Refrigerated air dryers are used in many industrial plants as a cost-effective method of removing water vapor from compressed air used to power tools and pneumatic machinery. However, different types of refrigerated dryers offer varying levels of energy savings and performance characteristics.
Cycling vs non-cycling dryers
Refrigerated air dryers use a refrigeration system to cool compressed air. There are two categories of refrigerated dryers:
Non-cycling refrigerated dryers operate the refrigeration compressor continuously once the unit is powered on, regardless of demand.
Cycling or thermal mass dryers are marketed as energy conserving dryers because they store cold energy and use it on an as needed basis. The cycling dryer works by using the refrigeration system to cool a mixture containing glycol and water. Heat is exchanged between the thermal mass and the warm air entering the system, cooling the air and warming the thermal mass. Once the temperature of the thermal mass rises above a certain point, the system turns on. The system turns off when the desired low temperature is achieved.
Non-cycling refrigerated dryers are designed to run continuously. So, it makes no difference if a facility is open or closed — a non-cycling dryer will operate regardless. On the other hand, cycling dryers turn on and off based on demand, making them much more energy-efficient. For example, a 5000 scfm non-cycling refrigerated dryer running continuously for 8,000 hours (or about one year) at an average energy cost of $1.64 per hour, would cost $13,120 annually in energy expenses alone. In the same scenario, a Parker cycling dryer, running at 70% load, would cost $9,100 annually — a $4,000 savings compared to the cost of operating a non-cycling dryer.
A cycling dryer for maximum energy savings
Parker Hannifin’s Gas Separation and Filtration division has introduced a cycling refrigerated air dryer designed specifically for heavy industrial applications. The Parker Magnum refrigerated cycling air dryer offers exceptional dew point control in a robust package equipped with the advanced control center microprocessor, the most intuitive controller available in the industry. The unique auto mode takes the guesswork out of managing operations allowing the control center to manage dryer performance resulting in maximum energy savings.
The Parker cycling air dryer offers unique features that make it more energy efficient and reliable than other cycling dryers on the market today.
Operate on compressed air temperature
Most cycling dryers operate according to the temperature of the storage mass, not the temperature of the compressed air. When the mass temperature reaches 40°F, the compressor turns on; however, the actual dew point temperature can be as high as 55° to 60°F. The Parker Magnum cycling dryer activates when the temperature of the compressed air reaches 39°F, allowing for a lower, more stable dew point.
Start in an unloaded state
The Parker cycling dryer starts in an unloaded state which means the system can perform unlimited starts and stops. Most cycling dryers start against full head pressure and are typically limited to six starts per hour.
Colder, smaller mass
The thermal mass in the Parker system consists of a fully flooded shell and tube heat exchanger. Compressed air flows through the inner tubes which are submerged in cold liquid refrigerant. The temperature of the refrigerant is allowed to drop as low as necessary to keep the air temperature between 34°- 39°F. A patented flood level control assures that no liquid refrigerant is returned to the compressor for maximum reliability. Most cycling dryers use a larger intermediate mass of glycol that must be cooled by refrigerant before it can cool the air. If the glycol mass is set at a low temperature of 34°- 39°F, the actual air temperature will typically be 10°- 15°F warmer. Less mass is required for the Parker system because it is colder.
Because the Parker system cools the air to a lower temperature, more water vapor is removed offering better protection for the metal in the air distribution piping, instrumentation, tools and product.
Less componentry for a reliable solution
The Parker system uses a single, semi-hermetic compressor unit that runs through one heat exchanger for maximum reliability. A 50%-100% backup compressor is available as an option. Other cycling dryer systems are more complicated and consist of multiple heat exchangers and hermetically sealed compressors that run at a relatively high RPM increasing the potential for service issues. Proper distribution of refrigerant through these multi-compressor dryers can be easily hindered by a restriction in any part of the system. If one of the compressors malfunctions, downtime could be extended with the additional time required for troubleshooting multiple components.
Other dryers use up to five times the number of components and refrigerant joints. The more parts, the higher the likelihood for service issues over the life of the system.
Unlike most cycling dryers, the Parker Magnum cycling refrigerant air dryer requires no pre-filters or after filters.
Designed for maximum efficiency and reliability
The new Parker Magnum cycling air dryers are designed for maximum energy efficiency and offer a number of benefits over existing cycling dryers currently on the market including:
- Dew point performance of 34-39°F at all operating conditions up to the maximum rating (even when compressor is off).
- Electronic rather than mechanical controls for instant response to changing conditions.
- Readout of lowest compressed air temperature (true dryer performance).
- Diagnostic codes for easy trouble shooting.
- Semi-hermetic compressors run at 1800 RPM for longer equipment life.
- Service isolation valves for all refrigeration controls and valves minimizes down time.
- 50% and 100% backup compressor available.
- Built-in, two-stage cold coalescer.
- Load-less start on refrigeration compressor allows for unlimited cycling.
- Mass can be smaller because it is much colder.
- Energy saving equal to or better than every cycling dryer available.
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This post was contributed by Allan Hoerner, product manager and Jennifer Fiorello, Compressed Air and Gas Treatment Technology blog team member, Parker Hannifin Gas Separation and Filtration Division.
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Facts You Need to Know About Drying Compressed Air