ACHRNEWS

Filter Driers: The First Line Of System Protection

September 3, 2004
At first glance, filter driers on air conditioning or refrigeration systems are exactly what their name implies - front-line protection designed to filter out contaminants and dry the refrigerant to avoid ice formation and oil degradation. They also, of course, must remove acids formed as a byproduct of moisture, oil, and heat.

But all filter driers are not created equal. And all are not prepared to handle the change and challenge coming with the advent of new environmentally friendly refrigerants.

Basically, three distinct types of filter driers blanket today's marketplace:

  • Loose fill driers - Filled with beaded desiccant held in the shell with mesh screens.

  • Molded core filter driers - A solid core of blended desiccant held together by a cured resin.

  • Compacted bead filter driers - A blend of beaded molecular sieve material and activated alumina held in place between two fiberglass pads, which are compressed by a steel spring.

    The Right Choice

    Of the three styles, the compacted bead technology offers a combination of features and functions designed to handle the array of filtering, drying, and removal tasks asked of a state-of-the-art filter drier. The EK Filter Drier from Emerson Climate Technologies Flow Controls (formerly Alco Controls) is a prime example. It is buffered by an initial 40-micron fiberglass filter that removes most of the contaminants and sludge, plus a 20-micron final filter that removes the remaining contamination.

    While the EK Filter Drier was designed primarily for commercial refrigeration systems, it is increasingly being used in premium air conditioning systems. This is why Emerson Climate Technologies has added it to the UltraTechâ„¢ Home Series products for residential systems.

    The EK Filter Drier differs significantly from units that have come before. For starters, there's the method of filtration. The EK Filter Drier uses a series of fiberglass media pads that capture and hold the various solid particles. The majority of filter driers, on the other hand, often simply use a molded desiccant core. The desiccants are glued together and used as the filter. This technique simply does not have the surface and depth capability to capture a large quantity of solid particles or collect the smaller particles that might get through the core.

    It is that ability to capture all of the smallest possible particles that sets the EK Filter Drier apart. That's because the filter has been designed and built with a pioneering technology that includes a very fine final filter that allows the EK Filter Drier to boost efficiency into the 99.9+ percent range. This means only one particle out of 1,000 passes through the drier the first time it enters the filter. This is 100 times better than the average filter drier: 1/1,000 versus 1/10. One-tenth equals just 90 percent efficiency. This patented pad also means there is minimal pressure drop; pressure drop is a problem that could eventually lead to lost efficiency and less cooling power.

    The EK Filter Drier’s 40-micron first filter removes most solid contaminants and sludge. The 20-micron final filter removes any remaining contamination. The specially formulated 75/25 desiccant blend protects polyolester (POE) oils.

    Added Advantages

    Other unique EK Filter Drier features actually went against the conventional wisdom. First, it accomplishes the primary filtration before the drying phase. The reasoning behind this approach is that by taking most of the dirt out ahead of the desiccants, the desiccants remain clean and better able to do their job of retaining water and acids. Second, the EK Filter Drier overcomes another flaw of earlier filters, which was the compacting of the beads by a spring at the filter's outlet end. This method meant the system flow tended to work in opposition to the spring and reduced the amount of compression on the beads. The beads themselves would become loose and roll against each other, eventually breaking down to create particles. Essentially, that turned the beads into mini-grinders that could wreak havoc on both the filter and the system. The EK Filter Drier turns the original concept around - it has a spring at the inlet end, allowing the spring to work with the refrigerant flow to better protect the desiccants.

    There is one other key EK Filter Drier design difference. Inside the spring at the inlet end are fiberglass pads that offer two-tiered filtering capabilities. One tier is a surface filtering action; the other is a depth filter. When dirt accumulates on the outside of the filter, it collects where the flow is lowest, caking around the pad and pushing the pads toward the outlet and further compressing the pads. In the normal course of system operation, whenever the refrigerant flow stops, the pad will relax and shed some of its accumulated dirt, which then falls away from the pad. When the system restarts, this dirt tends to become caught on the pad immediately downstream. And that effectively increases the amount of dirt the filter can hold before the pressure drop moves high enough to warrant the filter's removal and replacement.

    When it comes to its construction, the EK Filter Drier is buffered by two layers of fiberglass filters. The initial 40-micron layer removes most solid contaminants and sludge, while the second 20-micron final filter removes the remaining contaminants from the system. This double-layer protection helps ensure that the system will stay cleaner, longer, with a minimal pressure drop in the filter drier.

    The final outlet pad is what boosts the efficiency rating and allows the filter to capture virtually all particles, down to and including 20 microns. The advantage here is that by the time the remaining particles are so small, the inlet pad has become almost as effective a filter as the outlet pad. That means the EK Filter Drier delivers a lot of filtration compared to the amount of pressure drop. And it means it requires much less desiccant to do the same job.

    New Challenges, New Solutions

    As the industry shifts to higher-pressure environmentally friendly refrigerants such as R-410A (for use with commercial and residential air conditioning applications), filter driers face a new series of challenges. The EK Filter Drier brings built-in benefits in this area as well. The newer HFC refrigerants use synthetic polyolester (POE) oils, which demand a more effective filtration capability than did the previous mineral oil systems. Why? Because POE oil is more of a solvent than were traditional oils. POE does an effective job of stripping off and keeping afloat any particles that are on the surface of the tubing or left in the system when it was put together. That alone requires a better filtering alternative.

    Another factor is increased water capacity. POE oils are extremely "moisture loving" (hygroscopic is the technical term). And that can create problems. When enough water is present, POE reverts to its original chemical - an organic acid and an alcohol. While the alcohol doesn't affect the system greatly because it's picked up by the desiccants in the filter drier, it does reduce the filter drier's effectiveness with water.

    The EK Filter Drier has a blend of both high-water capacity desiccant, called molecular sieve, which traps water molecules flowing with the refrigerant, and a high-acid capacity desiccant, called activated alumina, which has slightly larger pores to trap and remove acid molecules.

    Meeting Tomorrow's Demands Today

    Compacted bead desiccant filter driers have additional advantages over competitive technologies, particularly those that use porous molded cores. In the latter case, whenever something is put on the surface to hold the core together, it leads to added resistance to mass flow; water or acid does not flow through that media easily so the desiccant can capture it. And that, in turn, effectively reduces the capability of the desiccant to work. The good news: the EK Filter Drier desiccant is not molded together - so it provides 100 percent desiccant utilization capabilities.

    In addition, the maximum working pressure of the EK Filter Drier line is 680 psig, one of the highest in the industry. Again, this is key when dealing with new refrigerants, especially R-410A, which has a very high pressure. The EK Filter Drier already has the working pressure capabilities to handle this increasingly viable refrigerant.

    Meets Copeland Recommendations

    Finally, Copeland Corporation, also part of Emerson Climate Technologies, recommends the use of no more than 25 percent activated alumina in the desiccant blend for new HFCs. This is because Copeland uses proprietary break-in lubricant additives for the initial startup of compressors and activated alumina can strip out these additives. Since Copeland and Flow Controls are both part of Emerson Climate Technologies, the engineers who developed the EK Filter Drier worked closely with Copeland to make sure it met this recommendation and resolve any compatibility issues surrounding the technologies.

    Conclusion

    Filter driers have a distinct mission: to take contaminants, moisture, and acid out of refrigerants. They're critical to prolonging the life of compressors and refrigerants. How critical? A recent Air-Conditioning and Refrigeration Institute (ARI) study showed that even weak acid circulating could reduce a compressor's life from 1 million hours to about 1,000 hours. The EK Filter Drier is one unit that delivers the across-the-board protection capabilities the systems of today and the refrigerants of tomorrow demand.

    Reprinted with permission from the Emerson Climate Technologies EK Filter Drier White Paper, Form No. 2004ECT-24. Flow Controls (formerly Alco Controls), part of Emerson Climate Technologies, is a leading provider of electronic and electromechanical controls for air conditioning and refrigeration systems. For more information, visit www.emersonclimatecontractor.com.

    Publication date: 09/06/2004