Breaking From Convention
- By Chin Lin
- April 1st, 2016
With building committees aiming high to achieve greater impact
in sustainability, design teams
are researching and benchmarking unconventional
solutions beyond the LEED checklist.
For several public schools built in the
northeast, this quest led to a bold break from
convention. These schools rely on dehumidification
displacement instead of air conditioning for cooling
classrooms and other student spaces.
The savings are significant: a reduction of at least 25 percent in
energy consumption and cooling system use over a conventional
fully air conditioned, variable air volume system. In new construction,
capital costs are reduced due to the ability to downsize HVAC
units and system chillers. Displacement also offers the added
benefit of superior indoor air quality because pollutants within a
room rise toward the ceiling as the warmed air rises.
Reduced Summer Use as an Opportunity
The majority of the square footage in a new school is dedicated to
classrooms, labs and other learning spaces. In most districts, these are in
use for nine months a year. The use of dehumidification in these rooms
will provide a comfortable and dry environment for students and faculty.
The target comfort level is typically 80 degrees and 50 percent humidity.
Obviously, geography determines where this is feasible. It can’t
be employed in year-round hot-and-humid weather regions. Yet
within a large swath of the U.S., there are relatively few hot and
humid days in the regular school year. For these districts, the dehumidification
opportunity is a viable option to achieve both cost
savings and predictable comfort.
The Conversation: You Want Us to Try What?
Departing from convention is never easy, and reaching beyond
the prescriptive green-building checklist requires confidence in the
outcome. We find that a two-stage process works best. First, a general
discussion of the system options, combined with a dialogue on the
individual community interest level in exploring a no-AC scenario
comprise an important first step. This often includes conversations
with administrators in districts using dehumidification displacement
to learn about their experience and user satisfaction.
Second, site-and-climate specific research by the design team,
including a 12-month temperature and humidity analysis, provides a
reliable scrutiny of conditions, cost and outcome. The team reviews expected
energy requirements for mitigating heat gain through favorable
building orientation, shading, window options, etc. to produce a detailed
and reliable model. This information is shared with the committee,
and adjusted during early design phases to improve performance.
Supporting Dehumidification with Best Practices
The success of a dehumidification strategy to keep classrooms
comfortable relies on best practices in sustainable design to reduce
heat gain. The insulating and infiltration treatment of the envelope
of the building is critical to the overall energy efficiency of spaces
where there is no conventional air conditioning. A well-insulated
building not only reduces the amount of heating and cooling required,
it also allows for the use of a smaller, more efficient boiler
and cooling system. This reduces initial capital cost and conserves
energy. Designing a super-efficient lighting system reduces the
level of heat inside, easing demand on the cooling system.
Choosing the proper positioning for the building is another key
to success. A design that optimizes the orientation of the classrooms,
ideally with a north and south-facing classroom layout, is less energy
intensive than ones that primarily face east or west. The north side
gets good, uniform skylighting that is easy to control. In any season,
the sun is the highest from the south and, therefore, is most easily
controlled to avoid interior glare and overheating. North and south
facades are also not subject to the same wide thermal swings over the
course of a typical day as east and west facades.
Verifying Value and Outcome
Post-occupancy metrics for schools utilizing dehumidification
for cooling are demonstrating its value while helping educate other
districts. Two years after opening its doors, the Claiborne Pell School
in Newport, R.I., is experiencing tangible energy savings by using
dehumidification to cool its classrooms. Noteworthy for other school
systems is the positive user comments and lack of complaints from
Pell School faculty and students, helping to confirm their choice.
For school administrators and community leaders, making a
classroom cooling choice that departs from the prescriptive path
can be difficult, even controversial. An objective process of evaluation,
custom data analysis and peer advice will bring clarity and
consensus to the decision.
This article originally appeared in the April 2016 issue of School Planning & Management.
Chin Lin, AIA, LEED-AP, is a senior associate with HMFH Architects of Cambridge, Mass. He is committed to proving that sustainable design can be practical and financially feasible for schools and public buildings.