HFC Refigerants and POE Lubricants - Part 2: How to combat water in the system [1]?

Refrigerant systems must be dry internally because high moisture content can cause ice to form in the expansion valve or capillary tube, corrosion of bearings, reactions that affect lubricant / refrigerant stability, or other operational problems. As with other components, the refrigeration lubricant must be as dry as practical. Polyolesters [POE] usually contains 50 to 100 ppm moisture in normal manufacturing. This amount may increase between time of shipment from the refinery and the time of actual use.

POE oils are quite hygroscopic in its properties.

Monitoring

To combat the detrimental effects of water in HFC and POE systems it is imperative to hold moisture levels as low as possible. It is generally accepted that water level must be maintained less than 50 ppm in the refrigerant and the same for the oil. Monitoring is therefore necessary. In order to monitor system water level a moisture indicator must be used that can sense changes in moisture in this ppm range.

Many commercial sightglasses cannot indicate a change at this level in liquid lines that exceed 100degF or 38degC. This means that harmful organic acids may be attacking system components while the indicator is showing 'dry'. The HMI and AMI moisture indicators have unique element that has the ability to change colour at low ppm levels so that proper action can be taken before any system components are damaged.

Filtering

Because POE lubricants are quite hygroscopic, when they are in a refrigeration system they should circulate through a filter-drier designed for liquids. A filter-drier must be installed in the line carrying liquid refrigerant or in a line returning lubricant to the compressor. The desiccants will remove some additives in the lubricants. It was necessary to redesign standard 'catch-all' filter-driers for increased water removal capacity to achieve these low moisture levels. Since no system is entirely devoid of water upon startup some organic acids will be generated and must be removed.

The desciccant formulation for the EK and UDK series of filter-driers was designed to provide the optimal mix of water capacity and acid capacity to ensure that both harmful contaminates are effectively removed. This desiccant mixture contains both molecular sieve and activated alumina. The molecular sieve is specially designed to provide maximum drying in today's systems. The activated alumina is ideal for capturing the large organic acids that the molecular sieve cannot.