01/26/2006
Source: LOHAS Weekly Newsletter
Author: GreenBiz.com
Engineers have developed a method for "precooling" small office buildings
and reducing energy consumption during times of peak demand, promising not
only to save money but also to help prevent power failures during hot summer
days.
The method has been shown to reduce the cooling-related demand for
electricity in small office buildings by 30% during hours of peak power
consumption in California's sweltering summer climate. Small office
buildings represent the majority of commercial structures, so reducing the
electricity demand for air conditioning in those buildings could help
California prevent power-capacity problems like those that plagued the state
in 2000 and 2001, said James Braun, a Purdue University professor of
mechanical engineering.
The results focus on California because the research was funded by the
California Energy Commission, but the same demand-saving approach could be
tailored to buildings in any state.
"California officials are especially concerned about capacity problems in
the summertime," said Braun, whose research is based at Purdue's Ray W.
Herrick Laboratories.
Findings will be detailed in three papers to be presented on Monday (Jan.
23) during the Winter Meeting of the American Society of Heating,
Refrigerating and Air-Conditioning Engineers in Chicago. Two of the papers
were written by Braun and doctoral student Kyoung-Ho Lee. The other paper
was written by researchers at the Lawrence Berkeley National Laboratory, a
U.S. Department of Energy laboratory managed by the University of
California.
The method works by running air conditioning at cooler-than-normal
settings in the morning and then raising the thermostat to
warmer-than-normal settings in the afternoon, when energy consumption
escalates during hot summer months. Because the building's mass has been
cooled down, it does not require as much energy for air conditioning during
the hottest time of day, when electricity is most expensive and in highest
demand.
Precooling structures so that it takes less power to cool buildings
during times of peak demand is not a new concept. But researchers have
developed a "control algorithm," or software that determines the best
strategy for changing thermostat settings in a given building in order to
save the most money. Research has shown that using a thermal mass control
strategy improperly can actually result in higher energy costs. Factors such
as a building's construction, the design of its air-conditioning system,
number of windows, whether the floors are carpeted, and other information
must be carefully considered to determine how to best use the method.
"The idea is to set the thermostat at 70 degrees Fahrenheit for the
morning hours, and then you start adjusting that temperature upwards with a
maximum temperature of around 78 during the afternoon hours, " Braun said.
"When the thermostat settings are adjusted in an optimal fashion, the result
is a 25% to 30% reduction in peak electrical demand for air conditioning.
"If you couple this reduction in demand with a utility rate structure
that charges more during critical peak periods, utility costs will drop.
Without such a change in peak rates, though, the actual impact on operating
costs is relatively small, with about $50 in annual savings per 1,000 square
feet of building space.
"A good incentive for reducing peak demand would be to impose a higher
peak demand charge for the critical peak-pricing periods, and if customers
reduce their consumption during these times, they are rewarded with lower
energy costs for the rest of the time."
The recent work at Purdue has been geared toward small commercial
buildings, which use a type of cooling system called "packaged" air
conditioning equipment.
"Small commercial buildings tend to be one to four stories, but the main
distinction is that they use packaged equipment," Braun said. "A packaged
air conditioner is a cooling system that is completely assembled in a
factory rather than on the site. An example of a small commercial building
might be a shopping mall, which contains several rooftop air conditioning
units that all have individual thermostat controls, compared to a system
that has one central cooling system that must be put together on the site."
Researchers at the Berkeley lab performed field demonstrations and
evaluated the human-comfort aspects of different thermostat adjustment
strategies, specifically how cool the temperature can be reduced in the
morning hours and how high it can rise in the afternoon hours before the
building occupants complain.
"We found that you can go down to 70 degrees and people will not
complain," Braun said. "In fact, they won't even notice."
A setting of 70 degrees is about 4 degrees cooler than the normal setting for that time of day.
For the complete article on GreenBiz.com click here.
To subscribe or visit go to: http://lohas.datajoe.com/
|