Set point adjustments save energy in industrial refrigeration
By Anatoli Naoumov
May 27, 2016 - How valuable would it be for your business to cut the energy use of an industrial refrigeration plant by 30% while supporting the same load? To do so with a short payback? What if incentives halved the payback?
By Anatoli Naoumov
We recently completed a pilot project at the refrigeration plant of an industrial bakery that reduces 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, and the work would not have been possible without plant maintenance manager Hasan Mustafa, with whom we co-operated and who provided diligent professional support to our efforts.
Energy use grows with condensing pressure
First, a brief technical introduction for non-engineers. A refrigeration plant can ‘produce’ a 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 (so long as pressure stays within spec), a reduction in pressure makes a big difference for the bottom line e.g. a 2 psig increase of condensing pressure raises energy use by 1-2%.
While this may not seem like much, industrial refrigeration plants were commonly set to high condensing pressure to simplify operation. This may have been OK while energy was cheap but, today, controls are getting cheaper as energy gets more expensive, so why not lower condensing pressure by 30-80 psig (pound-force per square inch gauge) thereby reducing energy use by 15-40%?
Not as simple as dimming lights
Along with reducing condensing pressure, energy use can be cut by floating condensing and suction pressure, optimizing hot gas defrosting, and optimizing compressor and condenser operating sequences.
Beware: reducing energy consumption in refrigeration systems 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.
Pilot proves concept in real life
Our pilot project aimed to demonstrate the economic viability of reducing condensing pressure in the real-world conditions of the industrial bakery’s refrigeration plant. Here is what we did:
• Conducted a thorough review of the cooling plant.
• Established the energy consumption ‘before’ baseline in relation to production through a regression analysis for the whole refrigeration plant (R2 of 88%).
• Conducted an energy software simulation for several levels of lower condensing pressure to forecast the reduction in energy use.
• Decreased condensing pressure from 180 psig to 150 psig.
• Collected the ‘after’ energy use and production data.
• Compared the actual reduction with the software forecast.
In the end, energy consumption of the whole refrigeration plant decreased by 13%, exceeding a conservative simulation forecast of 3.5%.
Further cuts through deeper changes and automation
Were the plant to overcome some minor technical barriers, we feel the refrigeration plant could further reduce condensing pressure, to below 100 psig.
According to our calculations, such a reduction would lower consumption by another 10% with no (or minor) capital investments. Properly installed and set VFDs (variable frequency drives) on the condenser fan, brine and circulation pumps would further reduce consumption by 15%.
Full implementation of these recommendations would reduce consumption by 38% with a payback of 1.25 years prior to incentives, and similar results can be achieved at most industrial refrigeration plants.
A managing partner at GreenQ Partners, Anatoli Naoumov, MBA, MSc, CMVP, has been involved in various areas of business analysis and development for over 15 years for companies in Canada, The Netherlands and Russia. He has been certified as measurement and verification professional (CMVP) by The Association of Energy Engineers (AEE) and The Efficiency Valuation Organization (EVO). He can be reached at firstname.lastname@example.org .