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UV Sizing Criteria
There are some factors that need to be considered when UV Sizing. The choices made by taking these factors into account determine the success or failure of the system.
When the UV lamp is used in the channel or in the air conditioning system, a certain contact time is required to affect microorganisms. Microorganisms moving in the flowing air are more or less exposed to UV radiation depending on the airflow rate. As the air velocity increases, the UV radiation effect decreases.
Similar to the filter selection in a ventilation system, the selection should be made by considering the airflow rate in the UV lamp selection. As airflow increases, the amount of UV radiation should be increased.
Cross Section Area
After the UV light leaves its source, it spreads in all directions and disperses into the environment. Its effect decreases inversely with the square of the distance from the source. Therefore, UV lamp/lamps should be placed in the duct and device homogeneously and should be able to see the whole airflow passing over them. It does not affect surfaces where UV light does not reach (see or reflect on).
Considering the temperature range in the air conditioning system, it can be said that the temperature does not have a significant effect on the inactivation of microorganisms.
The temperature has an effect on the performance of the UV lamp. Most UV lamps are designed to operate in an average range of 20-22 ° C and air velocities of 2-2.5 m / s. Apart from these values, the efficiency of the lamps varies. It should be learned from the UV lamp manufacturer how the lamp efficiencies change outside these ranges.
Due to the water vapour in the humid air, the movement of UV light decreases. As the amount of moisture in the environment increases, the passage and spread of light become difficult. This effect must be taken into account in UV lamp selection and calculations.
In addition, generally high relative humidity has a negative effect against the inactivation of microorganisms. As the relative humidity increases, it becomes difficult to neutralize microorganisms. However, this does not apply to all microorganisms. Therefore, it cannot be said that the increase in relative humidity will have a negative effect on all microorganisms. Therefore, UV lamp selection and system design should be made in accordance with the target microorganism.
In case UV lamps are used in humid environments, attention should be paid to IP classes and moisture should not enter the lamp.
Like visible light, UV-C light is absorbed by some surfaces and reflected by some surfaces. In order to have more effect, the volumes where UV lamps will be placed are requested to reflect the UV rays as much as possible. The reflection rates of some materials are given in Table 2. Since the reflection rate of aluminium is high, it is recommended that the inner surface of the channel where the lamp will be placed should be coated with aluminium.
UV-C Lamp Power
As the radiation power produced by the UV lamp increases, it is possible to provide more effective disinfection. However, considering the costs, contact time, cross-sectional area, etc. Together with other parameters such as the lamp power should be determined. The important thing is to determine the UV dose that will neutralize the target microorganism by considering the design conditions and to choose the appropriate lamp.
Since space is limited in canal and device applications, a high-intensity UV light is required. Microorganisms are generally exposed to UV light for a contact period between 0.1 s and 0.3 s in such applications. In surface disinfection, the intensity of the UV light may be lower as the contact times can be longer. As the contact time increases, the UV radiation effect increases.
Different doses of UV radiation are needed for each microorganism. As shown in Figure 3, viruses, bacteria and other microorganisms have different resistance to UV light. The values determined to inactivate the microorganisms after the experiments and called the k coefficient are given in Table 3. The larger the K value, the easier it is to inactivate the microorganism.
Table 3. K Factors at 90% Killing Effect for Some Microorganisms