Proceedings of Meetings on Acoustics

Transcription

1 Proceedings of Meetings on Acoustics Volume 19, ICA 2013 Montreal Montreal, Canada 2-7 June 2013 Architectural Acoustics Session 1aAAb: Cultivating the Sustainable in Architectural Acoustics 1aAAb2. Achieving Leadership in Energy and Environmental Design acoustical requirements in a commercial office project Ethan Salter* *Corresponding author's address: Charles M. Salter Associates, Inc., 130 Sutter Street, San Francisco, CA 94104, ethan.salter@cmsalter.com This paper will discuss a recently completed a Leadership in Energy and Environmental Design Commercial Interiors (LEED CI) office renovation project in San Francisco, California. The project had multiple aims: office space, test laboratory for new materials and technologies, and teaching tool for clients and students. The owner, an acoustical consulting firm, decided on LEED CI certification because of the belief that acoustic comfort could be achieved while simultaneously meeting other LEED requirements (e.g., design, products and materials, construction methods, and operations). Recently, acoustical requirements have been adopted into various LEED rating systems because occupant acoustic comfort in many LEED certified buildings has been poor. The organization responsible for LEED, the US Green Building Council, is taking steps to more comprehensively adopt acoustical standards throughout their portfolio. By using the LEED Innovation in Design (ID) Pilot Credit Library, projects can attempt to achieve a wider range of potential credits. One of those credits, Pilot Credit 24, addresses acoustic comfort, including sound isolation, speech privacy, background noise, and reverberation time. The project is one of the first to achieve Pilot Credit 24 requirements. This paper will discuss the project design objectives, Pilot Credit 24 requirements, and how the project achieved those requirements. Published by the Acoustical Society of America through the American Institute of Physics 2013 Acoustical Society of America [DOI: / ] Received 23 Jan 2013; published 2 Jun 2013 Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 1

2 INTRODUCTION This paper explains how a commercial office interior renovation project in San Francisco, California was designed to achieve the Leadership in Energy and Environmental Design (LEED TM ) Pilot Credit 24 requirements for acoustical performance. Pilot Credit 24 was developed so that a wide variety of projects receive credit for improved acoustical design. Although sustainable, green building is one of the dominant trends in architecture, development, and construction, post-occupancy evaluations (POE s) of green building occupants have found the acoustical environment needed improvement. As such, the USGBC promulgated Pilot Credit 24 as a way to bridge between current LEED TM rating systems for new construction and commercial interiors, which do not address acoustics, and future versions of LEED TM, which will include acoustical requirements (schools and health care facilities excepted). These projects have included acoustical design for some time. While this project has been discussed in other publications (Cavanaugh, et al, 2009), this paper details recent updates. This paper discusses occupant satisfaction in green buildings, the USGBC s process for promulgating Pilot Credit 24, an overview of the office project design, (including measured data), as well as how the project submitted information to the USGBC and subsequently achieved Pilot Credit 24 compliance. OCCUPANT SATISFACTION IN GREEN BUILDINGS Since 1996, the University of California, Berkeley s Center for the Built Environment (CBE) have surveyed thousands of occupants in hundreds of buildings across North America identify how satisfied occupants are with their air quality, lighting, thermal comfort, cleanliness, and acoustical comfort and privacy within (Jensen, et al 2005). The U.S. Government s General Services Administration (GSA) has also conducted surveys of their real estate portfolio (U.S. GSA, 2012). Since its inception, a growing number of buildings in the CBE survey incorporate aspects of sustainable or green design. Survey data show that while green buildings have higher overall satisfaction scores than conventional buildings, in the majority of green buildings, acoustical comfort and quality is rated worse than conventional buildings. By contrast, survey respondents say that they prefer many green design attributes, such as the increased access to natural light, or the use of building materials. Increasingly dense, open, collaborative environments, (and the corresponding reduction in closed offices), brings into sharper relief the trend of less-thansatisfied occupants. Although the relative lack of occupant satisfaction in open plan offices for various reasons has been noted previously (Veitch, et al, 2002), the contrast between green building occupants dissatisfaction with acoustics and satisfaction with other aspects of these spaces deserves further scrutiny. The trend of occupant acoustical satisfaction lagging increased satisfaction in other categories led the U.S. General Services Administration (GSA) to commission their Sound Matters study, completed in Intended as a guide for office design across the Government s portfolio as well as for the design public at large, this study provides a good quantitative background for how the interrelated concepts of occupant behavior, room acoustics, background noise, and sound isolation promote occupant comfort and appropriate speech privacy. WIDESPREAD ADOPTION OF ACOUSTICS INTO LEED TM RATING SYSTEMS The United States Green Building Council s (USGBC s) Leadership in Environmental Design (LEED TM ) rating system is perhaps the most well-known of many such systems developed around the world over the past 20 years. These rating systems not only address buildings impacts on the water, air, habitats, and materials of the Earth, but also their impact on people: the occupants, those living nearby, and because of a greater awareness of climate change consequences. Such systems are based on achieving both mandatory pre-requisites and credits, which are optional. As has been noted previously in the literature (Cavanaugh, et al, 2009), originally LEED TM did not have any prerequisites or credits that related directly at all to occupants acoustical comfort. Because of this oversight, some projects sought to achieve Innovation in Design, or ID credits, which a project could garner by either achieving a significant performance increase in a particular area, or else address an aspect of design that the base rating system did not include. In response to post-occupancy evaluation data, as well as continuing collaboration with their technical advisory groups and industry stakeholders (e.g., Acoustical Society of America, ASHRAE, ANSI, ASTM, Facilities Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 2

3 Guidelines Institute (FGI), and others), the USGBC has concluded that acoustical comfort in buildings is just as important as comfort in other areas. Beginning with the LEED TM for Schools rating system, the USGBC incorporated prerequisites and credits specifically for acoustics. Recently, as part of the preparation for the continuing evolution of the LEED TM rating system, the USGBC created the Pilot Credit Library. One of the most important new pilot credits is Pilot Credit 24 (PC24), the only one in the Library which addresses acoustical comfort. PC24 is designed for use by all new construction/major renovations (LEED TM NC), and commercial interiors (CI) project, which comprise the majority of new LEED projects. The indirect, unforeseen consequences of encouraging building designers to create energyefficient, materials-efficient buildings which ended up being poor acoustically are methodically being remedied. The USGBC has signaled the significance of building acoustics by incorporating new credits based on PC24 for acoustical performance into the upcoming LEED TM Version 4 (USGBC, 2012). SPEECH PRIVACY MEASUREMENT AND PREDICTION One of the most significant findings from the POE surveys is that there are widespread complaints from occupants in contemporary green buildings about a lack of speech privacy. Speech privacy depends on the source s noise level, the noise reduction of the partition(s) separating the two spaces, sound absorption in both the source and receive spaces, and the background noise level in the receiving space. By examining each variable, speech privacy predictions can be made during design (Salter, et al, 2003). Speech privacy (or lack thereof) in office environments is a common complaint (Salter, et al, 2012). LEED TM PILOT CREDIT 24 ACOUSTICAL CRITERIA Pilot Credit 24 (USGBC, 2011), addresses the following aspects of architectural acoustics: 1) background (HVAC) room noise levels; 2) speech privacy; 3) airborne sound isolation; 4) reverberation time (RT); and 5) paging, masking, and speech reinforcement. PC24 criteria were developed refined through consultation with the USGBC s technical advisory groups (TAGs), as well as industry groups such as ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers), ASA (Acoustical Society of America), ANSI (American National Standards Institute), and CEN (Comité Européen de Normalisation) (USGBC, 2012). 1. Room Noise Levels: Room noise levels should fall within the sound level ranges shown in the Air Conditioning, Refrigeration, and Heating Institute (AHRI) Standard , Table 15, shown here: TABLE 1. Background Noise Criteria. Building Type Room Type RC(N) or NC Range Office Buildings Executive and private offices 25 to 35 Conference Rooms 25 to 35 Open Plan Offices 40 Corridors and lobbies 40 to Speech Privacy: A project should meet the following speech privacy goals for enclosed rooms. Normal speech privacy should generally be provided between all enclosed, private spaces. Confidential speech privacy should be achieved between spaces occupied by different tenants, and for all other spaces deemed confidential by building occupants. The three metrics (AI, PI, and STI), are considered independent. TABLE 2. Speech Privacy and Intelligibility Criteria. Speech Privacy Goal Articulation Index (AI) Privacy Index (PI) Speech Transmission Index (STI) Normal < % 0.19 Confidential < % Sound Isolation: In lieu of Building Code requirements, a project should meet composite Sound Transmission Class (STC c ) ratings dependent on project type and room adjacencies (below for offices): Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 3

4 TABLE 3. Adjacency Combinations in Office Buildings, Relevant to Project Spaces. Adjacency Combinations STCc Standard Office Standard Office 45 Conference Room Conference Room 50 Office/Conference Room Hallway/Stairway Reverberation Time and Reverberant Noise Buildup: Pilot Credit 24 requires projects to meet reverberation time requirements adapted from ASHRAE s Performance Measurement Protocols for Commercial Buildings. Maximum reverberation times are for sound pressure levels in the 500, 1,000, and 2,000 Hz octave bands. TABLE 4. Reverberation Criteria. Building Type Room Type RT 60 (Seconds) Executive and Private Offices <0.60 Office Buildings Conference Rooms <0.60 Open Plan Offices (without Sound Masking <0.80 Open Plan Offices (without Sound Masking Paging, Masking, and Sound Reinforcement Systems: All large conference rooms seating more than 50 are required to consider electronic sound reinforcement and audiovisual playback capabilities, achieving: Minimum Speech Transmission Index (STI) of 0.60 or a Common Intelligibility Scale (CIS) of 0.77 at representative points of coverage to provide acceptable intelligibility from the system. 70 dba minimum sound level Maintain sound level coverage within ±3 db at the 2,000 Hz octave band throughout the space Sound Masking Systems should meet the following requirements: 48 dba maximum sound pressure level Loudspeakers provide uniformity of ±2 dba throughout their zones of coverage Suitable spectra shall be designed to effectively mask speech spectra PROJECT DESIGN GOALS In 2007, the acoustical consulting firm of Charles M. Salter Associates leased 4,500 square feet (almost 420 square meters) of space on the sixth floor of the historic Halladie Building in downtown San Francisco, California. The Hallidie building was the first all-glass curtain wall building in the western United States. Prior to being leased by Charles M. Salter Associates, the office space was used by a small call center, with perimeter private offices arrayed around a central open space. While the office was specifically intended to house the firm s technology consulting department as well as add formal conference and multipurpose space, from the outset it was designed to show different acoustical materials, design approaches to clients and students. Figure 1 shows the project floorplan. The firm s offices have occupied the fifth floor of the Hallidie Building for over 20 years. The new 6 th floor office included a reception area, nine private offices, open plan offices, multi-purpose area, conference room, and kitchen. The space has windows facing north, overlooking the building s loading dock and an alley. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 4

5 FIGURE 1: 130 Sutter Street, 6th Floor Office Space, with color coding for specific room types. Private offices (red), conference room (green), reception (blue), and copier room (orange) surround the center open plan and multipurpose areas (no color). Begun in earnest in 2008, the project sought to implement feasible methods of working within the LEED TM -CI system to achieve acceptable office acoustical comfort. The original plan was to emulate the then-new LEED TM for Schools rating system, which included for the first time prerequisites for acoustical performance (e.g., background noise and reverberation time). As part of the firm s due diligence, background noise measurements (NC) and airborne noise reduction (NIC) tests were conducted prior to demolition to measure baseline acoustical performance. In 2011, during the process of design, construction, occupancy, and LEED TM submittal documentation, Pilot Credit 24 (PC24) was initiated as part of the LEED TM rating system as a way for projects to incorporate acoustical requirements which addressed recent research and a greater range of requirements (e.g., speech privacy, paging and sound masking, sound isolation). The renovation achieved the following objectives: 1. Materials conservation and re-use: The office design included reuse of gypsum board, door hardware, and metal framing retained from the pre-demolition office. Interior partitions, window, and doors from the existing office space were reused where possible. 2. Construction waste management: Construction and demolition waste was diverted through recycling, minimizing overall landfill waste to less than 5% of the demolished material. Construction waste was removed and managed by the local solid waste authority, which collected and sorted outgoing materials. This streamlined the diversion and recycling processes. 3. Conservation of energy: Through the use of energy-efficient fluorescent and LED office lighting, lighting power density was reduced from 1.1 to.85 watts per square foot of occupied space. The lighting controls, which include ambient lighting controls and programmable touch-panels, are located throughout the space to reduce reliance on overhead lighting, and hence overall lighting load. 4. Improved mechanical ventilation: A new air handler and variable-air volume HVAC system was installed to reduce energy use and meet the requirements of the 2009 Title 24 California Code requirements for energy efficiency. It replaced an older constant-volume air system. The new system features four separate zone controls and variable-speed drive coupled to CO 2 sensors. The system intakes a higher volume of outside air than is required by State Code. After design and construction, building system commissioners verified the installed performance and functionality of the HVAC and lighting systems. 5. Environmentally-considerate materials: The materials for wall, ceilings and floors were chosen to for their multiple sustainable attributes. Materials included: a. Spaced wood slat ceiling panels made from locally-sourced lumber certified by the Forest Stewardship Council. The alternating wood slats and grilles reflect and absorb sound. b. Perforated wood panels constructed from fiber board with no added urea-formaldehyde. c. Monolithic-looking stretched-fabric system, that incorporated recycled plastic frames, formaldehyde-free glass fiber cores, and recyclable fabric faces. d. Bamboo and cork flooring surfaces were used in the conference room, kitchen and reception lobby, respectively. Both woods are considered "rapidly renewable" materials. e. Low-VOC adhesives, sealants, paints and coatings were specified Carpet was certified as Green Label Plus. All composite woods contain no added urea formaldehyde. 6. Acoustical design: The office acoustical design also increases employee comfort. It is well known that disappointment about office acoustics (primarily speech privacy) is the number one complaint in green offices. The acoustical design attributes for our offices includes the following: Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 5

6 a. Reduction of HVAC system noise was accomplished by specifying an air handler equipped with a variable-speed drive, internally-lined ductwork, and quiet variable-air volume (VAV) boxes serving multiple zones. b. Double glazed windows in the Conference Room to reduce noise from adjacent loading docks. c. Ceiling and wall surfaces were treated with sound-absorptive materials to control reverberation. d. Partitions between private offices were upgraded by adding pieces of reclaimed gypsum board (saved from the demolition), and using them to make the formerly ceiling-height partitions into ones that reached the deck above. Sound leaks in the existing partitions were also sealed. e. Electronic sound masking was installed throughout the office to provide uniform, calibrated background noise levels. f. In the open plan office area, tall, sound-isolating open office system partitions were augmented by a sophisticated sound masking system that allowed normal speech privacy for staff in these areas. g. Carpet tiles and cork flooring were used throughout the floor to reduce footfall noise and provide additional sound absorption. h. Doors to sensitive rooms such as the Conference Room and copier room were specified as soundrated assemblies. ACOUSTICAL TESTING RESULTS Pre-Demolition Acoustical Testing Results Prior to demolition of the prior office space, in late 2007 measurements were conducted of background noise levels of the constant-volume HVAC system (NC), and airborne noise reduction (NIC) between typical rooms. Background Noise Levels Table 5 below summarizes the measured data in four private offices and the Conference Room: TABLE 5. Results of pre-demolition background noise measurements in selected rooms. Rooms Measured NC Level (HVAC) Conference Room Office Office Office Office Airborne Noise Reduction Measurements Table 6 and Figure 4 below summarize a sampling of tests conducted between offices along the façade as well as the interior offices. Observations of the conditions of the partitions noted widespread construction deficiencies (i.e., sound leaks ) that limited overall noise reduction (e.g., window mullion-to-partition intersections, walls not sealed at the base, and electrical junction boxes that were not sealed). TABLE 6. Results of pre-demolition airborne noise reduction measurements. Source Room Receive Room NIC Rating NIC NIC NIC (Conference Room) NIC 34 The results of the pre-demolition measurements showed the following: 1) partitions were not adequate due to low airborne noise reduction and sound leaks between rooms, and 2) background noise levels were not appropriate either in overall level (dba) or spectrum. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 6

7 Post-Construction Acoustical Testing Results Background Noise Levels The mechanical design is to incorporate recommended mitigation to control air-handler and variable-air-volume box noise to meet the criteria summarized in the table below. Therefore, the room noise level criteria for Pilot Credit 24 to have been achieved. Mitigation measures include internally lined duct, controlling air velocities, and appropriately-rated diffusers. Vibration isolation for the mechanical equipment has been scheduled per ASHRAE 2011 Applications Handbook, Chapter 48, Table 47. Measurement results in each occupied area as shown in Table 7: TABLE 7. Results of Post-Construction Background Noise Measurements. Room Measured PC 24 NC Level NC Criteria (HVAC) Conference Room to 35 Office to 35 Office to 35 Office to 35 Office to 35 Office to 35 Office to 35 Office to 35 Office to 35 Airborne noise reduction and speech privacy Airborne Noise Reduction: NIC tests were conducted after construction to ascertain the improvement gained by raising the walls from partial (ceiling) height to full (deck) height, sealing the sound leaks, and also installing resilient neoprene clips in the partition between the Conference Room and the adjacent office. Table 8 below summarizes the post-construction NIC test results: TABLE 8. Results of pre-demolition airborne noise reduction measurements. Source Room Receive Room NIC Rating Change in NIC Over Previous Result NIC 32 Not tested NIC NIC (Conference Room) NIC Test results overall showed improvements of up to 3 NIC points when the standard partitions were augmented with reclaimed gypsum board and sound leaks sealed airtight. Improvements over previous were significant, however, in the 1/3 octave bands in the speech frequency range of about 315 Hz to 2,000 Hz. These two partitions showed improvements in airborne noise reduction of up to 8 db. The partition between the Conference Room and adjacent Office 613, upgraded with resilient neoprene clips, showed a 12 NIC-point improvement overall, and 1/3 octave band airborne noise reduction improvements (increases) of up to 20 db. The improvement in partition noise reduction improved speech privacy. Speech Privacy: The Pilot Credit 24 goals for speech privacy have generally been achieved through the use of room-specific partition type designations with associated acoustical performance. Measurements were conducted to quantify the speech privacy performance (e.g., normal or confidential ), between offices after the sound masking system was calibrated to its design noise level of 46 dba in the open plan offices and 42 dba in the private offices. The table below summarizes the results: Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 7

8 TABLE 9. Results of Post-Construction Speech Privacy Measurements. Source Room Receive Room Measured STI Speech Privacy Performance Conference Room 614 Office Confidential On Open Plan 617 Office Confidential On Office 611 Open Plan Confidential On Office 605 Office Confidential On Office 605 Office Just below Normal Off Sound Masking System Condition As can be seen from Table 6 above, the sound masking system was critical to achieving confidential speech privacy by the STI method. There was a difference of 0.15 (from 0.05 to 0.20), between when the masking system was turned on in the private offices to when it was turned off (and background noise was reduced). Post-construction Reverberation Time Measurements After the installation of sound-absorptive treatments throughout the project, reverberation time measurements were conducted to satisfy PC24 criteria, which require controlling reverberation in the 500 Hz, 1,000 Hz, and 2,000 Hz octave bands. Table 10 below summarizes the measured reverberation in the Conference Room, the open plan, and a typical private office: TABLE 10. Results of pre-demolition airborne noise reduction measurements. Room 500 Hz 1000 Hz 2000 Hz Open Plan Typical Private Office Conference Room CONCLUSION After submitting its LEED TM documentation in 2011, the project received notification that it met PC24 requirements in mid-2012, and received the commensurate Innovation in Design credit. As of the beginning of 2013, the project is still undergoing USGBC review of submitted documents, and the project is on track for eventual LEED TM Gold certification in This project demonstrated that an acoustically-comfortable office environment can be achieved by designing and constructing per the PC24 guidelines. Acoustics is as important to a building s occupants as its other attributes, and helps to provide a more flexible, useful, and comfortable environment. FIGURE 2: Photograph of completed office space. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 8

9 REFERENCES Cavanaugh, W.J, Tocci, G.T., and Wilkes, J.A., (2009). Architectural Acoustics: Principles and Practice, (Wiley & Sons), pp Jensen, K.L., Arens, E., and Zagreus, L., Acoustical Quality in Office Workstations, As Assessed by Occupant Surveys, Proceedings: Indoor Air Salter, C.M., Powell, K., Begault., D., and Alvarado., R., Case Studies of a Method for Predicting Speech Privacy in the Contemporary Workplace, University of California, Berkeley Center for the Built Environment (CBE), Summary Report, January Salter, C.M., and Lawrence, T.R., Acoustical Performance Measurement Protocols for Commercial Buildings, University of California, Berkeley Center for the Built Environment (CBE), Summary Report, January United States (US) General Services Administration (GSA) Sound Matters website and white paper, produced by GSA General Buildings Service. (last viewed 18 January 2013). US Green Building Council (USGBC) website explaining the LEED version 4 (V4) process: Accessed on 15 January US Green Building Council (USGBC) website explaining the LEED version 4 (V4) credits: Accessed on 15 January Pilot Credit 24 Library: Accessed on 15 January Veitch, J.A., Bradley, J.S., Legault, L.M., Norcross, S., and Svec, J.M., Masking speech in open-plan offices with simulated ventilation Noise: Noise level and spectral composition Effects on Acoustical Satisfaction, IRC IR 846, National Resource Council Canada, April Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 9