteria, which were based on recommendations from IESNA (2000) (see Table 1). For the open offices, 25 footcandles (fc) 269 lux and a 4:1 maximum-to-minimum illuminance ratio were selected as the ambient workplane illuminance and uniformity criteria. The task li
41、ghting contribution was set to 20-30 fc 215-323 lux additional, to meet the IESNA office recommendation of 30-50 fc 323-538 lux for general office task lighting overall. Additional lighting design expectations were also defined: accent lighting for architectural features, displays, and artwork; ease
42、-of-service; emergency and security requirements; and system durability. Energy subgoals were defined as well. EUI information about high-performance buildings is not prevalent enough to warrant system-specific design criteria, so the RSF started with a more pragmatic design approach. The ASHRAE/IES
43、NA 1The RSF project was certified under LEED v2.2; the new LEED 3.0 simulation-based compliance path for the daylight credit is slightly different. 612 ASHRAE Transactions90.1-2004 LPD limit for typical office space (per the building area method) was reduced by 30%, from 1.0 to 0.7 Watts/ft2 10.7 to
44、 7.5 Watts/m2. Additional energy-related subgoals included reasonable feature proportions and zoning consistent with annual daylight saturation. After lighting subgoals were defined, an iterative process of selecting and laying out electric lighting fixtures, estimating illuminance and uniformity, a
45、nd performing simulations in this case, using AGi32 (Lighting Analysts, Inc. 2010) for design validation ensued. The final primary light fixture selection for the open offices was a 92.8% efficient, direct/indirect pendant-mounted luminaire utilizing four-foot, 25-Watt T8 fluorescent lamps, which pr
46、ovide 25 fc 269 lux maintained illuminance at the workplane. Because these lamps are sometimes incompatible with dimming ballasts, the team required letters from all proposed lamp manufacturers that ensure extended dimming operation to 10% would not diminish lamp life. (Lamp striation at discrete di
47、mming levels and temperature conditions is still a possibility, but has not been observed in the RSF.) Task lights (6-Watt LED arrays on adjustable heads) were included as part of the procurement package and provided at all workstations. Compact fluorescent downlights, metal halide accent lights, an
48、d LED interior and exterior pathway lighting were also included. The final building LPD is 0.62 Watts/ft2 6.7 Watts/m2; a sampling of space-by-space LPDs is given in Table 1. Controls Philosophy The lighting controls were developed in tandem with the electric lighting design. Much like the electric
49、lighting quantity was “layered” with ambient and task contributions, layering of control types was also implemented. This approach was an attempt to balance energy (using electric lighting only where and when needed), cost, usability, and ease of commissioning. The latter two drivers came from previous experiences where an entirely automated lighting control system was confusing for occupants and frustrating for commissioning agents. This ultimately causes the system to never be implemented as planned, and results
