Cloudfridge: A Cloud-Based Control System for Commercial Refrigeration Systems

In California, commercial refrigeration accounts for 14% of electric energy usage, corresponding to 9,014 GWh per year and affecting more than 110,000 commercial establishments. A single walk-in freezer uses more energy than 5 single-family houses. Despite more stringent standards and utility programs promoting hardware improvements, controls systems used for commercial refrigerators are still primitive. In fact, in traditional refrigerators, the vapor-compression cycle is controlled with a simple hysteresis controller to keep the air cabinet temperature within a specific range. The controller does not account for system dynamics, energy consumption, utility prices or recurrent events such as food loading schedules and business opening hours. Also, demand response is precluded with these unsophisticated controls. With the help advanced control theory and efficient optimization algorithms, computerbased real-time optimization is now feasible and applicable in commercial refrigeration systems, but its practical use to date has been limited to industrial systems requiring expensive on-premise equipment and complex operations. This paper presents a novel hardware and software architecture that allows advanced control algorithms for commercial refrigerators to be developed, tested and deployed inexpensively. The aim of this new control framework is to optimize energy consumption as a software task, utilizing the benefits of lower cost computational resources inherent to cloud computing, minimizing on net overall energy usage of the refrigeration system. A prototype of the proposed system has been developed and tested under a California Energy Commission grant. Introduction There are more than 12 million commercial refrigerators installed in the US (Table 1). The vast majority of them, in particular walk-in coolers and freezers, food preparation equipment and reach-in refrigerators still use primitive controls. Cludfridge targets primarily this large base of unsophisticated systems. In a traditional refrigerator, a thermostat controls the vapor-compression cycle with a simple hysteresis scheme to keep the air cabinet temperature or in some cases the evaporator temperature, within a specific range. The thermostat functioning parameters are set at the time of fabrication and assembly, energy used is not measured and no factors relevant to energy consumption dynamics are taken into consideration. With the help of advanced control theory and efficient optimization algorithms, computer-based real-time optimization is now feasible and applicable in commercial refrigeration systems, but its practical use to date has been limited to industrial systems requiring expensive on-premise equipment and complex operations. This project demonstrates a new way of operating commercial refrigerators, reducing in a cost effective way their energy consumption while increasing their operational efficiency. The 1 Visible Energy, Inc. (2014) Cloud Based Refrigeration Control System, Final Report. California Energy Commission EISG Program, Grant #: 57509A/1211. http://www.cloudfridge.io/ 285 11©2014 ACEEE Summer Study on Energy Efficiency in Buildings method is deployed as an automated energy optimization service based on the unique characteristics of each refrigerator and business. Additionally, this approach allows for insights to be drawn across a wide range of installations. Network latency and security have always been challenges in the implementation of cloud-based control systems. Cloudfridge has been developed to provide secure and almost realtime communication between the device and the remote control algorithm. Table 1. Total installed base of refrigerators in the US in 2008 (DOE 2009a) Commercial Sector Technical Potential by equipment type Installed Base Total Primary Energy Consumption [Units] [TWh / yr] [TBtu / yr] (Supermarket) Display Cases 2,100,000 214 730 Compressor Racks 140,000 373 1,273 Condensers 140,000 50 171 Walk‐ins 245,000 51 174 (Non‐Supermarket) Walk‐in Coolers and Freezers 755,000 148 505 Food Preparation and Service Equipment 1,516,000 55 188 Reach‐in Refrigerators and Freezers 2,712,000 106 362 Beverage Merchandisers 920,000 45 154 Ice Machines 1,491,000 84 287 Refrigerated Vending Machines 3,816,000 100 341 Total 1,226 4,183