How In-Duct UV-C Lamp Arrays Affect Air Disinfection

From ASHRAE Journal Newsletter, Dec. 22, 2020

In-duct ultraviolet germicidal irradiation (UVGI) systems can be used to disinfect pathogenic particles transported by air moving through ventilation systems. The proper design of these systems is quite important for energy consumption and disinfection performance, according to a recently published Science and Technology for the Built Environment paper.

The paper, “Evaluation of In-Duct UV-C Lamp Array on Air Disinfection: A Numerical Analysis,” details a study in which the effect of four different lamp arrays within a square cross section ventilation duct on the average UV dose, UV dose distribution and disinfection rates were examined by the researchers by using computational fluid dynamics (CFD).

Researcher Yunus Emre Cetin of Karadeniz Technical University discusses the study and the paper.

1. What is the significance of this research?

It is a fact that respiratory diseases are a serious threat to public health and have negative consequences on society and the economy. Since we spend most of our daily life indoors, and due to airborne infectious diseases like the current novel coronavirus (COVID-19) pandemic, countermeasures that minimize the risk of airborne pathogen transmission are a must for providing a healthy indoor environment.

In this context, sterilization technologies such as UVGI units installed in ventilation ducts is a promising technology to satisfy those needs. UVGI lamps that emit UV-C radiation (wavelength from 200 nm to 280 nm) inactivate microorganisms by damaging their DNA.

The CFD simulations are a suitable method to quantify the disinfection performance of UVGI systems by revealing comprehensive results about the interaction of airborne pathogens with the airflow and irradiation field.

In our study, it is shown that the position and distribution of the UVGI lamp array on ventilation ducts have a notable role in the performance of these systems. As a result of the different lamp array configurations, the average UV dose rates received by the particles change; therefore, disinfection rates differ. Also, it is pointed out that different evaluation parameters exist, and for a proper assessment all parameters should be considered.

2. How does this research further the industry's knowledge on this topic?

By using CFD analysis, functional guides for practitioners can be obtained. During the planning stage, various design parameters can be evaluated and more effective UVGI lamp distribution can be realized in ventilation ducts in an energy-saving and efficient way. In this regard, designers can assess numerous parameters:

• The number and the length of the UV lamps could be adapted in relation to the size of the duct cross section and the supplied airflow rate to optimize the performance.
• Lamp positions under various duct forms like contracting, expanding or bending could be evaluated.
• Disinfection performance for different airflow rates, pathogens, duct materials, air temperatures, etc. could be considered.
• The performance of different UVGI lamps from the market could be calculated and compared.

3. What lessons, facts and/or guidance can an engineer working in the field take away from this research?

Engineers dealing with ventilation and UVGI systems would see that many in-duct UVGI lamps on the market do not have disinfection performance reports. Also, reports available are for just a few operating conditions.

For these reasons, engineers should consider different operating conditions by performing CFD simulations that can present detailed interactions of airflow, pathogen aerosol and irradiation fields of the UVGI lamps. Moreover, CFD simulations can help to overcome some other cases as well. Because of different HVAC system duct designs, lamp positions need to be optimized in accordance with the changing character of the airflow. Here, studied lamp configuration and position should satisfy the best possible disinfection performance of the system against a variety of pathogens. In our study, it is seen that even in a straight ventilation duct the change in the lamp configuration leads to notable performance differences.

Another point seen in our findings is the performance parameters taken into consideration for the evaluation and comparison of these systems. It can be stated that the average UV dose values, dose distributions and standard deviations of different cases need to be well understood for a proper comparison.

4. Were there any surprises or unforeseen challenges for you when preparing this research?

The modeling of airflow, aerosol trajectory and irradiation field need meticulous consideration in a CFD application due to the myriad number of modeling options and boundary conditions available. There are different turbulence models, radiation models and approaches to modeling particle transport in the literature.

In our case, these options were evaluated and compared with the utmost care. More important, the preferred numerical approach was validated with previous experimental measurements for reliable output.

5. What are the next steps to further this research?

There are multiple next steps that are required or can be followed to further this study.

There is a lack of experimental measurements available in the literature regarding UVGI systems. Multidisciplinary experimental investigations could be a solution to this deficiency. In this way, more data could be obtained for the CFD validation. Also, the susceptibility values of different pathogens could be clarified. On the other hand, a guideline can be prepared for practitioners in the HVAC sector by using optimized results gathered with the help of validated CFD simulations.