ASHRAE Journal- September 2008

the HVAC system and the outside airflow would be driven by equipment exhaust requirements. However, in an undergraduate chemistry lab, with a large number of fume hoods, the outside airflow would be highly dependent on the equipment exhaust requirements. Methods to reduce exhaust airflow in laboratories include VAV hoods, low-flow hoods and transfer air. In a VAV hood, the amount of air exhausted through the hood is varied based on the sash position to maintain a constant face velocity across the opening regardless of sash position. This approach is most effective in laboratories without high constant heat loads and where there are a large number of hoods. In laboratory spaces with a small number of hoods, high steady cooling loads, or high minimum air change rates, VAV hoods, with additional complexity and cost, may provide little or no benefit. In some cases, low-flow or high-performance hoods may be a good option to reduce exhaust airflow. These hoods require a lower hood face velocity to maintain containment and may reduce makeup air requirements, depending on the lab cooling load, minimum air change requirements and number of hoods in the space. With either VAV or high-performance hoods, an analysis of the space should be performed to ensure that the features of the system provide benefit. In addition to looking at the end devices, a designer should look at the supply side. The air requirement for laboratories is often stated as “Laboratories must be served with 100% outside air.”7 However, per AIHA/ANSI Z9.5-2003, Laboratory Ventilation, the actual requirement is that “Air from laboratories shall not be recirculated.” Recently, a new school of medicine, including a gross anatomy laboratory, was constructed. While the laboratory spaces have significant ventilation and exhaust requirements, the facility also included many offices, large lecture halls, and teaching spaces. The quantity of ventilation air to comply with ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, in these spaces greatly exceeded the airflow required to pressurize the building. Rather than relieve this excess ventilation air, it was routed as return air to the anatomy lab air-handling unit, reducing the outside airflow for that unit from 25,000 cfm to 5,500 cfm (11 800 L/s September 2008 to 2600 L/s). This had a net effect of reducing overall building energy consumption by 10%. Another option gaining some acceptance with laboratory planners is to actually return air from labs. Laboratory designers are recognizing that a “lab” can mean many different things. For example, is it necessary to exhaust the air from a physics or laser lab? The requirement for 100% exhaust really depends on what is going on in the space and the results of www.info.hotims.com/19354-22 ASHRAE Journal 31 http://www.est-aegis.com/aj2 http://www.est-aegis.com/aj2 http://www.info.hotims.com/19354-22

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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