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Go with the airflow

05 August 2017

Richard Betts discusses the importance of airflow in heating and cooling systems. 

Airflow is the single most critical element in the correct operation of air heating and cooling systems. Despite this most systems do not have the correct airflow, which results in compressors overheating, fans blowing hot air and the heat exchangers, at their heart, which cannot provide the capacity and comfort that they were designed to achieve.

Accurate cooling or heating analysis cannot be performed, system performance cannot be measured, and the servicing or commissioning process will be compromised if airflow is anything but correct.

We heat and cool air, humidify it, dehumidify it, clean it, move it, supply it, return it and try to monitor it. All of these processes are jeopardised if the designed airflow to the system is restricted.

Measuring, monitoring and maintaining correct airflow should be the first step when servicing equipment. It is the key component for proper equipment operation. Energy consumption is dramatically increased when compressors and fans have to work harder to maintain design output.

Also, if a compressor needs to be changed and the technician has not properly determined why it failed, the new compressor will fail for the same reasons. Indeed compressors installed by service technicians fail at six to seven times the rate of original equipment.

In most regions of the UK, pollen is a major contributor to the fouling of cooling equipment. This, combined with general debris caused by foliage, refuse and other airborne particulates, can have a significant impact on the day-to-day running of heating and cooling equipment.

Adding external filtration
No matter what food sector you work in there will be a requirement for cooling and adequate ventilation. HVAC systems vary but usually start with a cooling tower before moving onto the chiller and air handling units. Whether you have forced or induced draft cooling towers one of the major responsibilities is maintaining a clean water environment.

In any air handling unit, one of the major maintenance costs is the replacement of disposable filters. Filters are replaced once the pressure differential reaches a certain level. The dirtier the filter, the higher the pressure differential and the sooner you need to change the filters. There are many options available for HVAC retrofit to improve performance but one of the simplest methods of reducing demand for energy and labour resource is to protect the equipment that you already have. 

It has always been difficult to add filtration to cooling equipment (water and dry air cooled), small condensers and cooling towers, but products such as the RABScreen external filtration can now offer a solution to air intake debris, contaminated coils and clogged cooling tower sumps. These screens are fitted externally to help prevent contaminates in the air entering the system. This can save money by extending the life of disposable filters. It can also save as much as 30% of input energy on chiller coils and saves labour by reducing cleaning and chemical use.  As a result, the typical return on investment of fitting air intake screens is less than six months. 

During the summer months coil cleaning, changing of internal air filters and general HVAC maintenance must be carried out more frequently, consuming much of the engineering team’s routine programmed maintenance schedule.

Similarly, the correct monitoring of airflow through cooling towers will help to minimise the risk of decaying debris such as insects, seeds and pollen forming a nutrient source for the legionella bacteria.

Keeping HVAC airways clean will pay dividends as by doing so energy consumption is considerably reduced. It reduces the regular maintenance needed on cooling systems; and increases the efficiency of the equipment ensuring its long life well into the future.

Richard Betts is managing director of RAB Specialist Engineers.

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