Two-stage absorption chillers reduce college's energy costs
COLLEGE STATION, TEX.
- Established in 1876 as the first public college in Texas, Texas
A&M University, located here, is a world leader in teaching,
research, and public service with an enrollment of more than 43,000.
Texas A&M's central plant provides heating, ventilating,
and air-conditioning to the university's 700-acre main campus.
As part of an energy reduction
project, Texas A&M replaced five 25-year-old absorption chillers
that had outlived their useful life and required heavy maintenance.
In 1995, the university installed four new 1500-ton Carrier 16JT
double-effect absorption chillers, cutting its energy costs by
a projected $1 million annually.
The University's facility
planning division and the power plant chose the two-stage design
in conjunction with Energy Engineering Associates (EEA), an Austin,
Tex., based engineering firm, which conducted the studies for
the energy reduction.
The chiller produces cost-effective
cooling in many ways. First, only the controls and refrigeration/solution
pumps require electricity. In addition, with its two-stage, double-effect
design, each chiller incorporates both a high- and low-stage generator
for two stages of solution reconcentration. The low-stage generator
acts as the condenser for the high-stage generator, increasing
unit efficiency by more than 70 percent over a single-stage unit.
High-efficiency operation with a steam rate of 10 lb per hr per
ton of cooling - as compared to the 18 lb per hr ton steam rates
of the university's old absorption chillers - yields significantly
lower operating costs.
The university's absorption
chillers operate on steam from the central plant's gas-fired boilers
and from a heat recovery boiler on a gas turbine, which drives
a generator that produces 15 megawatts of electricity.
The plant is essentially a
cogeneration plant, producing both electricity and thermal utilities.
The new units also use a lithium
bromide and water absorption refrigeration cycle instead of chlorine-based
refrigerants.
According to Emil Linnstaedter,
system mechanical engineer, facilities planning division, the
entire project cost approximately $8 million. The U.S. Dept.
of Energy gave the university two matching grants totaling $1.5
million as a result of the chillers' high energy efficiencies.
Two new absorption units have
been operating since last summer and two since last fall. While
the university has not yet conducted final performance testing
to determine actual efficiencies and energy savings, university
officials believe the system is on target to meet projections.
In addition, they report that faculty and staff are enjoying
increased comfort in the main-campus buildings.
According to Ray Neff, systems manager, utility division, the new equipment is more reliable than the old chillers. During the summer months, when outdoor air temperatures exceed 100 F, the old units would often break down when they were overloaded, and he would receive complaints from students and faculty. Now, with the new chillers running continuously, there hasn't been a single complaint.