Heat regeneration dryers are desiccant dryers that use heat to regenerate the desiccant bed. These dryers are comprised of two towers that contain desiccant and valves that shunt the compressed air from one tower to the other for drying. Heat regeneration dryers regenerate the desiccant by heating the desiccant and forcing air over it. This air absorbs the water adsorbed by the desiccant allowing it to dry more air.

Advantages of heated dryers are less cost to operate and less compressed air is used in the regeneration of the desiccant compared to heatless dryers. Disadvantages are shorter desiccant lifespan and higher purchase cost compared to heatless dryers.

Heated dryers are usually used for volumes greater then 1000 scfm. These dryers have a dew point of -40 F.

There are three important factors when sizing a heatless dryer. These factors are the volume of air, the pressure, and the temperature of the air. Air driers are rated at 100 psig and 100 F. The cost of a heated dryer is determined primarily by the volume of air it can process in scfm and the type of dryer.

Internally heated air dryers use conduction to heat the desiccant and uses some of the dried air to regenerate the desiccant. This heating of the desiccant reduces the life span of the desiccant more than other heated types. This type of dryer uses about 2% of the compressed air of the system for regeneration, making it one of the least expensive to operate. It has a cycle time of four to eight hours.

Externally heated air dryers use some of the dried air and heat it before using it for regeneration. This air is not purged from the system; it is passed through the the drying tower and merged into the the stream. It has a cycle time of four to eight hours.

Externally heated purge air dryers heat some of the dried air for regeneration. This air is then purged from the system carrying with it the water absorbed from the desiccant. The dryer uses about 7% of the compressed air in the system for regeneration and have a cycle time of four to eight hours.

External blower purge air dryers use outside air to heat and regenerate the desiccant. After regeneration, this air is purged from the dryer. This type of dryer has a four hour cycle time, three hours with the heater on and one hour with the heater off so the desiccant can cool. There is a small dewpoint spike for a few minutes after the tower is switched to drying. Blower purge dryers are the most expensive to purchase, but they do not use any compressed air for regeneration.