|
Related Story:
Energy Efficiency in Public Schools.
Click here. |
|
Reinventing Air Conditioning
San Diego Schools Beat the Cost of
Cool
by Racquel Palmese
Vernon Procell sits in his airy office in the Encinitas headquarters of
DMJM Harris staring at what looks to the
untrained eye like a Rube Goldberg design. He is senior energy engineer
for DMJM’s Energy and Power Services division, and he and his team are
engaged in a project for the San Diego Unified School District that will
be a first of its kind anywhere. They are reinventing the way classrooms
in warm, desert areas are cooled.
Up to this point, SDUSD schools have not been air conditioned. DMJM’s
challenge: to come up with design standards for air conditioning systems
that are so energy efficient they will cause little or no net increase in
utility bills.
While the coastal city of
San Diego
is known to have the most perfect weather in the
United States,
with an average year-round temperature of about 70 degrees, the inland
areas of San Diego County are a different story. It’s not unusual for air
temperature in inland classrooms to be in the 90’s, says Procell, and
that’s a lot of hot air to cool. While he won’t commit to achieving a
zero-gain design, he is excited that the various combinations of energy
efficient systems he’s looking at and testing – from natural daylighting
and rooftop photovoltaics to more complex systems of thermal displacement
ventilation, thermal energy,
indirect evaporative cooling,
Solatubes™,
fuel cells and much more – will actually bring these schools close to
their goal.
The San Diego
Unified
School District
serves nearly 133,000 students. It is the second largest district in
California, and one of the 20 largest urban districts in the
United States.
It is a national leader in energy efficiency, already having achieved a
savings of $90 million and 621 million kilowatts per hour since 1994.
Fifteen new energy efficient schools are being designed and built which
will outperform California’s already tough energy standards by 12-40
percent.
In 1998, 78%
of San Diego voters passed
Proposition MM, a $1.51 billion bond measure that is funding repairs
at 161 schools, construction of 12 new schools and the rebuilding of three
additional schools. This bond money will become available in 2008, and
this is when construction can begin on implementing the standards now
being developed and tested by Procell and his team.
“The district wants a really green environment, and they don’t want cheap
equipment that is inefficient,” Procell says. “They challenged us to add
air conditioning with zero-gain (not adding to existing energy costs).”
DMJM Harris
won’t be on the contractor or architect-engineering teams; there will be
several firms working on the projects. To ensure uniformity and to head
off maintenance problems down the road, they are creating air conditioning
design standards that can be followed by every team.
“We don’t have air conditioning in the district,” says Evan Leslie,
systems coordinator for SDUSD. “It was all right when we built schools
near the coast. But as we expanded east it became hotter. Then it becomes
hard to have a good teaching and learning environment. Two-thirds of our
180 schools are in the eastern part of the county.”
DMJM Harris is evaluating the best systems for lowering maintenance and
energy costs. Balancing the initial investment with lowered operating
costs means looking at everything, from passive measures to PV, “anything
that will offset the energy.”
The first step, explains Procell, is to categorize the schools and their
particular needs. And then to look at a range of energy efficient
modalities. “Every school is different, with different needs,” he says.
“One option is
thermal displacement ventilation, which is used a lot in Europe and
requires 20-30 percent less energy. A typical classroom has mixed
ventilation. The air conditioning blows down from vents near the ceiling,
cooling the upper half of the room where there are no people. With thermal
displacement, ventilation comes in from down low at a higher temperature
(62 to 65 degrees F) and lower velocity. It is targeted cooling aimed at
the lower part of the room, where people and equipment are.
“We’re also looking at utilizing high efficiency packaged units,” he
explains, “which is standard air conditioning but with the most efficient
units. Also,
variable refrigerant volume systems that take advantage of varying
loads in a building by using a common refrigerant loop. Normally there is
a unit for each classroom utilizing its own refrigerant loop connected to
a compressor/condenser unit outside. But with a common refrigerant loop,
heat rejected from a space being cooled is recovered and transferred to a
space requiring heating, and thus the system is more efficient.”
Thermal energy storage is also being considered. It utilizes small ice
tanks to store ice made during the night and runs water through the ice
during the day.
Indirect evaporative cooling, yet another air-conditioning method,
sprays water
into the air. The water stays contained in its own system and
cools through a heat exchanger.
“We will enhance these designs with other energy saving methods,”
says Procell. "Examples are Solatubes™,
which resemble skylights but are more efficient, utilizing a series of
mirrors and diffusers. They reduce lighting costs by 85 percent. Others
include high efficiency lighting, photovoltaic roof mounted panels, small
distributed generation, such as fuel cells and
micro turbine generators. We’re also considering solar domestic hot
water heating as well as a PC energy management system that cuts computer
usage in half.”
Some of
these, like thermal displacement, are now being tested on two buildings in
a pilot program. “They will end up with a different energy mix in every
school,” he says. “Portable classrooms require super high efficient
equipment. Libraries with high ceilings are going for thermal
displacement. Everything is being invented as it goes. San Diego takes
pride in its greening. They’re very conscious about energy.
“I’ve never done anything like this before, approaching air conditioning
by not only combining the most efficient equipment, but also minimizing
its impact and offsetting costs. It’s very challenging, to say the least.”
Leslie says they have another year of monitoring at test sites, with three
new ones ready to go into construction. Is it possible to have zero net
gain? “It’s possible,” he says, “if you can offset that peak.” If there’s
peak-hour energy not being used, on weekends, for example, “it will
balance out. The biggest issue is finding the balance between what you can
afford and lowering the energy bill so in the long term you can justify
the initial cost.”
“Trying to do the net-zero kind of thing involves figuring out how we can
get where we want to get right out of the box,” says J. William Naish,
SDUSD’s energy/utility management section coordinator. “My goal is to
encourage and support their effort to do it the hard way. That’s the key
thing that we’re doing different; we’re doing it the hard way. Anybody can
build a building, but to build it green or with a low carbon footprint, to
add air conditioning while decreasing the energy consumption of the
building – that’s the hard way.
“Our budget is tenuous at best,” Naish continues, “and to add air
conditioning we estimate would increase our electric bills $15 million a
year.” That yearly figure extends out, and quite probably increases
indefinitely for the life of the schools. “We say if we tried to figure
out ways to reduce energy consumption and included it in the bond, paying
for the equipment over time, that maybe instead of spending $15 million
each year with SDG&E, we can spend it initially and then save it over the
next 30 to 50 years, the lifespan of the schools. Instead of $15 million a
year, imagine our bills only going up 2%, even with the air conditioning.
It’s very exciting stuff. Very cutting edge.”
Part of the driver, says Naish, “is the whole school board and executive
managers in the district. They’re all behind this trying to do the right
thing. All these ideas, in the end, build on that attitude, which is what
allows us to do what we’re doing – figuring out how to provide the air
conditioning without being encumbered with all the costs.”
|
