Energy Efﬁciency in
To design an optimum HVAC airside system that provides comfort and air
quality in the air-conditioned spaces with efcient energy consumption is a
great challenge. Air conditioning identies the conditioning of air for main-
taining specic conditions of temperature, humidity, and dust level inside
an enclosed space. The conditions to be maintained are dictated by the need
for which the conditioned space is intended and comfort of users. So, the air
conditioning embraces more than cooling or heating. The comfort air con-
ditioning is dened as “the process of treating air to control simultaneously
its temperature, humidity, cleanliness, and distribution to meet the comfort
requirements of the occupants of the conditioned space.”
therefore includes the entire heat exchange operation as well as the regula-
tion of velocity, thermal radiation, and quality of air, as well as the removal
of foreign particles and vapors.
Achieving occupant comfort and health is the result of a collaborative
effort of environmental conditions, such as indoor air temperature, relative
humidity, airow velocity, pressure relationship, air movement efciency,
contaminant concentration, illumination, sound and noise, and other factors.
Proper understanding of these factors and their respective effects on human
comfort and health leads to development of a proper HVAC airside design.
Those parameters were previously investigated to dene the acceptable design
and operating ranges to obtain the comfort and hygiene in the air-conditioned
spaces. So, this chapter evaluates the above parameters and the recent prog-
ress of HVAC airside design for air-conditioned spaces. The present study
aims to dene the current status, future requirements, and expectations.
9.1 Air-Conditioned Applications
Indeed, humans spend a great part of their lives in enveloped spaces, which
can be articially conditioned. The air-conditioned applications vary accord-
ing to the functionality and sensitivity degree of the application. These
applications can be divided into residential, commercial, and healthcare
applications. The healthcare applications and some sort of the commercial
188 Air Distribution in Buildings
applications have a critical inuence on human health. The following sections
evaluate the environmental conditions in these applications and review the
methods of control and monitoring.
9.1.1 Comfort Levels
Proper comfort level can be achieved by reaching the optimum conditions
of the indoor air temperature, relative humidity, and airow velocity. Indoor
air temperature is one of the most important conditions to provide optimum
comfort. The temperature regulatory center 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. An internal temperature less than about 27.8°C can lead to serious
cardiac arrhythmia and death, and temperatures greater than 46.1°C can
cause irreversible brain damage. Therefore, the careful regulation of body
temperature is critical to comfort and health.
This condition can inhibit or
promote the growth of bacteria and activate or deactivate viruses, in health-
care facilities. Some codes and guidelines specify the temperature (only) as
a measure of comfort and healthy. Local temperature distributions greatly
affect occupant comfort and perception of the environment. Furthermore,
high temperatures may cause increased outgassing of toxins from furnish-
ings, nishes, building materials, etc. Alternatively, ambient temperatures
that are too cool can cause occupant discomfort such as shivering, inat-
tentiveness, and muscular and joint tension. Relative humidity affects the
comfort feeling directly or indirectly by its inuence on the temperature.
Improper relative humidity conditions may cause a thermal sensation, skin
moisture, discomfort, and tactile sensation of fabrics, health, and perception
of air quality.
Elevated humidity levels are known to reduce comfort. At lower levels of
humidity, thermal sensation is a good indicator of overall thermal comfort
and acceptability. Most guidelines specify the range 35 to 50% as the optimum
conditions for relative humidity. A few codes raise the upper limit to 60% as
the accepted range, but this is not recommended according to the practice.
The airow velocity 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 specications, the optimum airow
velocity falls in the range of 0.2 to 0.25 m/s in the occupied zone.
184.108.40.206 Problem Identiﬁcation
Many of the HVAC applications suffer from poor distribution of the indoor
air temperature and relative humidity, as well as incorrect airow velocities.
This poor distribution arises from poor airow distribution and the presence
of thermal drift due to the buoyancy effect.