A refrigerated air dryer removes moisture from compressed air by cooling it to a low temperature, causing water vapor to condense into liquid water, which is then drained from the system. Similar to a home refrigerator, it utilizes a refrigeration cycle to cool a medium that the compressed air flows through, lowering its dew point and preventing condensation in downstream equipment. After cooling and moisture removal, the dry air is reheated, often by exchanging heat with the incoming hot air, to prevent re-condensation in the distribution system.
The main types of compressed air dryers are refrigerated, desiccant, and membrane dryers. Refrigerated dryers cool the air to condense moisture, desiccant dryers use a material to adsorb moisture, and membrane dryers use a semi-permeable membrane to separate and remove moisture.
Refrigerated air dryers
How they work: Cool the compressed air to a low temperature, causing moisture to condense out as liquid water.
Variations: Include both cycling and non-cycling models.
Desiccant air dryers
How they work: Use a desiccant material to absorb moisture and contaminants from the air.
Variations: Different regeneration methods include:
Heatless: Use a portion of the dried air to regenerate the desiccant.
Externally heated: Use external heat for regeneration.
Blower purge: Use a blower to regenerate the desiccant and are more energy-efficient.
Heat of compression: Use the heat generated during the compression process to regenerate the desiccant.
Membrane air dryers
How they work: Use a semi-permeable membrane to separate moisture from the compressed air.
Key feature: They have no moving parts and do not require an external power source to operate.
Yes, a refrigerated air dryer removes moisture by cooling compressed air to condense the water vapor into liquid. As the air cools, moisture turns into liquid water droplets, which are then separated and drained from the system. The dry air is typically reheated to prevent condensation from forming on downstream piping.
How it works
Cooling: The dryer uses a refrigeration system to cool the incoming compressed air, similar to how a refrigerator cools its interior.
Condensation: When the air is cooled, its ability to hold moisture decreases, causing the water vapor to condense into liquid water. For every 50F(10℃) drop in temperature, the moisture-holding capacity of air is reduced by 50%.
Separation: The condensed water droplets are separated from the air stream in a moisture separator.
Draining: The water is then collected and drained from the dryer.
Reheating: The dry air is reheated to a near-room temperature to prevent condensation from forming in the pipes after it leaves the dryer.
The most energy-efficient compressed air dryer depends on the application and required dew point, but for general use, refrigerated dryers are often the most efficient in terms of energy consumption and initial cost. For applications requiring a much lower dew point, energy-efficient desiccant dryers with advanced technologies like VSD (Variable Speed Drive), dew point controllers, and blower purge systems are the most efficient choices.
Refrigerated dryers
How they work: Cool the air to condense moisture, which is then drained away.
Energy efficiency: High efficiency for most general applications.
Best for: General manufacturing, automotive, and food and beverage industries where a pressure dew point between 3 to 10 ℃ is sufficient.
Desiccant dryers
How they work: Use a material like silica gel to absorb moisture from the air.
Energy efficiency: Can be less efficient, but advanced versions significantly improve this.
Best for: Applications that require ultra-dry air, below the typical limit for refrigerated dryers.
Energy-saving technologies:
Variable Speed Drive (VSD): Adjusts the dryer's operation based on demand, saving energy.
Dew Point Controller: Optimizes the regeneration cycles to reduce the amount of purge air used.
Blower Purge: Uses a blower to cool the desiccant instead of compressed air, which reduces operating costs.
Choosing the right dryer
For lower energy costs in general applications: Choose a refrigerated dryer.
For applications needing ultra-dry air: Select an advanced desiccant dryer with energy-saving features like VSD or blower purge to maintain efficiency.
To choose a refrigerated air dryer, you need to match its capacity to your compressed air system by considering factors like air flow, inlet and ambient temperatures, and desired pressure dew point. You will also need to decide between a non-cycling model (lower initial cost) and a cycling model (higher energy efficiency) based on your usage patterns and budget.
Key factors to consider
Air flow ((SCFM)): Select a dryer with a capacity that meets or exceeds your compressor's output to prevent the dryer from running at its maximum limit. Inlet air temperature and pressure: These values, along with ambient temperature, affect the dryer's performance. Standard specifications are often based on 100°F inlet air and 100 psig inlet pressure, so adjust your choice if your conditions differ.
Inlet air temperature and pressure: These values, along with ambient temperature, affect the dryer's performance. Standard specifications are often based on 100°F inlet air and 100 psig inlet pressure, so adjust your choice if your conditions differ.
Ambient air temperature: Higher ambient temperatures reduce a dryer's efficiency because it has to work harder to dissipate heat. Choose a dryer rated for your operating environment or consider a cycling model for better efficiency.
Desired dew point: Refrigerated dryers typically provide a pressure dew point of 2 to 10℃ which is sufficient for most applications. If your application requires a much lower dew point (e.g., for sensitive electronics or food processing), a desiccant dryer may be necessary instead.
Cycling vs. non-cycling:
Non-cycling: Runs constantly, has a lower initial cost, but is less energy-efficient if you don't need cooling all the time.
Cycling: Adjusts its operation based on air demand, resulting in significant energy savings over time. They are more expensive upfront but can be more cost-effective for varying loads.
How to choose based on your needs
For constant usage: A non-cycling model is a simple, lower-cost option if your equipment runs all day.
For variable usage: A cycling model (like a variable speed drive or thermal mass) will save energy and money over time by matching the compressor's load.
For applications with extreme cold: If any air lines or equipment are exposed to sub-freezing temperatures, a refrigerated dryer may not be suitable, and a desiccant dryer is a better choice.
For very low dew point requirements: If your application demands a very low dew point, a refrigerated dryer will not be enough. You will need to use a desiccant dryer instead.
A refrigerated air dryer typically achieves a pressure dew point of around 38F（3℃) to 50 F (10℃ ). This is because they cool the air to condense and remove water vapor, and freezing the moisture within the dryer must be avoided, which limits how low they can go. This dew point is sufficient for most general industrial applications.
Minimum dew point: The lowest dew point is usually around 38F（3℃) , which is considered the standard for many applications and corresponds to ISO Class 4.
Maximum dew point: The highest practical dew point is around 50 F (10℃ ) to prevent condensation in the downstream piping
Why it's a limit: The cooling process in a refrigerated dryer relies on the refrigerant cycle. To prevent the condensed water from freezing inside the dryer, which would cause damage, the air is not cooled below the 38F（3℃) mark
Contact Heng Sheng Filtration Today
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The difference is that air temperature is the actual, measurable temperature of the air, while dew point is the temperature at which water vapor in the air will condense into liquid water. In a refrigerated air dryer, the process cools the air to a specific temperature (the dew point) to remove moisture, but the dryer then typically reheats the air to a higher exit air temperature to prevent condensation in the pipes, creating a difference between the exit air temperature and the dew point.
Air temperature
Definition: The actual, physical temperature of the compressed air, measured with a thermometer.
Dryer function: The air enters the dryer at a higher temperature and is then cooled down. It is also reheated after the water is removed to prevent condensation in the downstream piping.
Exit temperature: The final air temperature after the dryer's refrigeration and reheating processes, which is always higher than the dew point.
Dew point
Definition: The temperature at which the air becomes saturated with moisture, and water vapor begins to condense into liquid.
Dryer function: The refrigerated air dryer's primary goal is to cool the air to a specific dew point to force condensation, allowing the liquid water to be drained.
Pressure dew point: In compressed air systems, the dew point is often referred to as the pressure dew point, which is a key performance specification for the dryer. For example, many refrigerated dryers achieve a pressure dew point of +38°F.
The relationship
The dew point is always lower than or equal to the air temperature.
The dryer cools the air to the dew point to remove water.
After removing the water, the air is warmed back up to an exit temperature that is higher than the dew point, but still below the original inlet air temperature. This temperature difference is crucial for the system's performance
Yes, a low dew point of refrigerated air dryer means the compressed air is dry because dew point is the temperature at which water vapor in the air condenses into liquid water. A low dew point indicates that there is very little water vapor present, meaning the air must be cooled to a much lower temperature before moisture will form, which signifies a drier air.
Pressure Dew Point (PDP): For compressed air, the relevant measurement is the Pressure Dew Point (PDP). This is the temperature at which water vapor condenses at the specific pressure of the compressed air system.
Low PDP = Low Moisture: A low PDP value means there are small amounts of water vapor in the compressed air.
High PDP = High Moisture: Conversely, a higher PDP value means there is more water vapor in the air.
Significance: In industrial applications, a low dew point is crucial to prevent condensation, corrosion, and other problems in pneumatic systems.
An adsorption dryer works by using a hygroscopic desiccant material, such as silica gel or activated alumina, to physically attract and hold water vapor from moist air, a process called adsorption. This is achieved in a two-tower system, where one tower dries the incoming air while the other is being regenerated by removing the collected moisture to restore the desiccant's capacity. The continuous cycling of the two towers ensures a constant supply of dry air.
Drying phase
Moist air is passed over a desiccant material in one of the dryer's towers.
The desiccant is a porous material that has a high affinity for water vapor, a property known as hygroscopicity.
Water molecules from the air adhere to the surface of the desiccant, removing them from the air stream and producing dry air.
This process continues until the desiccant in the tower becomes saturated with water.
Regeneration phase
When one tower is saturated, the air flow is switched to the second tower.
The saturated tower is then taken offline for regeneration.
The trapped moisture is removed from the desiccant, often by using a portion of the dried compressed air or external heat to raise the temperature, which drives the water vapor off the desiccant's surface. The regenerated desiccant is then ready for its next drying cycle.
A membrane air dryer works on the principle of selective permeation, where a bundle of hollow, porous polymer fibers separates water vapor from compressed air. As wet compressed air flows through the fibers, water vapor moves through the membrane's pores at a faster rate due to a pressure difference, while the drier air continues downstream. This moisture is then carried away from the dryer by a small "purge" or "sweep" air stream.
How it works
Compressed air enters: Filtered, wet compressed air enters a housing containing thousands of tiny hollow fibers.
Selective permeation: The membrane fibers have a special coating that allows water molecules to pass through, but not the air molecules.
Moisture removal: A pressure difference between the inside and outside of the fibers drives the water vapor to permeate the membrane and move to the outside of the fibers.
Dry air exits: The dry compressed air continues to flow through the center of the fibers and exits the dryer at nearly the same pressure as the inlet air.
Moisture is purged: A small amount of the dry air (purge air) is used to sweep the water vapor away from the outside of the fibers and vent it to the atmosphere. This process does not create liquid condensate that needs to be drained.
Adsorption dryers use hygroscopic materials to remove moisture from air, with common materials being activated alumina, silica gel, and molecular sieves. Each desiccant has different properties and is chosen based on the required dryness level and operating conditions.
Activated Alumina: A highly porous and durable material that is widely used, especially when the pressure dew point is - 40℃ or higher. It can have a high adsorption capacity but is not ideal for achieving very deep drying.
Silica Gel: Known for its high moisture absorption capacity, it is recommended for applications requiring a pressure dew point between -40℃ and -60℃. While it has a low mechanical strength, it can absorb up to 40% of its mass in water.
Molecular Sieves: These are synthetic desiccants with uniform pore sizes that allow for the selective adsorption of specific molecules. They have a significantly higher adsorption capacity than activated alumina and are necessary for achieving deep drying to very low dew points (e.g., -70℃）
Combinations: Sometimes, a combination of these materials is used, with materials like alumina or silica gel used for pre-drying and molecular sieves for eliminating residual moisture to achieve higher performance.
Yes, you absolutely need a line filter before a refrigerated air dryer. The filter removes bulk water, oil, and particulates that can damage the dryer and clog its components, ensuring it can function efficiently and the compressed air is cleaner.
Why a line filter is necessary before the dryer？
Protects the dryer: Compressed air from the compressor contains liquid water, oil, and dirt, which can cause wear and tear on the dryer's internal components.
Improves dryer performance: Removing these contaminants beforehand allows the dryer to focus on removing the remaining water vapor, leading to more effective drying.
Extends equipment life: By preventing the build-up of contaminants, filters reduce the risk of corrosion and other damage in the downstream piping and equipment, lowering maintenance costs.
The function of a compressed air filter is mainly removing contaminants like dust, oil, and water droplets from the air to protect downstream equipment and processes. It does this by using different filter types to capture specific contaminants: coalescing filters trap oil and water droplets, particulate filters remove solid particles, and activated carbon filters absorb odors and vapors.
What 's the function of a compressed air filters?
Remove solid particles: Particulate filters remove dust, dirt, and rust using a porous medium like paper or synthetic elements.
Remove liquids: Coalescing filters capture fine droplets of oil and water by forcing air through a material that causes the droplets to merge into larger ones, which then drain away.
Remove vapors: Activated carbon filters are used to absorb oil vapors, chemical fumes, and odors from the air.
Why filtering is important:
Protects equipment: By removing contaminants, filters prevent damage to downstream equipment and protect sensitive processes from contamination.
Ensures product quality: Filtering is essential in sensitive industries like pharmaceuticals and food & beverage to meet stringent quality standards.
Reduces operational costs: A clean air system reduces downtime and increases productivity by preventing issues caused by contaminants.
Improves safety: It helps protect personnel from potentially harmful aerosols, vapors, and other contaminants.
The compression process introduces lubricant and wear particles into the system, piping distribution and storage tanks foster contaminants in the form of rust, pipe scale and bacteria. At HSAIR you could find our compressed air filter with seven filtration grades, PF, AO, AA,AX,ACS, AR and AAR filters efficiently remove these contaminants to provide the best air purity and protect downstream equipment and your processes, saving costs.
Coarse Pre-Filtration
As a primary filter, particles whose diameter down to 5 μm can be removed, the max. residual oil content is negligible.
High Efficiency General Purpose
High efficiency general protection, dust particles, water mist & oil mist whose diameter down to 1μm can be removed, the residual content of oil mist does not exceed 0.6 mg/m³ (21ºC),1ppm(w), changed every 8000 hours.
High Efficiency Oil Removal Filtration
Dust particles, water mist and oil mist down to 0.01μm can be removed, the residual content of oil mist does not exceed 0.01mg/m³ (21ºC), 0.01ppm(w), changed every 8000 hours.
Ultra High Efficiency Filtration
Ultra-efficient filtration, solid particles, liquids, oil aerosols, odors, and vapors are effectively removed at a high efficiency of 99.99% as small as 0.01 micron, the residual content of oil mist does not exceed 0.001mg/m³ (21ºC),0.001ppm(w), changed every 8000 hours.
Oil Vapour Reduction
Activated carbon filter element made from thousands of activated carbon granules of sufficient thickness, giving a superior adsorption capacity on a longer time.Oil vapor &odor can be removed, the max. resident content of oil vapor does not exceed 0.003 mg/m³ (21ºC), 0.003 ppm(w), changed when oil vapor detected.
General Purpose Dust Filtration
Dry particle removal down to 1 μm, installed after adsorption air dryer, change every 6000 hours.
High Efficiency Dust Filtration
Dry particles removal down to 0.01μm can be removed, installed after adsorption air dryer, change every 6000 hours.
Usually in a compressed air system, a standard particulate in-line filter will remove dry particulate down to 5 micron in size. However, they will not remove oil mists. Oil-lubricated air compressors (such as rotary screw air compressors) will need an inline filter rated for both particulate and oil, such as a coalescing filter, activated carbon filters.
To choose an air line filter for your compressor, you must first identify the contaminants in your air (like water, oil, and particles) and determine the required air purity for your application. Then, select a filter with the appropriate efficiency for the particle size you need to remove, ensuring it is compatible with your compressor's flow rate and operating pressure. Finally, consider factors like maintenance costs and specific industry regulations, such as those outlined in ISO8573.
At HSAIR, we could supply aluminum alloy, stainless steel air filter housings for compressed air filters to meet your different demands.
At HSAIR, you could find our compressed air filters designed with 7 filtration grandes and the grades PF/AO/AA/AX could efficiently remove solid particles from 5 micron to 0.01 micron to protect your compressed air system.
Since 1998, YUKA has been focusing on high quality compressed air filters for global air compressors distributors, enjoying high reputation in China. During this period, we gain a lot of experiences how to open moulds and how to control the die-casting technology, then to a finished air filter.
✅ Over 27 Years of Air Filtration Experience
YUKA filters leverage a multi-layered coalescing technology to remove 99.99% of particulates down to 0.01 μm, oil aerosols, and water vapor. Ensure air purity compliance with ISO 8573-1 Class 1-4 standards, meeting the rigorous demands of oil drilling, pipeline operations, and refining processes.
✅ Robust Construction for Extreme Conditions
YD//YF/YFB Series Crafted from A-grade aluminum alloy and corrosion-resistant coatings, bear high-temperature (120°C) and BHL series stainless steel air filters air flow rate up to 300m³/min and chemically aggressive environments common in oil and gas applications.
✅Energy Efficiency = Cost Savings
Our ultra-low pressure drop design minimizes energy consumption in air compressors, reducing operational costs while maximizing airflow efficiency—critical for large-scale industrial operations.
✅ With TUV and in-house test Certificates
Compressed air quality is often specified by standards like ISO 8573-1, and filters are used to achieve the required quality classes.
✅ Equipment Protection:
Clean, dry compressed air is essential to prevent damage to sensitive pneumatic tools, instruments, and control systems used in oil and gas operations.
✅ Process Efficiency:
Contaminated air can negatively impact process efficiency and the quality of final products or operations.
✅ Safety and Purity:
Ensuring air purity is crucial for safety in potentially hazardous environments.