1、706 2009 ASHRAEABSTRACTThe development of spectrally selective low-e glass with its superior solar control and high daylight admission has led to widespread use of large-area, “transparent” or visually clear glass windows in commercial building facades. This type of faade can provide significant inh
2、erent daylighting poten-tial (ability to offset lighting energy use) and move us closer to the goal of achieving zero energy buildings, if not for the unmit-igated glare that results from the unshaded glazing. Conven-tional shading systems result in a significant loss of daylight and view. Can innov
3、ative shading solutions successfully balance the tradeoffs between daylight, solar heat gains, discomfort glare, and view?To investigate this issue, a six-month solstice-to-solstice field study was conducted in a sunny climate to measure the thermal and daylighting performance of a south-facing, ful
4、l-scale, office testbed with large-area windows and a variety of innovative indoor shading systems. Indoor shading systems included manually-operated and automated roller shades, Venetian blinds, daylight-redirecting blinds, and a static trans-lucent diffusing panel placed inboard of the window glaz
5、ing. These innovative systems were compared to a reference shade lowered to block direct sun.With continuous dimming controls, all shading systems yielded lighting energy savings between 43-69% compared to a non-dimming case, but only the automated systems were able to meet visual comfort criteria t
6、hroughout the entire monitored period. Cooling loads due to solar and thermal loads from the window were increased by 2-10% while peak cooling loads were decreased by up to 14%. The results from this experiment illustrate that some indoor shading systems can preserve daylight potential while meeting
7、 comfort requirements. Trends will differ significantly depending on application.INTRODUCTIONInterest in energy-efficient buildings has increased signif-icantly due to mounting concerns over the rising cost of oil, depletion of fossil fuels, and global climate change. The build-ing industry is feeli
8、ng more pressure to deliver building energy-efficiency and performance at levels significantly beyond what has been achieved in the past. It is common to hear design teams stating ambitious objectives of beating code by 30% to 50% or attaining zero energy building (ZEB) status through a combination
9、of efficient technologies, design, and renewable energy sources.The mission statements of US public funding agencies such as the US Department of Energy (DOE) and the Califor-nia Energy Commission Public Interest Energy Research (CEC PIER) program, who have sponsored this research, have long been fo
10、cused on the development and deployment of innovative, near- and long-term technological and design solu-tions to improve the nations energy security and ensure economic growth. Adoption of innovative emerging technol-ogies, however, has traditionally been slow. Industry has been cautious and risk a
11、verse over the past decades. With the stron-ger desire and pressure to meet the global challenges of today, demand has grown for innovative solutions that can deliver significant, reliable energy use and demand reductions, while meeting occupant comfort and other practical requirements.While the lev
12、el of motivation for energy-efficiency may have changed, the practical basis for business decision making has not. Architects, engineers, and building owners still require practical assurances that an energy-efficiency measure will Field Measurements of Innovative Indoor Shading Systems in a Full-Sc
13、ale Office TestbedE.S. Lee D.L. DiBartolomeo J.H. Klems, PhD R.D. Clear, PhD K. KonisM. Yazdanian B.C. ParkMember ASHRAEE.S. Lee, J.H. Klems, and R.D. Clear are staff scientists, D.L. DiBartolomeo and M. Yazdanian are principal research associates, and K. Konis is a graduate research assistant in th
14、e Building Technologies Department, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA. B.C. Park is a visiting researcher from Sejong University, Seoul, Korea.LO-09-067 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
15、 (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions 707deliver performance benefits reli
16、ably over the life of the instal-lation in a cost-effective manner and will not lead to any unfore-seen negative consequences. Utilities and regulators in some states like California must meet increasingly stringent energy, demand, and greenhouse gas emission reduction goals so data are needed to en
17、sure that efforts are targeted toward innova-tions most likely to deliver reliable, sustained reductions.Therefore, a primary barrier to accelerating market adop-tion of innovative technological solutions is a lack of sufficient proof or data, which is particularly difficult to obtain for enabling t
18、echnologies such as faade systems. Facades impact both the mechanical cooling, heating, and lighting energy end uses in a synergistic or tradeoff relationship. In terms of energy and comfort, many emerging faade technologies cannot be modeled routinely using traditional simulation tools or require a
19、 level of modeling finesse beyond the budget constraints of most building projects. Field studies or mockups of innovative technologies conducted by third-party entities or internally by the owner, design team, or utility can help to answer many of the practical questions regarding product features,
20、 appear-ance, operational characteristics, and utility of the technology. Obtaining sufficient experimental data to characterize energy savings and occupant comfort, however, is beyond the budget of typical projects.This study seeks to address the above context and barriers to market adoption by pro
21、viding comparative experimental performance data in a timely manner so as to support industry efforts to assess the potential of emerging shading-daylighting technologies in the short term. This phase of field work focused on indoor shading devices, which have potentially broad market applicability
22、in both new and retrofit markets in terms of ease of application and lower cost compared to core and shell improvements or renovations. Daylight-enhancing indoor shading systems and dynamic, motorized shades were evaluated. Outdoor shading devices are being studied in a second phase (June to Decembe
23、r 2008) since these systems can be more effective for low-energy cooling strategies and can be more easily regulated by codes and standards if perma-nently attached to the building.The experiment was designed to provide simultaneously-measured performance data on the wide range of parameters affecte
24、d by innovative window systems in order to quantify the tradeoff relationships between solar and glare control versus daylight admission. The experiment was conducted in a full-scale mockup of a south-facing private office over a solstice-to-solstice period in a temperate, sunny climate. Lighting en
25、ergy use, space cooling load and peak cooling load due to thermal and solar heat gains through the window, illuminance, and visual comfort data are given. Paired (same day) compar-isons were made between the reference and test cases, where the reference shade condition was set to a static position t
26、hat was mostly likely to balance the daylight and visual discom-fort requirements of the occupant.BACKGROUNDThe innovative shading systems used in this experimental test are emerging, commercially available or prototype tech-nologies with low market penetration. Each of the shading systems were desi
27、gned with the intent of balancing a number of competing design parametersview to the outside, daylight, solar control, glare protection, simplicity, and cost.There are several basic principles underlying the innova-tive systems. For systems that allocate different functions to different areas of the
28、 faade, view out is recognized as a key function and this is preserved by allocating view and glare control to the lower window zone with the function of daylight admission and redirection allocated to the upper clerestory zone. Daylight-redirecting systems use a combination of optics (geometry and
29、surface treatment) and automation in some products to redirect daylight to underlit zones further from the window and to improve luminance uniformity over the entire room cavity for better lighting quality. Automated shading systems are actuated in real time to manage daylight, thermal loads, comfor
30、t, and view in response to variable sun and sky conditions.Field studies evaluating the energy- and comfort-related performance of these various innovative systems are limited. Moreover, the studies that have been conducted have not investigated lighting, cooling, and comfort impacts simulta-neously
31、, limiting ones understanding on overall performance impacts. The International Energy Agency SHC Task 21/ ECBCS Annex 29 Daylight in Buildings Source Book (Ruck et al. 2000) classifies various innovative daylighting systems and provides practical information and measured illuminance data on each sy
32、stem. The data illustrates the efficiency of the various systems to redirect daylight but comparisons between different types of systems are difficult since the field data are given for locations world-wide. A field study was conducted at the National Research Council for various combinations of upp
33、er and lower Venetian blinds and lighting controls (Galasiu et al. 2004). Measured parameters included illuminance and lighting energy consumption. In many of these field studies, comfort is not evaluated as part of the study even though satis-faction of comfort requirements can have a significant n
34、ega-tive impact on energy-savings potential. Simulations facilitate parametric evaluation of emerging technologies in a more cost-effective manner. For example, Wienold (2007) presented a method for evaluating control algorithms for shad-ing devices using simulations where energy, daylight supply, v
35、iew and visual comfort are evaluated simultaneously. However, there is significant inherent value in field tests since no simplifying assumptions for sky conditions, operational characteristics, solar-optical properties, and so on are required. There are many field studies measuring the solar and th
36、ermal effects of conventional, static shading systems over the past several decades, but studies measuring innovative shading systems are limited. A study is anticipated from the University of Lund that has measured the lighting and cooling 708 ASHRAE Transactionsenergy savings resulting from daylig
37、ht-redirecting interior blinds (IEA ECBCS Annex 45 2007). Kuhn (2000) provides a calculation method to evaluate the solar shading perfor-mance of innovative internal and external shading devices with various control strategies, whose angle-dependent deter-mination of total transmitted solar energy w
38、as validated using calorimetric measurements.This study focuses on indoor shading solutions for a now prevalent faade type preferred by many prominent architects: highly transparent glass in large areas, often floor to ceiling in height. This trend has been made possible by advanced spec-trally-sele
39、ctive low-e windows that now deliver the same solar heat gain rejection as dark tinted glass but with a clear, trans-parent appearance. The rationale for its use is largely aesthet-ics but also a backlash reaction against the dismal “natural” lighting of dark tinted glass buildings. The daylighting
40、poten-tial of transparent faades is significant and will be an inherent property of the building throughout its 30-50 year lifespan, but without sufficient control will result in adverse impacts such as increased energy use, visual and thermal discomfort, and significant loss of view.The key questio
41、n this study seeks to investigate within the limited context of the experimental setup, therefore, is whether the inherent daylighting potential (ability to offset lighting energy use) of this type of faade can be maintained with innovative shading solutions when the following basic comfort criteria
42、 are met while preserving view:Direct sun falling on task surfaces or the occupant shall be blocked or mitigated for the majority of occupied hours. The orb of the sun should be blocked or mitigated.Discomfort glare should be minimized. In this study, this has been broadly interpreted to mean that t
43、he lumi-nance of room and window surfaces shall be maintained within prescribed levels commensurate with the task being performed in the space. Computer- and paper-based tasks were assumed in this study.The first two criteria can be satisfied through selection of the shading system materials and cal
44、culation of solar geome-try. The third criterion could not be satisfied a priori by the static and some dynamic or automated innovative technolo-gies and were therefore evaluated after field data were collected.METHODFacility DescriptionA 88.4 m2(952 ft2) window systems testbed facility is located a
45、t LBNL, Berkeley, California (latitude 374N, longi-tude 1221W). The facility was designed to evaluate the difference in thermal, daylighting, and control system perfor-mance between various faade, lighting, and some mechanical systems and occupant comfort and satisfaction with the tech-nology and in
46、terior environment under realistic weather conditions. The facility consists of three identical side-by-side test rooms built with nearly identical building materials to imitate a commercial office environment (Figure 1).Each test room is 3.05 m wide by 4.57 m deep by 3.35 m high (10 15 11 ft) and h
47、as a 3.05 m wide by 3.35 m tall (10 11 ft) reconfigurable window wall facing due south. The windows in each test room are simultaneously exposed to approximately the same interior and exterior environment so Figure 1 Exterior view of the LBNL Windows Testbed Facility (left) and floor plan (right).AS
48、HRAE Transactions 709that measurements between the three rooms can be compared. Incident solar radiation was minimally obstructed by exterior obstructions: hills to the east and trees to the west. The altitude of exterior obstructions is less than 20 for azimuth angles between 90-140 (0 = north) and
49、 less than 8 for azimuth angles between 240-270. Exterior surroundings immediately adjacent to the window consisted of a 6.1-m- (20-ft-) deep apron of black asphalt paving then a downward sloping hill and a mixture of vegetation and distant buildings.One desk was placed 0.76 m (30 inch) from the window against each of the two side walls. Other furnishings included a flat-screen LCD monitor and two chairs. There were no obstruc-tions to transmitted solar radiation or daylight immediately adjacent to the window. Interior surface reflectances of the floor, walls, and
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