HVAC Fan Energy Savings Outweigh UVC Consumption by 39% - Steril-Aire

For years, facility managers have shared anecdotal experiences and case studies demonstrating the ability of UVC for HVAC® systems to improve cooling capacity and reduce energy use. However, several recent studies have provided independent, third-party validation of the power of ultraviolet germicidal energy to boost HVAC system efficiency and slash energy costs. 

Researchers from the National University of Singapore (NUS) and Pennsylvania State University (PSU) confirmed that UVC irradiation effectively cleans cooling coils in HVAC systems, reducing energy usage and costs while significantly “enhancing coil energy performance.” 


How UVC enhances coil energy performance.

The study, “Effectiveness of an Ultraviolet Germicidal Irradiation System in Enhancing Cooling Coil Energy Performance in a Hot and Humid Climate,” evaluates the effectiveness of UVC for HVAC via a “before UV” and “after UV” comparison of coil performance. The field test was conducted using Steril-Aire® VO emitters (GTD 40) installed downstream of a cooling coil in a variable air volume AHU. 

The NUS/PSU collaborative research found that the overall coil thermal conductance (coil-heat transfer efficiency) increased by 10%, and the pressure drop decreased by 13%. Remember, the higher the pressure drop, the more energy it takes to move air through the air handler. 

Summary of Findings: 

  • UVC increases coil-heat transfer efficiency. Applying UVC to an AHU coil for ten months increased overall thermal conductance by 10% and decreased pressure drop by 13%. 
  • UVC drives rapid efficiency improvements.  Improvement in coil performance was most rapid during the first month of UVC application. 
  • UVC lowers fan energy consumption.  Fan energy use fell by 9% over ten months of UVC operation. 
  • UVC ROI.  Savings in fan energy were 39% greater than the energy used by the UVC lamps.

UVC for reducing HVAC energy use (ASHRAE RP 1738).  

These results were similar to those of a study sponsored by ASHRAE and conducted by Pennsylvania State University titled Field Measurement and Modeling of UVC Cooling Coil Irradiation for HVAC Energy Use Reduction.” Based on field tests, investigators found that UVC installed in a commercial AHU yields an average pressure drop reduction of 21% and a 14% increase in heat transfer coefficient.  

In this study, air handling units with UVC installed downstream of the coils extracted more heat, using less energy to perform the same task. Treating coils with UVC helped save roughly 4.5% in HVAC energy when modeled across multiple building types and climates.  

Specifically, researchers found that most energy savings derived from UVC occurred in fan energy (80%), followed by cooling (17%) and pump energy (3%). 

(i) Figure represents total HVAC energy saved, with the majority (80%) of savings attributed to fan energy

How biofilm impacts cooling costs and efficiency. 

In HVAC systems, condensation produced by cooling coils functions like a magnet, attracting dust and other particulates in the airstream. Once present, these particulates are a food source for bacteria and other microbes, which quickly multiply due to the moist and dark environment in the air handler that serves as an ideal growth medium.  

This biofilm acts as an insulator to prevent the efficient transfer of heat to the cooling coils, forcing the air handler to work harder to provide sufficient cooling and airflow to maintain set point temperatures. 

Surprisingly, it doesn’t take much biofilm to make a huge difference.  A layer of biofilm across the coil fins about as thick as a strand of hair can limit the space between coil fins, resulting in less efficient cooling by causing an increase in velocity and, thus, less time to transfer heat.  

How conventional thinking attempts to deal with the problem. 

Many of the typical ways to compensate for reduced cooling capacity caused by biofilm involve energy-intensive adjustments. Operators usually attempt to increase airflow or fan speed; when that’s not enough, they pump more chilled water and lower the chiller temperature. However, each of these interventions carries a hefty energy use penalty. 

Chemical and mechanical cleanings are costly and do nothing to prevent almost immediate future biological growth. In addition, pressure washing pushes bacterial contamination deeper into the coil, increasing pressure drop by restricting airflow and reducing the air handler’s ability to remove heat and effectively condition the air. 

How UVC solves the problem. 

Working 24/7/365 to halt the growth of bacteria and mold, UVC eliminates biofilm and makes the heat transfer process significantly more efficient and less energy-intensive.  

UVC is a simple, cost-effective solution to keep HVAC surfaces clean continuously rather than periodically/temporarily improving fouling. By adding UVC to the downstream or “wet” side of coils, where bacteria and mold have the best chance to thrive, operators can expect sizeable energy savings, lower maintenance costs, a system operating at its original design capacity, more comfortable building occupants, and better indoor air quality.  

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