Civil Engineering Reference
In-Depth Information
3 Ventilation and Infiltration in Buildings
In order to prevent health problems of the occupants, an adequate design of the
buildings' ventilation system is necessary to provide a good IAQ (Sundell et al.
2011
). The indoor dilution capacity of pollutants is much lower than outdoors,
making ventilation a critical issue. According to indoor ventilation standards, the
rate of ventilation in a building must be set in order to achieve an acceptable IAQ
(Olesen
2011
). Due to the increasing need of saving energy in recent years, there is
a tendency to decrease ventilation rates in buildings. The European HealthVent
project aims the development of health-based ventilation guidelines for
non-industrial buildings, considering both health and rational use of energy
(HealthVent
2013
).
The ventilation rate is the volumetric rate of outside air introduced to the
building, which can be defined per person (L/s
person) or per area (L/s
m
2
). The
minimum ventilation rate per person is set concerning the pollution emitted from
people occupying the space, such as odour and other bioeffluents, taking into
account the number of expected visitors and occupants. Different criteria should be
considered depending on the space to be ventilated: conference room, restaurant,
office, apartment, etc. (Olesen
2011
). The ventilation rate per floor area is set
concerning other indoor sources than people such as furnishing, cleaning products,
heating, ventilating and air-conditioning (HVAC) systems and ETS (US EPA
1990
).
In addition to indoor sources, ventilation effectiveness is also affected by
outdoor sources, season and climate. In buildings located in polluted areas, con-
taminated air could be introduced ventilation, resulting in the opposite effect that
required (Fisk et al.
2012
). That could occur in urban buildings located nearby
high-traffic road or in buildings located in industrial areas (Pegas et al.
2012
).
Ventilation effectiveness can seasonally change, being ventilation more efficient in
summer with respect to winter. Ventilation strategy varies with climate, being the
dominating systems in Europe natural ventilation, uncontrolled air infiltration and
window opening; bar northern Europe, where mechanical ventilation is frequently
used due to colder climate (Dimitroulopoulou
2012
).
Other causes of inadequate ventilation are infiltration and exfiltration and
incomplete mixing and distribution of clean air with indoor air, which may be due
to the inappropriate design of the filtration system. Infiltration is the air exchange
from outside into the building that occurs mainly by uncontrolled air leakage
across the building envelope, driven by wind, temperature difference and/or
induced pressures (Lazaridis
2011
). Infiltration and exfiltration may occur though
openings, joints, cracks and porous materials in the building. The air exchange
moving out of the building to outdoors is called exfiltration. Regarding IAQ,
infiltration and exfiltration should be considered when infiltration of polluted air
occurs (Wichmann et al.
2010
) and when pollutants are transformed while air
enters the building in some cases pollutants may be lost during infiltration (Liu and
Nazaroff
2001
). Air exchange rates between building zones in mixed-use buildings
