Is UVC-LED disinfection drone feasible?

- Sep 11, 2019-

The drones flying around have been hot spots in recent years, from the initial aerial photography, to drone lighting, drone ranging, drones to New Year, all kinds of bells and whistles.

Recently, Korean designers have brought a new concept to the UVC-LED drone for subway station disinfection.

As soon as the news came out, the industry's small partners talked about it: "When our UVCLED application is still tossing in various boxes and water dispensers, others have already played in the sky." Is this new application scenario whimsical or practical?

In fact, this kind of product that looks like a gimmick is not the first time in the industry.

In 2017, when NIKKISO announced the UVC-LED water sterilization module with 120LPM flow, many people felt that this is only a vase showing the strength of research and development. The high price can persuade the world to retreat.

However, the latest information indicates that after continuous optimization and one-year field experiment, this product has opened a breakthrough from aquaculture water sterilization and is moving into the field of water sterilization in factories and swimming pools.

The reason is very simple: this product captures the raw food of the Daiwa people who love aquatic products. The aquaculture process must be sterilized. This is the market that has solved the pain of traditional mercury lamp water sterilization products: the increase of water temperature affects the pH value of water and affects aquatic products. The taste and reaction with seawater minerals affect the use of scale on the glass surface.

The same performance and life cycle costs as mercury lamps, better aquaculture sales and lower maintenance costs are a direct manifestation of their economic benefits.

For the drone in front of me, I will also make a simple analysis from the three aspects of pain point, technical feasibility and economic benefit. I hope that I can throw a brick to attract jade and think together.

01 One product solves three pain points

The current way of disinfecting subway stations is this:

• For indoor air, ventilation and filtration are mainly used to improve air quality. The air conditioning system of some stations adopts medium-efficiency filtering equipment based on high-voltage static electricity. It is necessary to clean, disassemble and disinfect the air-conditioning system on a regular basis.

• Manually spray or wipe the disinfectant for key points such as handrails, seats, ticket machines, and escalators that the human body frequently touches. The disinfectant has a rapid, long-term killing effect on various pathogenic bacteria and is not corrosive to the facilities in the cabin.

The above disinfection methods have the following pain points:

• Excessive reliance on mechanical ventilation. Wind cycle sterilization is based on the principle of dilution, and the presence of poorly ventilated dead angles makes it difficult for harmful microorganisms to be completely removed in a short period of time.

• Microbes tend to multiply faster than kill. The spread of viruses and bacteria is closely related to temperature and humidity. The environment in the station is suitable for the growth of most pathogens, and the air duct of the air conditioning system becomes a hotbed for microbial reproduction. The ventilation system originally used for sterilization has become a tool for transmitting germs.

• Lack of ability to respond quickly and safely to emergencies such as outbreaks of malignant infectious diseases.

The subway station hall needs to introduce one or more disinfection methods to deal with the above risks. The UVC-LED disinfection drone is a good choice:

• Introduce this more targeted method of disinfection to ensure disinfection in poor ventilation or in dead spots. Increasing the sterilization rate can effectively inhibit the rapid propagation of harmful microorganisms.

• Suitable for surface disinfection of key locations, non-toxic and odor residue, without manual intervention, can achieve a lot of repetitive work during the subway outage. Path planning can realize the coordinated operation of multiple drones to disinfect the entire space without dead angle.

• A safe emergency response. UVC-LED has an effective killing effect on high-risk infectious viruses such as SARS, MERS, and flu. In an emergency, the drone can be the first to enter the space where high-risk virus may exist for observation and disinfection at any time. In order to prevent the virus from spreading, the drone can be concentrated to the designated location for destruction after the task is completed.

The subway coverage in South Korea is high and the density of subway stations is high. The MERS that broke out before was even disinfected throughout the city. I believe that in the search for new ways of sterilizing public places, they think more and more urgently than the Chinese. The UVC-LED disinfection drone solves three pain points at the same time, which is not possible with other disinfection methods. From this point of view, the emergence of this concept is not groundless.

02 Light source efficiency and endurance become bottlenecks

As a mounting platform for the sterilization module, the performance of the drone is closely related to the sterilization effect. The UVC-LED light source module needs to be matched with the corresponding heat dissipation and power supply module, which has certain requirements on the load and power supply capability of the drone. I used a domestic well-known brand, the four-rotor aerial drone with a take-off weight of 1400g as the object of transformation, to evaluate the sterilization ability.

Assuming that the UVC-LED sterilization module is used instead of the original shooting and image transmission module, the weight of the whole machine remains unchanged. However, due to increased power consumption, battery life needs to be re-evaluated. The drone has a battery capacity of 90Wh and a battery life of 30min. That is, the power consumption of the whole machine is about 180W. After the shooting and mapping module is removed, the power consumption of the drone motor and the flight control system is about 140W. The power consumption of the newly added UVC-LED sterilization module is calculated according to 100W. The total power consumption of the modified UAV is 240W. When the battery has the same take-off weight, the battery life is shortened to 20 minutes.

Regarding the placement position of the UVC-LED light source module, since the center of the drone is a gathering place of batteries, flight control devices, and various types of sensors, it is obviously not suitable for housing the light source module. It is a good way to disperse the light source module in the vicinity of the four rotors in the concept diagram. While dispersing the heat source, the wind flow of the rotor can also help to dissipate heat. In addition, such a design is also beneficial to increase the illumination range and light uniformity.

The wheelbase of this drone is 350mm, and the size and installation position of the four UVC-LED light source modules are as shown in the yellow position. According to the calculation of 4% photoelectric conversion efficiency, the light power of each light source module is 1000mw, the light exit angle is 30 degrees, and the light transmittance of air is calculated according to 80%/m. The optical simulation shows that the illumination area at a distance of 1 m (the lowermost receiving surface) is 0.65 square meters and the average light intensity is 0.5 mw/cm2.

Peer studies have shown that the same UV doses for common influenza and MRSA viruses are 7mJ/cm2 and 18mJ/cm2, respectively, at the same 99.99% kill rate. If the flu virus is used as the disinfection standard, a drone can achieve about 1 cubic meter of space disinfection in 15 seconds, and a drone can achieve 80 cubic meters of space during the life. An ordinary subway station hall is calculated according to an area of 10,000 square meters and an average height of 5 meters. It is necessary to dispatch 600 sorts of drones to achieve complete disinfection of the entire subway station.

Assuming that the WPE of the UVC-LED source is doubled, the drone's life time is doubled, and the sterilization effect is appropriately reduced. The number of drones in a subway station hall is expected to drop to less than 100.

In summary, the UVC-LED disinfection drone is technically feasible, but the sterilization space of a station is currently stressful for it, and perhaps a ward is more suitable for it.

03 Power saving and non-saving space sterilization method

In order to ensure indoor air quality, the subway station ventilation equipment is running for many years. Referring to the ventilation mode in the table below, the power consumption of the ventilation equipment is also 6.6kW during the outage period, and the power consumption will increase year by year as the running time increases.

With the existing technical capabilities, the use of UVC-LED drones to achieve a subway station hall sterilization requires a total of 600 sorties, a total power consumption of 5.4kWh. As the efficiency of the light source increases, this value will continue to decrease.

It is not difficult to find that the UVC-LED drone is a more efficient and energy-saving way to sterilize the subway space. However, this way of saving electricity does not save money.

With the improvement of UVC-LED efficiency in the future, the advancement of battery materials, even combined with wireless charging technology, can significantly reduce the number of drones required for space disinfection. In addition, the UAV can also perform part-time security monitoring and assist in manually checking the hidden dangers of the car and railway facilities. At that time, the concept could produce real economic benefits.