The advantages of thermal mass refrigeration dryers

The load on a refrigeration dryer depends not only on the volume of compressed air to be dried (the grey area on the graph below), but more importantly on how much water the incoming compressed air contains. This volume of water (moisture) increases as the temperature rises. The load on refrigeration dryers therefore increases dramatically when ambient temperatures are high – such as during the summer (the yellow curve on graph below). In contrast, the lower temperatures we experience during the winter months (the teal curve on the graph below) reduces the load on refrigeration dryers.

To maintain a stable pressure dew point throughout all of these fluctuations, refrigeration dryers should always be designed to provide sufficient performance during peak load times. They should also have additional capacity in reserve. Aside from these fluctuations in air flow and temperature, the output of a refrigeration dryer will constantly vary between 0 to 100% of capacity. 

So how can you ensure your refrigeration dryer is operating at its optimal energy efficiency under these circumstances? One way Kaeser has achieved this result in the latest Secotec range of refrigeration dryers, is with thermal mass control. This ensures energy is only used as and when needed across the entire load range – resulting in exceptional savings. 

How does thermal mass control maximise energy savings? 

Refrigeration dryer load constantly fluctuates between 0 and 100%. Using the Kaeser Secotec refrigeration dryers as an example, here – unlike conventional partial-load control systems – the thermal mass control precisely adjusts electrical power consumption during all load phases. 

In fact, almost 60% of energy cost savings can be saved with the Secotec refrigeration dryers, compared to refrigeration dryers with hot gas bypass control running at an average of 40% of capacity. As an example, the Secotec TF 340 model typically saves 20,000 kWh/year based on 6,000 operating hours. At a power cost of 15 cents/kW/hr that would equate to $3,000.00 of savings per annum! 

The graph below demonstrates the electrical power consumption under nominal conditions for a number of different refrigeration dryer control technologies.

The reason such results can be achieved is because in contrast to conventional systems, the thermal mass in Secotec dryers always remains cool. This means compressed air can be dried effectively even during start-up phases. The high-quality insulation around the thermal mass also helps to keep energy usage to a minimum. 

Compressed air drying with Secotec refrigeration dryers not only ensures exceptional energy efficiency, but also, thanks to their impressive capacity, provides low-wear operation. 

In conventional refrigeration dryers with switching operating modes but no additional thermal mass, the heat exchanger material itself is used as the thermal mass. In these dryers it is therefore necessary to switch the refrigerant compressors and fan motors on and off much more frequently, in order to maintain the required cooling performance. 

To reduce switching frequency and wear, the refrigerant circuit therefore only switches on at much higher pressure dew points. The resulting fluctuations in the pressure dew point negatively affect drying performance. This can be risky, since corrosion can take hold even with relative compressed air humidity of 40%. This means that corrosion can occur even without condensation formation. 

Refrigeration dryers such as the Secotec range from Kaeser on the other hand, ensure long-life operation thanks to their high thermal mass storage capacity. Once the thermal mass has been charged, the refrigerant compressor and fan motor can remain switched off for much longer without impacting pressure dew point stability.

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