Longer and Safer Flywheeling in Freezers

Protecting frozen food on its journey from the production facility to the customer’s shopping cart requires consistent temperature control. Each freezer managed by grocers, wholesalers, foodservice and food processors is a link in the cold chain that requires nearly constant refrigeration, and in turn requires a tremendous amount of energy consumption.

Balancing these two competing needs of temperature stability and energy costs is an old challenge that is only becoming more complex. As more renewable energy is installed, daily energy demand patterns shift and our overall energy needs grow, leading utility providers to face growing challenges in managing the electrical grid. In response, they have increased rates and instituted time-of-use and demand charges.

What is flywheeling?

The historical response to minimizing energy costs in refrigeration has been to implement flywheeling practices.  Flywheeling is sub-cooling frozen food during periods with lower energy prices so that refrigeration can later be cycled off and “flywheel” through a portion of the higher-priced period. When temperatures approach the upper limits, refrigeration systems are re-engaged. 

Flywheeling considerations

Flywheeling can be an effective strategy to cut energy costs, but there are several factors that should be considered when implementing these methods. First, operators need to recognize that the thermal mass being used to store and release that cold energy is the food itself. Even below zero degrees Fahrenheit, slow sub-cooling and gradual temperature increases cause large ice crystals to form inside the food, and those ice crystals have detrimental effects on the food quality. Secondly, although it is possible to offset some costs, sub-cooling still requires more energy consumption than steady operating conditions. Lastly, there should be intelligent systems in place that measure and respond to air and product temperatures, time-of-day and utility tariffs to ensure product protection during flywheel periods.

Safer and longer flywheeling periods

If these previous concerns are adequately addressed, the question many operators ask still remains: Are we maximizing the length of time and cost savings benefits of flywheeling? Thermal energy storage, or TES, addresses all these concerns and safely extends the length of time facilities can flywheel up to 13 hours per day.

TES systems from Viking Cold avoid using frozen food as the buffer for flywheeling by adding safe thermal mass in the form of phase change material (PCM). Each PCM formula leverages the natural properties of convection and latent heat absorption to store cold for future use, absorbs 50% to 85% of the heat infiltration, and maintain temperature stability. This alleviates the risk to food quality and shelf life during flywheel intervals, as well as protect food during possible power outages or equipment failures.

Implementing TES technology does not require the additional energy to sub-cool prior to a flywheel period. The intelligent sub-system controls make continuous real-time decisions that prioritize temperatures while maximizing energy reduction. This intelligence and the physical properties of PCM not only provide the flexibility to shift refrigeration run times, but they also increase efficiency an average of 26%.

Facilities with intelligent TES systems can maintain stable temperatures three times longer without active refrigeration and can therefor maximize their flywheel intervals. One TES study in a 93,000-square-foot frozen food warehouse has shown reduced energy consumption by 43% and peak demand by 29% for 13 hours each day.

Like any energy strategy, flywheeling should be implemented using all the best tools available. Thermal energy storage is the most effective technology to safely maximize cost savings while minimizing the risks of flywheeling.