How UV-C energy works in HVAC applications: Part 1

This first of this three-part series describes UV-C light and how it is applied as a clean-up tool in all types of air conditioning systems.

11/03/2013


Figure 1: This diagram shows the electromagnetic spectrum, with a breakout of visible light segments—colors. The UV spectrum ranges from 100 to 400 nm and is invisible. Courtesy: UV ResourcesLight energy in the ultraviolet-C (UV-C) wavelength has been used extensively in HVAC equipment since the mid-1990s to improve indoor air quality (IAQ) by eliminating the buildup of biofilms and other organic contaminants on the surfaces of system components, including cooling coils, plenum interiors, drain pans, and air filters. UV-C works by disassociating elemental bonds, which in turn disinfects and disintegrates organic materials.

In new systems, such buildups are avoided by the continuous cleaning of equipment with UV-C. In retrofit applications, UV-C eradicates organic matter that has accumulated and grown over time, and then prevents it from returning.

Although UV-C is a relatively simple technology, many engineers, building owners, and other facility professionals are mystified about how UV-C works and how to apply it cost effectively. Mystification leads to mistrust. 

This three-part feature addresses the aspects of UV-C technology and the applications that seem the most awkward using ASHRAE guidelines found in Chapter 60: Ultraviolet Air and Surface Treatment in the 2011 ASHRAE Handbook – Applications. This first installment describes the nature of UV light, that is, electromagnetic radiation at a wavelength of 253.7 nanometers (nm) labeled “UV-C,” and how properties of UV-C light have been applied as a clean-up tool within all types of air conditioning systems. 

The second part will explore how UV-C light is generated by lamps that are very similar to fluorescent lamps found in commercial ceiling light fixtures. The topics of lamp life and replacement schedules also are covered to set the stage for using UV-C lamps in HVAC systems. The final installment in the series will discuss how UV-C lamps are applied within HVAC systems to clean cooling coil surfaces, drain pans, air filters, and ducts for the purposes of attaining and maintaining “as-built” cooling capacity, airflow conditions, and IAQ.

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.

We all are familiar with the deleterious effects of UV transmitted by sunlight in the UV-A and UV-B wavelengths, giving rise to UV 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 UV-A and B, the UV-C wavelength 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. Learn more about the electromagnetic spectrum in a video from NASA

UV-C’s germicidal effects are well proven. It owes these effects to the biocidal features of ionizing radiation, that is, 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 sun striking living cells in the epidermis and killing them; the redness is the increased capillary action and blood flow enabling white blood cells to remove the dead cells.

Ionization drives UV-C’s power to alter chemical bonds. It 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 can render microbial replication impossible. After being killed, organic remnants are subject to photo-degradation (disintegration), a key feature of UV-C energy. 

UV-C is absorbed by the ozone layer and much of the atmosphere, and does not make it to Earth’s surface; vacuum UV resides principally outside of the atmosphere.

Exposure and consequent dosage is the quantity of UV-C light absorbed over a specific period of time. 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 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 of the UV-C wavelength, UV-C energy is easily directed deep into and throughout a cooling coil. 

The next installment in this three-part series will set the stage for using UV-C lamps to disinfect HVAC system components.


Forrest Fencl is president of UV Resources. He is the writer or co-writer of 15 patents, is an ASHRAE Fellow, and formerly an ASHRAE Distinguished Lecturer. He has authored numerous papers and articles and several ASHRAE Handbook chapters related to ultraviolet air and surface treatment



HUGH , CA, United States, 12/03/13 06:21 PM:

This article, like many, addresses the surface disinfection issue. However, from a disease transfer point of view treating the flowing air is the more demanding task, especially for microbes smaller than MERV 13 -14 can capture. The power level must be considered and must be orders of magnitude higher than the surface treatment due to the limited exposure time. It would be valuable to gather comments and guidance from experience including addressing any Ozone that may be produced with these higher power UVC disinfecting systems.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
Each year, a panel of Control Engineering editors and industry expert judges select the System Integrator of the Year Award winners.
Control Engineering Leaders Under 40 identifies and gives recognition to young engineers who...
Learn more about methods used to ensure that the integration between the safety system and the process control...
Adding industrial toughness and reliability to Ethernet eGuide
Technological advances like multiple-in-multiple-out (MIMO) transmitting and receiving
Virtualization advice: 4 ways splitting servers can help manufacturing; Efficient motion controls; Fill the brain drain; Learn from the HART Plant of the Year
Two sides to process safety: Combining human and technical factors in your program; Preparing HMI graphics for migrations; Mechatronics and safety; Engineers' Choice Awards
Detecting security breaches: Forensic invenstigations depend on knowing your networks inside and out; Wireless workers; Opening robotic control; Product exclusive: Robust encoders
The Ask Control Engineering blog covers all aspects of automation, including motors, drives, sensors, motion control, machine control, and embedded systems.
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
News and comments from Control Engineering process industries editor, Peter Welander.
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
This is a blog from the trenches – written by engineers who are implementing and upgrading control systems every day across every industry.
Anthony Baker is a fictitious aggregation of experts from Callisto Integration, providing manufacturing consulting and systems integration.
Integrator Guide

Integrator Guide

Search the online Automation Integrator Guide
 

Create New Listing

Visit the System Integrators page to view past winners of Control Engineering's System Integrator of the Year Award and learn how to enter the competition. You will also find more information on system integrators and Control System Integrators Association.

Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Control Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.