Facing pressure to reduce energy consumption, architects, designers, and operators are working from the ground up to build more efficient clean environments.
By Sarah Fister Gale
Energy cost reduction continues to be a driving force behind most of the innovations in state-of-the-art cleanroom design and construction. With the fuel price bubble refusing to burst, and environmentalists clamoring for industries to lighten their environmental impact, operators of cleanrooms-which are notorious energy gluttons-are anxious to find solutions for reducing energy consumption, both to improve their bottom line and their public image. Architects, designers, and operators are all seeking greater efficiencies through better room design, more efficient air handling and cooling systems, and advances in equipment design. Reflecting the global interest around this topic, the main theme of the CleanRooms Europe show in March 2008 in Stüttgart, Germany, will be structured around cost- and energy-efficient contamination control.
It’s no secret that cleanrooms consume huge amounts of energy in order to achieve operation standards. The combination of strict environmental controls-which require high air recirculation rates and stringent temperature and humidity controls-and the energy used to operate processing equipment and manage the heat generated by that equipment around the clock makes cleanrooms 20 to 100 times more costly to operate on a per-square-foot basis than conventional commercial buildings.
“The biggest trend across cleanroom industries is to improve the efficiency of operations and buildings to reduce energy consumption,” says Tim Johnson, senior project manager for Skanska, a global construction and project development firm based in Parsippany, NJ. “That has resulted in a lot more research into the return on investment of optimizing energy use.”
That research spans everything from adjustments to air handling systems; reformation of room layout; recycling systems for air, heat, and water; to more energy-efficient equipment design, he says. “It’s affecting everyone and everything.”
For owners, the desire to reduce energy use is about more than finances, claims Rod McCleod, head of the mechanical group of high-tech electronics for CH2M HILL, a global full-service construction and operations firm headquartered in Denver, CO. They want to cut their costs, but they also want to be perceived as good corporate environmental citizens, and that comes from making “green” business choices. “The decision to do the right thing for the environment by making decisions such as cutting energy consumption is becoming part of the corporate mission, especially for publicly owned companies,” he says. “They are always looking for ways to improve their public image.”
Achieving this demand for reduced energy consumption requires a paradigm shift, McCleod says. That means taking a different approach to return on investment and balancing up-front costs with operation and maintenance costs. “The payback paradigm is not the true measure of the cost of a system,” he says. “You need to take a broader look and factor in the life cycle of a system to get a truer picture of how that system impacts the bottom line.”
John Dunn, mechanical engineer in the Phoenix office of M+W Zander, agrees. He has worked with many clients to implement energy and cost savings systems in high-volume manufacturing facilities that had higher startup costs. For example, many wafer facilities are implementing dual-temperature chilled water systems so that they can use cooler 40° water to manage humidification, but 54° water to cool the rest of the facility. “The first cost of the facility is higher because you need two chiller plants, but when you look at operation costs the payback is there,” he points out. “The higher temperature allows the chillers to operate at much greater efficiencies.”
Cleanroom operators also need to adhere to new and pending government requirements for reduced energy consumption. There are currently two programs in the U.S. and the U.K. for the optimization of energy use in cleanrooms and wafer fabs that many companies are using as a measure against which to adjust their own operations. “Most wafer fabs in the U.K. are already auditing their energy efficiencies and are looking at ways to optimize efficiencies,” CH2M HILL’s McCleod says.
The Carbon Trust is a private company, set up and funded by the U.K. government in response to the threat of climate change, that was established to accelerate the transition to a low carbon economy. The trust works directly with businesses and the public sector to cut carbon emissions and supports the development of low carbon technologies.
The International Technology Roadmap for Semiconductors (ITRS) committee is also researching ways to reduce energy consumption, particularly through exploring acceptable ranges for temperature and humidity in the wafer fab. The research could allow looser specs for these factors, which can translate into lower operations costs. This is a delicate balance, however: Poor environmental control, particularly in respect to humidity, can directly affect the yield. If humidity levels are too low, static charges can build up, and high humidity levels promote corrosion or product degradation.
One solution that is gaining popularity is using high pressure water systems for humidification, says Dunn. Traditionally, facilities use a combination of condensed air and low pressure water to circulate humidification through the facility; however, the use of high pressure water-at up to 1,800 psi-doesn’t require condensed air, making it far more energy efficient, he says. “The water pumps may need part replacements every few months, but the energy savings from not running the air compressors is worth it.”
In industries with less stringent cleanroom humidification controls, such as solar wafer manufacturing, operators have many more energy-efficient choices for humidification systems, adds Jeff Baldel, a mechanical engineer at CH2M HILL. He notes that evaporative media systems, which act as a filter within air handling systems, can be installed and operated for one-thirtieth the cost of steam systems. “They don’t give the same controllability, but if a cleanroom can be operated to within plus or minus 5 percent of spec, it is a much less costly solution.”
Solutions are small but significant
There are no silver bullet solutions for cutting energy use in the cleanroom, says Bill Acorn, principal of Acorn Consulting Services, an engineering design and consulting firm in Tucson, AZ. The environmental requirements are specific and require a lot of energy to operate; however, adjustments can be made, he says. “The solutions aren’t radical; they are incremental.”
One of the most obvious and easiest ways to reduce waste in water and energy use is by implementing sleep mode on equipment, fan filter units (FFUs), and vacuum pumps when they are not being used instead of running them constantly, he points out. In some cases, auto-control FFU systems that automatically lower power consumption during non-use hours are saving facility operators energy while increasing the life of the filter and decreasing the amount of heat generated in the environment.
“It’s a circle of life. The energy used to operate the tool creates heat that requires cooling, which impacts air and water handling systems,” Acorn says. “Every time you put a cubic foot of air into the environment you’ve got to treat it, and that has a huge ripple effect on energy use.”
M+W Zander’s Dunn adds that FFUs are much more energy efficient than traditional air handling units and are more flexible. “If you discover an area in the cleanroom that is generating a lot of particles, it’s easy to move fan filter units closer to that area to solve the issue,” he says.
As the rooms get bigger and more equipment is added, the impact increases considerably. But small adjustments, such as using the “sleep mode” for tools, can have impressive results. According to a 2005 study by the International SEMATECH Manufacturing Initiative (ISMI), the global semiconductor industry could save nearly $500 million per year in energy costs by making modest improvements to its tools and facility support systems. ISMI found that many of its largest members were already seeing significant savings from reductions in cleanroom air velocity, air conditioning optimization, ultra-pure water reductions, use of high efficiency motors, and various other energy conservation activities.
The ISMI energy conservation study was prompted by member company and industry concerns over rapid spikes in energy costs, coupled with a continuing commitment to environmental best practices established by the World Semiconductor Council. The data, compiled by ISMI’s Environment, Safety and Health (ESH) program, also showcased success stories at member companies that adopted the consortium’s recommended practices.
ISMI has since published 26 technology transfer reports documenting best practices for energy and resource conservation, which include enabling and using the sleep mode in vacuum pumps; optimizing exhaust flows on tools; lowering cleanroom airflow through HEPA filters; optimizing nitrogen use and on-site nitrogen generation; and measuring key tools to optimize heat removal.
For example, ISMI’s ESH engineers have found that low-energy vacuum pumps use less than half the electrical power of current versions and can be idled during non-productive periods for an additional energy savings of 30 percent. Similarly, technologists have discovered that exhaust flows can be reduced by 30 to 80 percent without impacting yields or exposing workers to harmful emissions, for an annual savings of $600,000 per fab.
M+W Zander’s Dunn has seen a growing trend in high-volume manufacturing facilities to cut back on filter coverage in wafer fabs. “Because the product is isolated in cassettes and minienvironments, and due to the increasing use of automation, operators are dropping their coverage.” The reduced coverage cuts the startup costs of filters for a facility and reduces energy costs because less air is recirculated. “In the past there may have been too much coverage. With minienvironments we can move away from that.”
However, Acorn notes that cleanroom operators are not relaxing cleanliness standards as much as some industry reports would suggest. “We are still seeing a lot of ISO 4 and 5 spaces,” he says, noting that fear of the unknown is a contributing factor to the hesitation. “Even though the cost of keeping a room cleaner than it may need to be is significant, it is nowhere near the cost of a shutdown due to contamination,” he says. “If you make a $3.5 million investment in building a manufacturing facility, you don’t want to make a choice that loses you $100 million in yield. No one wants to be the first to fail.”
Figure 1. The need to reduce energy consumption has produced more efficient air handling designs. Above: This Compac Vane Axial fan system combines 85 percent efficiency with less static to offer customers lower brake horsepower and significant energy savings over the life of the unit. Right: Multi-fan arrays such as this Multipak system offer greater reliability with fan backup: In case of fan failure, the other three will speed up to maintain the system set point, and the failed fan can be replaced or maintained from outside the unit without shutting it down. Photos from M&I Air Systems Engineering, courtesy of EI Systems.Click here to enlarge image
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The additional reliance on minienvironments in order to relax cleanliness standards outside of the equipment offers further concerns for maintenance issues, adds Allan Chasey, associate professor at Arizona State University in Tucson, and director of Construction Research and Education for Advanced Technology Environments (CREATE), a research consortium of 25 companies representing the advanced technology design and construction industry. He is also head of the ITRS Facilities Group. “When you open the machine, the ambient air is not as clean,” he explains. That creates problems for maintaining standards.
Chasey believes that cleanroom designers and architects need to be more closely aligned with equipment manufacturers to establish tighter tolerances for installation, maintenance, and operation. “It all needs to operate like a Swiss watch.”
Air handling solutions
The demand for energy efficiency is also pushing air handler manufacturers to pursue more energy-efficient designs, says Richard Spradling, vice president of EI Systems, a technology solutions provider headquartered in Houston, TX. “The cost of energy is pushing innovation,” he says. “Engineers, architects, and owners are demanding more efficient systems and the market is responding.”
Spradling has seen dramatic im-provements in energy-efficient fan systems for high and low static recirculating fans and high static makeup handling systems. For example, M&I Air Systems Engineering’s Compac Space Fan System, which integrates noise absorption and flow control within the inlet and outlet components of the assembly, achieves up to 80 percent static regain of the axial fan’s annular velocity pressure, reducing energy consumption by up to 50 percent. “That translates to significant cost savings,” Spradling says, noting that an overseas client who pays $0.20 per kilowatt saved $400,000 in annual energy costs using 18 of these units.
Low-cost FFU control systems that are customizable and easy to install, as well as replacing traditional single-fan operations with multi-fan arrays, are also gaining popularity, especially in smaller facilities. Multi-fan arrays, such as Huntair’s Fanwall, or M&I’s Multipak system, break the air output load for air handlers into several smaller units for greater reliability and better operational efficiency.
Multi-fan systems offer many benefits, such as built-in redundancies, says Tim Loughran, managing partner for AdvanceTEC, a cleanroom design and construction company in Richmond, VA. “With a single, larger air handling unit, if it goes down the cleanroom goes down until you can get a replacement motor. That can take anywhere from four hours to two weeks,” he says. “But with a multi-fan system, if you lose one motor the others can compensate.”
Multi-fan arrays also allow for faster and easier replacements of motors because they are smaller and can realistically be stored on site; they also give operators the ability to customize the system to accommodate issues such as changes in filter cleanliness and airflow rates without affecting fan efficiencies.
With a single-fan environment, even highly effective, larger fans lose significant efficiency when they are run at lower load conditions. With a multi-fan array, operators can turn off individual fans so that the remaining operating units still function at peak efficiency rates.
The addition of heat-recovery chilled water systems, water reduction, recycling, and reclaim strategies and the use of variable frequency drives on large motors for increased efficiency all further help improve energy conservation in new and retrofit facilities.
Faster is still better
Along with reducing energy costs, cleanroom operators are still seeking ways to ramp up in less time for less money, and they want to achieve desired efficiencies faster than ever. Some designers in the industry are facing increasing frustration over the unrealistic expectations that can be laid at their feet by owners who want facilities up and running in record times.
“These facilities are more complex than ever, but they still want everything faster and cheaper,” says CREATE’s Chasey. He notes that facility sizes are increasing, with more equipment and more complex processing steps to support. The introduction of new production materials, gases, and chemicals into cleanroom operations-all of which create additional airborne molecular contamination issues and waste problems to deal with-makes these rooms increasingly complex. The continuous push to reduce geometries that require new equipment and all of the associated control designs that go with them also makes new and retrofit operations more complicated than ever to design and build. “Cleanroom owners want these facilities to be built in eight or nine months and they feel like the market should respond,” Chasey says. “It’s gotten to be absurd.” He would like to see the wafer fab industry embrace a stricter line increase in cleanroom complexity rather than the exponential growth that it currently supports.
Modular cleanrooms offer designers a faster ramp-up time because many of the pieces are prefabricated in the factory, taking less time to assemble, AdvanceTEC’s Loughran says. “Modular rooms take 50 percent less time to build, which substantially decreases the construction time on site.”
Figure 2. Modular cleanrooms offer faster ramp-up due to prefabrication that simplifies installation, walkable ceilings for easier maintenance, and utilities that are built in and connected after construction. Photos courtesy of AdvanceTEC.Click here to enlarge image
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Modular rooms also offer maintenance benefits because ceilings are walkable, and electrical and piping can be built into the system and dropped in after the room is constructed.
Air flow
In the meantime, designers are identifying ways to reduce the ramp-up time for new facilities, and the solutions are often found at the beginning of the design process, when alterations can be made before structures are built. At CH2M HILL, engineer Andy Solberg has found that computational fluid airflow dynamics software tools enable him to help clients cut weeks off of ramp-up time by running models of airflow patterns and how they will be impacted by room design and equipment layout decisions-prior to any construction.
“Often in the design phase, people confine their concerns to their specific part or area of the cleanroom without thinking about how their work impacts the entire bay,” he says. “For example, designs for photolithography can push air into other areas of the room.”
Before any construction is begun, Solberg’s team looks at issues such as filtration coverage; floor layout; under-floor barriers due to exhaust systems, utilities, and conduits; and the spaces blocked or left vacant around them.
Solberg notes that by doing airflow modeling prior to construction and incorporating the potential impact of different design choices into the airflow design, the team and client can avoid expensive and time-consuming mistakes during ramp-up, such as moving conduits or utility lines. “After you spend a lot of money building a new cleanroom, you don’t want to think about making changes,” he says.
The airflow in these rooms can typically be balanced in a matter of days, instead of the weeks it normally takes, he says, and all of the rooms CH2M HILL designs using this airflow modeling technique are certified as meeting clean requirements with minor or no alterations.
Figure 3. With its computational fluid dynamics models, CH2M HILL can help clients cut down ramp-up time by showing how the airflow will be affected by room design and equipment layout decisions. These images show calculated particle tracks in a ballroom-type cleanroom with 33 percent ceiling filter coverage. Images courtesy of CH2M HILL.Click here to enlarge image
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Using computational fluid dynamic models, CH2M HILL has been able to prove airflow distribution with particle, temperature, and pressurization data, and the models are used to develop specialized air handling systems, HEPA filter and ceiling systems, and flooring systems.
Cleanroom performance levels achieved through CH2M HILL’s design include stringent temperature and humidity specifications. Solberg also uses these models to develop site airflow characterization studies, plan for facility exhaust and air intake locations, and evaluate potential contaminant migration that could cause odor or molecular contamination issues. Using the tool, his designers can determine appropriate exhaust and intake locations, with necessary stack heights and exit velocities.
Interface plates accommodate expansion
Striving for longevity in new or retrofit construction, cleanroom designers are also seeking ways to design for future uses of expansions in the operating space to avoid costly shutdowns when equipment is added to an operation.
One promising solution involves installing interface plates throughout the cleanroom that allow for plug-and-play installation of new equipment for specific process steps that might someday be installed. “For example, in a new facility that will house eight etch tools for lithography, the designer may install another 12 interface plates in the bay for future expansions,” CREATE’s Chasey says. The interface plates are placed in the floor and include outlets for gases, electricity, water, and exhaust. “All you need to do is plug the new equipment in.”
Not only does this give the hefty investment in a new cleanroom a longer life cycle, it avoids the expense and mess of shutting down to install new tools, which otherwise requires tearing down walls to implement wiring and piping. “With interface plates, the final connections can be made and qualified as soon as the tool arrives.”
STMicroelectronics demonstrates how ‘clean’ can be ‘green’
Semiconductor giant STMicroelectronics’ public commitment to environmental responsibility has won it publicity, praise, and more than 50 international awards, including the European Business Award for the Environment and the inaugural Low Carbon Leader Award presented by the Climate Group. The company has also saved more than $60 million by cutting its energy usage and more than $20 million by reducing water consumption below baselines set in 1994.
“The foundations for our choice to be a sustainable business are ethical, social, and based on our interest in leaving a better world for our children,” says Reza Kazerounian, corporate vice president and general manager of ST’s North American region. “But we also believe that this commitment can make us stronger financially and help us attract the most responsible and competent people.”
STMicroelectronics’ Phoenix, AZ-based facility features a 20-kilowatt rooftop
solar array to help manage energy usage. Photo courtesy of STMicroelectronics.Click here to enlarge image
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ST’s drive for “zero impact on the environment” has social and economic benefits that are laid out in its publicly available “environmental Decalogue,” which outlines its goals to exceed regulatory requirements in both degree and timing. The Decalogue is a set of ten quantified, timed, and measurable targets that include minimizing the impact of its processes and products on the environment, maximizing the use of recyclable or reusable materials, and adopting renewable sources of energy where possible. Some specific goals include reducing total energy consumption (kWh per production unit) by at least 5 percent per year through process and facilities optimization, conservation, and building design; reducing water draw-down (cubic meters per production unit) by at least 5 percent per year through conservation, process optimization, reuse, and recycling; and reducing total emissions of CO2 due to energy consumption by at least 5 percent per year.
Over the past 15 years, STMicroelectronics has saved the equivalent of one nuclear power plant by lowering its energy needs, has planted 10 million trees to offset its CO2 production, and, in 2006, saved the equivalent of drinking water for 70 million people. The company is on track to achieve its goal of CO2 neutrality by 2010 by using more renewable energies, such as wind and solar, and by buying a greater percentage of its power from heat and power plants, which are more efficient and emit less CO2 per unit of energy. Part of achieving that goal resulted from building a 20-kilowatt solar power plant on the roof of the manufacturer’s Northeast Phoenix, AZ, facility.
“As a consequence of adopting sustainable business practices, we believe that well run corporations will necessarily be more profitable,” Kazerounian says of ST’s business case for its green initiatives. “We are convinced that environmental responsibility is compatible with the ability for ST to compete in the marketplace.”
