Fouled Cooling Coils

Is Your Cooling Coil Working Overtime?

Biofilm is the greatest enemy of an efficient HVACR system. When biofilm gains a foothold in the coils of your air handler, a slew of operational and efficiency issues will lower performance and drive up costs.

This is why it is important to have a routine preventative maintenance program designed to keep coils operating at peak efficiency.

Ideal Environment for Bacterial Growth

In an HVAC­R system, evaporator coils are vital for removing heat from occupied spaces.  As part of this heat-transfer process, the moist condensation produced by the coil acts as a magnet to attract dust and other particulates contained in the airstream.  Once present, these bacteria and microbes quickly multiply due to the moist and dark environment inside an air handler that serves as an ideal growth medium.

As the coil fins become packed with additional contaminants, pressure drop (or air resistance) across the coil increases, and less heat is removed. To overcome this loss in cooling capacity, the entire system must work harder. As heat transfer efficiency decreases, operators are forced to compensate with more energy-intense adjustments such as pumping additional chilled water and/or increasing fan speeds.

Ultraviolet (UV-C) is the cure. Light in the UV-C wavelength destroys coil/drain pan microbial infestations 24/7/365. The pressure drop and velocity of the air between coil fins (interstitially) are optimized, while fin and tube surfaces are kept clean to maximize system heat-exchange efficiency and rate.

Ripple Effect of a Fouled Coil

Because the coil is the point where heat is removed from conditioned spaces, the impact of a poorly performing or fouled coil can be numerous:

• Coil-Heat Transfer Efficiency: Biofilm acts as an insulator and prevents the efficient transfer of heat to the cooling coil. This also means the system must work harder to provide the necessary amount of cooling and airflow to maintain set temperatures.
• Energy Usage:  As less heat is removed, the system must run longer, consuming more energy. A dirty coil can reduce cooling efficiency by up to 20% and increase energy use.
• Occupant Health: Fouled coils contain biofilm and mold spores that can harbor pathogens and odors that create poor indoor air quality. According to an article from ACHR News, the spores in the air can aggravate asthma and other upper respiratory symptoms. It will also contribute to fatigue and common sinus infections.

UV-C: A Cost-effective Solution

By using UV‑C, an HVACR system’s coil can be kept clean while resolving all the adverse effects that result from a fouled coil:

System efficiency: UV-C eliminates and/or prevents the buildup of organic material on coils, drain pans, and interior air-handler surfaces to improve airflow and to return/maintain heat-transfer levels to “as-built” capacity. Meaning, less energy is needed to provide the necessary amount of cooling and airflow to occupied spaces. UV‑C installed in older systems can reduce energy use up to 25 percent on average.

Comfort and IAQ: Clean systems don’t contribute to foul odors, allergens, or pathogens in airstreams, and help sustain design temperatures and airflow. This translates to a comfortable environment with a high IAQ for building residents.

Occupant health: When UV‑C penetrates a coil, it eliminates airborne pathogens, preventing them from spreading throughout a building. This improves occupant productivity, and lower incidences of sick days, reduced hot/cold calls and other service requests. UV‑C efficiently destroys surface microbes and degrades organic materials that impede HVAC system efficiency, as well as contribute to allergies and airborne-transmitted diseases.

Cost: Costing only $0.15 per CFM (installed), UV‑C lighting is a cost-effective solution that can reduce energy costs and prevent the need for replacing an HVAC system. In fact, buildings with high-functioning HVAC systems have increased value and significantly decrease occupant turnover.