System cleanliness is next to indoor air qualityGood system hygiene increases efficiency, improves IAQ – and saves money. VERN KLEIN explains why – and offers essential advice on preventative maintenance.Does your building cosset people in air-conditioned luxury? Or does it subject them to air-conditioned misery? If cleanliness in an air-conditioning system is inadequately maintained, the results will include unpleasant odours, allergic reactions and the spread of diseases — in short, poor indoor air quality (IAQ). All these avoidable symptoms stem from microbes that gather and breed in dirt collecting on air-conditioning coils and in associated condensate trays. Take away the dirt, and these organisms will have nowhere to live. What’s more, keeping coils clean increases the effectiveness, energy efficiency and service life of the system — which means major cost savings. The following summary of the functioning of the coils explains how dirt affects both system efficiency and IAQ. The coils A typical air-conditioning system has an indoor cooling coil (evaporator) and an outdoor condensing coil (condenser). A building’s air is constantly circulated through the evaporator coil. Dirt in the air will stick to the condenser’s cooling surfaces as it passes over them. To minimise this and help prevent the recirculation of airborne dirt, a filter is often fitted. Unfortunately, filters are rarely 100% efficient — particularly at stopping very small dust and microbes. Dirt on the evaporator coil, and in the moist environment of its associated condensate tray, is the main habitat in the system for microbes. The job of an air-conditioning condenser is to dissipate heat absorbed from the refrigerant. The coil may be air-cooled or water-cooled and will accumulate dirt just as an evaporator does. If the condenser is indoors (in a large warehouse, for example) it can harbour microbes that affect IAQ. The refrigeration condensing units found in kitchens can also be breeding grounds if they are dirty. The costs Dirt coating the surfaces of any air-conditioning coil acts as an insulating blanket, which seriously affects its ability to function effectively. To achieve the same cooling effect, a system has to work harder. This uses more energy and puts extra pressure on its components — particularly the compressor, which is an expensive item to replace. At its extreme, breakdown of the compressor can lead to water leakage and damage to the fabric of a building. The microbes The main culprits involved in poor IAQ are fungi, bacteria and viruses. Bacterial activity often causes nasty smells. Fungi produce spores and defensive toxins which, along with the dead cells, waste materials and other by-products of the microbe colony, can trigger allergic reactions. The bacteria and viruses include organisms that cause disease in humans via airborne infection. All these contaminants are constantly being pumped into the air by dirty systems. Preventative maintenance To avoid all the problems described, coil cleaning needs to become part of a planned regime of routine maintenance. For each set of circumstances, you should obtain a specific coil-care product. A specialist like Advanced Engineering can point you to the perfect solution in each case. Some factors to consider are summarised below. The indoor coil, condensate tray and drains must be clean and free from debris. Choose a cleaner that is safe for indoor use. Avoid cleaners designed specifically for the external condenser coil, as they are often very heavy duty and can give off noxious fumes. There are general purpose cleaners available that are suitable for cleaning both condensers and evaporators. These tend to be environmentally friendly and are ideal for general maintenance. Disinfection Once clean, the indoor coil, condensate tray and drains must be disinfected to kill microbes. Grilles on ducted systems, and metal areas surrounding them can also be sanitised with the chosen product. Always ensure that any cleaning product claiming disinfectant properties meets the appropriate British and European Standards for both bactericide and fungicide. That means BS/EN 1040 and 1276 for bactericide and BS/EN 1275 and 1650 for fungicide. BS/EN 1276 and 1650 are the higher standards, demanding a higher performance from the disinfectant. It is most economical to choose a concentrated, combined cleaner and disinfectant product. This should be diluted with water and applied using a low-pressure sprayer. Other methods of application, including aerosols and ready-to-use hand sprayers, can be a great convenience for smaller systems or last-minute jobs. After cleaning and disinfecting, the unit is safe to be reactivated. All microbes have been killed. However, as soon as the coil is returned to use, dirt will start accumulating, microbes will start growing again, and smells will return. Depending on the environment, this can happen within two weeks. Long-term coil treatment This is the most effective way of ensuring that the indoor coil stays clean and has the smallest possible negative impact on IAQ. A 3-stage treatment is recommended. • Clean and disinfect the coil and condensate tray. • Apply a ‘stay-clean’ coating to the coil and condensate tray. This is not rinsed off. It remains in place (depending on the environment) for at least six to 12 months, acting like a non-stick layer and preventing dirt and microbes sticking to the treated surfaces. All this debris is washed into the condensate tray with the condensate. • Place a ‘stay-clean’ strip in the condensate tray. This strip will slowly leach out a disinfectant, killing any microbes washed into the tray and preventing further growth. The ‘stay-clean’ and condensate mixture will also clean and disinfect the drain lines as it washes away. As a finishing touch, a fragrance-enhancing gel can be added to the unit to give a pleasant just-cleaned freshness. Verne Klein is with Advanced Engineering Ltd, Guardian House, Stroudley Road, Basingstoke, Hants RG24 8NL.