areas or places with a constrained
ceiling height, because the height is
necessary to move warmed air out
of the space as it rises.
Using the Technology
in a Historic Building
Displacement ventilation is
more commonly used in new
construction, but the Commercial
National Bank retrofit shows that
the technology can work as a retrofit under the right conditions.
However, integration into an
existing building is inherently
more challenging than starting
from scratch, so you may run
into challenges along the way.
HKS conquered several hurdles,
1. Creating microenviron-
Zoning the displacement ventila-
ments. Thermal comfort was a key
concern for HKS, so the layout of
the floor included a diverse array
of free-address spaces so that
employees could move around and
work in the space that best met
their needs for light brightness,
temperature and other factors.
tion system properly required sev-
eral rounds of space planning to
define the microenvironments.
“We took a look at how light
within our space interacted and
at the lighting environment.
Once we understood our lighting environment and where the
most daylight was, we started
taking a look at the background
noise levels that we wanted to hit
and the activity level in spaces,”
“Once we had that in play, we
then chopped it up to look at how
best to thermally zone spaces to
satisfy as many types of thermal
choices, metabolic activity and the
type of work people do to make
sure they were productive. It was
a mapping exercise that was really
driven by the WELL Building
Standard that helped us establish
2. Considering complementary technologies. HKS considered
integrating chilled sails (radiant
cooling panels that resemble architectural clouds) but opted out after
their analysis showed it would
only increase thermal comfort by
another 10 percent or so, with no
financial return on investment.
“It was about a $200,000 add
that didn’t save us any more energy,” explains Zakrzewski. “There
was a balance point where we
figured that just having a displacement ventilation system rather than
a VAV system was good enough.
In warmer, more humid climates,
the radiant panel system probably
3. Specifying the right controls. HKS worked closely with
its mechanical engineers and
controls contractor to make sure
that the temperature variations in
the various microenvironments
could adapt as needed and that the
air handling units could modulate
Chris McHugh, partner with AKF Group, recommends
these five tips for making sure you get the most out of your
money when you install a displacement ventilation system.
1. Concentrate on system selection. In a displacement ventilation system, the air handling units require a higher discharge temperature and need a return air bypass to mix the
air, McHugh explains. Refrigerant-type cooling may make it
difficult to obtain the close temperature control you’ll need.
Chilled water systems are optimal for displacement technology. Pay close attention to diffuser placement and selection.
2. Height is critical. “Have someone verify the system by
doing a computational fluid dynamics model,” McHugh recommends. “That basically takes the geometry of the space
and looks at the temperature gradient and the mixing of the
air in a computer-simulated model to confirm design.”
3. Bring in a specialist. You really need a manufacturer that
specializes in displacement ventilation, McHugh stresses.
There are several choices on the market. Make sure the engi-
neer installing your system works closely with the diffuser
manufacturer to ensure optimal grille placement.
4. Spend time on layout. “The air should evenly cover
the space,” McHugh explains. “The air basically has to rain
sideways across the space and cover the entire thing, so
placement of the diffusers is critical. If you have an area that
doesn’t have a diffuser, you’re not going to have coverage
for air distribution.”
5. Know your building. Displacement ventilation technology
has its place, but McHugh recommends only using it in locations that are a slam dunk. “As with anything, don’t try to
apply it in an application that’s on the edge,” McHugh says.
“Really understand the application for which you’re trying
to use it, because if it’s applied wrong, it won’t work, just like
underfloor air distribution. Conventional diffuser design has
a lot more tolerance for in-between applications and places
where the systems aren’t perfectly sized. Displacement ventilation requires a lot of precision to lay it out properly.”
5Best Practices for Displacement Ventilation Integration