ASHRAE Journal - July 2020 - 65

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exposures. In the absence of effective ﬁltration of ﬁne
particles (PM2.5 and PM1), the share of external air in the
burden of disease due to indoor exposure reaches 60%
to 70%.5

Visual Comfort
Human vision is responsible for approximately 85%
of the information obtained from the environment.
Therefore, visual comfort has a signiﬁcant impact on
the quality of the interior. On the African savanna,
the number of sunny hours is vast, which ensures
very high light intensity as well as the desire to look
for shade. Close to the equator, the length of the day
and night are almost equal during the year. Such conditions shaped our daily clock of biological activity,
J U LY 2 0 2 0

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DEVELOPED BY JERZY SOWA BASED ON WEATHERONLINE DATA

Shelters constructed at the savanna were quite airy, so
air quality inside and outside the p=remises was virtually identical. In developed countries, a much tighter
building envelope acts as a double-sided ﬁlter between
the external and internal environment. For this reason, the composition of indoor and outdoor air differs.
Typically, in rooms one can observe an increase in the
concentration of carbon dioxide, a slight decrease of
oxygen, an increase in the amount of water vapor and
the elevation of many pollutants from building materials and equipment used.
For years, intensive ventilation of rooms was sufﬁcient to maintain good IAQ. In the 1980s, scientists
drew attention to the necessity of reducing indoor
emissions to improve IAQ, also potentially reducing
energy consumption due to the need for less outdoor air
ventilation.
In regions with high pollution of the atmosphere,
outdoor sources play a signiﬁcant role in indoor air

Tmean

Relative Humidity (%)

Indoor Air Quality

Air Temperature (°C)
Sunny Hours (h)

because of our roots in the savanna,
FIGURE 1 Tarangire National Park in Tanzania, East Africa.
regardless of where we live on Earth,
people try to maintain an indoor
temperature of 20°C to 25°C (68°F
to 77°F).
The building envelope in moderate
and cold climates passively changes
the temperature and humidity
parameters of the interior and protects people from rain and wind.
HVAC systems in modern buildings
help control the microclimate of
interiors. Remember that indicators
of general thermal comfort and local
discomfort relate to a "standard"
or typical person. Differences in
body structure, diet, illnesses, etc.,
lead to different thermal preferences. There is no combination of
indoor parameters resulting in more than 60% of satisFIGURE 2 Basic climatic data for Dodoma, Tanzania.
Sunny Hours
Tmax
Tmin
ﬁed people when answering the question "I want to be:
warmer, no change, cooler" (McIntyre test).3 At the same
35
time, about 20% of people would like the temperature
30
increased, and another 20% prefer reduced tempera25
4
ture. This fact indicates the vast potential of decentral20
ized control of HVAC systems.
15

SOURCE: WIKIPEDIA, PUBLIC DOMAIN

COLUMN IEQ APPLICATIONS

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ASHRAE Journal - July 2020

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