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The most important part

 

What is the most important part of the energy saving process?

Many people believe that it is energy saving equipment (PLCs, VFDs and etc). I, on the other hand, think that knowledge and experience are the most important parts of the energy saving process.

 

Knowledge.

To maximize energy savings, a refrigeration plant should operate at optimum (the best) set points. Unfortunately, we often just guess about these set points. Determination of optimum set points is not a simple task but is the goal in energy savings. To reach this goal, we must know where it is.

Example. The condensing pressure of a refrigeration plant was set to 120 psig. During summer operation, optimum condensing will be higher than 120 psig. During winter operation, optimum condensing pressure will be lower than 120 psig. An operating engineer should have information about optimum condensing pressures at difference ambient conditions. Based on this information they can set up the correct condensing pressure. Do you know your optimum condensing pressures at different ambient conditions?

Experience.

Sometimes we are right in our speculations of optimum set points. However, we can be wrong in the implementation of these set points.

During winter operation, optimum condensing pressure is lower than 100 psig. The operation of a refrigeration plant at the lowest possible condensing pressure is the right decision. The lower condensing pressure will be closer to the optimum and result in better plant efficiency. What is the lowest possible condensing pressure? This is a very important question because around 50% of annual operating time, a refrigeration plant runs at this condensing pressure.

Example. During winter operation, a refrigeration plant ran at 120 psig condensing pressure because of hot gas defrosting. However, a review of hot gas defrosting has shown that it can be done at 80 psig of condensing pressure. Hot gas supply, back pressure regulator settings, length of defrosting were optimized. Currently, this refrigeration plant successfully operates at 80 psig of condensing pressure. This tuning up of hot gas defrosting has saved 10% of energy use. Payback of this tuning up was 1 month, because mentioned energy savings were achieved without any capital investment.

 

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