Dealing With Starts, Avoiding Failures
Some recent developments in these areas relate to digital capacity modulation of a compressor and compressor protection to curtail failures. Case histories supplied by Emerson Climate Technologies show how both aspects were dealt with at a site in Canada and at a store in Michigan.
Discus + Architecture
In the Canadian situation, a digital capacity modulation upgrade was added to existing Intelligent Store® compatible Copeland Discus Digital™ compressors that use CoreSense Diagnostics. This took place at one of the stores owned by Sobeys, a national Canadian supermarket chain with more than 1,300 stores.
According to officials, compressor starts were reduced by 56 percent, reducing inrush current, thereby reducing stress and wear on compressors and contactors. The operating suction pressure range was narrowed by 85 percent allowing average suction pressure set points to rise by up to 4 psig. Case temperature fluctuations were reduced by up to 90 percent as shown by reducing the operating range of a dairy case from 15˚F to 1¼˚.
“Sobeys is recognized for the freshest produce, meat, and fish sold to our customers,” said Ken Flavin, manager of refrigeration and maintenance for Sobeys. “Discus digital compressors augmented that commitment by significantly reducing case temperature fluctuations.”
Reducing energy costs while preserving the perishable product integrity is a priority. Digital capacity modulation technology adds variable capacity unloading up to 90 percent of the compressor capacity. The extended range of unloading assumes the role of a swing compressor and reduces the cycling on all compressors that share the same suction group.
The digital capacity modulation technology, which is designed to review and adapt within seconds, delivered an unloading strategy to match the capacity with the product load over the variable operating conditions typical of supermarket applications, it was reported.
Compressor starts were reduced by an average of 56 percent and operating suction pressure increased, both contributing to reduced energy consumption.
After reviewing the results, a decision was made during startup to standardize on the digital capacity modulation technology for Sobeys’ new store building program, and a retrofit program was launched to identify existing Sobeys stores for upgrade.
Ron Kowalski, president of Premier Refrigeration Co. of Detroit said he is a firm believer that refrigeration problems can be avoided with regular maintenance and proper diagnostics.
When one major supermarket customer was ready to remodel, Kowalski looked for a solution that provided advanced compressor protection and would allow his technicians to quickly diagnose any problems.
According to Kowalski, the solution averted two potential compressor failures within weeks of startup. A $5,000 repair bill was avoided with no loss of product, and intermittent rack problems that would be impossible to detect were quickly diagnosed.
The decision was to use Copeland Discus® compressors with CoreSense™ Protection on the parallel refrigeration systems. After installation, the module issued a warning for one of the 25-hp compressors. The technician discovered that one of the contactor points was beginning to fail and was causing a momentary loss of a phase to the compressor. If this single-phasing was not addressed quickly, the compressor could have possibly failed, Kowalski said.
At a later date on the same system, the module alerted the contractor to another momentary, intermittent rack problem by issuing a high motor temperature alarm with a low oil warning notice.
This problem would have gone undetected without the advanced protection, Kowalski said. The contractor said he was able to correct the problem before it grew into a major failure.
By using the compressor as a sensor, CoreSense Protection monitors and interprets system and electrical information within the compressor, and can shut the compressor down before damage occurs. The technology alerts technicians to the most serious faults first so they can correct problems and prevent catastrophic compressor failures.
Publication date: 09/05/2011