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View Subscription Details: Letter ( 12/29/2015 ) - HTML Format

Tight budget

 

Unfortunately, many companies have tight budget of investment in energy efficiency of the refrigeration plants. Additionally, some companies have very strict requirements to energy efficiency projects. Typically, payback on investments in these projects should be 2 years. How can we achieve this short payback? I know only one way to minimize investments in energy efficiency and to achieve short payback on these investments. This is optimization of the refrigeration plant operation.

For example. Recently, I reviewed design and operation of one large production refrigeration plant. Initially, management of this plant invested $400,000 in sophisticated PLC, compressor and condenser fan VFDs. They achieved annual energy savings of 1,000,000 kWh. At energy rate of 0.12 $/kWh this company saved $120.000. It looks like good energy savings. However, this company was not satisfied with payback of 400,000/120,000 = 3.33 years. What did they do to improve payback? They invested additional $40,000 in optimization of the refrigeration plant operation. This optimization included:

  1. Floating condenser pressure based on wet bulb temperature of ambient air. Initially wet bulb sensor was located in the wrong place and it was showing wrong readings. This sensor was located in right place and wet bulb approach was changed several times per year to make sure that the plant operates at peak efficiency.
  2. Floating suction pressures. For many years suction pressures of this plant were not changed. However, we found that some pressures can be changed based on production requirements and energy was saved. 
  3. Optimized hot gas defrosting. Frequency of the defrosting was changed several times per year to make sure that evaporator is defrosted only when capacity dropped to 70 - 90%.
  4. Optimized compressors and condensers sequences. The correct sequences were chosen to maximize benefits of VFDs and equipment, which has the highest energy efficiency.

This optimization has saved an additional 1,000,000 kWh per year and this company has achieved required pay of 440,000/240,000 = 1.83 years.

This example shows how many companies can achieve their goals in energy saving process by optimizing operation of the refrigeration plants. 

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