Questions and Answers

Questions and Answers on 10 things you didn’t know about commissioning with UVC

How often do you recommend to perform the irradiance measurements?: ISO15858 states: 4.4.5 Measurements are performed at initial installation; whenever new UV lamps are installed

(newer lamp designs may provide increased irradiance), and whenever modifications are made to the UVGI system or room (e.g. adjustment of device height, location or position of louvers, addition of UVabsorbing or UV-reflecting materials, room dimension changes, modular partition height changes).

In practice this will be when lamps are changed.
Do you have data for healthcare facilities? Meaning a before and after installation?: I refer you to the following paper: Mphahlele.M. et al (2015) Institutional Tuberculosis Transmission: Controlled trial of upper room ultraviolet air disinfection – A basis for new dosing guideline
What about 222 nm UVC 222: The same principles apply but the safe exposure limit will be different for 222nm
Is it enough to declare UV Air disinfection luminaire which shows irradiance level of 0.2microW/cm^2 at the distance of 1.83m from the luminaire for a person of a certain height?: ISO15858 takes 0.2microW/cm2 for 8 hours as the maximum exposure, but you could take eg 0.1microW/cm2 for 16h. The height is mentioned in the standard but should be checked with the use. Anyone at 1.83m or below will be safe.
I mean like cooling coil disinfection systems: UV-C is used at the air intake by cooling coils to disinfect the surface of the coils to prevent bacteria growth. The purpose is not to disinfect the air.

You can get systems that place lamps in ductwork but the air must be passing at a speed which will ensure it is exposed to UV-C for sufficient time to ensure disinfection.
Please define average illuminance, average irradiance, planar irradiance, and spherical irradiance.: Average illuminance Illuminance averaged over the specified surface. (Usually taken as the average of a number of points on a horizontal surface)

Average irradiance Irradiance averaged over the specified surface. (Usually taken as the average of planar irradiance at a number of points on a horizontal surface)

Planar irradiance Quotient of the radiant flux of all the radiation incident at a point on a surface. Watts/m²

Spherical irradiance Quotient of the radiant flux of all the radiation incident on the outer surface of an infinitely small sphere centered at the given point, by the area of the diametrical cross-section of that sphere. Watts/m²
We are about to submit a project for the Mexico City Subway. How can we consider the use of space?: You would consider people standing but probably not present for 8 hours except maybe workforce. If the time spent in the area is less you could consider a higher max irradiance.
Mike, what have you found with plant degradation: We have some ongoing studies in this area
Are you familiar with the ASHRAE, American Society of Heating, Refrigerating and Air-Conditioning Engineers work on a new guideline for upper air systems?: Yes, we are in contact with Richard Vincent and Ed Nardell and the GPC37 committee whose work has informed the guidelines I described.
Is there a height where UVC not be effective?: It will be effective as long as there is circulation of air in the room into the path of the UV-C. With high rooms we usually keep the UV-C in the 3m-4m height zone rather than at the top of the room.
how to properly clean UVC ?: Use an Alcohol based product so as not to leave a soapy film on the lamp.
How can you tell if the air within the space is effective disinfected? Is there any measurement tools to measure it?: The only way to tell if the air is disinfected is to take samples and return to a laboratory to check growth on a Petrie dish. We base the effectiveness on previous scientific studies and relate our design performance to these studies.
How do we solve if there's a something blocking luminaire irradiation, say a projector?: This is something to check before installation so the luminaires can be located to avoid blocking.
Is there any indication of the number of upper-room UVC devices accordingly to the number of people in a room?: ACH guides recommend 10L/sec per person in a room. Convert this to Air Changes per Hour and design the UV-C installation to give the equivalent number of ACH.
To be clear; we only need to record and report on the highest value in a space does not take several readings and average that?: Correct, as we are considering safety Average has no meaning. We only need to look for the maximum.
You mentioned the high requirements to UV-C meters. Are all meters able to be accurate over that large range? If not, which UV-C meter do you recommend?: In the presentation I mention the specification for the meters. In our experience the Gigahertz is a good solution.
Regarding to the performance, is there any information that we should inform to the customer, after the measurements?: If you measure the output close to the luminaire you can confirm the system is performing as specified. However be careful as the beam is very narrow and readings can vary with a small movement of the meter. Ensure it is exactly between two louver blades.
What happen in rooms with 8 meters height? is the Upper Air effective?: It will be effective as long as there is circulation of air in the room into the path of the UV-C. With high rooms we usually keep the UV-C in the 3m-4m zone and don’t place them at the top of the room.
Where can a meter be purchased?: Products UVC Radiometers (gigahertz-optik.com)

Remember to also get the FOV80 adapter
What is the absolute minimum height we can fix a luminaire?: This will depend on the surface reflectances but I have designed solutions with ceilings at 2.3m.
What modelling platform are you using to model UVC?: We have an adapted version of Relux for UV-C calculations.
Are the disinfection gate and the household tools emit the same dose of 60 mj or what: All household tools are designed to ensure safe operation below that dose. In some cases they are designed to switch off if a person is present to ensure the maximum dose isn’t reached.
What modelling platform are you using to model UVC?: It will depend on the individual tool and the time it takes to disinfect.
Repeat commissioning and not just at installation was mentioned, how often should we be recommending that to the customer and should this be costed within a maintenance regime?: ISO15858 states: 4.4.5 Measurements are performed at initial installation; whenever new UV lamps are installed

(newer lamp designs may provide increased irradiance), and whenever modifications are made to the UVGI system or room (e.g. adjustment of device height, location or position of louvers, addition of UVabsorbing or UV-reflecting materials, room dimension changes, modular partition height changes).

In practice this will be when lamps are changed.
what will be minimum / maximum distance between two upper air?: If two luminaires are placed close together you can get a “hot spot” between them. We find ideally a minimum of 2m for the lowest power unit. Distances between luminaires can be increased by using a staggered arrangment.
How does air conditioning effect the installation. For example temperature change and air flow?: The greater the airflow from an HVAC system the better as this will help air mixing. The susceptibility is temperature dependent but the differences you get in a normal room are not significant in this.
According to the 'Artificial Optical Radiation Directive 2006/25/EC' the exposure limit in the work place was 30J/M2 .. is this still correct?: The dose of 30J/m2 is at a wavelength of 270nm with a Relative Spectral Effectiveness of 1.0. At 254nm (which we use for disinfection) the Relative Spectral Effectiveness in 0.5 hence the limit of 60J/m2. This often causes confusion.
Are the 222 nm UV-C -systems going to replace the 254 nm Upper Air Systems?: So far 222nm sources produce quite a wide beam of UV-C and tend to be applied as a surface disinfection solution. Their use for upper air will depend on developing more focusses beams.
Is there a defined rate of decreasing the intensity of the radiation per meter?: The same inverse square law applies as for light
How big is risk of having mutations under UV-c radiation with 254 nm?: There is no evidence of mutations caused by UV-C

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Questions and Answers on 10 things you didn’t know about commissioning with UVC

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