A Compressed Air Dryer is commonly rated for a specific moisture level (Dew Point) for a certain volume of air flow (CFM). This flow rating is typically based on a set of standard conditions (100 PSIG, 100°F inlet temperature, and 100°F ambient temperature). When conditions vary from this, you will want to reference your air dryers Correction Factors to determine it’s Actual Capacity.

Pressure – The water vapor content of air varies inversely with pressure—if pressure increases, it squeezes moisture out. Therefore, the higher the pressure, the better your dryer will perform.

Inlet Temperature – The water vapor content of air varies directly with temperature: if temperature increases, the air’s ability to hold water increases. As a rule of thumb, every 20°F rise in inlet air temperature may double the water load on a dryer. Therefore, the higher the temperature, the poorer your dryer will perform, and so it’s actual capacity is reduced.

Ambient Temperature – The Correction Factors for a refrigerated air dryer will take ambient temperatures into consideration. Much like the inlet temperature, the higher the Ambient Temperature, the worse the dryer will perform. However, keep in mind that Ambient Temperatures are also important when calculating the Actual Capacity of a desiccant dryer since there is a strong correlation between Ambient Temperatures and Inlet Temperature, coming from the air compressor.

By way of example, let’s take a look at the Capacity Correction Factors below for an RGD Refrigerated Dryer.

Let’s say we have an air compressor producing 900 CFM at 80 PSIG, with a discharge temperature of 110°F. The compressor room is a consistent 90°F and also in there we have RGD Dryer with a flow rating of 1,000 CFM. Will this dryer be sufficient?

Using the top table we find that at 80 PSIG & 110°F we have a correction factor of .82. One the bottom table we see the ambient temperature of 90°F has a correction factor of 1.06. The math works out to 1,000 x .82 x 1.06 = 869.2. So under this scenario, the dryer rated at 1,000 CFM won’t be sufficient to meet the actual demand of 900 CFM. At a minimum, you would need a dryer with the capacity rating of 1,035.5 (900 ÷ 1.06 ÷ .82) to meet the demand, under these conditions.