How to Choose between Desiccant Air Dryers (Regenerative) and Refrigerated Air Dryers
An air dryer is an important part of every compressed air system as it keeps compressed air free of moisture and contamination. Regenerative type desiccant air dryers and refrigerated air dryers both provide dry, high-quality air, but there are significant differences in how they work and the pressure dew points they can achieve.
Understanding these distinctions is important because the type of air dryer used plays a major role in the quality of compressed air, as well as system performance and operating costs. This blog will explore both technologies, highlight four key differences and provide guidance on the selection process.
Why Do I Need a Compressed Air Dryer?
Air compressors function by ingesting ambient air and compressing that air into a smaller volume. As a normal part of this process, moisture is concentrated. The resulting water vapor condenses into a liquid as the compressed air cools after leaving the compression chamber and if not effectively dried, can enter the distribution system.
Without an air dryer, excess moisture can accumulate and result in the following:
Impure air
Moisture trapped within the system can cause contamination that will reduce the quality of the compressed air. This is a dire situation in industries, such as food, medical device, pharmaceutical and electronics manufacturing, with strict air purity standards. (For detailed information on ISO 8573-1 Compliance for Compressed Air Quality, please see this blog.)
Poor product quality
Moisture and contamination within the compressed air system can be transferred to products as they are manufactured, which can reduce the quality and integrity of finished goods.
Equipment failure
Too much moisture results in rust, corrosion and contamination within the compressed air system. These conditions may cause failure of system components and connected equipment and tools.
Poor equipment performance
Because pneumatic tools and equipment rely on efficient passage of air throughout the system, blockages caused by rust and contaminants can prevent the equipment from performing to specifications.
While air dryers can prevent these issues, choosing the right technology is essential to ensuring dry, contamination-free air that meets the air purity requirements of the application. Below we will explore and compare two common air dryer types.
Understanding Refrigerated Air Dryers
A refrigerated compressed air dryer cools the air using heat exchangers, a refrigerant circuit and compressor. Incoming air is chilled, which causes the moisture to condense and collect in a separator until it is drained from the system, then, in most refrigerated dryers, the air is reheated by warm inlet air before entering the distribution system. Refrigerated air dryers are energy efficient, low maintenance, and durable. They are suitable for use in standard manufacturing and other applications that require air with no visible moisture and those with ISO Quality Classes 4, 5 and 6.
Understanding Desiccant Air Dryers
Desiccant air dryers for compressed air feature two towers filled with desiccant material. In operation, one tower actively removes moisture from the compressed air that flows through it, while the other tower regenerates, or removes moisture from, the desiccant until it is sufficiently dried. When material in the active tower becomes saturated, the dryer reverses operation so the tower with regenerated desiccant begins to dry treated air while the other tower regenerates the saturated desiccant. Desiccant materials are typically activated alumina, silica gel or molecular sieve. Desiccant air dryers are ideal in low-temperature climates where the compressed air is needed outdoors in winter and applications that require very pure and dry air, such as medical device, pharmaceutical and electronics manufacturing, as they can produce air that achieves ISO Quality Classes 1, 2 and 3.
4 Differences Between Refrigerated Air Dryers and Desiccant Air Dyrers
As you can see, these air dryer technologies have very different operating principles, but there are other important distinctions, as well. We will explore the differences between refrigerated air dryers and desiccant air dryers below.
Key differences between a refrigerated air dryer and a desiccant air dryer include:
| Operating principle | A refrigerated compressed air dryer dries the air using a heat exchange mechanism, while desiccant dryers for compressed air use absorbent materials to attract and remove moisture. |
| Costs | A refrigerated air dryer has a lower upfront cost, moderate maintenance requirements, and doesn’t require purge air, so it offers a lower operating cost than a desiccant air dryer, which has a higher initial cost and needs to have the absorbent material replaced on a regular basis. |
| Performance | Desiccant air dryers are capable of reaching a very low dew points of about -40°F or lower. In comparison, refrigerated air dryers can bring air down to a dew point of around 39°F. This means desiccant air dryers can get the air very dry, making them the more suitable choice in industries with significant moisture removal needs. (For more on how dew point impacts compressed air quality, please see this blog.) |
| Operating environment | Due to their different operating principles and design, the environment in which the dryer needs to be installed can be the deciding factor on which technology is best suited for the application. |
Questions to Answer When Choosing an Air Dryer
Understanding the key differences between a refrigerated air dryer and a desiccant air dryer will help make the selection process easier, as the required quality of air for the application and the location and operating environment play a significant role in which technology will be the best fit.
When selecting an air dryer, be sure to ask the following questions:
- Capacity? Maximum, average and minimum compressed air flow the dryer will need to handle.
- Pressure? Maximum & minimum.
- How dry does the air need to be for the application? Some industries, such as food and beverage, medical device and electronics manufacturing, must have very dry, very pure air to meet industry standards. However, other, less-regulated applications – such as painting booths – may also need very dry air to ensure product or finish quality. It is important to know if your application has a particular dew point and ISO air quality class requirement when selecting an air dryer.
- Maximum compressed air temperature at the inlet of the dryer and maximum ambient temperature? Most industrial compressed air dryers are rated at 100 degrees F at the inlet, and 100 degrees F ambient temperature. Higher temperatures will reduce dryer capacity, lower temperatures will increase dryer capacity.
- Compressed air demand? Both refrigerated and desiccant dryers offer features enabling improved efficiency for compressed air systems that have varying flow demands. For these applications it’s usually best to go with a cycling type refrigerated dryer or a desiccant dryer with dew point based controls which allows them to suspend operation when at less than full capacity.
Answering these questions should help guide you to the best air dryer type for the application, which is crucial in providing the proper air quality level, especially in industries that must meet a specific ISO air quality class standard. For assistance in choosing between a desiccant and a refrigerated air dryer, please reach out to the air compression experts at JHFOSTER.
