What Size Refrigerated Dryer Should I Buy?


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Although it seems obvious, sizing a compressed air dryer is not as simple as merely matching the size of the air compressor.

When you are based somewhere like Western Australia, you need to understand that we have a wide range of temperatures over the year so you need to ensure that your dryer can perform under all these conditions to ensure your compressed air meets your equipment’s requirements.

Air dryer ratings are affected by a number of factors, the most important of which are the inlet air pressure, the temperature of the inlet air, and the temperature of the ambient air in which the unit must operate. In Western Australia, these are quite often beyond the sizing of the dryer you choose so you need to ensure you speak to Nessco Pressure Systems the experts in compressed air.

Operating the dryer at lower than rated pressure causes higher than normal air velocities inside the dryer, making it harder to remove the moisture. Higher than rated inlet air temperatures introduces more moisture loading to the dryer, because for every 6c increase in air temperature, the amount of water vapour roughly doubles, making the refrigerant circuit work harder or loading the desiccant more. And because the moisture inside the dryer releases heat when it condenses, the heat exchanger circuit inside the air dryer (refrigerant types) needs adequate ambient air (or water) temperatures to remove the heat.

A typical worst-case scenario might be during the hottest, most humid day when the compressors are fully loaded during a system peak.

In order to prevent moisture from overwhelming the dryer, its capacity must be adequate to compensate for any excessive operating conditions.

You may ask if the inlet air temperature is cool, my pressure is high, and ambient conditions are much lower than specifications, can I reduce the size of the dryer? Well, the answer is yes, but this causes another problem: pressure differential. Passing more than rated air flow through a dryer causes significantly higher pressure differential than rated to develop across the dryer. This pressure differential causes the compressor to consume more energy due to higher than desired cycle frequency and higher discharge pressure.

Oversizing the dryer, on the other hand, causes less pressure differential, and if the dryer you select is a cycling style, its power consumption will reduce during normal conditions saving electricity costs.

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