Keeping Your Cool
The phrase “keeping your cool” generally means staying calm and relaxed in a tense situation. In today's world of high electrical energy costs, though, staying relaxed has become increasingly difficult, especially in the refrigerated storage market. Seventy to eighty percent of a refrigerated storage facility's electrical bill typically is attributed to the operation of the refrigeration equipment required to keep the facility cold. For the Albertsons Grocery Distribution Center in Tolleson, Ariz., the phrase “keeping your cool” took on both a figurative and literal meaning as the facility struggled to reduce its energy consumption.
Identifying Energy Use
Cursed by the Arizona climate, the Albertsons refrigerated facility requires a significant amount of ammonia refrigeration equipment to maintain the normal operating temperatures of the 7 million ft3 of refrigerated space. Determined to handle as much of the increasing electrical costs at their facility as possible before passing these costs on to their customers, the staff at the Albertsons contacted Advanced Energy Control (AEC) in Randolph, Wis., for help in the spring of 2004.The engineers at AEC first performed an energy audit on the refrigeration system at the Albertsons facility. The audit included a detailed analysis of the existing control system strategies, the operation of the 2,800 hp of ammonia compressor, the operation of 47 freezer and cooler evaporators, the system-pressure requirements of the three suction systems, and other mechanical refrigeration operations.
After analyzing the refrigeration system's operation, the AEC team researched the electrical utility company and its electrical rate structure and billing practices for the facility. By studying the “when” and “how much” of Albertsons' electrical utility bills, and by comparing this information to the refrigeration system's operation, AEC was able to provide Albertsons with a report detailing where the most energy savings could be recouped.
Achieving Better Control
The staff at Albertsons was surprised to hear that they could achieve significant energy savings by installing an AEC custom-designed computer control system. “Our existing system wasn't that old, so we had fairly good faith that it was operating properly. AEC showed us that there was much more we could do with their control system,” said the maintenance manager at the facility.The new control system was designed with several operational changes that were noted during the energy audit. The primary goals were to maintain the facility's temperatures and reduce the overall amount of the utility bills.
To begin, AEC designed the control system to allow the refrigeration system to best manipulate the electrical rate structure of the local utility and to eliminate the excessive electrical demand charges, which are based on the rate of usage of electricity, or how fast the facility uses electricity. Unfortunately, demand charges are billed on the highest rate of usage for each month. The utility was basically charging Albertsons for going too fast - essentially issuing a speeding ticket.
By monitoring the rate of usage of electricity for the entire facility, the AEC control system was able to adapt the electrical usage of the refrigeration system around the fluctuations in usage in the rest of the facility. For example, if the facility's conveyor system turns on and starts consuming a sizable amount of energy, the refrigeration system will back off on its consumption to compensate. This keeps the facility's rate of usage of electricity at a constant rate, thus eliminating excess demand charges.
The AEC control system also was designed to adjust the refrigeration load based on the overall cost of electricity, which varied depending on the time of day. At certain times of the day (known as “peaks”) as designated by the utility, the cost of electricity is higher than at other times. The Albertsons facility operates under five peak schedules every 24 hours. The control system was therefore designed to provide a minimal amount of refrigeration during the highest cost peak periods and to maximize the amount of refrigeration used during the lowest cost peak periods. All other peak times were scaled accordingly. This level of control allowed the refrigeration system to maintain room and product temperatures while still achieving the maximum amount of energy savings possible.
Reaping Continued Benefits
The AEC control system was installed by the end of June 2004, and the company immediately began to see substantial savings. “In the first two months with our AEC control system, we saved $40,600 over [the same two months in] the previous year, and we still maintained great temperatures,” says the maintenance manager at the facility. “We even saved money in July - and that is one of our hottest months.”After more than one full year of operating with the new control system, the Albertsons Grocery Distribution Center has saved just over $175,000 compared to the previous year. The total cost of its investment for the energy audit and advanced control system has already been recouped in energy savings. Even if the future continues to bring ever increasing electrical energy costs, this Albertsons facility will be able to keep its cool.
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