Product category:
Air Conditioning Services
News Release from: Hanovia | Subject: Ultraviolet (UV) disinfection
Edited by the Buildingtalk Editorial
Team on 25 August 2003
UV destroys airborne microorganisms
A method of controlling microbial contamination which is gaining increasing acceptance is ultraviolet (UV) disinfection.
Introduction It is well-known that air conditioning and ventilation ducts can become colonised by microorganisms such as bacteria and fungi as well as acting as a source of transmission for viruses These microorganisms can cause illness as well as reducing the shelf life of food and drink products within manufacturing plants
This article was originally published on Buildingtalk on 23 Jun 2003 at 8.00am (UK)
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A method of controlling microbial contamination which is gaining increasing acceptance is ultraviolet (UV) disinfection.
UV disinfects all incoming and recirculated air within HVAC systems, killing any fungal spores, bacteria or viruses present.
It is a low maintenance, environmentally friendly technology and is now a well-established method for reducing the spread of airborne contaminants in office buildings, laboratories and food manufacturing facilities.
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UV Disinfection Of Cleanroom Air
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Ultraviolet water disinfection specialist in China
Hanovia, specialising in manufacture of ultraviolet disinfection systems for water, wastewater, air and surface disinfection, has established a presence in China.
It is also being applied to reduce the incidence of nosocomial infections (infections originating in hospitals) within healthcare facilities worldwide.
How UV works UV light is generated when a small amount of mercury in a quartz tube (similar in appearance to a fluorescent strip light) is activated by applying electricity to both ends of the tube.
There are two principal types of UV lamps: low pressure and medium pressure.
Low pressure lamps are usually 1 metre in length and have an input power of up to 200 watts.
The lamps are up to 30% efficient, so can > emit up to 60 watts of germicidal UV light per lamp.
They have a life of about 10,000 hours and need to be left switched on, as frequent cycling (switching on and off) will damage the filament and shorten lamp life; they are also sensitive to outside air temperature, which can result in variations in UV output.
This type of lamp is best suited to disinfecting air spaces above water storage tanks.
They have a single UV output at 254nm and are often called monochromatic lamps.
High output versions are now being used that contain an alloy (or amalgam) of mercury and bismuth or indium; these lamps are not sensitive to air temperature and have been measured to have an efficiency of 32-35%.
Medium pressure lamps are typically 30cm in length and have an input power of up to 3,500 watts.
They are hot-running, with a surface temperature of 600-900oC, and need to have a nominal flow of air across them to keep them cool.
Lamp life is between 6,000-8,000 hours and the lamps have an efficiency of up to 23%.
Typically, a 3.5 kW lamp will have an output of up to 800 watts of germicidal UV light, so typically one medium pressure lamp has an equivalent output of 10-12 low pressure lamps.
They are used to treat large volumes of rapidly moving air and have a broad spectral output from 170nm to 450nm, giving them the name polychromatic lamps.
UV kills microorganisms by rupturing the chemical bonds within their DNA.
It is most effective between 240nm and 280nm, with a peak kill rate at 265nm.
The damage done is permanent and irreversible.
RNA, which is found in viruses, is destroyed in a similar manner.
Each organism has a different susceptibility to UV.
The amount of UV required to achieve a 90% kill is known as a D10 dose (expressed in mJ/cm-2).
Double the D10 dose achieves a 99% kill, three times a 99.9% kill, and so on.
System sizing The principle factors that affect the sizing of UV systems are as follows: Relative air humidity Duct dimensions and material of construction Air flow rate D10 of target species The relative humidity of the air has a significant affect on its ability to transmit UV light, with high relative humidity leading to a marked reduction in UV transmittance.
Duct dimension is also very important: the ideal profile for a duct is rectangular with the UV lamp inserted.
In addition to this, the construction material of the duct plays an important role and the correct choice is vital.
Maintenance UV systems are easy to install and virtually maintenance-free.
The only regular requirement being the replacement of the UV lamp every 6,000-8,000 hours, a quartz sleeve change every 2-3 years, as well as the periodical wiping of the sleeve with a soft clean cloth to remove any dust or other airborne deposits.
These are simple operations that can be carried out by on-site maintenance staff.
Applications for UV lamps UV - especially medium pressure - is now widely accepted by many process > users of air both in the UK and overseas.
A call centre in Surrey, for example, has observed a 40% reduction in staff absence due to sickness following the installation of a Hanovia UV system in the recirculating air duct at one of their offices.
To help protect its biotechnology laboratories from microbial contamination, Colgate-Palmolive has also recently commissioned Hanovia to install several UV disinfection systems within the in-line air ducting of its Salford facility.
According to the Engineering Services Manager, the UV systems have been working "exactly as intended" since they were installed.
In a 12-month study carried out at a large hospital in the north of England, a medium pressure UV system achieved a 98.9% reduction of air-borne pathogens within the hospital's air conditioning system.
In the tests, a range of organisms associated with nosocomial infection were treated with medium pressure UV lamps - both within the hospital air ducts and in controlled laboratory settings.
All the pathogens tested were found to be very susceptible to UV.
Research undertaken by the Campden Food and Drink Research Association on Hanovia's behalf has also demonstrated the effectiveness of UV on a wide range of common food spoilage organisms found in the ventilation ducts of food processing facilities.
Summary Medium pressure UV lamps are a reliable means of controlling airborne bacteria, fungi and viruses.
Their use is now widespread by companies concerned about the indoor air quality of their buildings, be they offices, hospitals, laboratories or factories.
Low pressure lamps are also suitable for certain applications, for example disinfecting the air spaces above water storage tanks.
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