Winters, Associate Editor
There was a time in the 1980s when sick buildings
were all the rage. Office workers and high-rise apartment residents
realized their hard-to-define maladies—everything from red eyes and sore
throats to fatigue and nausea—were the result of fumes from carpet
adhesives, cleaning fluids, fake leather upholstery, or mold growing in
the construction materials. Those chemicals would linger in interior
spaces because modern buildings were so airtight and were drawing in so
little fresh air from outdoors that the fumes were never completely
Even the headquarters of the Environmental Protection
Agency was affected.
Sometimes, ventilation systems weren't simply
passive elements in the problem. Bacteria growing in wet duct insulation
or standing water could create widespread illnesses or, in the case of the
Legionnaire's disease outbreak in 1976, even death.
But by the
early 1990s, ventilation standards were revised: More fresh air was to be
brought in, water would be better drained. But sick buildings haven't gone
away. Bernard Bloom, a senior environmental scientist at Versar Inc. in
Springfield, Va., is passionate about this point.
"Little kids are
still getting sick from being exposed to poorly ventilated school
buildings, from the way the ventilation systems spread germs and
contaminants around," Bloom said. "There's been a lot of hand waving about
indoor air quality, but few people have wanted to do the unsexy work of
doing the engineering. We have more knowledge than we use."
Bloom and others are calling for is a whole new way to cool and ventilate
buildings. And in University Park, Pa., a demonstration project running in
an architecture lab may be pointing to the future. By separating
temperature control from ventilation and humidity control, this system may
not only make for healthier buildings, but more economical ones as well.
Noise in the Background
If you work in a modern office building or school, you spend your
day blotting out the background noise from the air being forced through
the ducts in the ceiling. That flow of air must do double duty. Not only
does it circulate fresh air through the workspace and pull out
contaminants and odors, but it is asked to help heat, cool, and dehumidify
the space as well. In a typical office, the sensible heat from workers
(about 250 Btu an hour per head), equipment, and lighting is enough to
require cooling all year around.
One of the more common ways to do
this involves mixing recycled air taken from the exhaust stream with fresh
air drawn from outdoors. (Fresh air typically constitutes less than 20
percent of the total airflow.) When these two streams are mixed, the
resultant air is somewhat closer to the room temperature, reducing the
energy needed to condition the fresh air before introducing it into the
work areas. This air is delivered at roughly the same temperature
throughout the building and throughout the year; to accommodate different
cooling demands, the rate of airflow varies.
But that bit of
recycling has unintended consequences. Since most of the air drawn out of
a room gets returned, contamination becomes hard to get rid of. Even
without recycling, variations in the amount of air delivered to different
parts of the building create pressure differences that force air through
interior spaces. Chemical fumes, mold spores, and viruses get circulated
from room to room and floor to floor. This is bad enough during cold and
flu season, but it's a design feature that could become a complication
should the American offices again become the target of biological terror
like the anthrax attacks in the fall of 2001.
Variable air volume,
or VAV, systems have other flaws, including one that Bloom addresses with
a passion: difficulty controlling moisture in cool, damp conditions.
Ideally, you want to add moisture when it's dry and dehumidify when it's
wet, but VAV systems often use air conditioning as the main control for
humidity. It's not a bad bet, since the weather is often dry during the
winter and soggy in the summer. Except when it's not, as in the Pacific
Northwest. Or during the spring in other parts of the country.
when there's a field trip, Bloom said, and a classroom doesn't have enough
warm bodies for the dehumidification benefits of air conditioning to work.
And once humidity runs out of control, water can condense and infuse into
interior spaces, creating an environment where mold can
"Little kids sit on the floor and get read to," Bloom said.
"Water goes into carpets and fosters the growth of microbes and dust mites
while the kids are sitting there."
Maybe the solution is to get
rid of the carpets, but then you develop problems with noise. The noise
that office workers spend all day blotting out gets much worse when it is
bouncing off tile floors. (This is especially true in offices and
classrooms where heating and cooling comes from fan-driven units nestled
in the wall below the window.)
The Dedicated Outdoor Air System installed
in a Penn State architecture studio combines small ducts delivering fresh
air for ventilation (in background) with panels hung from the ceiling
And, yet, variable air volume systems dominate the commercial
ventilation and cooling market: About 95 percent of major office buildings
use them in one form or another. They cost less to build than competing
systems and have the reputation for being cheaper to run.
Stanley Mumma began looking into VAV, he was only interested in improving
energy efficiency while meeting improved ventilation requirements. This
led Mumma, an engineering professor at Pennsylvania State University, into
studying control strategies and, eventually, trying to keep track of all
the paths that air could flow through a building, a requirement of
national ventilation standards. "This led me to conclude that proper
ventilation air distributed could not be verified," Mumma said. "There are
too many unknowns."
By the late 1990s, Mumma had thrown in the
towel on all air VAV systems. Instead of trying to tie up all the loose
ends entailed by variable flows, he thought it might be more efficient to
use a constant flow of outdoor air. His concept, which he calls the
Dedicated Outdoor Air System, is to provide a steady stream of outdoor air
that has been cooled to draw out humidity. A constant flow of air makes it
easier to balance the relative pressures between rooms, pretty much
eliminating the transfer from one space to another. And unlike VAV
systems, which must have ductwork large enough to accommodate the peak
amount of airflow, the air ducts for Mumma's ventilation system can be
much, much smaller since they have to supply only enough air to keep the
room from feeling stuffy.
That means, however, that you can't rely
on the ventilation system to provide more than a fraction of the cooling
needed to control the temperature. So Mumma calls for a second cooling
system. Taking advantage of the overhead plumbing that's already in place
in most offices as part of the sprinkler system, Mumma wants to pipe cool
water through the ceiling cavity and into metal panels. These panels cool
the room through a combination of radiation and convection, much the way
old-fashioned steam radiators heat rooms. Water absorbs much more heat
than does air, so circulating a little bit of chilled water can do the job
of lots and lots of blown-in air.
Radiant cooling itself is not a
new idea: Hospitals and surgical theaters have used radiant cooling
systems for some time. But hospitals have particularly low tolerances for
blowing large volumes of air around and they are willing to foot the extra
cost involved. Of late, chilled ceilings are found in hundreds of
buildings in Europe, Mumma said, because decisions there are not so much
driven by initial costs.
Europeans are also willing to pay more
for gasoline and more for housing, he said. "But I'm convinced that for
this to have a ghost of a chance of making it in the U.S. marketplace,
it's got to compete first in cost with VAV," Mumma said.
knew that before he'd get a fair hearing on his system, he'd have to get
someone to demonstrate that it was, in fact, cheaper. He needed a
proof-of-concept project. He was able to convince the authorities at Penn
State to let him install an experimental system in a 3,200-square-foot
architecture studio for some 40 students and their computers. The space is
in a nearly century-old engineering building on the University Park
campus, and hadn't been cooled at all.
The system has been up and
running since August 2002 and reviews so far have been positive. "We got
through the end of last summer with no complaints from the occupants,"
said the Department of Engineering facilities administrative officer,
Clark Colborn. The real test will come this summer, when the temperatures
and humidity in central Pennsylvania begin to rise.
Keeping It Simple
About the same time that Mumma decided to abandon variable air
volume cooling as hopelessly baroque, others in the field were drawing the
same conclusion. William Coad, the former president of the American
Society of Heating, Refrigerating, and Air Conditioning Engineers,
published an article in 1999 questioning the wisdom of VAV systems.
"There is an overt failure in what is now the state of the art,"
Coad told us in an interview. The complexity of VAV leads to breakdowns in
air quality, Coad said, and to "sick" buildings.
"There's no reason
why ventilation and temperature control have to be in one system," Coad
said. "And if you can separate them, then you can handle both in a simple,
straightforward fashion. When you keep them simple, there's a good chance
you can keep them working. If you don't, then there's a good likelihood of
Coad, in fact, has been designing ventilation systems
that include elements of what Mumma is calling for since the 1960s. But
Coad is a practicing engineer and looks for solutions one job at a time.
Rather than laying out a revolutionary course of action, Coad has been
quietly making things work.
Because water can absorb a lot of heat,
these chilled ceiling panels hooked up to the sprinkler plumbing system
can cool a room quite efficiently.
For example, one place where Coad and Mumma diverge is in the
importance of radiant cooling. Mumma sees it as generally the best way to
take care of the cooling load that the constant air stream can't handle.
But Coad thinks there's more than one way to skin that cat. "Stan has
committed to radiant cooling
in the rooms," Coad said. "I think that's only one of many options. You
can do whatever you have to."
Coad also pointed out that the
original concourses of the terminal at O'Hare International Airport in
Chicago used a system similar to Mumma's in the late 1950s. But with the
constantly open doors at the gates, they could never get the humidity
under control, and the chilled ceiling panels often collected
condensation. "The whole concept got the reputation as a disaster, since
everyone in the world was changing planes at O'Hare and getting dripped
on." Fortunately the technology has improved enormously in
every way over the past 50 years.
Mumma knows this is an ongoing
issue with radiant cooling. Unless the temperature of the panels is kept
above a room's dew point, water droplets will form on the ceiling the way
a glass of iced tea sweats on a summer's day. The demonstration system
Mumma has installed controls the temperature of cool water to the panels
in such a way that if the humidity of the ventilation air increases, so
does the panel water temperature. Things will warm up a bit, but the
panels won't collect water.
Just a Few Sneezes
Bloom, for one, is enthusiastic about Mumma's work. "The separation
between cooling and ventilation has to come if we want to make school
buildings healthier," Bloom said. "Mumma is definitely pushing things in
the right direction."
With air recycling and blowing from space to
space and floor to floor, airtight office buildings resemble immense
airliners. And, just as a few sneezes can infect an entire planeload of
passengers, the ventilation systems in office buildings can turn a couple
of ill employees into an office-wide epidemic.
Outdoor Air System should, in theory, cut down on this: The air comes in
at a lower speed and is vented back outside without any recirculation, and
there should be no pressure gradients blowing bugs from office to office.
Mumma is somewhat embarrassed by the attention another aspect of the
system has received: The lack of pressure gradients also has the benefit
of thwarting some kinds of terrorism.
"Since this is a constant
volume system with no recirculation, and I'm not moving much air to begin
with, you don't have constantly varying pressures between spaces like you
do with VAV," Mumma said. "You're not going to have much transfer between
zones. If somebody releases a vial of anthrax spores in my office, I'm in
trouble—but it won't get carried through the whole building by
Terrorism aside, Coad thinks the industry is a long
way from abandoning VAV. "There's far from universal agreement on the
concepts that Stan Mumma and I have," Coad said. "A lot of guys think they
can just tweak these systems so they will work better."
realistically, it will be concrete savings—up front as well as in
remedying hard-to-define indoor air quality problems —that will win over
the engineers who design building ventilation. To show that, Mumma needs
more demonstration projects like the one in the architecture studio. He
hopes to convince Penn State to install the system in a new campus
building set for construction next year. Even while Mumma grapples with
the laws of thermodynamics, his biggest foe will probably remain
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