Energy use reduction at industrial refrigeration plant through adjustment of operating set points

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  • Can your refrigeration plant work cheaper

Energy use reduction at industrial refrigeration plant through adjustment of operating set points

How valuable would it be for your business to cut the energy use of an industrial refrigeration plant by 30%, while still supporting the same load? To do so with a short payback? What if incentives halved the payback? This is what we are doing.

GreenQ Partners has completed a pilot project at a refrigeration plant of an industrial bakery that has proven a way to reduce energy use by 38% with a payback of 1.25 years prior to incentives. The project has been completed and approved by CLEAResult for incentives under the Detailed Engineering Study framework. This project would have been impossible without the close cooperation with plant maintenance manager Hasan Mustafa, who provided diligent professional support to our efforts.

Similar results can be achieved at most industrial refrigeration plants.

In refrigeration energy use grows with condensing pressure

A brief technical introduction for non-engineers is due. A refrigeration plant can “produce” similar amount of cold while working at different levels of condensing pressure. While the level of pressure makes only a small difference for the compressor as long as pressure stays within specs, a reduction of pressure makes a big difference for the bottom line:  a 2 psig increase of condensing pressure raises energy use by 1-2%. This may not seem like much, but while energy was cheap, industrial refrigeration plants were commonly set to high condensing pressure to simplify operation.  Today, when controls are getting cheaper and energy more expensive, condensing pressure can be lowered by 30-80psig, thus reducing energy use by 15-40% at most plants.

Energy use reduction in refrigeration is not as simple as dimming lights

Along with condensing pressure reduction, energy use can be cut by floating condensing and suction pressures, optimizing hot gas defrosting, and optimizing compressors and condensers operating sequences. Beware: reducing energy consumption in refrigeration system is rarely as simple as dimming the lights. Typically, the following barriers should be overcome: hot gas defrosting, liquid supply, oil carry-over, oil cooling, and so on. A deep understanding of refrigeration technology and the design of a particular system as well as diligent implementation are paramount to cutting costs while maintaining a reliable operation.

Our pilot project has proven the concept in real-life conditions

Our project aimed to demonstrate the economic viability of condensing pressure reduction in the real-life conditions of a refrigeration plant and industrial bakery.

Here is what we have done:

  • Conducted a thorough review of a cooling plant
  • Established the “before” energy consumption baseline in relation to production through a regression analysis for the whole refrigeration plant; R2 of 88%
  • Conducted an energy use software simulation for several levels of lower condensing pressure to forecast energy use reduction
  • Decreased condensing pressure from 180psig to 150psig
  • Collected the “after” energy use and production data
  • Compared the actual reduction with the simulation forecast

In the results of the study project, energy consumption of the whole refrigeration plant decreased by 13%, exceeding a conservative simulation forecast by 3.5%.

Further cost cutting through deeper changes and automation

In our consideration, this refrigeration plant allows for further reduction of condensing pressure below 100psig, when some minor technical barriers are overcome. According to our calculations, such a reduction of pressure will lower consumption by another 10% with no or minor capital investments.  Proper installation and setting of VFDs on a condenser fan, brine pump, and circulation pump will further reduce consumption by 15%.

Full implementation of these recommendations will reduce consumption by 38% with a payback of 1.25 years prior to incentives. All proposed measures are subject to a 50% incentive.

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