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VENTILATION


1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50


$0


MERV 4


MERV 7


MERV 11 MERV 13


MERV 14 MERV 16 MERV 15 $100 $200 $300 HEPA $400 $500 Annual cost Figure 6: Relative risk of influenza transmission vs annual cost of filter operation and equivalent outdoor air (OA) rates.


air are far higher than the levels to successfully sterilise cooling coil surfaces, resulting in a far higher number of UV lamps being placed in front of the coil, with much greater power consumption.


n The cooling effect of the coils reduces the UV intensity of lamps positioned downstream of the coil by over 50%, and this cooling effect reduces the UV irradiance of the lamp, and results in a significant loss of efficiency.


n The orientation of coil cleaning bulbs facing the coil surface means that the air stream is exposed to the UV light for only a very short period, which is insufficient to provide the LD90 dose necessary to kill the target pathogen(s).


n There is no opportunity to install UV reflective materials in front of a coiling coil to concentrate the UV light, as is done within in-duct UV installations, resulting in a far lower kill efficiencies per kWh of electricity used.


n Combining coil cleaning applications with air disinfection is inefficient from a power consumption perspective, and does not achieve either objective effectively. This approach can result in an insufficient LD90, or excess power consumption with little or no benefit in terms of pathogen removal.


Conclusion The St Luke’s Hospital study is one of the first large-scale field tests demonstrating


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the effectiveness of UVGI air disinfection on clinical patients in a working hospital, and providing evidence to support the decision of many healthcare facilities to install UV air disinfection systems in their buildings. These UV systems have been installed to complement existing filtration methods, rather than replacing them. When selecting UV systems for air disinfection, particularly in a healthcare setting, it is critical that the installation is sized correctly for the target pathogens, considering the residence time of the airstream in the duct, as well as duct size and shape.


n This article, titled ‘Health outcomes associated with ultraviolet (UV) airstream disinfection’, was originally published in the March 2022 issue of Healthcare Facilities, the official journal of the Institute of Healthcare Engineering, Australia. HEJ thanks the author, the IHEA, and the magazine’s publisher, Adbourne Publishing, for allowing its reproduction here in slightly edited form.


Further reading 1 ASHRAE Handbook (2019). Chapter 62: Ultraviolet Air and Surface Treatment. https://tinyurl.com/52dbe7rf


2 Kowalski W. (2009). Ultraviolet Germicidal Irradiation Handbook (UVGI) for Air and Surface Disinfection. Springer- Verlag Berlin Heidelberg, 2009. https://


When selecting UV systems for air disinfection, particularly in a healthcare setting, it is critical that the installation is sized correctly for the target pathogens, considering the residence time of the airstream in the duct, as well as duct size and shape


26 Health Estate Journal August 2022 tinyurl.com/4nxcz7yh


3 Stawicki SP, Wolfe S, Brisendine C, Eid S, Zangari M, Ford F et al. (2020). The impact of comprehensive air purification on patient duration of stay, discharge outcomes, and health care economics: A retrospective cohort study. Surgery 2020; 168 (5): 968-974. https://tinyurl. com/4dua95ey


4 Information on the above air purification technology as in 3 above can be viewed at: https://patents.google.com/patent/ US8252099B2/en


5 ASHRAE Filtration and Air Cleaning Summary. https://tinyurl.com/yeytnezn


6 Let there be light. Ecolibrium, April 2021; 20.2: 38-42. https://tinyurl.com/ mrxp36vp


7 Vlachokostas A, Burns CA, Salsbury TI, Daniel RC, James DP, Flaherty JE et al. F. (2022). Experimental evaluation of respiratory droplet spread to rooms connected by a central ventilation system. Indoor Air 2022; 32 (1): e12940


8 Azimi P, Stephens B. (2013). HVAC filtration for controlling infectious airborne disease transmission in indoor environments: Predicting risk reductions and operational costs. Building and environment 2013; 70:150-160.


9 ASHRAE Filtration and Air Cleaning Summary. https://tinyurl.com/yeytnezn


10 Morawska L, Tang JW, Bahnfleth W, Bluyssen PM, Boerstra A, Buonanno G et al. (2020). How can airborne transmission of COVID-19 indoors be minimised? Environ Int 2020 Sep; 142: 105832.


12 Morbeck DE. Air quality in the assisted reproduction laboratory: a mini-review. J Assist Reprod Genet 2015: Jul; 32 (7): 1019-1024.


12 Lau J, Bahnfleth W, Freihaut J. Estimating the effects of ambient conditions on the performance of UVGI air cleaners. Building and Environment 2009; 44 (7):1362-1370.


$600 $700 $800 $900


Mean relative risk (RR) of infection


Phoenix OA Chicago OA


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Charlotte OA


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