All frozen foods have temperature requirements to maintain quality and shelf life as they travel throughout the cold chain to our plates. Maintaining these temperatures during each leg of that journey requires refrigeration equipment to run nearly 24/7, and that continuous run time requires a lot of energy. Over the years many efficiency technologies (LED lighting, VFD motors, automated doors) have provided some incremental energy consumption reductions, and alternative energy sources (solar, wind) have been implemented to lower reliance on expensive grid-based energy.
Many regions have time-of-use or demand charges that increase energy costs during specific hours of the day. These costs have driven some operators to adopt an operational technique called flywheeling, also known as floating, to avoid a portion of these expensive time intervals. Flywheeling is when a facility super-cools the frozen food and the room to a much lower temperature than normal during low priced hours and then cycles off, or greatly reduces, active refrigeration operating during the higher priced periods of the day. As upper-temperature limits are approached, refrigeration systems are re-engaged to bring temperatures back down. By employing flywheeling techniques, operators are using the food as a temperature capacitor, or battery, to lower their energy costs.
If energy costs are reduced, why shouldn’t frozen food producers, foodservice distributors, third-party logistics companies, and grocers use frozen food as a battery? Using thermal mass to maintain temperatures is mathematically sound, but frozen food is not the most effective thermal medium to maximize the energy-saving benefits of flywheeling and increases risks to food quality and shelf life.
In terms of energy use, traditional flywheeling shifts when energy is used, but the facility and the food actually requires more energy during the super-cooling periods. Though the cost of this additional electricity may be less expensive during off-peak periods, the additional energy also increases that facility’s carbon emissions during the super-cool period. This is detrimental to sustainability initiatives and Scope 3 emissions standards of customers and distribution partners.
Using food as the thermal battery also limits the length of flywheeling periods and the associated energy savings. There are other materials that can absorb more heat (with a higher thermal capacity) and absorb and release that heat faster (with a higher heat transfer rate) than frozen food. Many facility owners now utilize Thermal Energy Storage (TES) technology from Viking Cold Solutions.
These TES systems include safe thermal mass in the form of an environmentally-friendly phase change material (PCM) that attracts, absorbs, and stores up to 85% of the heat infiltration while protecting the food. Their PCM has 300 times more thermal capacity and a heat transfer rate eight times higher than frozen food. The PCM and the system’s intelligent controls prioritize temperature requirements while extending flywheeling periods up to 13 hours per day without risking food quality or safety.
Additionally, TES systems increase refrigeration efficiency and reduce overall energy consumption resulting in substantially reduced energy costs as well as lower emissions.
Flywheeling’s cyclical nature is inherently problematic for frozen food because the food can change temperature multiple times per day. Dr. Dennis R. Heldman, Professor of Food Engineering at The Ohio State University and member of the Scientific Advisory Council for the World Food Logistics Organization’s (WFLO) and the Global Cold Chain Alliance (GCCA) says, “Even at zero degrees Fahrenheit, a small amount of water remains unfrozen in all frozen foods. So, any increase in temperature increases the amount of unfrozen water and the potential loss of quality.” Heldman continues, “As water re-freezes during a decrease in temperature, larger ice crystals form that can disrupt the structure of food and cause additional loss of quality and shelf life.” Utilizing TES systems ensures that the PCM absorbs the heat before the food and minimizes the threat to quality and shelf life caused by flywheeling on the food.
Numerous cold storage operators around the globe benefit from Viking Cold TES systems, and many utilities and power providers incentivize efficiency and energy storage technologies. Recently, in Massachusetts eight facilities including sites owned by the world’s largest third-party cold storage company, the world’s largest foodservice distributor, numerous frozen food processing companies, and a food bank received fully-funded TES systems from their utility. The utility is incentivizing them to flywheel on TES technology during specific high demand hours of the day.
The economics of the global cold chain are highly dependent on the amount of energy used and the cost of that energy. Techniques and technologies employed to manage that energy must take into account the economic benefits, the quality and safety of the food, and the sustainability of the facility. Installing thermal energy storage rather than using frozen food as a battery can maximize the economic benefits of flywheeling, minimize the environmental impact of the facility, and better protect the quality of the food we put on our tables every day.