Ultraviolet Energy Slashes HVAC Energy Use By Up To 20%

It seems like a daring claim: “add a low-cost, ancillary light fixture, and watch this magic bullet cut energy use, reduce maintenance and improve HVAC/R airflow and IAQ.” How could something so simple generate such striking results – is it true?

The quick answer is “yes”, more than true. Light in the UV-C wavelength (254nm) removes and prevents microbial buildup and growth as well as organic materials buildup. This buildup accumulates in all commercial air handlers to a greater or lesser degree and serves as an obstacle between the air and the cooling coils surfaces, thereby reducing heat transfer efficiency. Once this insulating material is removed, original efficiency and airflow levels return.

Now, a bit longer answer.

As air-conditioning equipment ages, its ability to maintain adequate space temperatures and humidity levels declines. Most often, that’s due to the air-handling-unit (AHU) cooling coils’ decreased ability to remove heat from the air. Evidence shows this drop in performance, also known as coil-fouling, can occur within five years of startup (and less) due to the gradual buildup of contaminants on coil surfaces.  This accumulation of material means the AHU’s coil is removing less heat and the fan is moving less air, and as a result, the space temperature and humidity are elevated. This may not be noticed by operators early on, but when it happens it’s often too late for coil cleaning, and UV could be the only choice. These statements come from many current users of UV and from ASHRAE as well.

Of course, there are energy and other cost penalties associated with coil fouling, when the facility engineer attempts to compensate for the reduced airflow and loss in heat transfer capability. Typically, the first step to compensate for this loss is to increase airflow, as advised usually by the engineer of record. The next is to reduce the temperature of chilled water entering the system, both of which are very costly to support from an energy standpoint.

It’s very important to note that even small changes in airflow and coil temperatures can dramatically impact cooling capacity. Therefore, both airflow levels and coil temperatures must remain at ‘as-built’ conditions for a system to use only that amount of energy, as when new. The most cost effective way to ensure this is through surface irradiation by a UV-C lighting system, according to ASHRAE.

UV-C for Surface Irradiation

The benefits of UV-C surface irradiation systems include maintaining indoor air quality and comfort levels with “minimal wasted energy”. For new systems, UV-C maintains ‘as-built’ conditions from the very beginning. For retrofit applications, UV-C removes organic accumulation and growth on coil surfaces on both the outer and inner surfaces, and similarly, it cleans drain pans and other interior surfaces. Shortly following the UV-C application, the surfaces stay clean to maintain original specification conditions thereafter, as long as the lights are maintained.

Performance losses from contaminant buildup have led many building operators to retrofit their air-conditioning systems with UV-C light systems after coil cleaning attempts have failed. ASHRAE sates in Chapter 62, ASHRAE 2019 Handbook—HVAC Applications, UV-C technology can reduce mold and biofilm, coil pressure drop and coil-cleaning needs. ASHRAE also recommends UV-C irradiance levels, which are specifically followed in all UVR sizing methodologies whether automated or manual.

UV-C systems are easy to size, purchase and install. Many users report that their cost for an installed UV-C system featuring high output lamps was about $0.10 per cfm. They are typically installed horizontally 12 inches away from the coil’s surface; however distances of 3 – 30 inches will work fine. They are normally installed downstream of the cooling coil in the direction of airflow. This is favored because the air downstream is saturated and drain pans are often extended in this location to catch raw water carry-over. The cost of operation is far less than 1% of the power required to operate the air conditioning system, and yet UV typically restores 15% or more in capacity!