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View Subscription Details: Letter ( 05/25/2011 ) - HTML Format

We are OK


I asked many people about energy efficiency of their refrigeration plants. Very often I have got the answer that they are OK.

How do we make conclusions about energy efficiency of our refrigeration plant? Usually, we compare information of current operation with previous experience in our life. Majority of the operators did not see refrigeration plants that operate at condensing pressure below 110 psig. They honestly believe that 110 - 120 psig is the best condensing pressure for their refrigeration plants. Do not blame them, because for many years they saw only typical operation of the refrigeration plants. To save energy, we should achieve energy efficient operation. However, there is significant difference between typical operation and energy efficient operation. To achieve maximum energy savings, a refrigeration plant should be operated at optimum (the best) condensing pressure all year around. During winter operation, optimum condensing pressure can be as low as 50 - 60 psig. Some may think that it is impossible to operate a refrigeration plant at condensing pressure below 100 psig. I believe that more than 95% of the refrigeration pants can operate at condensing pressure below 100 psig. Definitely, there are several barriers to operate a plant at such low condensing pressure, but every barrier has a solution.

Recently, I visited one refrigeration plant that was operated at 60 - 70 psig of condensing pressure for 99% of the winter operating time. Sometimes this pressure was slightly increased for hot gas defrosting. This operation is very close to the optimum. Compressor operation at 60 - 70 psig of the condensing pressure is 30 - 40% more efficient than compressor operation at 100  - 110 psig. If you think that minimum condensing pressure 100 - 110 psig is OK, think again. There is a lot of room for improvement.  


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