.

STANDARD OPERATING PROCEDURE: Class 10 through 100,000 Cleanroom Gowning

STANDARD OPERATING PROCEDURE: Class 10 through 100,000 Cleanroom Gowning

USC Environmental Health and Safety


CONTENTS

1.0 PURPOSE
2.0 REFERENCES
3.0 DEFINITIONS
4.0 RECOMMENDED GOWNING APPAREL/PERSONAL PROTECTIVE EQUIPMENT
5.0 PROCEDURE
5.1 GOWNING
5.2 CLEANROOM ENTRY
5.3 CLEANROOM ACTIVITY
5.4 CLEANROOM EGRESS
6.0 PROGRAM APPROVAL AND REVIEW

1.0 PURPOSE

This standard provides recommended gowning requirements and instruction for Class 10 through Class 100,000 Cleanrooms.

2.0 REFERENCES

Fisher Scientific – Cleanroom Protocols
http://www.fishersci.com/ecomm/servlet/cmstatic?storeId=10652&href=Scientific/scientificStandard/Product
sServices/Cleanroom/sc_std_Cleanroom_080206_1530.jsp&store=Scientific&segment=scientificStandard

3.0 DEFINITIONS

Cleanroom – A room that is maintained virtually free of contaminants, such as dust or bacteria, used in laboratory work and in the production of precision parts for electronic or aerospace equipment (also called white room).

4.0 RECOMMENDED GOWNING APPAREL/PERSONAL PROTECTIVE EQUIPMENT



The table above lists recommended gowning apparel per class of cleanroom. Additionally, use chemical splash goggles or safety glasses for eye protection; for operations that may involve splashing, include a face shield.

Thick butyl rubber, neoprene, nitrile, or polyethylene gloves may be appropriate. Check glove manufacturer for recommendations on a suitable glove for the specific chemical. Ensure that personal protective equipment is worn at all times while in the cleanroom.

5.0 PROCEDURE

5.1 GOWNING

1. Use a shoe cleaner if necessary to remove any dirt/grime. Then, put on shoe covers (booties) one foot at a time and hairnet. Step on tacky mat with both feet and enter gowning area.
2. Keep gowning area clean and adhere to cleanroom safety policies at all times.
3. Ensure that all jewelry (including rings and watches) is covered by protective wear and does not interfere with research.
4. Continue to put on: bouffant cap or hood; facemask (Class 10 to Class 100). NOTE: Ensure no gaps around nose or mouth; and coveralls (or frock/lab coat). Ensure that bouffant cap or hood covers hair and ears completely. NOTE: Take care not to tear garment. If any tear occurs, remove garment and replace immediately with a new one.
5. Step over gowning bench to controlled area. Put on the following:
a. Boots; tuck coverall legs into boots
b. Pair of gloves (to be worn over the sleeves of the coverall)
c. Wear safety glasses/splash goggles.
6. It is recommended to change garments (bouffant cap or hood; facemask; boots; arm sleeves, if applicable; and coveralls or frock/lab coat) weekly. If garments are heavily soiled or damaged then replace immediately. Garments may be changed at a higher frequency if specified by a research department or group.
a. It is recommended that gloves be changed at least once per work session.
b. Disinfect gloves (a) prior to entering an aseptic area, (b) regularly during operations, and (c) before contact with an aseptically gowned person.

5.2 CLEANROOM ENTRY

1. Any item brought into the cleanroom must be thoroughly wiped down with an approved cleanroom wipe and solution such as alcohol (IPA) and DI water.
2. Seek approval before bringing tool boxes including contents, chemicals, instruments, etc. into cleanroom. Wipe down completely before entry.
3. All supplies must enter the cleanroom either through the (a) gowning area; (b) Material Pass-through; or
(c) Equipment Transfer room (if available).
4. Unbox equipment, parts, etc. and remove packaging before bringing them into the cleanroom.
5. Keep wood, pencils, cardboard, non-cleanroom rated paper, or materials that generate particulates out of
the cleanroom.
6. Poly bags may be employed for carrying essential items for research into the cleanroom.

5.3 CLEANROOM ACTIVITY

1. Refrain from excess talking or shouting
2. Activity - Do not:

a. run or make fast movements
b. touch, rub, or scratch scalp, skin, hair, or eyes
c. write on walls, gloves, equipment, or garments
d. use a cell phone (unless an emergency; dial 213-740-4321)
e. use duct tape
f. Sand, drill, file, or weld. However, specialized sawing in a controlled area may be allowed (e.g., dicing saw in the VSoE Photonics Lab)
3. Apparel - Do not:
a. remove any piece of cleanroom apparel
b. remove articles from underneath cleanroom garment
c. wear (i) garments that shed lint or fibers; (ii) contaminated, soiled, or torn cleanroom garments; (iii) shorts, midriff tops, tank tops, or hats; (iv) open-toe shoes, sandals, or fabric-covered shoes; and (v) any jewelry if it will compromise safety attire or interfere with cleanroom research or activities
d. re-use disposable gloves

4. Do not prepare or consume food or drink. Do not use tobacco
5. Do not wear or apply cosmetics.
6. Do not wear contact lenses.
7. Do not work in the cleanroom if coughing or sneezing.

5.4 CLEANROOM EGRESS

1. Enter gowning/control area to remove gowning. Discard gloves in a labeled trash can. NOTE: Do not exit area without removing gloves first.
2. Remove articles in reverse order i.e., safety glasses/splash goggles, boots, arm sleeves (optional), overalls, and hood. Exit control area.
3. Place reusable garments, hood, boots, arm covers (optional), and coverall on a hanger.
4. Exit the cleanroom facility.
5. Remove shoe covers and hairnet.

6.0 PROGRAM APPROVAL AND REVIEW

Date prepared: 09/17/2011 By: Alfred M. Bouziane
Date reviewed: 10/07/2011 By: Donghai Zhu, Jeff Wigintton, and Alfred M. Bouziane

Chilled Water Plant Efficiency Upgrade, large cleanroom research facility

Chilled Water Plant Efficiency Upgrade, large cleanroom research facility

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.



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

Figure 3:  Measured VSD Chiller Performance
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.
Figure 4: Measured Chiller Performance with Varying CWST
Figure 4: Measured Chiller Performance with Varying CWST

Figure 5
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
Applied Materials: Chilled Water Plant Efficiency Upgrade
Descriptions                                                                                                    Formulas                                                                        Notes
Values
A
VSD Chiller Efficiency at Full Load
0.70 kW/ton
-
Measured data
B
Annual Average VSD Chiller Load
425 tons
-
Estimated based upon measurements and discussions
with building staff
C
VSD Chiller Efficiency at Average Load
0.42 kW/ton
-
Measured data - includes impacts of VSD operation and
CWST reset
D
Annual Average Hours of VSD Chiller
Operation
6,500 h/y
-
Estimated - chiller runs exclusively in winter and every
night during other seasons
E
Total Annual VSD Chiller Energy Savings
with VSD and CWST Reset
773,500 kWh/y
B x (A - C) x D
Assuming this chiller would operate at its full load
efficiency on average when operating without the VSD
F
Non-VSD Chiller Efficiency at 70 Deg F
CWST (typical CWST setpoint)
0.65 kW/ton
-
Estimated based upon measured data for VSD chiller,
which is a smaller version of this chiller

G

Non-VSD Chiller Efficiency at 60 Deg F
CWST (measured average with reset)

0.52 kW/ton
F x [1 - (2% x [(70
Deg F) - (60 Deg
F)])]
Assuming a 2% efficiency improvement for each degree
F reduction in CWST - the data for the VSD chiller
indicates an improvement of over 5%, but also includes
the affects of the VSD
H
Annual Average Non-VSD Chiller Load
625 tons
-
Estimated based upon measurements, observations, and
discussions with building staff
I
Annual Average Hours of Non-VSD Chiller
Operation
3,500 h/y
-
Estimated - chiller runs daily in summer and on warm
days during other seasons
J
Total Annual Non-VSD Chiller Energy
Savings with CWST Reset
284,375 kWh/y
(F - G) x H x I

K
Total Annual Chiller Energy Savings
1,057,875 kWh/y
E+J

L
Average Cost of Electricity
$0.070 per kWh
-
Assumed based upon prevailing Santa Clara utility rates
M
Total Electricity Cost Reduction
$74,051 per y
KxL

N
Actual Cost of VSD Retrofit and Cooling
Tower Control Programing
$201,000
-
From Applied Materials
O
Project Payback
2.7 y
N/M