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Types of Air Dryers, Made Easy

Types of Air Dryers

Before we talk about the different types of air dryers we need to talk about why you need a dryer. Having a dryer is a crucial part of producing high-quality air and making sure your system can keep operating smoothly. Dryers are responsible for removing the moisture and water vapors from your air stream. As we know, moisture is the enemy of all compressed air systems. It ruins the piping, can cause condensate build-up, and creates problems downstream. Now it may seem obvious that the best way to fix this is to install an air dryer, a machine built to remove condensate from the air stream.

However, the fix is not quite that simple. Yes, you need a dryer to remove condensation, but what type of air dryer do you need? Well to answer this, you need to know what your air is being used for and the quality standards for that application. Every use of compressed air is unique in its own way. Some applications require air with an extremely low dewpoint, others just need a large majority of the moisture removed, and some need super high-quality air with no moisture whatsoever in it.

To reach each one of these standards, the air needs to go through different processes. Low dewpoints can be achieved through the use of desiccant dryers, while general moisture removal can be accomplished through the use of a refrigerated dryer, and if you have a low need for compressed air, you may end up using a simple membrane dryer to remove the moisture for the health of your pneumatic tools. But what is the difference between these different types of dryers and what makes them unique?



It Isn’t as Simple as Dry or Wet Air

Picking the right dryer is not as simple as we would like. We need to break down the environment that this air is being compressed in and the uses of that air. The factors you need to be aware of are:

  • Air and environmental factors
    • Inlet air pressure
    • Inlet air temperature
    • Ambient air temperature (and water temperature if condenser is water-cooled)
    • Installation environment of the dryer
    • Maximum air flow in standard cubic feet per minute (scfm)
    • Desired pressure dew point
  • Dewpoint and relative humidity

These factors are important for properly sizing your dryer, and in some cases determining the type of dryer you need as well. The air and environmental factors are important to be aware of because at a certain temperature, the air can flow at a much slower rate than it is rated for at 100℉ and 100 PSI. Sometimes it can be difficult to determine these things as well, and if that is the case, feel free to visit our CFM calculator for dryers here. When it comes to dewpoint and the humidity of the environment, it goes hand in hand with air quality standards.

If you are in a relatively humid environment and your industry requires high quality air, you are going to need to get a different dryer than someone who may be using their compressed air in a typically dryer, cooler environment and the air quality standards are not as severe. You also need to be aware of how seasons change the conditions in your compressor room. Do you have to worry more in the winter or in the summer? The key to finding the right dryer is balance and finding equipment that can handle the highs and lows of your operation.

Each type of dryer has different applications that it excels in and others where it may fall short. And to make matters more confusing, there is no clear-cut winner overall. Instead, these individual characteristics of your application and environment need to be taken into consideration. With that in mind, there is a simple way to tell which dryer would be best suited for you, and that is the Class of Air Quality Standards in your industry. Anything Class 3 and above need a desiccant as refrigerant dryers can only go up to Class 4 Air due to the means by which the air is dried.

Now let’s break down the different types of dryers and what each one is typically used for. We will discuss the basic functions of each type of dryer so you know how and when to use each type of dryer. This way you can make the best possible decision for your air system.


The Types of Air Dryers

Refrigerant Air Dryers

Refrigerant dryers are an excellent choice for those who meet the following conditions:

  • Ambient temperature is less than 40°C/104°F
  • Prevent condensation
  • Dew point around 3°C-4°C/37°F-39°F

These dryers work very similarly to the way our air conditioning does at home. The air is passed through a heat exchanger which has been cooled off by the internal refrigeration. This process both cools the air and causes moisture to condense by reducing the temperature. Depending on the style of dryer, this process can be constant or operate on a cycle that helps improve energy efficiency. These dryers are the most energy efficient of the bunch as they allow heat transfer to do most of the work and the machine has to focus on maintaining the refrigeration level.

Refrigerant dryers pose the risk of freezing the pipes in suboptimal conditions. If the temperature of the air at the inlet is too low, it can cause the moisture to freeze as it passes through the heat exchanger and is effected by the refrigerant. Not only can the temperature cause a problem when the ambient air is too cold, but the opposite can have negative effects on the system as well. If the ambient or room temperature air is over 104°F it can become too hot for the dryer to handle and result in excess moisture continuing downstream, as well as slowing the movement of the air in your system.

Do to these restrictions, refrigerant dryers cannot reach some of the more stringent ISO Standards for industries with higher quality control. Due to this fact, these dryers have a lot of great applications and can be extremely beneficial to the health of your air system, but they cannot provide those same benefits for every application or even every location.

If your compressor is lacking an aftercooler, which you should have for the health and longevity of your system, or the compressor room has a temperature surpassing the 40°C/104°F threshold then you should invest in a High-Temperature Dryer that is built to handle those conditions. These dryers are refrigerant dryers that have been manufactured to go beyond where the traditional refrigerated dryer might fall short.


Desiccant Air Dryers

When it comes to desiccant dryers, which are also known as adsorbent, the rule of thumb is if you need a low Pressure Dewpoint or high quality extra dry air there is no question. Desiccant dryers can drop the PDP of the air down to -40°C/-40°F or -70°C/-94°F, depending on the level of drying. The ability of these dryers to drop PDP to such a low temperature is second to none when it comes to removing moisture from the air and making sure that moisture does not condensate again during use.

Now you might be wondering how exactly these dryers work. Adsorbent dryers typically consist of two different towers filled with an adsorbent called desiccant. The air is passed through one tower and as it passes over the beads, the moisture and humidity is collected by the beads from the air. The air only passes through one of these towers at a time, and by alternating which tower the air is passing through, it allows the tower that is shut off to dry the adsorbent and help extend the lifespan of the desiccant beads.

This process of drying the desiccant is often sped up through the use of purge air, air pulled from the air stream to be sent down the other tower and expelled out the bottom. Reaching such low PDPs comes at the cost of valuable air being lost to help dry the beads. It may seem detrimental to lose this valuable air, but if this was not part of the process the air quality would not be able to meet Class 1, 2, & 3 ISO Standards. Each dryer excels in different areas but at a different cost and that is why it is important to review your needs when buying new equipment.


Membrane Dryers

Unfortunately, membrane dryers, are considered the red-headed stepchild of compressed air dryers. Using condensation to remove the water vapor from the air stream, they are on there way out of the industry. The process does not yield as efficient of results as the other methods of drying air. However, that does not make them completely useless. If you are looking to simply remove condensate from your air to prevent moisture buildup in your air system, they are an affordable option and take up much less space than the other options.

Membrane dryers need to be adequately sized to the air flow to ensure the most moisture is being collected from the air stream and removed properly. These dryers can be easily overwhelmed and fail to remove water vapor which will cause problems downstream. If you choose to use one of these dryers it is incredible important to size it properly, or else you will be spending more to fix your system than the initial cost of a refrigerant dryer would have been.


Before You Buy

As you have probably noticed, there is no one size fits all when it comes to air dryers, in fact its the opposite. Each application needs something specific. These specifications mean a lot of variables need to be accounted for when considering an upgrade or a replacement.

If you are looking to get a new dryer but still need help making sure you get the right equipment, you came to the right place. All of this information on properly sizing, air purity classes, means of drying the air, are all incredibly important but can be overwhelming. If this is the case feel free to reach out to one of our representatives who are knowledgeable in compressed air and want to make sure you get the right fit.

If you would rather do it on your own, we totally understand, but we still want to make sure you get the right equipment. Feel free to use the resources on our site such as our Dryer Sizing Calculator or any of the free information located under Warthog University. Our goal is to change the way you buy compressors online and that starts with the customer having the agency to make their own choices while being informed and knowledgeable about the products.


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