Air Filters

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Most cooling towers work on the basis that ambient air is drawn over a flow of warm water, which causes some of it to evaporate and be absorbed by the airflow.

The heat required to evaporate this water is derived from the water itself. This action causes the water to cool. The net result is that the air leaving the tower is saturated with water vapour and sometimes droplets whilst the remaining water leaving the cooling tower has been cooled. This process is known as evaporative cooling.

A mechanical fan system draws air from the bottom of the tower, through the fill, assisting with the heat exchange process before then exhausting it into the atmosphere. A simple process but one which can often cause serious health and safety issues.

Part of the process of drawing air into the tower also brings with it airborne debris such as seeds, leaves and insects. This debris will settle in the fill pond and gradually rot to produce a sludge which provides a nutrient source for bacteria. In some cases this build up of debris can lead to an outbreak of Legionnaires’ disease; a potentially fatal pneumonia caused by droplet inhalation of water contaminated by Legionella pneumophila bacteria. The bacteria can multiply in conditions where temperatures are between 20-45°C and nutrients are readily available.

In order to minimise the risk of Legionnaires’ disease and comply with the requirements of the Approved Code of Practice (ACoP) L8, a regular cooling tower chemical treatment should be performed in order to clean and disinfect the system. This cleaning process removes fouling that can provide favourable environmental growth conditions for Legionella bacteria.

The normal process involves cooling tower chlorination which involves additional bio-dispersant, physical cleaning and then further post chlorination before the system is returned safely to service.

This maintenance is part of a programme that will involve the sampling and testing of water at regular intervals and is completed by specialist contractors.

Increased debris will increase the nutrient source and allow the bacteria to multiply exponentially.

Prevention is better than a cure therefore the best way to reduce the build up of debris is to stop it from being drawn into the air intake system in the first place.

Air intake filter screens, such as those manufactured by Permatron, can be located on the exterior of a cooling tower. This provides an external filter to minimise the impact of airborne debris in the vicinity.

As air is drawn through the air intake filter screen, it creates an electrostatic charge that attracts and traps airborne debris. The screens improves laminar air flow and reduces the sludge build up dramatically. Air filter screens are the first line of defence when it comes to reducing the risk of an outbreak of Legionnaires’ disease. Furthermore, the use of air filter screens reduces the use of chemicals and can reduce maintenance schedules by as much as 60%.

For further information about how air filter screens are improving the efficiency of HVAC equipment and protecting cooling towers from the potential lethal build up of bacteria, contact RAB Specialist Engineers Limited.

This article was produced by Richard Betts, Managing Director at RAB Specialist Engineer


Bio:  Richard has worked in the M&E Building Services industry for over 35-years.

In 1994 Richard formed ECEX, focusing on the M&E Building Services market and specilaising in procurement and supply of sub-contract labour to the industry. In 2012 Richard sold his interests in ECEX and formed a new business, RAB Specialist Engineers which focuses on the supply of air intake filter screens, ductwork, insulation & pipework, and key areas of building maintenance. 



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UK:  Businesses waste several hundreds of thousands of pounds on unnecessary cleaning and maintenance of heating and ventilation equipment.

Businesses throughout the Thames Valley region are paying higher energy bills and expensive maintenance costs in order to keep their heating, ventilation and air conditioning (HVAC) equipment running effectively, claims RAB Specialist Engineers.

Simply by fitting a new external air filtration device, supplied by the Newbury-based start-up firm, could result in total savings of more than £2m for many businesses operating air handling equipment in the Thames Valley area.  Made from a washable polypropylene material, the simple filter screens can be fitted over air intake equipment. The screens act as a primary pre-filtration defence against large volumes of airborne debris, which, over time, can cause extensive damage to sensitive HVAC equipment.

RAB Specialist Engineers, which provides consultancy and air handling engineering services to the building services sector, says the savings are based on figures representing just 50% of the number of businesses occupying the 12 million ft2 of office space currently available in the Thames Valley region.

Airborne debris, such as domestic waste, carrier bags, leaves, pollen and insects, is the leading cause of fouling and clogging of cooling towers, heat exchangers, air cooled chillers, rooftop units and other HVAC systems according to local entrepreneur and businessman Richard Betts.

Identifying a niche in the air handling market, and with over 30 years’ experience in the industry, Richard Betts explains how a simple preventative measure to stop airborne debris from entering HVAC equipment could save millions of pounds in unnecessary replacement and maintenance costs.

“Our research shows that when air handling equipment becomes clogged up with debris, internal components such as dirty condenser or evaporator coils restrict the airflow through the equipment and increases the amount of energy required by compressor motors to maintain optimum performance.  Studies show that air handling equipment, which is commonly used by many local business premises, will use up to 30% more energy if external air filtration equipment is not fitted. Furthermore, higher operating pressures and temperatures will reduce the life expectancy of these valuable assets and can result in compressor failure.

Essentially, a compressor is the heart of any air conditioning or refrigeration system and without it, cooling cannot take place. This can be a facility manager’s worst nightmare as compressor replacement is the most expensive repair on any HVAC system.

Rising energy prices are forcing many businesses to implement smart energy efficiency measures. Fitting air intake filter screens from an experienced company such as RAB Specialist Engineers, is one way energy and facility managers can achieve this goal, while at the same time reducing extensive maintenance costs and extending the life of expensive HVAC assets.

When you consider the cost of maintaining HVAC equipment that hasn’t been fitted with air intake filter screens in terms of servicing time and replacement parts then the screens make financial sense. Typically, businesses will see a return on investment in less than two years.

Air intake filter screens are already used extensively in a number of different industry sectors throughout the US.  Companies such as Starbucks are using them on refrigerated food displays, Harvard Law School has fitted them to filter out fine construction dust on its louvered air intake systems and Motorola has installed them on its two-way radio transmitting station located on the 108th floor of the Sears Tower in Chicago.

Here in the UK we’re dealing with an increasing number of new enquiries every day and we’ve already supplied one of the UK’s leading supermarkets with air intake screens for its cooling plant, which had become inefficient due to plastic bags and other debris blocking the filters.

Managing Director Richard Betts is currently offering expert advice and a range of engineering services to businesses looking to reduce energy costs and improve the efficiency of HVAC equipment. For a breakdown of the energy calculations and maintenance costs used by RAB Specialist Engineers, click here.


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