Designing a new high school to be 40% more efficient than ASHRAE 90.1 – 2001 energy
requirements is a feat in itself. To achieve this degree of efficiency on a very limited capital
budget while designing a state-of-the-art, energy-demanding technical high school is an even
greater feat. This is exactly what the StudioJAED architectural and engineering firm
accomplished at the Providence Career and Technical Academy (PCTA) in Providence, RI, to
comply with the design requirements of the Northeast Collaborative for High Performance
PCTA opened its doors to its first
class of students on September 2,
2009, after 212,000 sq ft of new
construction plus 72,000 sq ft of
renovation in the previously existing
Hanley classroom building. Now, one
of New England’s premiere technical
high schools, PCTA features hightech classrooms, equipment, labs,
media centers, athletic facilities, and
other amenities for a high-quality
education. The school offers nine
vocational programs including
automotive technology, construction
technology, cosmetology, culinary
arts, and HVAC, in addition to a
required college-prep curriculum of
math, science, and English.
The school building was designed to satisfy the full requirements of NE-CHPS, whose mission is
to promote school environments that are not only energy- and resource-efficient, but also
healthy, comfortable, and well lit. Oftentimes, highly efficient buildings mean premium costs.
Because PCTA, like many public schools, was no stranger to budget constraints, designers had to
limit initial costs in creative ways.
This school saved both on installation and energy costs by
installing a two-pipe, dual temperature HVAC system with an
ERV system to control humidity.
A CREATIVE SOLUTION
A major design directive to save on construction costs led PCTA to install a dual–temperature,
two-pipe HVAC system. In contrast to the more common (and more expensive) four-pipe system
where heating and cooling are available at any time, two-pipe systems cannot engage cooling
coils to reduce humidity on cool, damp days while in the heating mode. The solution to this
dilemma was to install Airxchange energy recovery wheels containing a silica-gel desiccant for
moisture transfer. By rotating between building exhaust and outdoor intake air streams, the
wheels remove moisture from outdoor air on damp days and reject it into the exhaust air stream
to keep indoor relative humidity at a comfortable level.
Engineer Brian Zigmond, a principal of StudioJAED, stated, “Since the school utilizes a twopipe system, we needed a way to mitigate humidity issues typical to the area during ‘shoulder’
seasons. Rejecting as much humidity as possible back to the outdoors with an energy recovery
wheel is the most practical solution available. We’ve had success with implementing energy
recovery wheels in new and existing schools. Given school budget constraints, installing energy
recovery wheels to save on up-front and operating costs is a no-brainer.”
REDUCING LOAD EARNS AN A PLUS
StudioJAED also realized during the planning phase that energy recovery would have to be
incorporated into the design of PCTA’s HVAC system if the 40% energy reduction goal were to
be achieved. The team chose to utilize a combination of AHUs and standalone energy recovery
ventilators (ERVs) with Airxchange energy recovery wheels to provide outdoor air to PCTA’s
new and retrofitted classrooms, labs, auditorium, and media center.
The Airxchange wheels help to condition 45,215 cfm of outdoor air by continuously recycling
the heating or cooling energy (depending on the season) from the exhaust airstream. On peak
design days, the energy recovery wheels reduce the outdoor air load by as much as 80%.
The ability of Airxchange wheels to save on energy is evident at PCTA, especially during the
heating season. In the first winter of operation, David Gaudet, PCTA facility manager, kept his
eye on the boilers to ensure they were able to handle the load. He was surprised at how
infrequently the boilers actually started up. “I kept waiting for the boilers to fire on cold days.
But the energy recovery wheels were able to heat the outdoor air enough to significantly reduce
boiler operation. The wheels keep the supply air in a nice comfortable zone where frequent
additional heating is not required,” he said.
With rising fuel prices, the conditioning provided by the Airxchange wheels to reduce boiler
operation generates tremendous cost savings. PCTA HVAC technician Brian Polak added that he
was able to shut down the entire boiler system for a few hours to perform emergency work
during one of the coldest days of the winter without the system being negatively affected. The
ERV/AHU system with Airxchange wheels keeps the school in the “comfort zone.”
THE RESULTS SPEAK FOR THEMSELVES
PCTA operates in the 43 kBtu/sq ft range, which is about 40% lower than the national average
for all high schools, not just technical schools. The improved efficiency yields huge savings on
utility bills. Through their reduction in outdoor air load, Airxchange energy recovery wheels
account for an estimated $28,000 in annual utility savings. Because of PCTA’s Northeast
location, the majority of the savings are realized in the heating months, but because Airxchange
wheels exchange moisture and maintain superior IAQ, they benefit the school year-round.