Inactivation testing performed at the Fuji lab helped determine wavelength effectiveness. Results showed that a 265 nm wavelength was 20 percent more effective than 280 nm against C. sphaerospermum. Klaran UVC LEDs emit peak wavelengths in the 260 nm to 270 nm range, which give them a unique advantage over all other UVC LED manufacturers.
Effect of Wavelength on Cladosporium sphaerospermum Inactivation
|265 nm||280 nm|
|LRV Reduction||Dose (mJ/cm2)|
Once testing baselines were confirmed, the mold species was replaced with Cladosporium halotolerans, which is a more relevant and difficult microbe. Further, C. halotolerans is more common across the globe and one of the most prolific within homes and HVAC systems.
Static testing performed at the Crystal IS biolab in Green Island showed that the required dosage for inactivating C. halotolerans is 23 percent higher than C. sphaerospermum.
Crystal IS helps companies understand the differences between use of visible LEDs in luminaires and UVC LEDs for treatment and disinfection. We provide simulation and design support surrounding use of our LEDs for a specific application. Therefore, we include the most realistic scenarios even if that means increasing the challenges associated with a successful design.
The most realistic scenario involved using UVC LEDs to prevent growth inside an HVAC system. In this experiment, the treatment surface was HVAC coils, and we set up a UVC dosed coil, positive control, and negative control. It is important to note that constant exposure to UVC light is not required to prevent growth.
A periodic dose (ranging from 14 to 120 mJ/cm²) was applied every 12 hours. Results demonstrated that 28.8 mJ/cm² can prevent one of the most difficult microbes from growing on a coil surface. With the specific UVC LED board, this was 4 minutes of treatment every 12 hours.
Below, you can see a time-lapse video showing the testing of C. halotolerans with a Klaran UVC LED treated coil on the left and positive control on the right. Average intensity across the surface of the coils was .1mW/cm². A 9 LED module with 70 mW Klaran UVC LEDs was set at approximately 10 inches.
There is ample documentation around the use of UVC for surface treatment in HVAC systems. ASHRAE TC 2.9 sponsored a research project at Pennsylvania State University entitled “Field Measurement and Modeling of UVC Cooling Coil Irradiation for HVAC Energy Use Reduction.” The study included some conservative results as compared to some field studies but still found an average pressure drop reduction of 21 percent and increase in heat transfer coefficient of 14 percent. Meaning improved temperature efficiency and less cycle times for fans, cooling components, and pumps. This equates to HVAC energy savings of 4.5 to 30 percent depending on system size and condition.
So how can UVC LEDs help improve on the old technology?
First, UV lamps contain mercury which will soon be phased out. This also means additional cost to dispose of used lamps. Lamps like heat that they don’t get within an air flow. This results in lower actual performance than calculated. This normally isn’t an issue because lamps are constantly on, which provides dosages needed for surface treatment. However, the thermal cycling within HVAC systems impacts lamp lifetime performance, so lamps need to be replaced at least once per year. The analog ballast is typically more expensive and prone to failure versus the digital components used with LEDs. LEDs are a point light source, meaning you can take advantage of getting power to the target surface without the need for reflectors (reflectors and fixed lamp shape can cause additional pressure to drop within the system).
While those factors highlight the need to consider the full system design- rather than the light source, only- the major advantages of LEDs are energy and maintenance costs. Doing some basic comparisons of using a lamp versus LEDs in a 4-ton residential unit, the LEDs only require 10 to 20 percent of the lamp power requirements. The largest value propositions are the costs and associated service fees for lamp replacement. LED designed systems can operate for the life of an HVAC unit.
Crystal IS looks forward to working with HVAC manufacturers to develop the next generation of HVAC surface treatment solutions. Contact us today to learn more about using our Klaran UVC LEDs.