ASHRAE Journal- September 2008

the risk analysis. With increasingly sophisticated laboratory equipment, quantities of chemicals and the associated risks are being reduced in many facilities to where returning lab air from such dry lab spaces may be appropriate. Obviously, input from the laboratory planner, facility health and safety officer, and users are required to determine if returning air is appropriate. However, exhausting all air from spaces where there is no or miniscule risk to health or safety without considering options is inappropriate as we look to create facilities that minimize environmental impact. Reducing exhaust quantity and the corresponding makeup air should be a high priority in designing a sustainable laboratory. Minimize Air Change Rate Requirements No single subject generates more discussion in ASHRAE Technical Committee 9.10, Laboratory Systems, than the topic of determining the appropriate minimum air change rate in laboratories. Air change rate is calculated by dividing room volume by exhaust airflow in cfm. ACH is often inappropriately used to indicate a safe level of dilution. However, AIHA/ANSI Z9.5 indicates that ACH is a poor indicator of lab safety. Technical publications such as ASHRAE Handbook, NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals, and AIHA/ANSI Z9.5 provide some historically used values but these values are rules of thumb and are not based on a specific scientific basis. However, since these numbers, generally six to 12 air changes per hour, are recommended, a laboratory designer would be open to scrutiny for deviations from this range. The goal of minimum air change rates is to ensure that, even in the case of some undefined chemical spill, some level of safety, either for exiting or spill clean up is maintained. An analysis of chemical spills of 1 L (0.26 gallon) of various chemicals charted against the number of air changes necessary to maintain the environment below the TLV, shows that for a majority of chemicals, six air changes per hour provides a safe environment. Several other chemicals exist, such as formaldehyde, where the air change rate necessary to maintain a safe environment after a 1 L (0.26 gallon) spill exceeds 50. Increasing the minimum air change rate from six to eight or even 10 provides no significant benefit in this situation, but does come at a significant energy penalty, especially in laboratories where the cooling loads and exhaust requirements are low. ASHRAE is working with other organizations such as CDC and AIHA to explore developing a laboratory classification system that could provide some guidance to laboratory designers regarding appropriate design including minimum air change rates. Once the required minimum air change rate is defined, using setbacks to reduce the minimum during unoccupied periods should be considered. Energy Recovery www.info.hotims.com/19354-15 Once the amount of outside air used to meet the cooling and ventilation requirements is minimized, the next target should be to capture energy from the exhaust streams to precondition the required makeup air. Historically, runaround heat recovery September 2008 32 ASHRAE Journal http://www.connfab.com/ash.html http://www.connfab.com/ash.html http://www.info.hotims.com/19354-15

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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.