Environmental Engineering Reference
In-Depth Information
4. Higher consumer disposable income
5. Increased cash flow in the local economy
6. Improved trade balance by increased export earnings (or less import
spending) helps alleviate trade deficit of Arabian countries
7. Avoid future energy deficit as power demand rises
7.3.2 Comfort Levels
7.3.2.1 Introduction
Thermal comfort is satisfaction with the thermal environment. Because
there are large variations, both physiologically and psychologically from
person to person, it is difficult to satisfy everyone in a space. The envi-
ronmental conditions required for comfort are not the same for everyone.
Extensive laboratory and field data have been collected that provide the
necessary statistical data to define conditions that a specified percentage of
occupants will find thermally comfortable. This is used to determine the
thermal environmental conditions in a space that are necessary to achieve
acceptance by a specified percentage of occupants of that space. There are
six primary factors that must be addressed when defining conditions for
thermal comfort. A number of other, secondary factors affect comfort in
some circumstances [2].
The temperature regulatory centre in the brain is about 36.8°C at rest
in comfort and increases to about 37.4°C when walking and 37.9°C when
jogging [2]. High temperatures may cause increased out gassing of toxins
from furnishings, finishes, building materials and so forth. Alternatively,
ambient temperatures that are too cool can cause occupant discomfort
such as shivering, inattentiveness and muscular and joint tension. Relative
humidity plays an important role in the comfort feeling, affecting the
comfort feeling directly or indirectly by its influence on the temperature.
Excessive relative humidity levels are known to reduce human comfort.
Most guidelines specify the range of 35%-50% as the optimum conditions
for relative humidity. The airflow pattern plays an important role in the
comfort sensation and also in the scavenging of the hazards and airborne
particles. According to the results of research and the standards specifica-
tions, the optimum airflow velocity falls within the range of 0.2-0.25 m/s in
the occupied zone.
7.3.2.2 Problem Identification
Many of the HVAC applications suffer from poor distribution of the indoor
air temperature and relative humidity as well as from incorrect airflow
velocities. This poor distribution arises from poor airflow distribution and
the presence of thermal drift due to the buoyancy effect.
