Maintaining air quality where a clean atmosphere is required can be at odds with maintaining uniform comfort temperatures. The secret is close control of the incoming air temperature and velocity. Eric Fenton of Reznor explains.
Specialised environments, such as ‘clean room’ manufacturing, present particular challenges in terms of air quality and heating. The prime requirement is obviously to maintain internal air that is free from dust particles and other contaminants that might jeopardise the production process.
A regular air change rate, involving the introduction of large volumes of fresh filtered air, will achieve this. However, pumping untempered air into the building will cause sharp dips in temperature that may leave staff shivering and uncomfortable. Equally important is close control of supply air temperature, otherwise overheating will occur.
The ideal solution can be achieved using a heating system that inputs large volumes of filtered air without significant air movement. Air quality will be maintained by slight pressurisation of the interior, which keeps air moving gently through the building by forcing ‘old’ air out via natural ventilation points and replacing it with ‘new’, filtered air.
However, once steady state conditions are reached within the building – ie. the internal temperature is appropriate for working and the air quality suitable for the manufacturing process – the temperature of the incoming air becomes critical. It must match internal temperatures by +/-1°C, otherwise comfort conditions may be compromised as the temperature fluctuates with the input of fresh air.
Close control of the discharge temperature of the fresh air is essential. This can be most easily achieved using a specialised fast response modulating burner control on the heater, as was the case with the Reznor unit supplied to Safeline UK Ltd.
Safeline is the world leader in the manufacture of metal detection equipment. It custom-makes machines for detecting minute fragments of metal in pharmaceutical, food and chemical processing. The company produces 6,000 complex metal detection units each year – around one quarter of the entire global market. The machines use patented Zero Metal Free Zone technology to ensure highly accurate metal detection sensitivity.
Safeline’s manufacturing processes necessitate a clean environment and a high level of air extraction and consequent replacement with tempered make-up air. Fresh, filtered air is delivered into the building at controlled velocity and temperature to rebalance internal pressure, maintaining both the required air quality and a constant 19°C comfort temperature.
A heating and make-up air system comprising six Reznor RPVE 2095 gas-fired air handling units, equipped with 409 grade stainless steel heat exchanger and fast response modulating burners, was installed.
The units were positioned externally, mounted at 4.5m from floor level on steelwork stillages, to ensure the heating process was entirely separated from the ‘clean room’ production process.
Warm air for comfort heating is introduced into the working area through six perforated pvc ducts. Air is forced into the duct, inflating it and forming ‘mini nozzles’ at each of the small perforations along its entire length enabling the tempered air to permeate the atmosphere at controlled temperature and speed. The result is uniform temperature, reduced stratification and air distribution that is even throughout the building.
The fast response modulating burners in the Reznor air handling units ensure that the air is delivered at critical temperature; the perforated ducts control the velocity. Slight air pressurisation is created in the building that effectively maintains a constant natural through-flow of air.
In Safeline’s case, the Reznor system was also fitted with air pressure sensors that ensure the correct levels of make-up air are introduced as necessary, in order to compensate when air is mechanically extracted following use of process spray booths.
The overall result is a contaminant-free atmosphere that is also comfortable for employees – the ideal clean room working environment.
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