Collaborating engineers complete project in 14 weeks
by Kevin M. Lichtfuss, P.E., CS
An energy-efficient, innovative, easy-to-maintain, and cost-effective design coupled with an expeditious construction delivery schedule is essential to the success of any high-tech start-up.
Alfalight Inc.(Madison, WI), a high-power diode laser manufacturer, was looking for such a design. They selected The Durrant Group Inc., a Dubuque, Iowa-based family of companies that provides architectural, construction management and engineering services.
The design team consisted of the author, Kevin Lichtfuss principal of Durrant's mechanical engineering division, and Ken Hoefer, senior mechanical designer. Lichtfuss and Hoefer worked closely with the owners' representative, the architect/design-builder, sub-contractors and equipment vendors in a peer-to-peer relationship to get full cooperation and buy-in from all parties.
(At right) Deemed ISO Class 6, Alfalight’s cleanrooms are said to perform at ISO Class 5 levels.
The 20,000-foot facility cost an estimated $2.5 million to build, and the cleanrooms were among the most complex projects in the realm of HVAC design. Add to that a 14-week design/construction schedule and a modest budget, and that makes for a challenging and complex project. The design significantly overlapped construction, and much of Alfalight's production equipment needs were not known until late in construction. Occupant safety was an important requirement for Alfalight because its facility uses highly toxic chemicals in its processes. Safeguards were put in place in the event of a leak or accident. The HVAC system, which is controlled automatically, was designed with gas monitoring and evacuation systems to meet this requirement.
A major component of the success of young high-tech companies is the ability to turn a profit quickly in order to show a return on its investment. This project was completed within its schedule and under budget.
Participating consultants on this project included Craig Cheney, Alfalight's equipment engineering services manager; Carl Ruedebush, president, and David Nelson, director of engineering of Ruedebush Development, also of Madison.
Cheney was instrumental in selecting and coordinating the design team. He provided the information necessary, as it was available, to the project team. Ruedebush and Nelson provided the general construction and architectural services for the projects.
Durrant provided HVAC and electrical design. Plumbing systems were designed and built by the plumbing contractor Monona Plumber (Madison) while process piping was done by Alfalight.
Equipment space between cleanrooms provides ease-of-access and maintenance without violating cleanrooms with 150 air changes/hour (or once every 23 seconds).
The main equipment room, outfitted entirely with components and controls from Carrier Corp. (Syracuse, NY) designed as a two-level concept, takes advantage of a 20-foot high ceiling while conserving floor space. A 50,000-cubic-feet-per-minute (CFM) air-handling unit was elevated with a full-length grated floor system to ensure accessibility of all components. The unit has dual wall construction, containing pre-filters, a hot water heating coil, a chilled water cooling coil, a fan section, final HEPA filters and an atomizing type humidifier that is supplied with high-purity water.
High-efficiency pulse combustion boilers were chosen for energy conservation. An outdoor air-cooled chiller was selected for its year-round operability, ease-of-maintenance, and long-term energy efficiency and savings. The building's automation system controls the HVAC functions, while monitoring other process piping systems and gasses. The 50,000-CFM unit supplies plenum above the 7,500 square feet of ISO Class 6 cleanroom space with 50-degree (Fahrenheit) HEPA filtered air. Secondary air handling units located in the plenum are accessible via a catwalk system and supply each individual cleanroom through ceiling mounted HEPA filter diffusers.
Cleanroom temperature is maintained at 68 degrees, ±1 degree at a humidity of 45 percent, +/- 5. Static pressure is maintained at .04, +/- .01. Each room is maintained by injecting primary 50-degree air into the individual secondary units in response to a signal from a room thermostat. This was devised to eliminate the need for any piping above the cleanrooms and to enhance operation and maintenance. While the goal was to achieve ISO Class 6 classification in all eight suites that make up the clean space, a particle count in one 500-square-foot area revealed that the room was functioning at an ISO Class 5 rate.
The technical value to the engineering profession is an example of how a low-tech approach can and should be considered for high-tech, complex projects. Working closely with the mechanical contractor and equipment vendors, the system was pieced together based on performance, cost, efficiency and delivery time. Even locations of the various components were arranged based on anticipated arrival and the general construction timetable. Essentially, every facet of the design and construction had to mesh perfectly with major equipment ordered well in advance of the design.
Today's business world moves at breakneck speed. Therefore, it is imperative that the construction industry does its best to match this pace. Alfalight's HVAC system is the centerpiece of the facility's operation. Cleanroom facilities are typically designed and constructed over a period of 12 to 24 months, depending upon size and complexity. Certifications of ISO Class 6 or better are most often achieved following several weeks of careful planning and programming. Specialized cleanroom equipment is often used in the design of the HVAC system. A 14-week schedule meant that this process would not work, even if highly compressed. Instead, these tasks, while compressed, happened consecutively.
Shortcomings of using conventional HVAC equipment and concepts had to be overcome by thinking out of the box and approaching the challenge from a completely new perspective. As a result, the Alfalight project highlights cutting-edge innovation and techniques that can and should be considered for similar and related applications.
The complex Alfalight facility was designed and built within time and budget, and incurred no change orders. Built at a savings of over $500,000 to the client (due to an efficient design/build project delivery system), the Alfalight project was a major success story.
Cost effectiveness, ease of maintenance, and overall efficiency of a semiconductor cleanroom were important to the client. The project was completed in 14 weeks from “shelled” building with dirt floor to occupancy.
Kevin Lichtfuss is principal of the mechanical engineering division of The Durrant Group Inc., a Dubuque, Iowa-based family of companies that provides architectural, construction management and engineering services.