Week 11

 Indoor Environmental Quality: Acoustic and Indoor Air  

Gina Christopher 

ACOUSTICS 

Acoustics is the study of sound. How sounds move through a space is a function of the shape of the space and the materials and finishes used within. Unwanted sound is called noise. Sound waves can be refracted, reflected, diffracted, and diffused. Sound pressure is measure in decibels (dBa). The limit of human comfort is about 110-120 decibels. Typical materials are rated with a noise-reduction coefficient (NRC). This is the materials ability to absorb sound. Sound transmission class (STC) is the capability of a material to absorb sound. This takes into account the entire frequency spectrum and the associated transmission loss (TL) to provide a single number that describes sound transmission for typical human hearing.  Reverberation describes the sound that is built up in a room over time (echo). Reverberation can be controlled, and different reverberation times (RT) are preferred for different facility types. RT is very important when designing auditoriums, classrooms, lecture halls, music rooms, and performance facilities.

The primary goal for acoustical design within most spaces is to achieve some level of speech privacy for the occupants. Sound waves travel directly through wall studs from one room to another. Breaking the path of travel of the sound wave can prevent this transmission od sound. Staggered wall studs will help prevent this direct transfer. Generally, designers should keep the room volume low when low reverberation times are desired. In music halls and other spaces that need higher reverberation times, larger spatial volumes are desirable. The open-office configuration poses a variety of acoustical challenges with regard to both noise and privacy. Open-office acoustical partitions can be used to reduce unwanted sound between workstations. These systems work best when proper layout is combined with sound-masking white noise and acoustical ceiling tiles. To effectively block unwanted voice transmission, partitions need to be at least 5 feet high. For medical facilities HIPAA privacy requirements demand that personal medical information be protected, so sound-separation in check-in areas is important. Also, studies show that unwanted noise can lead to a variety of health problems. 

Interior materials have different sound-absorption qualities. Absorbing materials include carpeting, acoustical ceiling tile, and textiles. Different types of spaces need different levels of acoustical control. Acoustical clouds and canopies can be used to address noise and privacy issues. 

INDOOR AIR QUALITY (IAQ)

Humans spend 90 percent of their life inside of a building. The quality of the air inside of a building in impacted by several factors: the HVAC system, access to natural ventilation, the interior materials, the interior furniture, fixtures, and equipment and moisture within a building. Indoor pollutants consist of undesirable substances that make their way into the air supply. These include volatile organic compounds (VOCs) released by indoor products (also known as off gassing), biological contaminants, minerals, radiation, metals, and water vapor that can lead to mold spores. Radon is invisible, tasteless, and odorless and may be killing as many as 20,000 Americans per year. Many indoor materials release odors into the environment in a process known as off gassing. Some of these may be toxic. Building related illness (BRI) is caused by an accumulation of these indoor pollutants and contributes to sick building syndrome (SBS). Perhaps the best-known example of BRI is Legionnaire's disease. This disease is associated with buildings that are air-conditioned. Poor indoor air quality can lead to a variety of physical symptoms ranging from mild to severe reactions. These include irritation of eyes and throat, dizziness, fatigue, and asthma. The most efficient method of treatment is to remove the source of the contaminants. Improved ventilation and the use of air cleaners and/or air purifiers will also reduce the effect of VOCs.   

SELECTIONS CRITERIA 

Selecting interior materials and furnishings for good IAQ and sustainability requires that a holistic approach be taken including the use of LEED criteria, VOC content or emissions life cycle assessment and the embodied energy of materials. The life cycle assessment of a material involves looking at all aspects of the life cycle material extraction, where it was made, transportation costs, how long it lasts, and what happens when it is no longer usable. A complete cradle-to-grave analysis will make it easier to assess the real sustainability of a product. The embodied energy of a material takes many of these factors into consideration. This is the amount of energy used to create a material from extraction, through production and installation and eventually disposal. As a result of LEED and other sustainable design initiatives, the use of materials with VOCs has been rapidly diminishing and is now tracked by manufacturers as well as regulated.      

COVID 19 VS. INDOOR AIR QUALITY 

COVID-19 has had a significant impact on indoor air quality, both positively and negatively. COVID-19 negatively impacted the quality of indoor air due to the virus being in the air, which caused a lot of people to take extra caution inside buildings, such as wearing masks. On the positive side, the pandemic led to a noticeable decrease in atmospheric nitrogen dioxide levels which is a harmful air pollutant. The pandemic also highlighted the important of indoor air quality, as the virus can linger in the air posing a risk of airborne transmission. This led to a greater focus on improving air handling systems as well as incorporating more cleaning/circulating devices inside buildings.