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View Subscription Details: Letter ( 06/06/2006 ) - HTML Format


 As I mentioned in the previous newsletter, different industrial refrigeration compressors have similar energy efficiencies at identical suction pressure and discharge pressure.

It is a different story for evaporative condensers. These condensers come in frame size. Several models have the same frame, but different heat rejection efficiency (MBH/HP). This is because for higher capacity unit, additional heat rejection is being added primarily with additional airflow or additional condenser energy. Therefore, heat rejection efficiency of different condensers with the same fan type (axial or centrifugal) can very up to 50 %.

Another important factor is that centrifugal fan units usually require 50% to 100% more fan power than axial fan units. As shown above, one condenser can use significantly more energy than another one of identical capacity.

Condenser energy efficiency is a major factor in determination of condenser sequence.

Example. We have refrigeration plant with 6 condensers. First one in condenser sequence operates 12 months (8760 Hrs). Last one operates just 1 month (744 Hrs) during the period of hottest ambient conditions. First condenser is using 50 HP.  Last one is using 30 HP. Capacity of these two condensers are identical. If we switch these condensers in

condenser sequence, we will save  50 - 30 = 20 HP  for a period of 11 months (8016 Hrs).
At energy rate 0.1$/KWh, total energy savings would be

(20 x 0.75 = 15 KW)   15 x 0.1 x 8016 = $12,024.

New condenser sequence will save us $12,000 without any capital investment.

Recently, I visited one production facility inOntario. They have a refrigeration plant and the condenser power of this plant is around 400 HP. I suggested to them a new optimum condenser sequence that immediately saved 120 HP of  condenser power. Estimated annual energy savings of this action would be around $30,000. This company was planning to get similar energy savings by buying compressor VFD for $100,000. Assume that payment for a new optimum condenser sequence would be $5,000. This company will get a return on investment in condenser sequence 20 times ( 2,000 % ) better than investment in compressor VFD.  It looks like too good to be true, but these are the real life numbers.

Probably, not everybody agreed with my statement (March 2006 newsletter) that operating savings are significantly more cost effective than designing energy savings. However, the example mentioned above is proving that small investment in optimization of refrigeration plant operation will give you much better return than investment in energy saving equipment.

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