ASHRAE Journal - February 2014 - 62

COLUMN IAQ APPLICATIONS

Ventilation, Crowds
And the Common Cold
BY YUEXIA SUN, PH.D., MEMBER ASHRAE; AND JAN SUNDELL, M.D., MEMBER ASHRAE

The influence of building characteristics including ventilation on the spread of viral
respiratory infections has begun to receive increased attention from the public,
government, media and scientists. However, few studies have examined ventilation and its possible association with airborne infection transmission. This column
summarizes the paper by Sun, et al.,1 that found a lower incidence of common cold
infections to be associated with higher ventilation rates in college student dormitories
located at Tianjin, China.
Methodology
As part of the "Dorm Environment and Occupants'
Health" study at Tianjin, China, the authors analyzed
common cold infection incidence of 3,712 students living
in 1,569 dorm rooms in 13 buildings. Dorm buildings
had three to 12 floors, with 26 to 43 dorm rooms per
floor. Dorm rooms consisted of a simple bedroom. Each
floor provided two washing rooms and restrooms. Six
bachelor students, four master students or three Ph.D.
students shared one dorm room with a volume of 50 m3
to 70 m3 (1,766 ft3 to 2,472 ft3). The average density was
5 m2 (54 ft2) per person. Ventilation for all dorm rooms
consisted solely of opening doors and windows, plus
uncontrolled infiltration.
In Phase I of the study, common cold infections were
self-reported by students in a questionnaire. In Phase
II, air temperature, relative humidity and CO2 concentration in dorm rooms were measured for 24 hours.
The ventilation rate at night was calculated from an
analysis of the build-up period of metabolic CO2 produced by sleeping occupants (1 a.m. until 8 a.m.).2
Associations between varying rates of natural ventilation
and common cold infections were analyzed by logistic
regression models.

Results
In the questionnaire survey of Phase I, 249 out of
3,436 (7.3%) students reported six to 10 common
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colds in the previous 12 months, while 94 (2.8%)
reported more than 10 common colds. Based on the
questionnaire data from Phase I, 238 dorm rooms with
473 students were inspected and measured in Phase II.
The studied dorm rooms represented different building structures, construction periods, locations and
occupancy levels.
The ventilation rates for rooms measured in the
heating season, during which door and windows
were closed, had a median of 3 L/s (6.4 cfm) per
person.3 Ninety percent of the dorm rooms had
a ventilation rate less than 8.3 L/s (17.6 cfm) per
person.
Self-reported common cold incidence is compared for
different occupancy levels in Figure 1.
Figure 2 shows the association between ventilation rates
per person and common cold infection in six-person
rooms. There appears to be a clear relationship between
ventilation rate and common cold infections among
college students in dorm rooms.
Figure 3 shows that the infection rate of common
cold in buildings constructed after 1993, in winter,
is dependent on the mean ventilation rate. There
were seven buildings constructed after 1993 in this
Yuexia Sun, Ph.D., Member ASHRAE, is an associate professor at the School of
Environmental Science and Engineering, Tianjin University, Tianjin, China; and Jan
Sundell, M.D., Member ASHRAE, is a professor at the School of Architecture and an
adjunct professor at School of Medicines, Tsinghua University, Beijing, China.

ASHRAE Journal - February 2014

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