Civil Engineering Reference
In-Depth Information
Fig. 8.17
Independent natural and mechanical ventilation
types, the fi rst natural ventilation system relies on the wind effects to create the
required ventilation inside the building, while the second natural ventilation system
relies on the temperature difference between the inside and outdoor air which cre-
ates the resultant air movement inside the building.
Most of the hybrid ventilated building designs fall into one of the following three
categories: independent natural and mechanical systems (Fig.
8.17
), mechanically
assisted natural ventilation systems (Fig.
8.18
), and naturally assisted mechanical
systems (Fig.
8.19
).
In an independent natural and mechanical system the building has two com-
pletely independent systems. The control system either utilizes one system for a task
in the building and the other system for another task in the building (e.g., mechanical
ventilation system for the summer and winter seasons and natural ventilation system
for spring and fall seasons), or switches between the modes in different occasions
for the same task in the building (e.g., mechanical ventilation system for occupied
hours and natural ventilation system for unoccupied hours in same day).
In a mechanically assisted natural ventilation system, the basic system which is
serving the building is a natural ventilation system. During the periods of time that
only by natural ventilation the required results are not achievable a mechanical sys-
tem (usually a supply or exhaust fan) improves the required pressure difference to
facilitate proper ventilation.
Finally a naturally assisted mechanical ventilation system is designed based on a
main mechanical ventilation system with very low pressure drop, where stack
effects inside or wind effects outside of the building can assist the ventilation pro-
cess by generating the majority of the required pressure for the air movement.
