By Simon Blake
Installing ultraviolet lamps in HVAC ductwork used to be all about indoor air quality. But for many commercial and institutional customers, better IAQ is just a happy side effect in an effort to maximize HVAC system efficiency. (Part I of this article, covering residential UV, appeared in the March issue of P&HVAC.)
The entire approach to marketing UV in the institutional, commercial and industrial sphere has changed dramatically in recent years. “IAQ is now number three on the list,” remarked Aaron Engel, vice president, business development, for Fresh Aire UV Canada, Montreal.
“Now you install UV systems on the large evaporator coils in the air handlers and reduce maintenance costs, improve equipment efficiency and, oh, by the way, we improve indoor air quality. The industry has found that even a slight biofilm fouling on the evaporator coil, so thin that you probably wouldn’t notice it with your eye, causes a tremendous loss in heat transfer.”
A typical HVAC/R system creates condensation “that, combined with the dark, sustenance-rich environment, provide a perfect breeding ground for performance-robbing microbes on coils,” noted Daniel Jones, president and co-founder of UV Resources, Santa Clara, Calif.
Biofilm, in effect, insulates the fins on the coil and all components have to work harder, resulting in increased wear on equipment and increased energy costs. A UV-C system reduces pressure drop and increases heat transfer by the coil. This makes UV a ‘green’ product because it increases the efficiency of the equipment. “There is a real cost saving associated with a better running system,” added Engel.
The U.S. Department of Energy (DOE) reports that HVAC/R systems account for 30 to 50 percent of a building’s energy use. Installing a UV system will typically reduce energy costs by about five to ten percent, reported Jocelyn Dame, president, Sanuvox Technologies Inc., Montreal. Add the reduction in coil cleaning costs and the savings can be significant in a large building. However, it is important not to over-promise energy or cost savings, he added.
And while IAQ may be a tough sell to building owners, the reduced time off for sickness among employees is a genuine benefit.
Today there are many commercial/institutional applications for UV-C including hotels, airports, office buildings, hospitals, schools, outpatient centres, etc.
Other UV-C applications include upper-air/room UV-C systems, which are installed in communal spaces, such as in-patient and waiting rooms, corridors and break areas to interrupt the transmission of airborne infectious agents.
Airborne droplets containing infectious agents can remain in room air for six minutes or more, said Jones. UV-C energy can destroy those microbes in a matter of seconds. They operate 24 hours a day for continuous control. They are typically mounted seven feet above the floor and have been shown to reduce the total number of colony-forming units of any pathogen in a room by more than 90 percent.
Selling UV systems
The majority of UV systems installed today are retrofits. They are installed because the property is having a problem with coil fouling, where they can provide an immediate improvement and a noticeable cost savings in coil cleaning.
Building managers have been very receptive to this approach, reported Dame.
Selling a system for a new building can be a tougher. The savings on day one will be zero because the coils will be clean. The money is saved over time by preventing fouling and the related increased energy and coil cleaning costs.
The best approach is to specify the minimum number of UV lamps required to keep the coil clean to keep the initial cost down, he added.
Location, location, location
Like the residential systems we looked at last month, there can be an upstream or downstream installation. For coil cleaning, the concentration of microbial load is on the wet side as well as in the drain pan, said Engel. He suggests the most beneficial location for a UV coil application is on the downstream, wet side of the coil, so the UV germicidal light can continuously disinfect the coil and drain pan as well as the AHU system.
For high-level airborne disinfection, the lamps can be installed parallel to the airstream to maximize dwell time, delivering exponentially more UV to the moving air.
Some consideration has to be given to the mounting system as that can be a significant part of the cost of installing UV. There are many options – standoff brackets, magnets, etc. – check with the manufacturer for recommendations.
Sizing the system
HVAC/R contractors and engineers should defer to manufacturers of UV-C fixtures for the proper equipment and sizing of UV systems.
Manufacturers offer sizing software that allows the engineer or contractor to take the size of the coil and figure out the best configuration for UV lamps. “This is where the industry will suggest an engineered solution rather than just putting a lamp in front to the coil and saying ‘We’ll do some magic,’” said Dame.
“Since HVAC/R equipment can be large or small, applying the correct UV-C system becomes imperative, both for performance and ease of installation,” said Jones.
A large air handler would typically use a system installed within the plenum with longer lamps, up to 61” in length. On the other hand, a rooftop system might use a 4X UV-C fixture mounted on the exterior of the unit with the lamp(s) protruding into the plenum. Lamp sizes from 33 to 45 inches are typical.
Today, most manufacturer sizing recommendations are guided by the ASHRAE Applications handbook, which advises that 100 µW/cm2 at the farthest-away corners of a coil will accomplish the results desired: maintaining a clean coil or cleaning up a fouled coil.
To take this one step further, added Jones, it has been found that an 80 Watt, 36-inch high output UV-C lamp met all of the ASHRAE criteria on a coil that was one meter square, or had 10.76 square feet of surface area.
“If the lamp wattage is divided by the square footage of the coil surface [(80/10.76) = 7.43,] we see that about 7.5 lamp watts per square foot of coil surface area will more than meet the ASHRAE recommendations. This then provides a simplified way for contractors to properly size UV installs for most any coil, large or small,” he added.
There are now smart phone apps that can simplify the sizing and selection of UV systems. Using the apps can be as simple as inputting the height and width of a cooling coil to get product recommendations and pricing.
There’s a much greater awareness today as building managers and engineers attend trade shows and realize they can improve their coil and air handler efficiency with UV, noted Dame. “We still do not have a trend of everybody specifying UV in new buildings. If that were the case, I would not have time to speak to you,” he laughs.
The future could well be different. “There’s not a building that goes without filters today,” he remarked. “But filters were not invented to improve air quality; they were invented to protect equipment from getting dirty. Later they found that it also helped the building’s air quality, so maybe some day every building will go up with UV in it too.”