Deep ultraviolet (UVC) light has long been used for surface treatment within HVAC systems. UVC can prevent the growth of bacteria, mold, and biofilms on surfaces (e.g. coils, drain pans, plenum wall, humidifiers, fans, and filters) which can lead to higher system efficiency and lower maintenance costs.
In this article, we explain the difference between mold treatment and prevention, share results of a mold treatment experiment (with time-lapse video), and explain how UVC LEDs surpass the traditional technology (i.e. mercury-based lamps) for surface treatment.
Prefer to watch the webinar? Watch: HVAC Surface Treatment using UVC LEDs
UVC is of interest within HVAC systems for surface and air treatment. The design of UVC systems for surface treatment applications provides some residual air disinfection, but air disinfection will not be discussed here because the benefits of lower cost surface disinfection within HVAC systems provide a compelling value proposition even without air treatment considerations. That said, Klaran UVC LEDs are used for air treatment in several customer products, such as the Haiku ceiling fan.
In order to narrow the focus of the experiments, mold was chosen as the test microbe since it is widely known to be among the most difficult to inactivate.
There are two levels of UVC exposure that we discovered during testing and seen in previous research:
Inactivation of existing microbial contaminants within HVAC systems is possible with UVC treatment but is not typically reasonable for two main reasons. First, particularly when it comes to mold, despite the inactivation the spread of dead spores within a system can still cause health related issues. Second, in most cases, UVC systems are installed in new systems or in an existing HVAC unit which would be cleaned as part of the installation process. So, the use of UVC for prevention of microbial growth is the most cost-effective and likely design scenario.
For these reasons, this article focuses on using UVC LEDs for surface treatment in order to prevent mold growth on surfaces, and presents examples of specific testing on HVAC coils since this is the most difficult challenge in respect to dosage rates and surface type.
Initial lab testing was performed at the Crystal IS biolab (Green Island) and at the Fuji facilities in order to determine the static dosing amounts that are required to inactivate mold and verify repeatability. Cladosporium sphaerospermum was used at both locations. While there was some variation in LED arrangement and distance, the dosage results matched.
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.