What Is a Refrigerated Air Dryer?
The idea behind refrigerated air dryers is simple – even if the hardware isn’t.
Compressed air goes in warm and carrying moisture. The dryer pulls that temperature down to a controlled point, and that change does the work. Once the air cools, the moisture drops out of suspension, turns into liquid, and can be separated and drained before the air goes any further.
This produces dry compressed air suitable for general industrial use.
Refrigerant dryers are used by most factories because they are cheap and work well. For water, they usually get an ISO 8573-1 Class 4 purity rating. This standard stops indoor pipes from getting liquid water in them.
Why Is Moisture a Problem in Compressed Air?
Compressing atmospheric air concentrates water vapour.
At 7 bar(g), cubic metres of compressed air hold significantly less moisture than ambient air. Excess moisture condenses immediately. In Scottish humidity, a compressor generates litres of liquid water per shift.
This moisture travels directly into distribution piping and equipment. The effects happen right away:
- Corrosion: Water sitting in the system slowly attacks the pipework. Over time, that turns into rust, leaks, and pressure losses that are hard to ignore.
- Tool Failure: Moist air strips lubrication from pneumatic tools. Once that film is gone, wear accelerates and failures aren’t far behind.
- Contamination: Moisture carries dirt and oil with it. When that ends up in the air line, finished products can be damaged or written off entirely.
- Microbial Growth: In food and pharma environments, wet air doesn’t just cause technical problems. Once moisture is present, bacteria don’t need much encouragement. They can start forming quickly – and when they do, hygiene controls, safety margins, and compliance all start to erode.
How Does a Refrigerated Air Dryer Work?
The cooling process is fully contained. There’s no venting to atmosphere – the dryer relies on a sealed refrigeration loop that circulates continuously inside the unit.
That loop isn’t designed for room air. It’s designed for the realities of compressed air at high pressure, allowing the system to cool consistently while maintaining safe, dependable operation.
- Air Entry: Saturated compressed air enters the dryer.
- Pre-Cooling: Before any active cooling happens, the dryer reuses cold from the outgoing air to knock the edge off the incoming flow. That simple handover reduces the load on the refrigeration circuit.
- Active cooling: The compressed air first passes through a heat exchanger. Here, heat is transferred into the refrigerant circuit. That pulls the air temperature down to its dew point – typically around 3°C.
- Condensation: As the temperature drops, the air can’t hold on to that moisture any longer – so it starts to fall out of suspension.
- Separation: Those droplets are then caught by a water separator, and an automatic drain valve clears the condensate from the system before the air moves on.
- Reheating: The dry air is reheated by the incoming air. Reheating prevents sweating on distribution pipes.
Atlas Copco Dryer Ranges
Design Air (Scotland) Ltd supplies specific Atlas Copco models tailored to different operational requirements.
- FX Series: Compact, simple units. Suited to smaller workshops or constant demand applications.
- FD Series: Robust industrial dryers designed for high reliability in varying ambient conditions.
- FD VSD (Variable Speed Drive): These units adjust the refrigerant compressor speed to match airflow demand.
- Note: FD VSD models are most effective in facilities with variable air demand. Energy savings are lower in constant-flow environments.
Correct Sizing Matters
An undersized dryer cannot stabilise the dew point.
The cooling circuit can’t keep the target temperature if the airflow is too high or the inlet temperature is too high. The dew point goes up. Water passes straight through the system. Incorrect sizing is a major cause of moisture problems.
System inefficiencies can be identified with a Compressed Air Energy Audit.
When Is a Refrigerated Dryer Suitable?
Refrigerated dryers are the standard solution for indoor installations.
They maintain a pressure dew point of +3°C. This is sufficient for manufacturing, automotive, and assembly tasks where the factory temperature never drops below freezing.
The +3°C Limit
A refrigerated dryer has a hard lower limit. Once you push past a pressure dew point of about +3 °C, the condensed moisture starts to freeze inside the heat exchanger. At that stage, cooling the air any further doesn’t help – it creates blockages and risks damage instead.
Cold Weather Risks
Cold conditions create their own problems.
Any pipework that runs outdoors, or through spaces without heating, is exposed to freezing temperatures. If those surfaces drop below the air’s dew point, the moisture still in the system doesn’t drain – it freezes.
Once ice starts forming inside the pipes, flow quickly becomes restricted. Sometimes it stops altogether.
You should use desiccant dryers instead for jobs that need dew points to be below zero.
Maintenance and Common Issues
Regular maintenance prevents water carryover.
- Clean Condenser Coils: When dust builds up, airflow suffers. As it accumulates, airflow is choked back – this makes cooling performance tail off, and the dew point edges higher.
- Check Drain Valves: A blocked drain valve fills the separator with water. Water re-enters the airflow. Zero-loss electronic drains reduce air loss and prevent stuck-open failures.
- Service Intervals: Routine checks should be part of an air compressor service plan. This ensures the refrigerant charge and electrical components are healthy.
Dryers showing consistent fault codes or high dew point alarms may require a professional compressor repair service. This prevents damage to downstream equipment.
Compliance and Standards
Compressed air systems must meet specific regulatory standards.
- ISO 8573-1: This defines air quality classes. A functioning refrigerated dryer delivers Class 4 air (Water).
- F-Gas Regulations: The refrigerants in these systems aren’t open for general handling. EU Regulation 517/2014 still applies in the UK, and it clearly restricts who is allowed to work on them. Any maintenance involving the refrigeration circuit has to be carried out by an engineer – but they must have the appropriate F-Gas certification.
- WRAS: To follow water authority rules, condensate discharge to mains needs to separate oil and water.
System performance can be verified via an ISO 8573 air quality test.
Refrigerated vs. Desiccant Dryers
| Feature | Refrigerated Dryer | Desiccant Dryer |
| Dew Point (PDP) | +3°C | -40°C to -70°C |
| Primary Use | General Industrial / Indoor | Critical / Outdoor / Medical |
| Typical Industries | Manufacturing, Machining, Workshops | Pharma, Food Processing, Electronics |
| Cost | Lower Capital & Running Cost | Higher Capital & Running Cost |
| Maintenance | Low | Moderate to High |
Conclusion
Refrigerated dryers take out a lot of moisture from compressed air.
They stop rust, cut down on downtime, and meet ISO 8573-1 Class 4. Atlas Copco FD and FD VSD dryers work well and cost little to run on Scottish industrial sites.
Secure Your Air Quality
Make sure that systems are the right size and follow the rules.
For expert help with choosing, installing, and maintaining a dryer, get in touch with Design Air (Scotland) Ltd.
