ASHRAE Journal - August 2008 - (Page 30)

to ensure performance. While oversizing may be conservative, there is the potential for increased equipment costs, increased utility costs, and wasted energy. As with any system, a balance must be struck between performance and price. UVGI Standards More Susceptible Vegetative Bacteria Organism Group Vegetative Bacteria Member Group Staphylococcus aureus Streptococcus progenies Escherichia coli Pseudomonas aeruginosa Serratia marcescens Although application support for UVGI technologies is growing and many successful systems have been installed, there are still no industry standards for rating the effectiveness of UVGI devices and systems. A recent EPA publication stated: “The most important needs in the area of UVGI are industry standards to rate devices and installations, as well as guidance for installation and maintenance.”11 ASHRAE and others are working to meet these needs. In 2003 the ASHRAE technical activities committee approved a task group to focus on ultraviolet air and surface treatment (TG2.UVAS), which became standing Technical Committee (TC) 2.9 in 2007. Also in 2003, ASHRAE approved the formation of a standards project committee (SPC-185) to develop testing standards for UVGI air (185.1) and surface (185.2) disinfection systems. Both standards are under development. Current Best Practices for Common UVGI Conﬁgurations Mycobacteria Mycobacteria Mycobacterium tuberculosis Mycobacterium bovis Mycobacterium leprae Bacterial Spores Bacterial Spores Bacillus anthracis Bacillus cereus Bacillus subtilis Fungal Spores Less Susceptible Fungal Spores Aspergillus versicolor Penicillium chrysogenum Stachybotrys chartarum Figure 1: General ranking of susceptibility of various organism groups to UVC inactivation with examples of species from each group. When applying in-duct UVGI for surface disinfection, it is best to start with clean surfaces. Coils and drain pans should be cleaned, especially if there is coil fouling or microbial growth. UVGI is applied by mounting UVC lamps in proximity to the cooling coils and spacing lamp ﬁxtures to allow an even distribution of energy. Reﬂectors may be used to In-Duct UVGI focus UV energy onto the surface (Figure In-duct UVGI systems, as the name 3). Fixture arrangement tools or design implies, are installed inside ventilation recommendations are available from most ductwork or inside AHUs (Figure 2). Figure 2: Typical in-duct UVGI installation manufacturers to aid in outﬁtting larger When selected to produce appropriate with lamps mounted downstream of the cool- systems. Lamps may be mounted on the irradiance levels, in-duct systems are ing coil and drain pan. upstream or downstream side of the coil effective for surface and air disinfection. The goal of surface and at any angle, as UV energy will penetrate into the ﬁns disinfection is to reduce or eliminate microbial growth on in- from either direction. It is often better to locate ﬁxtures downternal surfaces of HVAC systems, typically cooling coils and stream of the coil because of space availability, and mounting drain pans. The goal of air disinfection is “on-the-ﬂy” inactiva- lamps downstream often provides improved irradiation of the tion of microbes suspended in the air as it moves through the drain pan. While the exact mounting location of the lamps is dependent duct or AHU. In-duct UVGI should always be used in combination with on the AHU design and the particular lamps used, mounting ﬁltration. Filters help protect UV lamps from dust that may lamps within 3 ft (0.9 m) of the coil is common practice, and reduce UV output, and enhances the air cleaning capabilities the lamps are generally operated 24 hours per day, seven days 30 ASHRAE Journal ashrae.org August 2008 This year, a new chapter on UVGI technologies was published in the ASHRAE Handbook—HVAC Systems and Equipment.1 The information presented in the handbook chapter draws from the pertinent scientiﬁc literature and the collective experience of engineers, lamp manufacturers, and system designers familiar with UVGI applications. The result is a current best practices guide for common UVGI systems used with mechanical ventilation systems to disinfect air-handling unit (AHU) surfaces, improve indoor environmental quality, and to reduce the likelihood of airborne disease transmission. A summary of the current best practices for in-duct and upper-air UVGI systems detailed in the new Handbook chapter is presented here. of the system. Filters remove larger microbes like fungal spores that are more resistant to UVGI, while UV inactivates more susceptible organisms like bacteria and viruses. It is recommended that the highest-rated ﬁlter the fan motor can handle be used, while still providing adequate airﬂow to the space. Surface Disinfection http://ashrae.org

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

ASHRAE Journal - August 2008 Contents Commentary Industry News Letters Meetings and Shows Maintain to Sustain—Delivering ASHRAE’s Sustainability Promise Ultraviolet Germicidal Irradiation: Current Best Practices Improving Humidity Control With Energy Recovery Ventilation Single- or Two-Stage Compression Data Center Cooling: Using Wet-Bulb Economizers Building Sciences InfoCenter Practical Pointers Products Emerging Technologies Washington Report People Special Products Classified Advertising Advertising Index

ASHRAE Journal - August 2008

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