Adding Ultraviolet Disinfection Systems to Schools’ COVID Defenses: A Background Briefing

  • The length of the chamber in which flowing air is exposed to UV-C light;
  • The number, type, power, and configuration of UV lights in the chamber;
  • Reduction in a UV lamp’s output of UV-C radiation due to degradation over time, variation in temperature, or the presence of dust and humidity on the lamp;
  • The speed at which air containing viral particles is flowing through the chamber;
  • The turbulence of the airflow; and
  • The amount of dust and humidity in the airflow (more of either reduces the UV radiation dose that viruses receive).
  • How long a duct will be required to install sufficient UV-C lamps to achieve our target incremental reduction in viral particles (this will vary with lamp power and other design factors)?
  • Which UV lamps will we install (e.g., widely used tubular lamps versus waiting for LED lamps that are still in development)?
  • How to measure and track these lamps’ actual radiation output (their visible light can remain constant even as their radiation output decreases)?
  • How to size UV radiation exposure area given the inevitable degradation of UV lamp performance over time?
  • How to control vibration caused by other elements in the HVAC system that can degrade UV lamp performance?
  • How to control temperature, dust, and humidity levels in the duct section where UV lights are installed, all of which can degrade system performance and cause disinfection results to fall below the indoor air quality target?
  • How to take the impact of turbulence into account when designing the installation (there are some examples of computational fluid dynamics models being used for this purpose)?
  • How to control ozone generation (and stay within regulatory limits for exposure to it), which can be a by product of UV disinfection, depending on the system configuration?
  • How to control the degradation of materials (e.g., polymers) that can occur due to exposure to UV radiation?
  • Incremental capital costs for UV-C systems in schools. This includes engineering, UV lamps and reflectors and their associated installation costs, new sensors (to measure lamp radiation output), safety equipment and new procedures, and additional engineering, equipment, and installation costs needed to address issues related to airflow, temperature, dust, humidity, vibration, and ozone generation.
  • Having weakened the correlation between the level of CO2 and viral particles in a classroom, new equipment and/or third services and procedures will be required to measure and monitor the level of viral particles.
  • Incremental operating costs include consumables such as UV lamps, incremental energy costs, incremental cleaning of the duct and lamps, incremental training, and the cost impact on maintenance routines (including the possible cost of outsourcing UV-C maintenance, and enabling those service providers to access school premises).
  • The economic cost of higher CO2 levels in classrooms and its impact on student achievement and other results (assuming the installation of UV-C disinfection results in a reduction in ventilation rates).
  • The economic value of the incremental reduction in COVID infection risk due to the incremental reduction in the level viral particles in classrooms.

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