Energy efficiency is a fundamental aspect today in air conditioning systems. To achieve that efficiency, proper cleaning of the coils plays a fundamental role.
Mayra M. Lira*
Any heat exchanger demands less energy if it is free of dirt. We know this almost by intuition, it may seem logical that every unit works better when it is clean. However, it is until very recently that there are formal studies that prove it: in 2006 ASHRAE published a document entitled "Study that proves that the cleaning of coils saves energy" whose conclusion was that you can save from 10% to 15% in electricity consumption, also finding that other indicators such as dehumidification can be improved, comfort and the accumulation of mold and bacteria simply by cleaning periodically.
Ten years have passed and cases have been analyzed and more studies have been conducted: according to the U.S. Department of Energy "a dirty capacitor can increase energy consumption by up to 30% ... fouling coils can decrease capacity by 7% and increase electricity consumption by 10%, with a net reduction in compressor efficiency of 16%."
In Latin America and in particular in Mexico the numbers can be very different. A dirty 10 TR unit can decrease by up to 70% of its capacity, that is, work as if it were 7 TR and require replacing its parts prematurely. When dirt prevents heat exchange from taking place according to the design conditions, it is convenient to take into account a fouling factor when calculating the thermal loads of the system.
As global warming advances and living standards rise, especially in countries with emerging and developing economies, energy demand increases. The new generations are born and grow up in air-conditioned environments, from the home, the car, school, work and entertainment centers, If we take into account that air conditioning and heating systems consume about 40% of the energy in the world, how much global savings could we achieve if they were kept clean? We would harness energy resources for sustainable purposes.
Why is there no periodic cleaning?
An important reason to space the cleanings as much as possible is the difficult access to the condensing and evaporating units and ducts in your case, fortunately little by little the space to carry out the maintenance is considered from the design of the buildings. Other times the safety of the contractor is not contemplated and put at stake, not to mention the discomfort and lack of water and electricity supplies on site.
In the case of evaporators, it is even more complicated to perform periodic maintenance because they are usually located in places close to people, such as minisplits. Handler panels with Cassette and Fan Coil ducts or systems present specific problems, but the most common is the lack of accessibility. In evaporators, efficient and thorough cleaning is very important. It becomes critical if they are located in hospitals or industries where air quality is decisive. Lack of water, drainage and electricity on site complicate cleaning or cause it to be done poorly causing long-term damage from lack of rinsing or not cleaning completely.
One more reason not to clean is the required downtime, especially in the industry, because it implies an opportunity cost with obvious economic loss, although seeing it well, the loss would be greater if it were not realized. Here expert technicians with suitable tool are required to do the maintenance fast, correct and efficient.
The above factors are important, but the most determinant is subconscious, we consider that cleaning can wait, we do not see it as a critical point. Until we notice the dirt overflowing, we hear strange noises, we smell something "weird" or the electricity bill arrives.
Specialized tools and chemicals for cleaning HVACR coils
To perform an effective cleaning it is vital to use the tools and chemicals designed to completely remove dirt from the elements that make up the heat exchangers. Cleaning chemicals are necessary because water will never dissolve greases, dusts and scale, nor will it kill bacteria. Using tools whose purpose is different from cleaning air conditioning units can be counterproductive.
In the specific case of coils, not rinsing a chemical completely causes it to remain on the surfaces forming an insulating layer that attracts more dirt and can also corrode metals. When the right tool is not used to apply the water or cleaner with sufficient pressure and angle of penetration, there is a risk of pushing the tanks into the panel, forming a barrier to the passage of air or water.
Full rinsing with plenty of water is the key to the long life and savings in energy consumption of a unit.
Suggested tools for good cleaning
1-Clean brush of soft and long bristle to remove surface dirt.
2-Dry-wet vacuum cleaner. To remove particles deeply, it is advisable to use a HEPA filter or protect yourself with a mask.
3-Comb to straighten aluminum fins. Plastic combs are for the most commonly used aluminum gauges in air conditioning and metal ones for cooling evaporators that have greater spacing between fins.
5- Flashlight or lamp to check if there is hidden incrustation, it is important to determine the type of dirt and thus choose the right chemical. Also to know if in the end it was possible to remove the dirt completely and there was nothing left between the fins.
6- Tool to unclog drains. You will save a lot of time and effort if before applying water and chemical you make sure that the waste is directed towards the condensate drain. You can use a dry-wet vacuum adapter or any other instrument that allows drainage pipes to be left free.
7- Funnel bags for cleaning minisplits and cassette units. To clean without getting dirty around or having to disassemble. They direct water and chemical into a bucket.
Tools for washing, rinsing, recirculating and descaling evolve
1-An economical option to apply the chemical in coil is to use an atomizer adaptable to liter containers to later rinse it with a hose jet or with an atomizer. The disadvantage of the atomizer is that it dispatches chemical with insufficient pressure to get the cleaner to penetrate between the fins, it has no spray angle and dirty areas remain that will be a source of accumulation of dirt and bacteria. Hose rinsing is not very accurate and parts may remain uncleaned, or parts inside or around may get wet.
2-Low pressure sprinklers. They have a manual pump and are usually of different capacities, chemical or water can be applied and it is possible to dilute the chemical in them, the pressure may not be enough to pass through some capacitors. Not recommended for rinsing due to its low volume of outlet water so it is better to use a hose or pressure washer.
3-Guns for connection to hose with dosage of liquid chemical or in tablets. Practical and economical, they allow to apply chemicals and rinse with the pressure of the water supply. They only work on capacitors.
4-Multipurpose electric pressure washer. Very practical and economical. The problem is that they usually provide more pressure than the recommended 400 psi and provide a minimum volume of water per minute. They can bend fins. They are not made to resist harsh chemicals and not all of them are dosed.
5-Portable pressure washers for air conditioning coils. There are several types; with rechargeable battery, electric with option to hose. They dispatch 2.5 gallons of water or chemical per minute with pressures of 120, 200 and 400 psi which ensures their penetrability and abundant rinsing. The advantage is that they have multiple rods and nozzles to apply in difficult places inside the units. The rechargeable battery allows you to carry water and chemical to the rooftops, inside transport units and spaces where charging with cables, chemical and hoses is not possible.
6-Vacuum cleaners for dry cleaning. They have a HEPA filter and their brushes and accessories are designed for ACR units.
7- Industrial pressure washers for coils. They are usually mobile to transport water and chemical to any place in the plant or building. They dose chemical and water at 400 – 600 psi and can be electric or rechargeable battery, they have a variety of rods and nozzles of different angles and sprinkled.
8- Equipment for cleaning and disinfection with steam. When water use is limited and sanitizing is required at the same time. Its use is not yet widespread.
Different chemicals, different results
1-Acidic base cleaners. They are ideal for descaling, polishing and quickly returning efficiency to coils, however they are highly toxic and corrosive to the skin and some materials.
They usually combine fluorhydric acid, phosphoric acid and detergents, when reacting it penetrates and lifts the salts that form crust. It requires moistening the panel before applying. They form a lot of foam product reaction with metal, its smell is strong, contact with the skin should be avoided, burning takes time to appear, it should be used with protective lenses and gloves in well-ventilated places. They are usually diluted 1:3 to 1:5 Deep rinsing is critical.
2-Non-corrosive alkaline and corrosive alkaline. Their Ph is contrary to acid and should never be mixed. Corrosive alkaline cleaners contain sodium hydroxide or potassium hydroxide along with detergents and additives, remove grease and other types of dirt, do not descale or polish as well as an acid, but are less dangerous since the burning of their contact is felt immediately and forces washing. Their pH is greater than 10 and they are usually diluted 1:2 to 1:15. They must be used with personal protective equipment.
Alkaline and non-corrosive coil cleaners can contain a mixture of surfactants, descaling agents and additives to make them as effective as a corrosive. Very sparkling and unscented. Their dilution is 1:4 to 1:15 and they do not damage the blue or gold protection of the fins, they are the most recommended to clean microchannel and spriral coils.
3-Disinfectant cleaners. They are alkaline base cleaners that in addition to removing grease and dirt, eliminate bacteria, mold and algae. They can contain the biocide plus surfactants and additives or be simply the sanitizer, form foam and are more recommended in evaporators and handlers in critical areas.
4-Tablets. The cleaner is sprayed and compacted into tablet form for use with a special gun that connects to a hose and doses chemical and water by throwing them under pressure. It is a practical way to clean large condensers and evaporators, especially when traveling or cannot transport liquid.
5-Solvent-based cleaners. They are used to remove frost, ice, cigarette smoke, grease and corrosion particles. Concentrates, they can be used in evaporators located in freezers. The benefit is its quick and minimal drying or without rinsing. Some cleaners can be flammable, they are ideal when water is not available.
In addition to energy and operational efficiency benefits, regular cleaning of coils also improves the life of system components and indoor air quality; a fact that has forced the cleaning of coils to have a regulatory character in critical areas such as hospitals, pharmaceutical plants, food and conservation.
In cooling coils, it is common for microbiological contaminants to grow. Contaminants such as bacteria, fungi and mold can form colonies between aluminum fins within air conditioning systems generating toxic allergens known as Molecular Organic Dust. POM has been associated with health problems in buildings. The accumulation of contaminants also reduces the effectiveness of heat transfer and the efficiency of the system. Frequent cleaning reduces this buildup.
Recommendations
The proper pressure for washing coils should be less than 400 psi so as not to bend the fins.
The spray angle should not be less than 15°. Make sure it penetrates the liquid perpendicular to the fins.
Apply the chemical from the bottom up to the coil and rinse from top to bottom.
Rinsing is the most important part of the cleaning procedure!
* Mayra M Lira, is the director of the company Clinest. You can write to your email: [email protected]
Outstanding: Cancun is the city with the first place in Mexico in electricity consumption. 70% of Quintana Roo's electrical energy is consumed by air conditioning systems.
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