Environmental Engineering Reference
In-Depth Information
achieving optimum air quality. The ventilation system design must, as much
as possible, provide air movement from the clean to the less clean areas.
This rule requires great care in designing the airside system and in select-
ing the design of the airside system of neighbourhoods. There are relative
interactions among the conditioned neighbouring spaces. The air distribu-
tion and movement efficiency can be considered as the simultaneous indica-
tors of comfort and air quality. There are several important considerations
that characterise the air distribution in air-conditioned spaces. First, the flow
is generally turbulent, and buoyancy effects are often significant. Then the
transverse transport effects are of particular interest in these flows. In that
case, combined heat and mass transfer processes prevail, and coupled trans-
port mechanisms are generally present. Undesirable airflow between rooms
and floors is often difficult to control because of open doors, movement of
staff and patients, temperature differentials and stack effect. Although some
of these factors are beyond practical control, the effect of other factors may be
minimised by terminating shaft openings in enclosed rooms and by design-
ing and balancing air systems to create positive or negative air pressure
within certain rooms and certain areas (Figure 7.7).
Contaminants can be classified in four broad headings, each of which
represents a wide variety of pollutants: organic compounds, inorganic
compounds, particulate matter and biological contaminants. It should be
understood that these classifications are intended to facilitate the categori-
sation of contaminants. Although the pollutants are classified into these
categories, certain contaminants may belong to two or more classifications,
400
5
ASHRAE design conditions
DB 38.9 °C, WB 24.4 °C
Gymnasium hall
4.5
350
Gymnasium hall
4
300
3.5
Guest room
250
3
200
2.5
ASHRAE design conditions
DB 38.9 °C, WB 24.4 °C
Guest room
ASHRAE design conditions
DB 38.9 °C, WB 24.4 °C
Operating theatre
2
150
1.5
Operating theatre
100
1
50
0.5
At 40 °C DB
0
0
24
26
28
Outdoor wetbulb temperature, °C
30
32
FIGURE 7.7
Outdoor conditions and thermal loads.
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