Condenser Receiver Care - 2012-10

The Condenser Receiver  

In designing refrigeration systems, the condensing temperature for water cooled units using R507 is normally assumed to be from 70° F to 80° F. When the facility can provide water to the condenser receiver at the design flow rate, pressure, and temperature, the condenser receiver will work properly if it has been maintained. However, a frequent source of refrigeration problems involves the condenser receiver.

The problems that are most common with the condenser receiver are:

  • Too High a Head Pressure

The maximum relief valve pressure using refrigerant R-507 is 350 psig, or 365 psia. The normal operating head pressure for 3 to 15 horsepower compressors is 175 psig (190 psia) and for 20 horsepower units and above the normal operating head pressure is 190 psig (205 psia). By design, the water regulating valve to the condenser receiver reaches maximum flow when the pressure rises to 230-240 psig (245-255 psia). Beyond this head pressure there is no additional water flow available to compensate for the higher compressor heat loads.

High head pressure is most often because of non-condensables or over charging. Both are discussed at great detail in our "Fundamentals I: Basic Freeze Dryer Operation and Maintenance" workshop, and are also addressed in other Tech Tips. For more information about our workshops view our training page.

High head pressure can also be caused by inadequate heat transfer from the refrigeration circuit to the cooling tower circuit. This can result in a feedback loop whereby higher head pressure results in more heat, which cannot be transferred which results in even higher head pressure, etc.

 

  • Water Flow, Pressure or Temperature Out of Specification

Water pressure and temperature problems, and sometimes flow rates, are usually associated with the cooling tower. Maintenance of cooling tower items such as filters and pumps should be considered as critical as those of the freeze dryer itself. The filter should be cleaned to a regular maintenance schedule, at least yearly as a minimum. The baffles in the cooling tower affect its cooling capacity and should also receive attention. A leaking, worn, or failed pump can be a cause of low water flow and pressure.

 

  • Clogged Condenser Receiver Tubes

Clogged tubes can be caused by the water quality and by the location of the tower to the prevailing winds. Hard water, water with high mineral content, can build up on tube walls reducing heat transfer efficiency and slowing the water flow. Airborne dust and dirt can collect in the tower and be transported by the water to the condenser receiver. When the dust and dirt reach an area where the flow rate is reduced, they settle in the tubes and form a sludge further restricting flow and reducing heat transfer.

This is both a cooling tower maintenance issue and a condenser receiver maintenance issue. The tower must be able to provide clean quality water at the minimum design water flow rate and pressure called for in the freeze dryer utilities specification. In addition to pump and filter maintenance, a tower water treatment plan should be developed and followed based on a chemical analysis of the water supply. Finally, the condenser receiver tubes need to be inspected, and cleaned if needed, at least once a year to prevent the buildup of scale.

A refrigeration system is only as good as its ability to get rid of the heat it has absorbed, and the condenser receiver is the single point of contact between the refrigeration loop and the cooling tower loop. The condenser receiver must be maintained to insure proper heat transfer if the system is to work at optimum efficiency.

 

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Tech Tips Home

These technical tips are for use by qualified maintenance personnel who are familiar with their specific freeze drying equipment. These tips are intended only as general guidelines. Lyophilization equipment is frequently custom configured and some tips may not be appropriate for all freeze dryers. Always read and follow the directions of your equipment's maintenance manual. If you would like to discuss one of our tech tips, please contact Dave Clayton at 215-672-7800 ext-1376.


 

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