Keeping condensing and cooling coils clean increases their efficiency by 15%-30% depending on what research paper you read. The problem with most of these coils is they are difficult to get at or inside the AHU and require shutting the system down - which may not be a viable option.
In spring Cottonwood is in the air in mass quantity and starts to clog your chiller coils, or fill your water cooled chiller basin and the Spring PM schedule usually involves an inspection and cleaning of these critical components. Though it may be nice to get up on the roof on a sunny 50/60 degree Spring day after being stuck inside all winter there are usually more important things on the PM list during the change-over season. Installing a cottonwood screen can take a multiple hour chore and turn it into a 5 minute task!
“But we can’t just skip cleaning the coils!” And we’re not suggesting you do that, but there are some simple cost-effective technology available to you now that can significantly reduce the time it takes to clean coils or even eliminate the build-up on the coil that gets them dirty in the first place. Whether you maintain a large AHU, some rooftops, a large cooling tower, or air-cooled chillers there are solutions that can help your equipment operate at system design year-round by keeping the coils clean without constant maintenance.
Durable, UV-resistant screening has been developed specifically for the purpose of keeping cottonwood and other debris from getting in your cooling towers or embedded into your condensing coils. This technology has been around for several years and there are several manufacturers that make the product. With a typical airflow resistance of 0.02” w.c. these solutions allow for air to move through the coil or tower almost unhindered but will prevent cottonwood, pollen, and other common debris that clog fins and traps. The best part from a maintenance side is it can remain up year-round (it is designed specifically for this application) and cleaning the coil is now as simple as brushing off the screen with a broom. An added benefit is the screen also acts as a barrier from hail stones and other debris that would damage coil fins.
Cooling coils present a whole different set of challenges as they are located within the AHU/RTU. For some older air handlers access to these coils may be near impossible, RTU cooling coils usually need to be split to get deep within the coils that are protected by usually minimal filtration. Larger air handlers with coils several inches deep present an issue of how do we clean it without just embedding the debris in the middle of the coil. Foaming chemical cleaners and compressed air have been the standards, but they require a lot of downtime for the system and in some settings that is not practical or requires it done during a time that creates overtime hours which can get very costly very quickly for the maintenance engineering department.
The good news about cooling coils is that with the correct application of UV-C light on the cooling coil you should never have to clean them again. These systems emit an incredibly narrow, intense band of light that bounces off the aluminum fins penetrating deep within the coil. When the light comes in contact with the material plugging the coilit breaks down the material at a cellular level. This reaction reduces the sludge, mold, bacteria, or whatever else is stuck in your cooling coil to water vapor meaning no excess material is then put into the airstream. When turned on the presence of the light will clean up the coil and prohibit the formation of new blockages - meaning once UV-C is installed and the bulbs are changed approximately every 18 months so they maintain adequate UV-C output coil cleaning will be a thing of the past and it will operate as close as possible to system design. Again, there are many different companies that offer this technology.
UV-C technology has been used in various applications since the 1920s, then it was a control measure that helped eradicate tuberculosis in the United States. In countries where TB is still a problem, and where we are seeing a resurgence of TB in the United States it is still commonly used for that purpose. Water treatment has also been a popular application, in some small residential pools and hot-tubs “filterless” systems are possible due to adequate UV-C output in the recirculation system of the water. Coil irradiation has been around for over 20 years, but modern advancements in the technology have brought acquisition, installation, and replacement bulb costs down to a level where it is becoming more common. Often times payback for coil irradiation systems are 3–9 months, which is especially important for climates like ours that have limited cooling seasons.