Civil Engineering Reference
In-Depth Information
And the following conditions in the building generally increase the chances of
effi ciently utilizing the natural ventilation mode in a hybrid ventilation system: (1)
larger rooms with high ceilings, (2) available clean outdoor air, (3) possibility of use
of outdoor air openings without risking the security of the building or increasing the
noise pollution risk, (4) and exposed thermal mass in the building structure.
A thorough discussion about advanced hybrid ventilation technologies along
with useful case studies can be found in Heiselberg's research “Principles of Hybrid
Ventilation” (Heiselberg 2002 ).
8.14
HVAC System Selection
Selecting the proper system for the application in hand has been subject of many
discussions, and different methods have been proposed to improve the potential of
the best possible system selection in the industry. Relying on expertise of the expe-
rienced engineers in the fi rms has been the fi rst source of infl uence on selection of
the proper system for designing the projects since early years of modern building
system design in different engineering fi rms. In this method the most experienced
engineer of the design team due to his/her experience suggests the proper system
that could satisfy the required conditions for the application. The main problem
with this method is that each experienced engineer and for that reason each design-
ing fi rm has its own expertise in design of some specifi c type of systems, which
tends to infl uence how the proper system has been selected for the application. This
helps to avoid extra time and money required for research, learning and execution to
the perfection of the other possible systems. Of course this method may results in a
very high quality building system design that in exchange will protect the design
team from the possible mal-operation of the building HVAC system and therefore
the possible future lawsuits. But the negative side of using this method can be the
missing opportunity for designing of even better and more effi cient systems and
saving money and energy that could come from a better system choice.
Creating matrices that compare and grade the positive and negative effects of
important characteristics of each alternative system has been offered by different
resources as well.
This procedure usually starts with the design engineer selection of two or three
proper systems for the design application. His next step is to create a list of the fac-
tors that may have signifi cant importance on his decision for selecting the proper
system, and assign two numeric values (usually between 1-10 and 1-100) to each
factor regarding each alternative system and its degree of importance based on his/
her judgment. Finally a weighted average of all these factors will represent the over-
all best alternative system to be selected as the system type.
This method has its obvious advantages over the previous method since it gener-
ates a comparison among the possible alternatives, and provides the designer with a
quantitative measure for this evaluation and comparison. Another important benefi t
of this method is that it can force the designer to think about important parameters
and factors that could affect the fi nal product in advance.
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