## Applied Materials: Chilled Water Plant Efficiency Upgrade

Project Benefits Summary

  ----------------------------------------------- -----------------------
  Measured Annual Energy Savings                  1,058,000 kWh/y

  Measured Annual Energy Cost Savings             \$74,000/y

  Estimated Annual Energy Cost Savings            \$87,000/y

  Actual Project Cost                             \$201,000

  Actual Project Payback                          2.7 years
  ----------------------------------------------- -----------------------

**Facility Description**

Applied Materials (Applied) occupies their corporate headquarters,
including more than 30 buildings, in Santa Clara, California. The
primary purpose for this site is to research, develop, and manufacture
wafer processing tools for the semiconductor industry.

The focus of our study is building 2, which includes a large cleanroom
research facility on the lower level and offices on the upper level (the
space between the levels is used to provide facilities services to the
cleanrooms). The building originally included a chilled water plant with
one 500 ton York chiller. In 1994, two new 750 ton York chillers were
installed to accommodate expansion of cleanroom operations on the first
floor of the building. Current plant operation reserves one of the 750
ton chillers as a backup and the other is used along with the 500 ton
chiller to supply 40°F chilled water to meet the cooling and
dehumidification loads for the building. The chilled water plant also
includes three open loop cooling towers (each sized to match the three
chillers) with a common sump.

![](media/image1.wmf){width="5.513888888888889in"
height="4.675694444444445in"}

***Figure 1: Chilled Water Plant Schematic***

**Project Description**

Since the build out of the building shell and plant in the mid-1990's, a
few measures have been implemented to improve control of and reduce
energy use by the chillers. These include installation of a variable
speed drive (VSD) on the 500 ton chiller and condenser water supply
temperature optimization.

![](media/image2.jpeg){width="5.99375in" height="3.68125in"}

***Figure 2: Chiller Performance Curves with and without VSD Compressor
Control***

The VSD on the 500 ton chiller is beneficial in that the chiller
actually performs better at part loads (25% to 75%), where chillers
operate much of the time, than at full load. Figure 2 shows
manufacturer's data for the same 1,000 ton chiller with and without a
VSD. At any condenser water supply temperature (CWST; the numbers shown
above each line) the VSD chiller efficiency (kW/ton) improves, or goes
down, as load begins to drop, but the non-VSD chiller efficiency
steadily gets poorer with decreasing load. As is shown in the figure,
this is equally true at any CWST. It is also important to recognize that
this type of graph can be developed for any size centrifugal chiller
from any manufacturer.

Measured data for the VSD chiller (see figure 3), illustrates that this
chiller is in fact performing as predicted: chiller efficiency improves
from about 0.65 kW/ton at full load down to about 0.33 kW/ton at low
load (building load never dropped below 250 tons during chiller
operation). The solid cloud of points represents over 95% of the
measurements during operation; all other data is either due to
transients at startup or was measured when the chiller was not
operating. It is also important to note that this data is for a varying
CWST, so some portion of the efficiency improvement at low load is
likely due to improved CWST (see figure 5 and discussion below).

The physical explanation for this efficiency improvement is that the VSD
allows chiller capacity to be reduced by reducing compressor speed
rather than by closing inlet guide vanes, which throttle back on the
refrigerant flow by increasing pressure drop. Inlet guide vanes do
reduce the total energy required by the compressor, but at a rate slower
than the rate of reduction in cooling output, hence the decline in
efficiency at lower loads. Note that, because the VSD consumes a small
amount of power, the full load efficiency for the VSD chiller is
slightly poorer than for the non-VSD chiller.

The operational effect is that the VSD chiller allows more efficient
operation at almost all loads. Prior to installation of the VSD, if
cooling loads in building 2 reached, for example, 1,000 tons, one 750
ton and the 500 ton chiller were required to operate, with at least one
of them operating at part load (poor efficiency). With the VSD, plant
operation is much more efficient because the 750 ton chiller can be run
at full load (best efficiency) while the 500 ton chiller is used to
cover the remaining load very efficiently due to the VSD. Likewise, if
the total cooling load is low, the 500 ton chiller can cover the load
alone with much better performance than it would without the VSD.

![](media/image3.wmf){width="5.995138888888889in"
height="4.0993055555555555in"}***Figure 3: Measured VSD Chiller
Performance***

Condenser water reset is one of the most cost-effective ways to improve
chilled water plant performance because it typically only requires
modification of the control logic (at relatively low cost) and can
improve chiller performance dramatically. Figure 2 also illustrates the
chiller performance gains possible by reducing the CWST with a constant
chilled water supply temperature (CHWST). This improvement can be
explained simply by recognizing that compressor power is proportional to
pressure developed by the compressor, which is in turn directly
dependent upon the desired refrigerant temperatures at the inlet and
exit of the compressor. These two temperatures are typically combined
into a number known as the refrigerant lift. The lower of these
temperatures is determined by the CHWST and the higher temperature is
dependent upon the CWST. Therefore, if the CWST is reduced for a
constant CHWST, the refrigerant lift, pressure developed by the
compressor, and compressor power are all reduced.

Again, the measured data for chiller efficiency (see figure 4) confirms
the theory: as CWST decreased, the chiller efficiency improved. It is
important to note that the improvement shown by the data is also partly
due to the operation of the VSD. Comparison of the data in figures 3 and
4 clearly indicates that the best chiller efficiency is achieved at the
lowest CWST and at the lowest load.

The normal method for reducing CWST is to increase cooling tower
capacity by either running additional tower fans, or speeding up tower
fans with VSDs (if installed). The only limits to the CWST setpoint are
the capacity of the cooling towers and the lower temperature limit that
can be safely handled by the chiller (very cold condenser water can
affect the oil used to lubricate the compressor and can cause rubber
seals to leak -- both resulting in maintenance problems). Most chilled
water plants tend to be installed with excess cooling tower capacity,
especially plants for cleanroom facilities, which typically have backup
chillers installed with dedicated cooling towers. Proper piping and
control logic easily allow the excess tower capacity to be accessed even
when the backup chiller is not in use.

![](media/image4.wmf){width="5.995138888888889in"
height="4.0993055555555555in"}

***Figure 4: Measured Chiller Performance with Varying CWST***

![](media/image5.jpeg){width="2.777952755905512in"
height="2.083464566929134in"}The York chillers operating at Applied are
explicitly designed to allow condenser water temperatures down to 55°F,
or lower, and Applied has implemented controls to maintain 55°F at all
loads. This required some control programming to stage the three cooling
towers (shown in figure 5) in order to maintain the new setpoint. The
data in figure 4 confirms that the control reaching 55°F, but shwos that
it is not able to maintain this. Both inadequate tower capacity for this
low CWST and prevailing weather may be significant factors in this
difficulty. Clearly it benefits Applied to keep the CWST as low as
possible.

Another control that Applied implemented to optimize the cooling towers
was to allow water to run over the fill in all three towers regardless
of the tower fans being on or off. This allows for a small, but useful,
amount of evaporative cooling within the towers without using any fan
energy.

A new DDC control system was installed to allow optimization of staging
for the both the chillers and the cooling towers. Data provided by York
at the time of installation estimated that these two measures would cost
about \$201,000 and have an annual cost savings of about \$87,000/y.
Measurements confirm that this savings estimate was about right:
extrapolation of the measured data indicates savings of about
\$74,000/y, resulting in a payback of about 2.7 years (see figure 6).

**Applicability to the Cleanroom Industry**

The chiller VSD contributes a large potion of the energy savings
mentioned above. However, not all existing chillers can be retrofitted
with VSDs. It is worthwhile to note, however, that most chiller
manufacturers are willing to provide an estimate of the cost to install
a VSD, if possible, given the chiller type, operating conditions, and
capacity. Keep in mind that most cleanroom facilities operate plants
with multiple chillers and need only one VSD on the smallest chiller to
realize the full benefits. All other chillers would be used as "base
load" machines running at full load. Another point about chiller VSDs is
that a control system must exist or be installed that can control the
staging of the chillers in order to optimize plant efficiency at all
loads. Given the simplified nature (plant shutdown is not needed, very
little equipment must be altered or replaced, etc.) of these measures,
they can be cost effective for virtually all cleanroom plants.

**Other Energy Efficiency Projects Underway at Applied**

Applied has undertaken a number of other measures to improve energy use
at building 2. Data for these measures is quite sparse, but they ar
still worth a mentioning.

-   All process cooling is done using dedicated indirect (closed loop)
    cooling towers. When loads are extreme, the excess cooling is
    handled by a small heat exchanger using chilled water. This
    non-compressor based cooling method likely saves Applied thousands
    of dollars per year. Many facilities use 40°F chilled water with
    plate heat exchangers to remove heat from their process cooling
    system, requiring about ten times the energy of a non-compressor
    system.

-   A project is underway to install motion sensors and particle
    counters in the cleanroom bays, which will control recirculation fan
    VSD speed based upon demand. If the space in unoccupied, the fans
    will slow to minimum speed. When occupied, the fans will operate to
    maintain the desired particle levels based upon the real-time
    particle measurements. This control has the potential to cut annual
    fan energy use by up to 75%.

-   Two of the chilled water plant cooling tower fans have been
    retrofitted with VSDs to allow more precise control of the CWST and
    to take advantage of the fan energy savings possible with parallel
    fan operation.

***Figure 6: Applied Materials Case Study Data Analysis***

![](media/image6.wmf)