Acoustics and Indoor Air Quality

 Sound and air quality are elements of an interior space that are crucial not only to the design but the comfort and health of the space. These elements may not be something most people think about when in a space but, for interior designers these are extremally important. Having proper acoustics within a space, especially in commercial spaces, helps to keep individuals comfortable in the space. Indoor air quality can directly correlate to human health, so this cannot be taken lightly. 

Acoustics

Most people, including myself, think noise and sound are the same thing however they are not. Noise is defined as "unwanted sound" (Tucker page 236) and is undesirable in interior spaces. Sound is a quite  interesting thing because there are different waves and different ways they behave. Reflection refers to the return of sound from a surface, this causes the sound to be mirrored back into the space. Diffraction is the capability of a sound wave to bend through openings, which can be caused by temperature changes. Diffusion is when the sound waves produce random distributions when it comes in contact with an uneven surface. All of these different types of waves are taken into consideration when designing spaces, in order to create the best possible acoustics within the space. The best way to control th sound waves is through absorption, which is when sound energy is converted into heat. Materials like acoustics panels are able to absorb sound and are rated with NRC to rate the effectiveness of the absorption. This rating is calculated by an arithmetic average of a material's absorption coefficient at 250, 500, 1000, and 2000, hertz. This then translates to SAC (sound absorption coefficient) values, which are rated on a scale 0-1. Along with NRC ratings, materials also have sound transmission class (STC), which is "the capability of a material to absorb sound, and takes into account the entire frequency spectrum and the associated transmission loss to provide a single number that describes sound transmission for typical human hearing" (Tucker page 238).  Below is a chart of different STC ratings depending on the materials used in a wall, and whether or not it was a single or double wall. 

The graphic below shows examples of a low and high NRC rating, this illustrates what the sound waves are physically doing to create these ratings. 

Indoor Air Quality

It is commonly thought that more pollutants occur outdoors with thing such as vehicle and factory fumes however, there is about two to five times more pollutants indoors. This is due to VOCs (volatile organic compounds) in materials and furnishings. These are often due to the types of chemical treatments placed onto items such as fabrics. The treatments do offer things such as stain resistance, flame resistance, etc. but can also off-gas harmful chemicals into our spaces. These chemical treatments can cause negative affects on human health an possibly result in "sick building syndrome". This syndrome occurs when an individual exhibits symptoms such as headaches, nausea, kidney and nervous system damage, and immune system suppression. Now just because chemical treatments can create health issues, most times there are acceptable levels that do not cause health related issues. Good indoor air quality is referred to as "air in which there are no known contaminants at harmful as determined by cognizant authorities and with which a substantial majority (80% or more) of people exposed do not express dissatisfaction" (Tucker page 251). Luckily, with the rise in the LEED criteria, indoor air quality is taken more seriously which means more steps are being taken to ensure safe materials. The life-cycle assessment of materials has become something that is done more frequently. This entails monitoring materials from the time it was made to the time it is disposed of or recycled. This information can show if there are any correlation between the product and, for instance, individuals getting sick. If there was a correlation this would cause action to be taken to remove this material and declare it unsafe. LEED sets standards for all materials concerning VOCs, this controls materials from paint to fabrics.  In addition to having materials being safer, proper ventilation in a space is also crucial for a good IAQ. Fresh air entering into a space in one way to help create good air quality, it helps to freshen up the space and also allow old air to escape the space. Having new HVAC that is running often to create circulation in the space is another way in which IAQ can be improved. Below is a diagram that shows the different levels of VOCs. 

Post Covid IAQ

Since Covid has entered into the world, it has had quite the effect on interior designers especially where IAQ is concerned. People have become more aware about how easily sickness can spread, and that poor air quality in interior spaces can essentially make it a breading ground for sickness to spread. Some of the things I have learned in my interior design classes this semester is how this is handled in public spaces. For starters air filters are becoming, more often than not, HEPA filters. HEPA stands for high efficiency particulate air {filter}. It has become an industry leader in the past year due to claims that it can "remove 99.97% of dust, pollen, mold, bacteria, and any airborne particles within a size 0.3 microns" (EPA.gov). Along with higher quality air filters, HVAC systems are running more often than they were previously. This is to help clear out the air after air exchanges, the more air exchanges in a space the more the HVAC system must run. While this is beneficial for IAQ, it drives the costs up for maintenance of buildings. In addition with these two changes cleaning in common spaces has also been increased, when the germs are disinfected in a space it helps contribute to safer cleaner air as well. 

Resources:

What is a HEPA filter? | US EPA