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Cleanroom Energy Benchmarking

Cleanrooms are common in universities, government labs, hospitals, and in the automotive, aerospace, biotechnology, pharmaceutical, and electronics industries. Although energy costs are high, cleanroom owners and operators have little information about how to improve their efficiency. Likewise, little information is available to highlight best practices for the design of new systems. To evaluate the energy efficiency of heating, ventilation, and air-conditioning (HVAC) systems, simple comparisons of energy use per square foot are of little value, since process-related energy (heat load for the HVAC systems) varies greatly from one facility to another.

An EETD research team has conducted a study to benchmark energy performance in cleanrooms. The project developed a benchmarking strategy to obtain the energy end-use breakdown in various industries, and to enable comparisons between cleanrooms housing various processes. Metrics were developed to allow comparison of energy performance of key systems and components.

Study Method

The metrics allow comparison of widely varying HVAC systems regardless of the design configuration, cleanliness class, or the cleanroom process. By using metrics compiled from design or measured data, this methodology facilitates direct comparison of energy-intensive systems and components.

HVAC performance was measured in terms of cubic feet per minute (cfm) per kW. In a few cases, actual measurement of airflow was not possible due to operational concerns. In those situations, balance reports, energy management control systems data, or design values were used along with actual power measurement. This metric (cfm/kW) was useful for comparing operating efficiency in spite of wide variations in process loads in the room, HVAC system and component design, cleanliness requirements, and other environmental variations. Similar metrics were useful to evaluate other systems performance, such as kW/ton or kW/gal, which were used to compare HVAC water systems.

The team obtained benchmark data for fourteen cleanrooms in semiconductor manufacturing, semiconductor equipment manufacture, electronics research, and disc drive manufacturing. Different cleanliness classes were included in the study; however the sample size of the study was too small to draw conclusions by a cleanliness grouping. Where design data were available, the actual operating efficiency was compared to the design values.

Discussion

Energy end use was determined for each of the cleanrooms. The data made apparent that the electrical loads serving the HVAC system and the process systems account for the majority of the energy use. As expected, the relative percentages for each end use varied based on the type of process and variations in the HVAC system design. HVAC energy use in the measured cleanrooms accounts for 36 to 67% of the total facility energy. While the relative percentages vary primarily because of the magnitude of the process system energy consumption and the cleanliness class of the room, the HVAC systems clearly are the dominant contributor to energy intensity in cleanrooms.

Comparison of system efficiency results showed that variation by up to factors of 10 was occurring in the study even though the study covered a small sampling of rooms. To illustrate the potential operating cost ranges for one of these systems (the air recirculation system), a theoretical room size and electricity cost were assumed resulting in a range from $40,000 to over $400,000 annually (see Figure 1).

Estimated annual kWh cost for a 1,000,000 cfm class 100 re-circulation system based upon actual measured efficiencies.

Figure 1. Estimated annual kWh cost for a 1,000,000 cfm class 100 re-circulation system based upon actual measured efficiencies.

Recommendations

Although the benchmarking results are useful to begin to bracket the range of operating efficiency, the sample size is not large enough to truly begin to identify best practices. As a result of the study, several recommendations emerged to make energy benchmarking a more robust tool for industry use. Recommendations for further work in cleanroom benchmarking are:

  • Expand the data set to include a statistically significant number of cleanrooms in each industry or process that uses cleanrooms.
  • Expand the data set to include a statistically significant number of cleanrooms of each cleanliness class.
  • Develop an energy self-benchmarking protocol for general industry use.
  • Develop a web-based data-base of energy benchmark data.
  • Develop and publicize best practice metrics from expanded data set.
  • Publicize the non-energy benefits identified through benchmarking in case studies.

Energy benchmarking is an effective tool to identify the energy-intensive systems and components in cleanrooms. Through benchmarking, a baseline can be established and then monitored to track energy performance over time. High energy use can highlight attractive energy efficiency improvement areas, maintenance or operational problems, and can lead to identification of best practice values.

— William Tschudi and Tengfang Xu

For more information, contact:

  • William Tschudi
  • (510) 495-2417; fax (510) 486-4089
  • Tengfang Xu
  • (510) 486-7810; fax (510) 486-4089

Complete Report

This research was funded by the California Institute for Energy Efficiency (CIEE) and Pacific Gas and Electric Company.

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