When your process depends on very dry and clean compressed air, moisture isn’t just an inconvenience – it’s a genuine contamination and reliability risk. That’s why a Desiccant Dryer is often the right choice for industries like food and beverage, breathing air, and any site where pipework or plant sees winter temperatures that can drop below the safe operating window of a refrigerated dryer eg 3C.
Below is a practical guide to why dryness matters, where it matters most, and how to choose between heatless and heat-regenerative desiccant drying.
The real problem with moisture in compressed air
Compressed air naturally contains water vapour. As air is compressed, that vapour becomes concentrated – and once the air cools anywhere in the system (aftercoolers, receivers, distribution pipework, point-of-use), water condenses.
That condensed water can lead to:
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Microbial risk (especially when air contacts product, packaging or contact surfaces)
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Corrosion inside receivers, pipework, valves and pneumatic devices
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Product defects (smearing, fish-eyes in paint, poor adhesion, inconsistent filling/packing)
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Instrument and control issues (sticking valves, drifting pneumatics, blocked silencers)
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Freezing in cold areas
A properly specified Desiccant Dryer targets a much lower pressure dew point (PDP) than refrigeration (which can only achieve 3C) – typically -40°C PDP (and lower when required), meaning the air stays dry even when temperatures fall.
Food and beverage: dryness and cleanliness protect product, brand and compliance
In food and beverage, compressed air is often used for:
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blowing and conveying
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filling, capping and packaging operations
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product drying and air knives
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actuating valves in hygienic process areas
Where compressed air can come into direct or indirect contact with product, packaging, or food-contact surfaces, contamination control becomes critical.
ISO 8573-1 and BCAS best practice (food grade air)
ISO 8573-1 expresses compressed air purity as [Particles : Water : Oil].
BCAS food and beverage guidance (Best Practice Guideline 102 in an earlier published edition) sets out recommended ISO classes for direct contact and indirect contact, and also highlights microbiological concerns and verification methods.
You’ll commonly see:
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Direct contact: ISO 8573-1 [1:2:1] (Particualte class 1, moisture -40°C PDP and oil class 1)
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Indirect contact: ISO 8573-1 [1:2:1] (Particualte class 1, moisture -40°C PDP and oil class 1)
Therefore it is critical to install a desiccant dryer with adequate filtration for both contact and non contact applications in this market sector.
Breathing air: dew point must prevent condensation and freezing (EN 12021)
Breathing air has its own rules because the risk to the user are far higher.
Under BS EN 12021, there must be no free liquid water, and the air needs a dew point low enough to prevent condensation and freezing. Where the temperature of use/storage is known, the pressure dew point must be at least 5°C below the lowest likely temperature. A refrigerant dryer can therefore be used if the ambient temperature does not drop below 8C during the year. If it does drop below 8C, then it is a legal requirement to use a desiccant dryer to ensure safe use of breathing air.
Beyond food, beverage and breathing air, desiccant drying is commonly justified where moisture directly impacts quality or reliability, for example:
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Laser cutting & instrumentation air
Dry, clean air helps avoid moisture-related issues in sensitive valves, controls, and high-performance processes (especially where air quality is part of repeatable cut quality and machine reliability).
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Pharmaceutical / medical packaging and clean manufacturing zones
Where compressed air can contact packaging or clean environments, low moisture reduces condensation risk and supports contamination control.
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Painting, powder coating, printing
Moisture can cause defects (blistering, fish-eyes, poor adhesion) and inconsistent results – low PDP air is often critical to ensure high quality.
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Outdoor process skids & pneumatic controls
Anything outside (or partly outside) is vulnerable to winter freezing and water condensing in the pipework.
Heatless vs heat-regenerative Desiccant Dryer: what’s the difference?
Heatless (pressure swing adsorption):
A heatless desiccant dryer regenerates by using a portion of the dried compressed air as purge air. Typical purge losses are often in the region of 15–20% of dryer rated flow. These are often used in small to mid sized systems, they are robust and have a lower upfront cost.
Heat-regenerative (heated / blower purge / “zero purge” variants)
Heat-regenerative designs use added heat (and sometimes a blower) to regenerate the desiccant more efficiently, reducing the amount of compressed air sacrificed as purge.
Depending on design, purge consumption can be much lower than heatless – and some blower/closed-loop concepts aim for near-zero compressed air purge.
These are often used for larger flow rates and plants that operate 24/7. They have a higher capital cost but offer reduced running costs.
If you would like to discuss your air treatment requirments further, please contact the team on 01359 272828 or email david.wood@avelair.co.uk