First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 71

exhaust
High-level exhaust exit
ensures complete empty-
ing of warm air in ceilling
spaces

Exhaust plenum at slightly
negative pressure,
induced by north flues*

Undulating con-
crete ceilling line

displacement air
Boundary layer cre-
ated by displacement
air supply

25 ° C

22 ° C

Occupant and equip-
ment heat plumes

temperature
gradient

0.2 ms -1
20 ° C

healthy air
100% outside air
supply to sealed ac-
cess floor plenum

floor diffusers
Floor-mounted, user-con-
trolled air diffusers with
“twist” outlets, encourage
air to mix, improving circulation

AIRFLOW-OFFICES

Figure S2.8 Cross section of a chilled beam used in cooling an interior office environment.
Courtesy of the city of Melbourne, Australia,
http://www.melbourne.vic.gov.au/info.cfm?top = 171&pa = 1943&pg = 1937.

The contact angle indicates whether cohesive or adhesive forces are dominant
in capillarity. When

λ values are greater than 90 ◦ , cohesive forces are dominant;

90 ◦ , adhesive forces dominate. Thus, when is dependent on both the type

of fluid and the surface to which it comes in contact. For example, water-glass
λ =

λ < λ

0 ◦ ; ethanol-glass 0 ◦ ; glycerin-glass 19 ◦ ; kerosene-glass λ = λ = λ =

26 ◦ ; water-paraffin 140 ◦ . At the base of the

capillary fringe the soil is saturated without regard to pore size. In the vadose
zone, however, the capillary rise of water will be highest in the micropores, where
relative surface tension and the effects of water cohesion are greatest.
Capillarity and surface tension are important properties in nature, such as
the movement of fluids in roots and leaves. As such, designers wishing to take
advantage of the concepts of biomimicry introduced in Chapter 1 need to have
a working knowledge of these properties.
Another property of environmental fluids is the mole fraction . If a composition
of a fluid made up of two or more substances (A, B, C,

107 ◦ ; and mercury-glass

λ = λ =

... ), the mole fraction

( x A ,x B ,x C , ... ) is the number of moles of each substance divided by the total