Ensure Good Ventilation to Avoid Health Hazards !!!
All occupied buildings require a supply of
outdoor air. Depending on outdoor
conditions, the air may need to be heated
or cooled before it is distributed into the
occupied space. As outdoor air is drawn
into the building, indoor air is exhausted or
allowed to escape (passive relief), thus
removing air contaminants.
The term “HVAC system” is used to
refer to the equipment that can provide
heating, cooling, filtered outdoor air, and
humidity control to maintain comfort
conditions in a building. HVAC systems range in complexity
from stand-alone units that serve
individual rooms to large, centrally
controlled systems serving multiple zones
in a building.
Some buildings use only natural
ventilation or exhaust fans to remove odors
and contaminants. In these buildings,
thermal discomfort and unacceptable
indoor air quality are particularly likely
when occupants keep the windows closed
because of extreme hot or cold temperatures.
In order to exhaust air from the building,
make-up air from outdoors must be
brought into the HVAC system to keep the
building from being run under negative
pressure. This make-up air is typically
drawn in at the mixed air plenum as
described earlier and distributed within the
building. For exhaust systems to function
properly, the control air must have a clear
path to the area that is being exhausted. To prevent operating the building under
negative pressures (and limit the amount of
unconditioned air brought into the building
by infiltration), the amount of make-up air
drawn in at the air handler should always
be slighter greater than the total amount of
relief air, exhaust air, and air exfiltrating
through the building shell. Excess makeup
air is generally relieved at an exhaust or
relief outlet in the HVAC system, especially
in air economizer systems. In
addition to reducing the effects of unwanted
infiltration, designing and operating
a building at slightly positive or neutral
pressures will reduce the rate of entry of
soil gases when the systems are operating.
The selection of a specific ventilator should be based on the following factors:
- Job details such as the atmospheric hazard, the size of the confined space, etc…
- Airflow required
- Airflow volume required at the end of the duct to control the hazards present; and
- Breeze to ensure worker comfort in the space.
- Duct friction loss to ensure adequate air volume reaches the end of the duct.
Aims of HVAC Control Systems:
HVAC Control Systems are used for the following benfits:
- Lower energy cost.
- Lower operations cost.
- Increase flexibility.
- Ensure quality building environment.
