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High Condenser Approach in Water Cooled Centrifugal Chiller

Mechya (Mechanical) (OP)
9 Jul 06 10:03
Hi to all
I am aware of the fact that high condenser approach is caused due to fouled condenser tubes and/or low water flow in a shell and tube condenser of a water cooled centrifugal chiller. Are there, any other reasons for the high condenser approach?. Would like to get the experts view on this subject.

Thanks in advance.
quark (Mechanical)
9 Jul 06 22:59
That is mainly due to the fouling of the condenser, if the increase in approach is gradual. If there is a drastic increase, check for the presence of air in the system.

Yorkman (Mechanical)
10 Jul 06 18:47
Quark is right, if this is a low pressure machine the presence of air should have your purge working and purging above normal. If the amount of air in the system is real bad, you might even see some unusual pressures in the evaporator. For example the saturation temperature of the refrigerant will be higher than your leaving chilled water temperature while running.
  If this is a high pressure machine I would look at the condenser tube fouling first, but remember that sloppy maintainance can result in air getting into a high pressure machine too.
  Another way to verify air in a machine requires you to shut down the machine as well as the chilled and condenser water pumps for several hours and let the temperatures in the machine to equalize to ambient. The saturation temperatures of the refrigerant should match the internal water temperatures. This is hard to do if you only have one ciller in the system.

I'm not a real engineer, but I play one on T.V.
 A.J. Gest, York Int./JCI

imok2 (Mechanical)
11 Jul 06 1:54
Higher approach temperatures are prime indicators that heat transfer efficiency is decreasing due to such factors as minerals, scale, mud, algae, and other impurities which increase thermal resistance and degrade the overall performance of the heat exchanger.
Although they will be phased out by 2020, low-pressure chillers are still commonly used. Their evaporators operate in a vacuum and use either CFC-11 (now phased out) or the alternative, HCFC-123. It is difficult to create a perfectly sealed unit, so non-condensables (air and moisture) leak into the chiller. Non-condensables create two problems
1. In that they offer no refrigeration effect, even though the compressor uses energy to move them. At the same time, they can blanket tubes with air, preventing them from doing any heat exchange work.
2. Non-condensables also contain moisture, which causes acids to form within the chiller. These acids can damage motor windings and bearings. In addition, non-condensables lower the real efficiency of the chiller from the rated performance by as much as 8% at 60% load and 14% at 100% load.

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