Civil Engineering Reference
In-Depth Information
As it can be seen, the delivered air to the building through an air conditioning
system should not only be capable of providing the needed cooling, humidifi cation,
dehumidifi cation, and heating for the purpose of creating a functional and comfort-
able environment for the building occupants but also should be clean and healthy
and have a high quality to protect the occupants against possible health-threatening
issues created by substandard air quality as well.
Other than the outdoor air that enters to the building through the air-handling
units, more outdoor air can fi nd its way into the building through other sources such
as cracks and openings. Among many other contributing factors to a lower quality
air inside the building uncontrolled moisture and contamination need special atten-
tion, and proper means for controlling the sources of these problems in the building
shall be designed and planned in order to make sure that a building with a minimum
acceptable indoor air quality is constructed and could be maintained.
Keeping the humidity of the building within an acceptable range has been defi ned
by different standards and literatures and is an essential source of people's comfort
and health, and also building functionality. Any additional humidity beyond this
recommended levels, is unwanted moisture. Unwanted moisture inside the building
can be the result of the moisture penetration through the building envelope, conden-
sation of water vapor over the interior building cold surfaces, improper pressure
relation design of the building in respect to the outdoor, etc. Condensate generated
over the cooling coil within the air handling unit and the water that is used for water-
ing indoor plants and decorative water features are examples of the other sources that
can contribute to accumulation of unwanted moisture inside the building. The exces-
sive indoor moisture generated by any of these sources, can cause undesirable condi-
tions such as building surface mold, uncomfortable condition and even occupant
sickness. On the other hand excessively less moisture than what is recommended by
the related standards can easily decrease people's level of comfort as well.
Similarly, the contamination inside a building can be the result of introduction of
low quality outdoor air, lack of proper exhaust from the building, and lack of proper
air balance in the building, etc.
Obviously, understanding the nature of these problems and of course fi nding
proper methods of preventing the occurrence of these problems are essential factors
for providing a building with high indoor air quality. In the rest of this chapter I will
discuss common moisture and contaminants issues and also methods of preventing
the complications that could be created by them in more detail.
6.2
Moisture Control
Proper moisture content in the building indoor air has a signifi cant effect not only
on the level of comfort of the building occupants, but also on protecting vulnerable
material which are sensible to the indoor air humidity level, such as topics in librar-
ies and art works in museums. Experience has shown a relative humidity of 45-55 %
is considered to be the proper level of humidity in most applications, while this
