HVAC system downtime during coil cleaning can compromise humidity and temperature control, potentially leading to air quality or comfort problems. Florida Hospital has found that high-output ultraviolet-C lights installed in the AHUs reduce or eliminate coil- cleaning programs — yielding ongoing energy savings, a reduction in HVAC system maintenance, and the elimination of cleaning chemicals. The facility also reports IAQ and infection control benefits as the regimen continues.
Florida Hospital's (FH) experience with ultraviolet-C (UVC) began in 1998 after seeing a presentation on the technology at an ASHRAF conference. A new generation of UVC devices promised to offer an improvement over the UV lights that were long ago popular for upper air disinfection in hospitals and other health care environments. Unlike the upper air devices, the newer UVC lights were engineered specifically to provide peak output under HVAC conditions. Output of these devices was reportedly so much higher than conventional UV tubes in cold and moving air that they could be installed just downstream of a cooling coil to eradicate bacteria, viruses, and mold.
Upon learning about the benefits of the new UVC fixtures, FH staff felt that the potential for the health care system was enormous. FH is an acute-care health system with more than 2,800 beds throughout Florida. With a network of 17 hospitals and 12 walk-in urgent care centers, FH treats more than a million patient visits per year and is the second busiest system in the country.
To test the efficacy of the UVC devices, we decided to install the lights in AHU #107, a 27-year-old, 6,000 cfm unit located at the main Orlando campus. A UVC Emitter manufactured by Steril-Aire, Inc., was specified for this and for subsequent installations. We selected AHU #107 because the coil and drain pan areas had a very visible buildup of mold, and the coil was clogged to approximately 50%.
Within weeks after the UVC installation, static pressure over the coil decreased from 1.8 in.wg to just 0.7 in. wg. Air velocity over the coil more than doubled, from 230 fpm to 520 fpm. Both the coil and drain pan areas looked absolutely clean, with no more visible evidence of mold or organic buildup. The air exiting wetbulb temperature from the AHU also decreased significantly, from 57° F (before UVC) to 53° (with UVC). We calculated the increase in capacity to be 95,245 Btuh or approximately 7.9 tons of air conditioning. If we use 1 kW/ton and multiply by 24 (hours/day) by 365 (days/year) by $0.07 (our electric rate), we arrive at a total of $4,867 in savings for this one unit. The total installed cost of the UVC Emitters was less than $2,000. Given the number of our facilities and the number of AHUs in these facilities, we estimate yearly energy savings well into the six figures. This estimate does not include additional savings for reduced maintenance.