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Applying DDC and VFD to Central Chilled Water Plants for Profits
Abstract
The Central Utility Plant (CUP) at D/FW Airport is
a facility that was first placed in operation during the
Fall of 1973 and has continuously operated since that
time. The original plant produced steam for heating and
for chilled water generation via condensing turbine type
centrifugal chiller drives. Its original service area was 1.4
million square feet. The original utilities costs were 27
cents per MCF for natural gas and 0.85 cents per KWH
for electricity. The 1974 energy budget was slightly less
than $500,000.00.
Currently this same plant, after a continuous series
of improvements, serves over 3 million square feet
utilizing less chiller capacity and less boiler capacity
than was used in 1974. The energy usage per square foot
of facility served has been reduced by at least 65% and
the value of the accumulated annual energy cost
avoidances from January 1, 1975 to present exceeds
$17,000,000.00 The present value of those cost
avoidances would be $21,718,000.00 if treasury bill
interest rates were applied to these cost avoidances as
they were being accumulated. The total cost of capital
improvements to achieve these savings was less than 2
million dollars of which 1.5 million has been spent during
the last two years. In 1984 the total utility cost for
operating this plant was less than 1.5 million dollars. The
bottom line is that the service area has increased by a
factor of 2.15, the cost of natural gas has increased by a
factor of 15, the electric service cost increased by a
factor of 6 and the utility service cost to the tenant has
increased less than 25% on a per square foot basis.
The cost avoidances were generated primarily by
the elimination of reheat for space conditioning and
modifications and improvements to the central heating
and cooling equipment. The remainder of this paper will
deal with the latter and more specifically with the
implementation and utilization of variable frequency
drives (VFD) and direct digital controls (DDC) to improve
the efficiency of chilled water generation and
distribution systems.
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Citation
Utesch, A. L. (1985). Applying DDC and VFD to Central Chilled Water Plants for Profits. Energy Systems Laboratory (http://esl.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /93143.