ASHRAE Journal - September 2013 - 66

technical feature

Dissecting Interactions
Among IEQ Factors
By hal levin, Fellow aShRae; and Steven J. emmeRich, memBeR aShRae

Many aspects of indoor environmental quality (IEQ) and the technologies
that control or otherwise affect it are interactive and often closely connected.
Yet the technologies to control the indoor environment are usually designed,
installed and operated without considering the interactions. This has important implications for the design and construction of buildings as well as for
operation, maintenance, and troubleshooting in occupied buildings.
ASHRAE Guideline 10, Interactions Affecting the
Achievement of Acceptable Indoor Environments, was published in 2011 to call attention to, and provide understanding of, the many interactions that designers might
not have previously recognized or understood.
Indoor air quality (IAQ), thermal environment, sound,
and light are widely regarded as the primary factors for
defining the acceptability of an indoor environment. Many,
if not most, of the same technologies are used to control the
thermal environment and IAQ. Many of the same technologies have impacts on the acoustic environment. Together
with illumination, the collection of environmental control
technologies can have dramatic impacts on building energy
use and occupant environmental health.
Each of the primary factors includes several separate
aspects. Within the thermal comfort factor alone, there
are four environmental aspects (temperature, air speed,
humidity, thermal radiation) and two human factors
(level of physical activity and thermal insulation of
clothing) that determine human responses to thermal
conditions.1 These aspects interact to produce the overall environment and exposure that determines human
experience and perception of the thermal environment
and thermal comfort.

Interaction Examples
Outdoor Air Ventilation Requirements
Ventilation requirements should strongly depend on
pollution sources and on human occupancy and activity. ASHRAE Standard 62.1 and 62.2 are based primarily
on perceived air quality and establish ventilation rates
based on occupancy and area requirements. Buildings
with few indoor pollutant sources need less outdoor
air ventilation to maintain pollutant concentrations at
acceptable or healthy concentration levels. Individual
occupant differences such as health status (including
but not limited to circulatory disorders or hormonal
dysregulation) can also affect thermal comfort and lead
to a host of other interactions.
Where outdoor air quality is poor, ventilation to dilute
pollutants from indoor sources with outdoor air may
result in less healthful or acceptable indoor air quality.
The level or removal efficiency of outdoor air filtration and air cleaning to control outdoor air pollution
depends on outdoor air quality, ventilation flow rates,
and the requirements related to the intended uses of
the indoor environment. While the size of particles in
outdoor air determines the filter type (e.g., as indicated
by the minimum efficiency reporting value [MERV])

aBout the authoRS Hal Levin is a research architect at Building Ecology Research Group in Santa Cruz, Calif. He is a member of the committee for ASHRAE Guideline 10,
Interactions Affecting the Achievement of Acceptable Indoor Environments. Steven J. Emmerich is a research engineer at the Engineering Laboratory, National Institute of Standards
and Technology in Gaithersburg, Md.
66

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ASHRAE Journal - September 2013

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