Digital Commemorative Magazine - 37

Figure 1.1
Ceiling diffusers push
55° air at high speed

Traditional Overhead
Air System

Displacement Ventilation
System

+ Supply at breathing level
+ Conditions occupied area

Occupied
Zone

Temperature and
pollutants are mixed
uniformly throughout

Displacement Ventilation
As concern about airborne threats and diseases
continues to rise, ASHRAE looked for solutions that
would best ensure clean air and optimize indoor air
quality (IAQ). In the new global headquarters,
displacement ventilation was used to address the
more densely populated spaces, including the
many training areas and conference rooms. The
overhead mixing system that existed in many areas
of the original building prior to the renovation was
typical to what is seen in many traditional oﬃce
spaces. (See comparison in Figure 1.1)
For the retroﬁt project, new displacement
ventilation supply diﬀusers were located evenly
throughout the rooms and integrated into the walls

Warmer air (~65°F)
supplied at low speed

to supply air at a low level directly into the occupied
zone. With displacement systems the supply air
rises around thermal sources, such as occupants,
equipment and lighting, and in doing so carries
contaminants and particles upward and out of the
breathing zone, resulting in a cleaner space.
Several independent studies on facilities renovated
with DV have shown signiﬁcant improvements in
IAQ, which has also been tied to notable reductions
in respiratory and asthmatic cases. (See Figure 1.2
for CFD results of a recent school study comparing
DV to a mixed system.)
In that DV relies on natural convection to move
the air throughout the space, it is extremely energy
eﬃcient. Since air is being pulled through the
space by thermal plumes created by heat sources

Figure 1.2 Natural Convection visual chart compared to a mixed system.

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