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Optimization of Industrial Refrigeration Plants: Including a Case Study at Stonyfield Farm Yogurt

Industrial refrigeration can be found in many types of applications ranging from ice making to food processing to product preservation. Industrial refrigeration typically represents one of the largest loads in a facility whenever required for manufacturing processes. A refrigeration system is made up of different components including compressors, evaporators, condensers and controls. Each component may be from a different manufacturer in custom engineered systems, or equipment may come as an integral packaged unit. Custom systems are generally an assembly of components that have been tested and rated individually under design operating conditions but not necessarily rated as an integral, coordinated system. Therefore, in the assembled refrigeration plant, there is a possibility that the individual components may not provide optimum operation based on the deviation between the actual operating conditions and the test conditions as well as the interactions between the different components in the system. Consequently, the final refrigeration plant may not operate optimally, resulting in lower operating efficiency and higher operating costs. The factors that influence the refrigeration system energy use are the inherent efficiency of the design and refrigerant, the condition of the equipment, the control strategy, and the load profile of the system (deviation of the operating cooling loads from the design cooling loads). In many cases, the installed refrigeration plants can benefit from an optimization process that incorporates monitoring of key operating parameters resulting in subsequent control adjustments and or system operational changes based on the assessed data. This paper will: provide an overview of typical industrial ammonia refrigeration systems; discuss the various components of the system including the compressors, condensers, evaporators and controls that make up a refrigeration system; and present typical energy saving strategies pertaining to the operation of multi-stage compressor systems, the use of evaporative condensers and floating head pressure controls, and sequencing optimization strategies. Furthermore, simple low cost approaches to reduce refrigeration loads will be discussed. A case study will be presented that illustrates the concepts associated with the refrigeration system energy savings opportunities discussed in the paper. Stonyfield Farm Yogurt, a well-known, environmentally and socially progressive manufacturer of a wide variety of all natural and organic yogurts and ice cream, has undertaken a remarkable set of energy efficiency initiatives at their facility. They have participated in their local utility energy efficiency programs provided by Public Service Company of New Hampshire (PSNH). The studies, assessments, and installation discussed in the case study were developed through technical assistance efforts sponsored by PSNH. We will discuss the details of Stonyfield’s refrigeration plant and system, and present results associated with the refrigeration system energy optimization conducted at the facility.