What Is the Actual Achievable Pressure Dew Point (°C) of a Refrigerated Air Dryer?

Product brochures from different manufacturers list various rated pressure dew points for refrigerated air dryers, 

including 0°C, 1°C, 1.6°C, 1.7°C, 2°C, 3°C, 2~10°C and 10°C (10°C can only be found in overseas product literature). Such inconsistent data creates difficulties for users during equipment selection. 

Therefore, an objective discussion on the practical achievable pressure dew point of refrigerated air dryers carries substantial practical value.

Normally, the final cooling temperature of compressed air inside the evaporator is 3–5 °C higher than the refrigerant evaporation temperature. 

Excessively lowering the evaporation temperature brings no practical benefit. In addition, limited by the efficiency of the air-water separator, 

a small amount of condensed water will re-evaporate into water vapor during heat exchange inside the pre-cooler, raising the moisture content of compressed air.

Taking all these factors into consideration, it is extremely challenging to maintain the pressure dew point of a refrigerated air dryer below 2°C. 

Rated values such as 0°C, 1°C, 1.6°C and 1.7°C often contain more commercial promotion elements than practical performance, which should not be over-relied on.

In practice, achieving a pressure dew point below 10°C is already a strict requirement for manufacturers. 

The Machinery Industry Standard JB/JQ209010-88 Technical Specifications for Refrigerated Compressed Air Dryers specifies that the pressure dew point 

of refrigerated air dryers shall be 10°C (under corresponding operating conditions). 

Meanwhile, the national recommended standard GB/T12919-91 Purification Equipment for Marine Control Air Supply stipulates the atmospheric dew point 

of refrigerated air dryers at -17 ~ -25°C, equivalent to 2~10°C under 0.7 MPa working pressure.

Most domestic manufacturers specify a range for the pressure dew point of refrigerated air dryers (for instance, 2–10°C). 

The lower limit ensures no icing occurs inside the dryer even under minimum load conditions, while the upper limit defines the moisture content standard to be achieved under rated operating conditions. 

Under favorable operating conditions, it is feasible for a refrigerated air dryer to deliver compressed air with a pressure dew point of approximately 5°C. This range marking method can be regarded as rigorous.