ASHRAE Journal- September 2008

systems have been used in laboratory systems due to simplicity, flexibility and the assurance of no cross-contamination between the exhaust and makeup airstreams. Unfortunately, these systems are only about 50% efficient in capturing sensible heat and capture no latent heat. In some laboratory facilities, a better approach for heat recovery is the use of desiccant wheels. With this system, the exhaust and supply airstreams are brought adjacent to one another, and sensible and latent energy is captured via a rotating metal or fibrous wheel impregnated with desiccant material. Energy recovery wheels can have total efficiencies of about 80%. While the energy recovery wheels have improved efficiency, they also have a potential for cross-contamination of the exhaust and supply airstreams. For this reason, wheels have historically only been used for laboratory general exhaust. Fume hood exhaust and other highly corrosive or toxic exhausts were handled with separate systems, perhaps with a separate runaround heat recovery system. Some facilities are now using energy wheels in combined general laboratory and fume hood exhaust systems where the number of fume hoods is small compared to the general exhaust requirements. In this application, it is necessary to analyze the chemicals to be used in the facility and the implications of a spill inside a hood to determine if cross-contamination would provide an unacceptable supply air condition. Where the risk assessment shows that some chemicals or processes are inappropriate for the energy recovery wheels, some hoods connected to an independent exhaust system can be provided. While this design approach is not widespread, its use is growing. Minimize Distribution Energy minimize penalties. For example, heat recovery coils in the supply and exhaust airstreams increase the system resistance and fan energy necessary to move the air. Often these fan energy penalties can reduce the energy savings and greatly increase the payback for heat recovery systems. Thoughtful design features, such as a small bypass in parallel with heat recovery coils or wheels can greatly reduce the pressure drop across the device when not in use and maximize the energy savings. Traditionally, exhaust stacks have been designed with constant speed exhaust fans at a high velocity discharge to, along with a high stack, eject the effluent out of the recirculation zone around the building (Chapter 16 of ASHRAE Handbook— Fundamentals). This high velocity discharge can add 0.5 in. w.c. to 1.0 in. w.c. (125 Pa to 249 Pa) of pressure to the system and, with constant speed fans operating 24 hours a day, the energy use can be significant. While uncommon, multiple alternatives to the traditional approach exist including: • Variable discharge velocity with CFD or wind tunnel confirmation of safety; • Special discharge dampers that permit variable speed fans with constant discharge velocity; • Multiple fans with fan staging; and • Staging multiple stacks off a common exhaust header. Conclusion Finally, we should reduce the amount of energy required to distribute the supply and exhaust air. Many of the options in this category apply to all building types. For example, lowpressure drop coils can be used. Variable speed drives can be used to match the system to the load. Air distribution systems should be designed for low velocity with carefully selected fittings and to avoid system effect. Laboratory specific issues include: thoughtful consideration of the exhaust system design, minimizing penalties associated with heat recovery, and analysis of exhaust stack discharge options. In the exhaust system, exhaust devices with similar pressure requirements should be grouped together to minimize fan static pressure requirements and energy use. For example, a Type B2 biological safety cabinet has a pressure drop of about 2.0 in. w.c. (498 Pa), while a fume hood and the general exhaust grilles may have a pressure drop of only 0.15 in. w.c. (37 Pa). If a small number of devices with high-pressure-drop forces the operation of the whole larger system at a higher pressure, then energy is wasted. A more sustainable approach would be to separate the high-pressure drop systems onto a dedicated exhaust system and operate the larger system at a lower, more efficient pressure. While designing energy recovery systems, it is wise to look for creative ways to gain additional use from the system and 34 ASHRAE Journal Laboratories require significant resources to construct and operate and the number of laboratory facilities will continue to grow. HVAC designers should consider methods to reduce a facility’s impact on the environment by reducing water use and recovering water for reuse where appropriate. While the designer’s first obligation is to the safety of the laboratory users, visitors and maintenance personnel, it is possible to creatively reduce the energy use of facilities. Reducing quantities of outside air used for cooling and ventilation, using recovered energy, and reducing distribution energy are methods to design sustainably. Together owners, users, architects, laboratory planners and engineers can find creative ways to design safe and sustainable laboratories for the future. References 1. United States Environmental Protection Agency and Federal Energy Management Program. 2000. Laboratories for the 21st Century: An Introduction to Low-Energy Design p. 1. 2. Cordes, E. 2008. “Federal Funding for Research: Implications for Lab Design.” Keynote Speech, Laboratory Design Conference. 3. Perkins+Will. 4. Frenze, D., S. Greenberg, P. Mathew, D. Sartor, and W. Starr. “Right-Sizing Laboratory Equipment Loads.” Lawrence Berkeley National Library, November 2005. 5. ANSI/ASHRAE/IESNA Standard 90.1-2004, Energy Standard for Buildings Except Low-Rise Residential Buildings. 6. Rumsey, P. and J. Weale. 2007.” Chilled Beams in Labs: Eliminating Reheat & Saving Energy on a Budget.” ASHRAE Journal 49:(l):18. 7. United States Environmental Protection Agency and Federal Energy Management Program. 2000. Laboratories for the 21st Century: An Introduction to Low-Energy Design p. 2. ashrae.org September 2008 http://ashrae.org

Table of Contents Feed for the Digital Edition of ASHRAE Journal- September 2008

ASHRAE Journal- September 2008 Section: Contents Contents Section: Commentary Options for Sustainability Section: Industry News The Silk Route for Energy Solar Thermal Is Unrealized Opportunity Industry Groups Sue City of Albuquerque Section: Letters Letters Section: Meetings and Shows Meetings and Shows Section: Feature Articles Article-Radiant Floor Cooling Systems Article-HVAC Design for Sustainable Lab Article-Mixed Mode Ventilation Article-Single- Design Considerations For Active Chilled Beams Article-Acoustic Design In Green Buildings Article-Teams, Contracts & BIM Section: Building Sciences Some Old Lessons Distilled Section: Washington Report Energy in Federal Buildings Section: Products HVAC&R Product Showplace Section: Emerging Technologies Toplighting & Lighting Controls For Commercial Buildings Section: Special Products Fans & Blowers Section: Classified Ads Classified Ads Section: Advertising Index Advertising Index

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