May 12, 2020 The Science Behind UV-C Energy: What Is It?
What is UV Energy?
UV light comprises a segment of the electromagnetic spectrum between 400 and 100 nm, corresponding to photon energies from 3 to 124 eV. The UV segment has four sections, labeled UV-A (400 to 315 nm), UV-B (315 to 280 nm), very high energy and destructive UV-C (280 to 200 nm), and vacuum UV.
Most of us are familiar with the harmful effects of UV energy transmitted by sunlight in the UV-A and UV-B wavelengths, giving rise to UV “sunburn” inhibitors, or blocking agents, which are found in glasses and lotions. We are also familiar with products engineered to withstand the effects of UV radiation, such as plastics, paints, and rubbers. However, unlike the UV-A and UV-B wavelengths, the UV-C band has more than twice the electron volt energy (eV) as UV-A, and it is well absorbed (not reflected) by organic substances, adding to its destructiveness.
UV Energy’s Killing Power
UV-C’s germicidal or germ killing effects are well proven. The UV-C wavelength owes these destructive effects to the biocidal features of ionizing radiation, or more simply, UV-C does far more damage to molecules in biological systems than can temperature alone. Sunburn, compared to the sensation of warmth, is one example of that damage. Sunburn is caused by sunlight striking and killing living cells in the epidermis; the resulting redness from a sunburn reflects the increased capillary action and blood flow that allow white blood cells to remove the dead cells.
It is this ionization function that drives UV-C’s power to alter chemical bonds. The 254 nm wavelength carries enough energy to excite doubly-bonded molecules into a permanent chemical rearrangement, causing lasting damage to DNA, ultimately killing the cell. Even a very brief exposure to UV-C can permanently eliminate microbial replication. In other words, UV-C exposure kills bacteria and other infection-causing microbial (and efficiency-robbing) organic contaminants. After being killed, organic remnants are subject to disintegration.
This organic disintegration byproduct is important from a HVAC/R efficiency perspective. By eliminating accumulated organic materials and biofilm growth in commercial air handlers, the use of UV-C significantly improves airflow and heat-exchange efficiency levels. In other words, the addition of UV-C improves occupancy comfort levels while reducing energy use by up to 30 percent once capacity has been restored.
A 2010 study commissioned by ASHRAE and the Air Conditioning, Heating, and Refrigeration Institute (AHRI) found that even the most sophisticated organic compounds suffer from exposure to small dosages of UV-C energy. Because UV-C lamp installations in HVAC applications operate 24/7, time is infinite, so surface materials are both disinfected and disintegrated. Once gone, they won’t re-form as long as the UV-C energy (lamps) are maintained.
Unlike manufactured compounds, the mostly simple organic debris as found on coil surfaces are fairly easy to degrade. And because aluminum is among the best inorganic reflectors, UV-C energy is easily reflected deep into and throughout a cooling coil.