{"id":62966,"date":"2018-06-11T09:37:37","date_gmt":"2018-06-11T13:37:37","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=62966"},"modified":"2018-06-11T09:37:37","modified_gmt":"2018-06-11T13:37:37","slug":"understanding-the-basics-of-uv-c","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/understanding-the-basics-of-uv-c\/","title":{"rendered":"Understanding the Basics of UV-C: What are the benefits for commercial HVAC\/R applications?"},"content":{"rendered":"
\"Images<\/a>
Images courtesy UV Resources<\/span><\/em><\/figcaption><\/figure>\n

by Daniel Jones
\n<\/strong>As air-conditioning and refrigeration equipment ages, its ability to maintain temperatures and humidity levels declines. Most often, the culprit is reduced coil heat-transfer effectiveness, with air-handling unit (AHU) cooling coils less able to remove heat and moisture from the air. These inefficient heat-transfer rates derive primarily from the buildup of organic contaminants on and through the coil\u2019s fin areas. Such buildup can be eliminated through the use of ultraviolet (UV) germicidal energy (UV-C light).<\/p>\n

In the UV-C wavelength (253.7 nm), the light disassociates molecular bonds, disinfecting and disintegrating organic materials. Contrary to popular belief, UV-C lighting systems are not an exotic, new technology. They have been employed extensively since the mid-1990s to significantly improve HVAC\/refrigeration (HVAC\/R) airflow and heat-exchange efficiency, which can reduce energy use by up to 25 percent. Although UV-C by itself does not save energy, it restores cooling capacity and airflow to increase the potential for energy savings. In fact, researchers have found exposing a fouled cooling coil to UV-C results in a 10 percent decrease in pressure drop and a 14.55 percent increase in heat transfer coefficient levels at reference conditions. (For more on this research, see J.T. Firrantello, W.P. Bahnfleth, R. Montgomery, and P.K. Kremer\u2019s \u201cField Study of Energy Use-related Effects of Ultraviolet Germicidal Irradiation of a Cooling Coil,\u201d from 12th<\/sup> REHVA World Congress CLIMA 2016 [Aalborg, Denmark].)<\/p>\n

This impacts energy use. As a cooling coil ages, microbial growth on the surface of its fins impedes its ability to remove heat from the air, thereby causing the temperature of the leaving air to increase. Additionally, the layer of growth produces pressure drop because it decreases the space between the coil fins, causing an increased demand on the fan to compensate for the additional pressure in the system. Many facilities speed the fan up and decrease the chilled water to meet demand for cool air. These measures typically add to energy use. By cleaning with UV-C, which reaches deep into the coil, the system can be \u2018de-tuned\u2019 to its original operating condition and save energy.<\/p>\n

In new\/original equipment manufacturer (OEM) equipment, UV-C keeps cooling coil surfaces, drain pans, air filters, and ducts free from organic buildup for the purpose of maintaining as-built cooling capacity, airflow conditions, and indoor air quality (IAQ). In retrofit applications, UV-C eradicates organic matter that has accumulated and grown over time, and prevents it from returning. UV-C accomplishes this for roughly $0.15 per CFM.<\/p>\n

UV-C is a relatively simple technology; it merely involves shining lamps onto surfaces and adding simple on\/off controls to facilitate maintenance. Nevertheless, many professionals are mystified about how the process works and how to apply it cost-effectively. It is important to address these aspects of UV-C technology and the applications that seem the most awkward, referencing American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) guidelines found in Chapter 60.8, \u201cUltraviolet Air and Surface Treatment,\u201d in the 2015 ASHRAE Handbook\u2013HVAC Applications.<\/em><\/p>\n

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\"Figure<\/a>
Figure 1: This diagram shows the electromagnetic spectrum, with a breakout of visible light segments\u2014colors. The ultraviolet (UV) spectrum ranges from 100 to 400 nm and is invisible. <\/span><\/figcaption><\/figure>\n

UV-C basics
\n<\/strong>People are familiar with the harmful effects of UV from sunlight in the UV-A and UV-B wavelengths, which give rise to sunburn and the need for UV inhibitors or blocking agents (found in glasses and lotions). However, unlike UV-A and UV-B radiation, the UV-C wavelength has more electron volt energy, and is absorbed (not reflected) by all organic substances, increasing its destructiveness. Given these properties, why is there not more discussion about protecting oneself from UV-C exposure outdoors? The reason is UV-C is absorbed by the ozone layer and much of the atmosphere, and does not reach the Earth\u2019s surface.<\/p>\n

So how much UV-C is needed to destroy organic matter? A 2010 study<\/a> commissioned by ASHRAE and the Air-conditioning, Heating, and Refrigeration Institute (AHRI) found even the most sophisticated organic compounds suffer from exposure to HVAC\/R dosages of UV-C energy. As UV-C lamp installations in HVAC\/R applications operate continuously, a well-distributed dose similar to visible light is all that is needed.<\/p>\n

When it comes to worker safety, there is not specific legislation relative to UV-C exposure. However, Occupational Safety and Health Administration (OSHA) does provide guidelines. Using a \u2018typical\u2019 UV-C installation, one can reach maximum UV-C exposure in less than 10 seconds. For this reason, it is recommended any HVAC\/R access point have a safety interlock switch to prevent accidental exposure to the UV-C energy inside.\u00a0<\/strong><\/p>\n

UV-C lamps and lamp replacements
\n<\/strong>Modern UV-C lamps are very similar to the fluorescent lights typically found in ceiling fixtures. (Read more here<\/a>.)\u00a0Both lighting types operate using identical electrochemical processes. They employ an electric discharge created through argon gas striking mercury vapor to generate an invisible photon with a wavelength of 253.7 nm.<\/p>\n

\"Figure<\/a>
Figure 2: Single-ended UV-C lamps are easily installed in commercial and residential air-conditioning units.<\/span><\/figcaption><\/figure>\n

UV-C lamps differ slightly from their fluorescent counterparts in that their glass envelope must be a highly engineered shell transparent to UV-C. This allows the 253.7-nm wavelength to escape through the lamp envelope unfiltered. Fluorescent lamps use ordinary glass, which blocks the UV-C wavelength. The engineered glass is also internally coated with phosphors. The UV-C energy is contained to excite the phosphors to glow (i.e.<\/em> fluoresce) in the visible light range. (Read more here<\/a>.)<\/p>\n

A typical UV-C lamp produces about 90 percent of its energy in the UV-C wavelength. Of the other 10 percent, approximately four percent energy is given up as heat, and the rest (about five percent) is in the visible light range that is medium blue (Figure 1). This color results from the argon gas in the lamp envelope (see photo).<\/p>\n

According to most lamp manufacturers, UV-C lamps typically provide more than 80 percent of their initial output over a 9000-hour period. Such lamps should be continuously operated, the corresponding 8760 hours of a year-long 24\/7 schedule fit conveniently into annual relamping schedules.<\/p>\n

Attempting to run UV-C lamps longer than 9000 hours will produce individual lamp outages, requiring maintenance staff to monitor them routinely to know what to replace. This individual swapping out of lamps requires a larger inventory of replacements for when the lamps begin to fail in larger numbers. The replacing of a UV-C lamp is as easy as replacing a fluorescent tube above a work bench. However, they are typically in more inaccessible locations, such as the plenum of an air handler downstream of a cooling coil. Replacement costs are typically less than $0.04 per CFM.<\/p>\n

Like fluorescent lamps, UV-C lights come in a variety of types and sizes, including single- and double-ended. The former is used in several lamp systems, some of which allow them to be inserted into the airstream through a plenum or duct, typically downstream of the cooling coil (Figure 2). Double-ended lamps have pins at both ends and are installed into specific-length fixtures, usually containing the ballast as a fluorescent fixture does. Typically, all types are available in standard- and high-output (SO and HO) configurations. The difference between the two is their watt and ballast ratings. HO lamps are usually recommended because they are less expensive on a watt-per-lamp basis.<\/p>\n

One could also opt for encapsulated lamps, which have a transparent fluorinated ethylene propylene (FEP) coating over the glass envelope. This option hermetically seals UV-C lamps in case of breakage. Should an accident occur, broken glass and mercury will remain within the lamp.<\/p>\n

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\"Photo<\/a>
Photo \u00a9 BigStockPhoto.com<\/span><\/em><\/figcaption><\/figure>\n

The advantages of UV-C
\n<\/strong>UV-C systems provide several benefits when applied to HVAC\/R systems, including:<\/p>\n