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Refrigeration dryers: Selection matters

11 August 2015

BCAS is asked for its views on a wide range of compressed air topics. Here, Greg Bordiak, technical officer, focuses on one of the questions that he is frequently asked: Are all refrigeration compressed air dryers the same?

The refrigeration dryer is often vital to the production of compressed air in terms of both output and quality, so why do purchasers treat them as commodities? 

Popular because of their adequate performance in general-purpose compressed air applications, refrigeration dryers are relatively low cost, easy to maintain and well supported by manufacturers and distributors. 

Are all refrigeration dryers therefore the same, and should price and delivery be the top and sometimes only criteria when deciding which brand or type to select? 

What purchasers should be looking at first and foremost is what dew point is required? Then they should consider the total cost of ownership, which includes, reliability, maintenance, and warranty.

The dew point performance has to be the most important parameter, otherwise why buy a dryer?

Selecting the correct dew point is usually fairly simple. Machinery manufacturers will often specify the dew point required for correct operation or – even better – give an ISO 8573 classification, which includes permitted humidity, particulates and hydrocarbon contents. 

There are some industry norms and specifications too. For example, if you are a food manufacturer and adhere to the British Compressed Air Society’s Best Practice Guideline, written in conjunction with the British Retail Consortium (BRC), then compressed air that does not come into contact with the product can be 3°C pressure dew point. This would need to be -40°C if compressed air was to come into contact with the product. 

So are all refrigeration dryers reaching the same dew points? A BCAS member believes this is not the case. 

The member, who is frequently measuring dew points on all brands of dryers, argues there are some products which, at the rated flow and the not too arduous British temperatures, are only hitting a dew point of 7°C. The member believes this is sometimes due to a lack of maintenance, and sometimes due to the actual dryer type or its quality. 

Refrigeration dryers are typically selected for use in ‘general purpose’ compressed air applications such as operating pneumatic tools, general spraying, blasting, pneumatic cylinders and simple valves and actuators. 

The total cost of ownership varies significantly across the competitive offerings in the UK. When calculating the life cost it is important to add the capital, installation, electrical input and maintenance costs with another cost, which often gets omitted – the cost of the pressure loss through the dryer, which can be significant and can increase if maintenance is neglected. 

The other parameters are not as dramatic but can still hide some pitfalls. Maintenance costs for refrigeration dryers should be very low and limited to cleaning and filter changing. If the product loses gas, consideration should be given to the regulations as to who can carry out the maintenance on the products. For most industrial units this means an FGAS qualified person will be required. 

The warranty is also something to consider carefully. Some manufacturers offer three years with no red tape, simply requiring proof of following the manufacturer’s instructions and correct installation, which is important for ventilation. Others may only offer one-year statutory warranty in order to keep the capital price down. 

Another important parameter is the maximum inlet temperature permissible. In the UK we see 30°C occasionally, but the temperature in a badly ventilated compressor room could easily be 40°C, giving a 50-55°C inlet temperature to the dryer. A compressor with a dirty, built-in after cooler could add another 5°C easily, and we’re then at the maximum temperature for many refrigeration dryers. 

If the purchaser is sending plant to Southern Europe, for example, then the scenario is even worse. 

Although important considerations, perhaps questions relating to price and availability should be lower down the list when it comes to choosing your next refrigeration dryer?