Facing-ever increasing demands for higher energy efficiency and lower global warming potential refrigerants, the food industry is witnessing a transition away from a traditional centralized approach to the control of refrigerated cases toward a decentralized—or distributed—approach. This method relies on individual controls—case controllers—placed on each refrigerated case that work independently and ensure the most efficient operation of the case, while helping to guarantee food safety and quality.
Control, One Case at a Time
Until recently, supermarkets relied on a single central control device to monitor and manage multiple refrigerated units in a store. However, the introduction of case controllers changed this approach, first in Europe and later, in the early 1990s, in the United States, as energy prices climbed and the food industry became better acquainted with the proven technology.
Installed on individual refrigerated units, case controllers provide a single point of control for all aspects of a refrigerated unit. The controllers incorporate a processor with defined algorithms, using inputs (sensors) and outputs (relays) and solid-state electronic expansion valves. Settings are programmed directly into the case controller, giving operators the ability to manage the electronic expansion valves and control lights, fans, defrost and anti-sweat heaters. The controls also offer night setback features, dual temperature switching, walk-in control and cleaning functions. All information about the case is shared with the system manager for remote or local viewing of the operation.
Today, the popularity of case controllers continues to grow. The increasing cost of energy, along with the number of experienced technicians, has improved the return on investment and reduced payback time associated with case controllers. And because the controllers contribute to lower energy consumption, they also support a growing interest in reducing carbon emissions and embracing green technology.
Installation Costs Decrease
In addition, because case controllers become the point of electrical distribution and perform all the tasks associated with a case, fewer (at least 50 percent less) electrical components—such as wiring and breakers—are required. This means less time running cables. The need for manual superheat adjustment is eliminated because electronic expansion valves (EEVs) have replaced traditional thermostatic expansion valves (TXVs).
Both of these changes mean reduced labor costs. In fact, field experience shows that savings of 50 percent have been achieved in the area of labor. And because the knowledge base continues to increase with experience, the bidding process is more accurate. Rebate programs tied to energy consumption can further reduce the costs of installing a distributed case control system. In the end, a typical store in the United States that measures approximately 65,000 square feet and uses a case controller setup can save, on average, as much as $84,000 in installation costs.
The fact that case controllers and their related expansion valves are compatible with a variety of refrigerants, including CFCs, HCFCs, HFCs and CO2, also increases the popularity of the controls. In fact, the limitations of the mechanical expansion valve and its slow response time make case controllers a requirement for CO2 systems.
Making the Case for Reduced Energy Consumption
The increasing popularity of case controllers is fueled by the benefits they offer. Reports of reduced energy consumption can be attributed to the continuous measurement of superheat and the controller’s ability to precisely match the refrigerant load within the system. This contributes to a 12 percent reduction in energy use.
Case controllers also offer significant energy savings in the form of intelligent defrost control. Case control input and operational data is used to measure ice buildup, initiating the defrost cycle only when ice buildup registers. This buildup is minimized thanks to continuous adaptive superheat control, which strives for stable superheat across the entire evaporator and, thus, reduces the need for defrosting. Field experience using adaptive defrosting demonstrates the ability to go more than one week without defrosting.
Store owners also appreciate the case controller’s ability to integrate with the control system while meeting the needs of the modern supermarket. The controller communication network provides the comfort of having a fully monitored refrigeration system 24 hours a day, seven days a week, ensuring optimum food safety and quality.
Fewer Components Mean Less Maintenance
In addition, case controllers eliminate the need for extra components. Solenoid valves, for example, are no longer necessary, as the expansion valve performs tasks associated with these valves. These examples of reduced hardware also result in lower costs and fewer solder joints.
Case controllers also reduce ongoing maintenance requirements and the associated costs for a variety of reasons. For example, inputs (sensors and transducer) eliminate the need for the manual periodic adjustment of expansion valves, and remote diagnostic capabilities improve visibility on the current operation, along with history logs. And because each case is individually controlled, a single case can easily be shut down when maintenance is required. When merchandising needs require changes to operating temperatures within a particular case, temperature changes can be accomplished by a switch or remotely without generating a service call. Case lighting schedules can also be controlled remotely at the system manager level or directly at the controller.
In addition to maintenance benefits, case controllers help to ensure food quality and safety. Combining case control algorithms with electronic expansion valves minimizes swings in the case temperature, while built-in and remote display options allow for continuous visibility of case temperature and current status.
Case controllers reduce ongoing maintenance requirements and the associated costs. In addition, product temperature probes can be used to simulate product temperature within the case.
Study Demonstrates Value of Case Controllers
A recent study conducted by the Biberach University of Applied Sciences in Germany confirms the benefits case controllers offer. This study compares the energy consumption of two branches of the Edeka supermarket chain, each with relatively small footprints. One was fitted with a standard, centralized control setup and the other was retrofitted with a decentralized system that features Danfoss ADAP-KOOL case controls. After two years, the results show the branch that was optimized with case controllers and matching EEVs reduced its energy consumption by an average of 23.2 percent, resulting in a payback of just one year. At the same time, the controllers ensured food quality, decreasing food loss.
Real-world examples like this one support a shift from centralized control systems to distributed control systems that rely on case controllers. The results consistently show installation costs are reduced and energy is saved. At the same time, store owners find that reliability is ensured, food is preserved and control and maintenance is made simpler.
Keith Baughman is the Training Manager for Danfoss. Chris Brown is an OEM Applications Engineer for Danfoss.