5-5.ACOUSTIC QUALITATIVE DIAGNOSTICS
1.Exterior equipment and noise mitigation design(qualitative&quantitative)
2. Building envelop noise isolation
3.Background noise control
4. Indoor vibration strategy
In order to investigate the acoustic comfort in Pearl River Tower, our team has taken measurement of the sound pressure levels at different floors(figure 1,figure 2)and compared the results with Indoor Ambient Noise Levels in Spaces When They Are Unoccupied (dB(A)) from BS 8233 Code of Practice for sound insulation and noise reduction for buildings.(figure 3).
Figure 1 sound level meter ( by author)
Figure 2 sound level meter( by author)
1.Exterior equipment and noise mitigation design(qualitative&quantitative)
A typical office floor in a United States building would be designed to have noise levels around 30 to 40 NC (noise criteria scale)—it’s difficult to get levels lower than that due to VAV boxes, fan coil units and mechanical room fan and/or compressor noise. Modeling shows that Pearl River Tower occupants will enjoy spaces that are a quiet 25 NC.
The Pearl River Tower’s wind design is based on a small turbine (almost 10 ft or 3 m in diameter) by English manufacturer Quiet Revolution(figure 4) . Each of the design’s four turbines has a rated performance of 10,000 kWh per year. SOM pulled in the largest wind engineering and consultancy in the world to help them with testing and modeling for the wind design—Canadian firm Rowan Williams Davies & Irwin Inc. (RWDI). RWDI’s models helped to size and place the turbines and provided suggestions to SOM for selecting turbines—considering maintainability issues, noise, and vibration issues. One of RWDI’s tasks was to model wind potential. Power potential for wind is a cubed relationship, Frechette said. Air is pulled through the building, accelerating the speed of the wind by more than two times—and increasing its power potential by a factor of eight. For this site, models showed that average wind speeds of 9 mph (4 m/s) will speed up to as fast as 18 mph (8 m/s) when they are sucked through the building openings. “In essence, one wind turbine located in one of the openings could theoretically produce the energy of eight turbines somewhere else,” said Frechette. “So, this building has power comparable to 32 turbines.” The turbines are estimated to provide 1% of the building’s energy needs.
Through the holes in the envelope by the negative pressure on the leeward south side, accelerating winds to speeds of about 18 mph. Modeling and wind tunnel testing show this design has a power potential capacity of nearly 15 times more than a typical stand-alone wind generator—in this case about 1% of the tower’s power needs. The design was based on using four small wind turbines manufactured by Quiet Revolution, which have a capacity of 10,000 kWh per year.
Figure 4 Wind small turbine (Stewart, 2006, Fortmeyer, 2007)
Figure 5 The structure of the envelop (Stewart, 2006, Fortmeyer, 2007)
2.Building envelop noise isolation
The transparent glass on the envelope can reduce the noise from outside efficiently which means a quieter environment is more suitable for occupants to stay in this building , meanwhile the transparent glass can increase the sunlight into the buildings.(figure 5)
3.Background noise control
Green features can also be used to weaken the noise in the buildings., plants can help to reduce the noise in the buildings, the green plants can provide a better mood for occupants which may reduce the influence of noise.(figure 6)
Figure 6 Outside greenery distribution (by group)
4. Indoor vibration strategy (qualitative &quantitative)
“... Carpet is one of the most practical and cost-effective products available for controlling noise in the built environment.” Dianne Williams, Graeme E Harding and Associates, Consultants in Acoustics, Noise and Vibration
Carpet improves room acoustics in that it acts as a sound absorber and also dampens any impact noise in a room, such as that arising from footsteps, furniture movement and dropped objects. In contrast, a hard, flat flooring surface is more likely to actually generate impact noise and also act as a sound reflector which, in turn, intensifies the level of noise in a room. Overexposure to noise can have a negative effect on our health and well-being, the seriousness of which will be determined by the amount and constancy of noise exposure (i.e., the greater the noise and the longer it lasts the worse will be the effects). Results of unwanted noise range from sleep disturbance and impaired concentration to raised blood pressure, hearing loss and a range of stress-related illnesses. Additional effects include loss of productivity in the workplace and learning difficulties in the classroom. Carpets are one of the few materials that can control noise in three ways: reducing airborne sound, surface noise and sound transmission to rooms below.
The Pearl River Tower uses the acoustic carpets which can reduce airborne noise by 35%, in other words an NRC of 0.35, a high pile weight wool carpet recorded an NRC of 0.55 in tests carried out for the US Carpet and Rug Institute (CRI). In much earlier research, tests of wool carpets of varying construction produced average NRC values of up to 0.46, while with underlay, values of around 0.5-0.7 were achieved [6], which is as good as those of specialized acoustical materials. Sound absorption will be lower if the carpet backing is too impermeable, as it will impede the penetration of sound waves through to the underlay. Cut pile carpet will absorb more sound than loop, because of the more open nature of its surface. Overall, by reducing the noise levels and reverberation times, wool carpet improves a room’s acoustics. Background noises disappear, speech comprehensibility increases and occupants automatically speak in a softer, more relaxed voice, rather than generating even more noise by trying to make themselves heard above the sound around them.
Figure 7 The interior acoustic carpet of Pearl River Tower （by group）