Step in the right direction

A few years ago, I wrote in one of my newsletters about the right sequence for energy savings in industrial refrigeration. This sequence is:

1.     Initial optimization of a refrigeration plant operation. This step should be done by the operators.

2.     Final optimization of a refrigeration plant operation. This step should be done by a consultant.

3.     Capital investment in energy saving equipment.

Recently, I have found that several companies have initiated strategy of optimizing operation of their refrigeration plants. I think that this is a good step in the right direction. However, there are several misconceptions in this process. I will review couple of these misconceptions.

1.     Minimum condensing pressure of 100 psig is the best for our refrigeration plant.

Optimum (the best) condensing pressure depends of wet bulb temperature of ambient air. Majority of the refrigeration plants in North America have winter optimum condensing pressure below 100 psig, often this optimum pressure can be as low as 50 - 60 psig. This means that these plants have room for improvement. There are several barriers to low condensing pressure but every barrier has a solution. I know several plants that are operated at condensing pressure as low as 70 - 80 psig and many refrigeration plants can run at similar condensing pressure as well.

2.     We increased suction pressure to improve the efficiency of our refrigeration plant.

When you increase the suction pressure of a refrigeration plant, the temperature difference between evaporating temperature and air temperature will be reduced. This means that the capacity of each operating evaporator will decrease. To handle existing refrigeration load, additional evaporators should be operated. Fans of these evaporators will use additional energy and this energy will be released into the refrigerated room as parasitic refrigeration load. Additional compressor energy should be spent to remove this parasitic load. Higher suction pressure will increase the efficiency of the compressors, while often reducing the efficiency of the whole refrigeration plant. My research has shown that to get maximum efficiency, a refrigeration plant should be operated at optimum suction pressure all year round, regardless of refrigeration loads.

If you optimized the operation of your refrigeration plant and believe that this operation is optimal, think again. Very often, there is room for improvement. Find experienced consultant who will be able to review your current operation.