Comfort Considerations in Net ZEBs: Theory and Design - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 139

rates and the corresponding noise levels are relatively low. Regardless,
HVAC systems (e.g., fans and ducts) can be a source of unwanted noise and
careful design is important.
As for other forms of occupant comfort, metrics for quantifying acoustic
comfortarediverseandcomplex.Metricsforinteriorsurfacesincludesound
transmission class (STC), which quantifies a surface's ability to block sound
from being transmitted, and noise reduction coefficient (NRC), which
defines the fraction of sound that is absorbed upon hitting it. Speech
intelligibility indexisameasure ofhowclearlyoneoccupantcanhearothers
and has been used in numerous postoccupancy evaluations of buildings
(Hodgson, 2008; Newsham et al. , 2013). Ambient noise level, measured in
decibels (dB), indicates the magnitude of background noise in a space. A
noise criterion (NC) level of between 30 and 40 is acceptable (Hodgson,
2008). Normally, noise levels are based on an A-weighting, which defines
the human ear's hearing ability at different frequencies.
3.5 Indoor Air Quality
Indoor air quality is a measure of the healthiness and comfort of air in
buildings. IAQ gained considerable attention during the oil embargos of
the 1970s when building operators significantly reduced ventilation rates
in an effort to reduce energy use. While this strategy achieved its original
objective, it resulted in very poor air quality and many health effects that
became known as sick building syndrome (SBS) (Redlich, Sparer, and
Cullen, 1997).
Contaminantsintheairarenormallycategorizedasgaseous,particulates,or
microbial. These vary in harmfulness and at least a dozen official standards
impose limits on safe levels, depending on exposure duration (Charles et
al. , 2005). This brief section provides an overview of IAQ, including some
common contaminants and design and operational strategies to mitigate
high levels of indoor air contaminants.
The main contaminants of concern or interest include: tobacco smoke,
radon, molds, legionella, carbon monoxide, bioeffluents, volatile organic
compounds (VOCs), asbestos fibers, ozone, and carbon dioxide. Details on
these contaminants and recommended maximum exposure levels can be
found in ASHRAE Standard 62.1 (ASHRAE, 2010) and reports by the US
EPA (2013). Their origin can be materials and substances that are indoors,