Air conditioning and heating account for around half of all operating costs in a typical commercial building and that makes dirty, inefficient systems eye-wateringly expensive to operate. Effective coil maintenance (including regular filter replacement) is one of the simplest yet most effective ways of improving HVAC system efficiency.
As Richard Betts, MD of Rabscreen, explains, HVAC coils work on the principle that the fins attached to the refrigerant pipework receive unrestricted cooling air to reduce the temperature of the refrigerant: “The greater the surface area of the fins, the higher the efficiency of cooling. When dirty, there is a thermal blanket over the fin. A 1mm layer of dust will reduce the efficiency of the coil by 21% and increase the energy used by up to 30%.”
Frank Intrieri is vice president of sales for Goodway Technologies, a sister company to SpeedClean, a manufacturer of HVAC maintenance tools. He agrees that airflow is greatly diminished if coils and fins are not cleaned regularly: “The HVAC unit is going to run inefficiently, so it will work harder and may struggle to get to the temperatures required. Electrical bills are going to increase, and the system will break down more frequently.”
However, as Andy Harvey, marketing manager of Advanced Engineering, points out, not all coil cleaning solutions are created equal: “While there are a wide range of cleaning options available, some are better than others. We’re aware of some products that leave coils appearing clean and shiny. But, on closer inspection, the chemical has etched onto the coils, damaging them and reducing their efficacy.”
Indeed, there are a variety of ways to clean coils and they vary enormously in effectiveness, warns Intrieri: “Some applications can combine water and chemicals, some of which are harsh or high acidity, and those can also do damage, eating away at the aluminium fins on a HVAC coil. Ideally, if you are going to use a chemical, use a biodegradable, non-acidic alkaline-based one.”
Intrieri’s company offers cleaning products for low pressure cleaning using a self-advancing foam cleaning chemical. This expands deep into the coil beds and, as it does so, it dislodges dirt and debris trapped between the fins: “Instead of pushing the dirt and debris into the coil and embedding it deeper, we try to push it from the inside out.”
However, chemical cleaning is not the only way to keep HVAC coils in pristine condition. Another way is to employ ‘Active Field Technology’ (AFT). Coils provide a breeding ground for mould, bacteria and viruses, which can cause operational issues, potential litigation and, in certain severe cases, loss of life.
Microbial build-up on the heat exchange plates and drain pans of the cooling coils results in increased resistance to air flow and a loss in thermal efficiency. AFT is designed to keep the air conditioning coil clean and free of bio-contaminants, including viruses, bacteria and bio-film.
Robert Axon, director of UV Technology Global, explains that AFT uses a ‘non-ionising’ field created using low power alternating current. This can destroy airborne bacteria, viruses and volatile organic compounds as they pass through its destructive electron field.
He says: “AFT is scientifically proven to reduce particulate and airborne pathogens to less than 0.1 micron without the use of inefficient, energy consuming passive filtration. Depending on the filtration installed, AFT can reduce your HVAC system energy footprint by over 50%.”
While acknowledging that coils can be cleaned in several ways, Betts believes they all have inherent risks. He says, for example, that soft brushes will remove surface dust, but they can also drive dust between coil fins, exacerbating the contamination problem, and hose washing using low-pressure water flow tends only to remove surface debris from the fins.
With typical chemical and low-pressure washing, meanwhile, the chemicals are left to soak into the debris, which is then rinsed off with a low-pressure hose. Betts again: “This is more effective than the first two options, but not too environmentally friendly.” Besides, coil cleaning is only half the job. Panel and cartridge filters in a HVAC system also need to be changed, ideally every 90 days, according to Intrieri. It has been estimated that air indoors is 70% more polluted than outside air. Poor indoor air quality is said to be among the top public health risks.
This is where HVAC air filters come in. They trap and hold a wide range of particles and contaminants. There are several benefits to changing air filters, including healthier indoor air, increased efficiency (and money savings) because the HVAC system isn’t working as hard, and increased longevity of the HVAC system with fewer system failures. It’s also environmentally-friendly, because if the system is working harder, it uses more energy, electricity and more greenhouse gases are produced.
Of course, prevention is better than cure, and that is why Betts advocates a physical barrier between HVAC coils and the outside air – external filter screens.
For Intrieri, there are advantages and drawbacks to using screens. “In some applications, they can work if they’re installed correctly, as long as they’re not decreasing the airflow to the point where it’s starving the coil. If the airflow is diminished getting to the coil, the motor inside the air handler is going to compensate and work harder [which will increase energy usage].”
However, according to Betts, by creating a static charge that attracts and traps airborne particulates, air intake screens prevent sensitive components and cooling and condensing coils from contamination without restricting airflow. He says: “Our business is about keeping the coils and filters clean. Disposable air handling unit filters, which protect the internal coil, get less efficient with face loading; 16,000 panel filters would fill eight shipping containers with landfill debris because they cannot be recycled. We can make them last up to 60% longer between changes.”
He claims that air intake screens extend the time between external coil cleans, don’t alter the discharge pressure, maintain efficiency, reduce environmental impact of chemical cleaning and mechanical damage, and are easy to see when dirty.