Optimizing Comfort and Aesthetics
- By Dan Petrescu
- July 1st, 2016
has grown in popularity for use in
schools over the last decade, but is
sometimes written off as cost-prohibitive when
paired with a radiant heating system, which
can have higher up-front installation costs.
However, displacement ventilation is a viable
alternative to a traditional, all-in-one HVAC
system. In most locations, inherently energy-efficient displacement
ventilation provides sufficient cooling while creating design
opportunities to optimize the teaching and learning environment.
How DV Systems Work
Unlike traditional, all-in-one HVAC systems that cool and recirculate
indoor and outdoor air, displacement ventilation draws in
only fresh air from the outdoors, and uses enthalpy-wheel energy recovery
to cool the air slightly by transferring energy (heat) between
incoming air and return air within the system’s air handlers. Then, a
cooling coil smaller than those in traditional systems cools the air to
around 65 degrees F — significantly warmer than the 55 degrees F
typical of a standard system. Once cooled, the air is distributed horizontally
to each classroom and then flows gently downward through
vertical ductwork behind interior walls, and out through perforated
metal diffusers near the floor. The air in the classroom stratifies as
warmer air is naturally displaced toward the ceiling. The warm air
then enters return louvers at the ceiling, cycles through the enthalpy
wheel, and is exhausted outside the building.
The gentle (low velocity) airflow and use of 100 percent
outdoor air has three significant comfort benefits. First, by not
forcing air out of diffusers near the ceiling (at high velocity),
displacement ventilation systems eliminate the cold “wind
paths” and inconsistent temperatures noticeable with traditional
systems. Second, displacement ventilation systems offer no
acoustic distractions or interruptions; they are virtually noiseless
because they don’t require loud, powerful fans. Finally, there
is less agitation and recirculation of particulates, indoor dust
and allergens that settle in ductwork. The placement of supply
diffusers near the floor also helps reduce mixing of these irritants
and the low-velocity airflow is less likely to agitate irritants.
In combination, these occupant-first benefits make comfortable
temperature a passive, pleasant experience — no one has to
scramble for a sweatshirt when powerful fans turn on.
Daylight and Learning
Less visible but impactful from a space-use perspective are the
space-saving features of displacement ventilation systems. Since
they aren’t sized to provide full cooling and heating functionality,
the mechanical units are smaller than those in traditional, fullsized
HVAC systems. The corresponding reduction in ductwork, in
some cases up to a 50-percent space savings, provides opportunity
for larger windows and higher ceilings. Space is at a premium
in many schools, and when adding floor space isn’t feasible, tall
windows and high ceilings can create an open aesthetic in an
otherwise constrained space. Increased daylight in classrooms has
also been correlated with improved social and cognitive development
in children, as well as improved reading and test scores.
Though displacement ventilation diffusers are typically larger
than traditional HVAC diffusers, their location low on interior
teaching walls or integration into the base of wall cabinets makes
Finally, displacement ventilation systems offer energy efficiencies
over traditional systems due to their inherently different capabilities.
Displacement ventilation doesn’t offer full cooling, saving
schools energy costs a traditional system would use cooling air to 55
degrees F. Since the air is stratified, with comfortably cool air flowing
into the classroom and remaining where people occupy the space
while warmer air rises toward the ceiling, displacement ventilation
significantly reduces fan use — a traditional system relies on fast,
fan-driven airflow to force cold air downward through hot air at the
top of a room. These fan energy costs are further reduced when heating
is a separate radiant system; in cooler months, fans mustn’t blow
warm air down, against its tendency to rise. Though up-front installation
costs for the paired system may be higher, when considered on
a life-cycle basis, displacement ventilation is often less expensive.
It’s easy to think about school design only in terms of classroom
shape, building layout and finishes such as furniture and teaching
technology. By considering how educators and students experience
the learning environment in both active and passive ways, school
planners can create a holistic design that incorporates both a beautiful
aesthetic and optimized learning environment.
This article originally appeared in the July/August 2016 issue of School Planning & Management.
Dan Petrescu AIA, LEED, is an associate at Hennebery Eddy Architects, Inc., a Portland, Ore.-based architectural, interior design and planning firm with a specialty focus in historic preservation and sustainable design. For more, information, visit www.henneberyeddy.com.