1、NA-04-7-3 Using Benchmarking to Identify Energy Efficiency Op portu n ity The Labs 21 Approach in Cleanrooms: William Tschudi, P.E. Member ASHRAE AB ST RACT Laboratories for the 21st Century (Labs 21) has devel- oped energy benchmarking protocols for use in high-tech buildings, with the objective of
2、 improving energy ejciency. Prior energy benchmarking in cleanrooms has identified a wide range of operating eficiencies in HVAC systems. This paper updates previous benchmarking eforts and provides ideasfor use of benchmark data to improve energy eflciency. The benchmark data highlight the fact tha
3、t some systems are signijicantly more energy eficient than others in achieving the same cleanliness. These high-performing systems can help to identib design and operation strategies.for new and existing facilities. The metria developed through Labs 21 and prior work can be used to benchmark widely
4、disparate systems. Cleanroom owners can use energy benchmarks to establish eflciency requirements for new design projects. For example, air change rates, as measured, vary considerably. The bench- mark results suggest that lower airflow usingsign$cantly less energy can achieve the desired cleanlines
5、s levels. The design concepts that produce highly energy ejcient systems are examined in this paper. Better integration of observed best practice concepts into cleanroom design should be possible based upon benchmark guidance. INTRODUCTION Integrating energy-efficiency improvements in clean- room HV
6、AC systems can be a daunting task. There are as many differences of opinion as to whether cleanroom energy efficiency should be pursued and how to best achieve improve- ments as there are different system configurations and equip- ment. Traditionally, the industry has relied on everything from rules
7、 of thumb to sophisticated computational fluid dynamic Peter Rumsey, P.E. Member ASHRAE analyses in the design of cleanroom HVAC systems. Manu- facturers of cleanroom HVAC specialty equipment highlight features of their equipment that frequently overlook their energy implications or, worse yet, prov
8、ide conflicting claims. Add to this a climate where speed to market creates schedule pressures for cleanroom operators and designers, and it becomes very difficult to know how to set and achieve energy- efficiency goals. Knowing what is achievable in the special- ized market of cleanroom HVAC system
9、s becomes nearly impossible. This paper explores the use of a technique that is advo- cated by Laboratories for the 21st Century (Labs 21) and used in many other business practices and for continuous process improvement. It is possible to apply the findings from energy benchmarking to improve the ef
10、ficiency and performance of complex cleanroom HVAC systems. By observing actual energy use in operating cleanrooms, trends can be identified and the better performing systems and components can be identified. Armed with this knowledge, an engineer can design and speci improvements to existing system
11、s and set chal- lenging goals for further improvement in new designs. Bench- marking actual energy use through direct measurement gives an accurate picture of the current operational status, but it also can reveal best practices that can be employed to achieve more efficient systems. The systems and
12、 strategies that produce better results can lead the way for better performance in retro- fit and new construction. By studying the better performing systems, engineers can debunk old myths (“cleaner environ- ments need more airflow”), replicate good designs (low pres- sure drop systems), and develo
13、p innovative methods for further improvement. William Tschudi is a project manager with the Applications Team in the Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, Calif. Peter Rumsey is a principal of Rumsey Engineers, Oakland, Calif. 770 02004 ASHRAE.
14、Figure I Measuring airflow to determine air change rates. A building owner can compare performance against systems of similar cleanliness class to see how their systems compare to others. Metrics that compare the efficiency of WAC systems and components (such as cfm/kW and kW/ton) are used to avoid
15、the need to compare production metrics (such as kwlproduct produced), whichvary significantly from indus- try to industry and from process to process within industries. This paper reviews the results of an energy benchmarking study where energy data were obtained for 14 cleanrooms. The benchmark res
16、ults were examined to identify the systems and components that performed well from an energy perspective. Armed with this information, designers and building owners can establish efficiency targets and achieve them by following the concepts that were utilized in the better performing systems. BACKGR
17、OUND Prior benchmarking work was useful in highlighting cleanroom HVAC system performance variations. Even though cleanroom HVAC systems typically utilize a large percentage of total building energy (up to 50%), some systems were observed to be operating significantly better than others. The energy
18、benchmarking included large central plant heating and cooling, air recirculation, makeup, and exhaust ventila- tion. Recirculation airflows were of particular concern since the measured energy efficiency varies considerably based upon cleanliness class, air change rates, and individual oper- ating p
19、references. The Institute of Environmental Sciences and Technology (IEST) provides recommendations for air change rates in cleanrooms (IEST 1993), yet measured results drew little similarity to the recommendations. Air change rates exceeded recommendations in some cases and fell short in others, yet
20、 all cleanrooms were satisfactory for their intended function. Our understanding is that the recommendations by the IEST were established many years ago from a generally accepted consensus based upon acceptable operating experk ence, but they do not take into account later studies by orga- nizations
21、 such as Sematech and MIT. As the benchmark data confirm, it is possible to achieve acceptable performance with significantly lower airflow. Makeup air requirements, although usually driven by building and fire codes exhaust requirements and/or insur- ance requirements, were usually measured to be f
22、ar in excess of the minimum. Even though absolute quantities of exhaust and makeup can be debated, minimizing these amounts to achieve a safe environment should be the goal. Benchmark data show that there is wide variation in the relative air move- ment efficiency for these systems. Central chilled
23、water plants were also a focus of the study. Here, system configurations, chiller efficiency, and supporting system component efficiencies interacted to produce wide variation in overall efficiency. The benchmark results were reviewed against the charac- teristics of the individual systems. The bett
24、er performing systems and subsystems were examined to identify the features that contributed to the improved energy efficiency. These areas each exhibited large variations in energy perfor- mance for the same basic function. When reviewing the data, a logical first question was, “What are the charac
25、teristics ofthe better performing systems?” followed by “How can profes- sionals in the cleanroom industry better adopt current best practices?” USE OF ENERGY BENCHMARKS The metrics advocated by Labs 2 1 and used in cleanroom benchmarking allow comparisons of widely varying HVAC systems regardless o
26、f the design configuration, cleanliness class, or the process occurring in the cleanroom. By examining the data, it is clear that all systems are not created equal. Some systems performed extremely well compared to others serving the same contamination control function. For this paper, several metri
27、cs are examined to highlight how benchmarks can help to identify better energy performance. Using this information, cleanroom owners and designers may choose to implement the better performing designs that yield more effi- cient operation. Although the sample size for benchmarking performed to date
28、is limited, many “best practices” and areas where future improvements could be made were evident. ASHRAE Transactions: Symposia 771 Description Recirculation air-handler efficiency Makeup air-handler efficiency Makeup air Recirculation air Recirculation air Most benchmarks provide indication of how
29、efficiently the systems are designed and operating. Performance such as cfm per kW (i.e., how efficiently air was being moved) was directly measured. In some cases where direct measurement was not possible due to operational concerns, balance reports, EMCS readings, or design data were used. Unlike
30、benchmarks such as W/ft2 where comparisons of HVAC performance can be masked by process loads or other factors, the metrics exam- ined here facilitate comparisons. Table 1 illustrates the key HVAC metrics that were examined. The most energy-intensive systems in the benchmarked cleanrooms were examin
31、ed. The cleanrooms studied included five Class-10 (IS0 Class-4), seven Class-100 (IS0 Class-5), one Class-1 00/1,000 (IS0 Class-5/6), and one Class- 10,000 (IS0 Class-7). Results were analyzed to understand the rela- tive ranges of operating parameters and to determine the reasons for the better per
32、forming systems and components. Only the class 10 and class 100 systems had sufficient bench- marks to analyze. At the time of the benchmarking, individual recommendations were made at each facility based upon observations and the work completed up to that time. This review, having the luxury of rev
33、iewing all of the data, as well as the previous recommendations, identified several key focus areas. The benchmark data suggest focusing on the measures discussed below as a way to achieve better energy efficiency. To fully take advantage of benchmark results to identi however, if a new chiller is g
34、oing to be bought, the incremental cost of the VSD chiller in a continuously operating cleanroom would pay for itself in a matter of months. The benchmarking data also verified that often the actual load is significantly lower than the design load. This would lead us to conclude both that fewer (or
35、smaller) chillers can typically be purchased, and that VSDs are only needed on a small portion of the chillers. In both cases, the cost of the more efficient system would be lowered to levels that are likely to be comparable with stan- dard system costs. Mitchell Swann, Vice President, MDC Systems,
36、Berwyn, Pa.: The presentation touched on RO/DI system (skid) energy use. Would it be useful to establish strict utility use limits for “outsource” skids, such as purified water, process gases, or compressed air? Would this help to “incentivize” the skid suppliers and “outsourced” service contractors
37、 to provide more efficient systems? Tschudi: The key to outsourced utilities is to meter the energy use of the outsourced utility and have the provider pay for that energy. Often, outsourced utility providers are not responsible for the energy costs. Therefore, there is no incentive for them to keep
38、 energy costs under control. E. Wayne Phillips, Assistant Experimental Facilities Engi- neer, NASA-Goddard, Greenbelt, Md.: The presenter showed a chart with numerous differing facilities/cleanrooms using differing air changes for similar cleanroom classes. Are the cleanroom air changes at these fac
39、ilities within recom- mended ranges or are they operating below recommended ranges? The reason for this question is that fabrication clean- rooms often require greater air changes, whereas interferom- etry cleanrooms (for example) often want less than recommended air changes to minimize thermal grad
40、ients at optics. Tschudi: Close to every facility that we benchmarked was operating at air change rates that are below recommended minimum airflow rates. The reasons for this are typically energy savings. We agree that other process-related reasons do occasionally come into play; however, each facility was meet- ing its contamination control objective. ASHRAE Transactions: Symposia 775
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