The dairy industry relies heavily on refrigeration to maintain product quality and food safety throughout the production chain. As summer temperatures increase and production volumes grow, dairies face rising cooling demands and more pronounced peak loads. These challenges are particularly relevant in regions with limited grid capacity or high electricity costs, where efficient use of energy is becoming increasingly important.
This project, carried out by SINTEF Ocean in collaboration with Rørosmeieriet AS, investigated how cold thermal energy storage can improve the energy efficiency and operational flexibility of dairy refrigeration systems. The work focused on the use of ice slurry technology as an alternative to conventional cooling solutions, with the aim of reducing cooling peak loads, improving system efficiency, and supporting future production growth.
Understanding the challenge
Milk must be kept at low temperatures throughout the entire value chain. Under normal conditions, milk arrives at the dairy with a stable temperature, but during periods of high ambient temperatures larger cooling loads occur at the milk intake stage. These temporary demand peaks can place considerable stress on refrigeration systems and may ultimately limit production capacity.
Traditionally, refrigeration plants are sized to handle the highest expected peak loads, even if those conditions occur only a few days each year. This leads to oversized systems that often operate away from their optimal efficiency point.
Thermal energy storage as a solution
Instead of increasing refrigeration capacity, the project explored whether thermal energy storage could be used to decouple cooling production from cooling demand. By producing and storing cooling energy during periods of lower demand, such as at night, stored cooling can later be used to cover short-term peaks during milk reception and processing.
Two storage technologies were evaluated:
- Ice slurry storage, based on a mixture of fine ice crystals and water produced using supercooling technology.
- Pillow-plate storage, where phase-change materials freeze and melt between heat exchanger plates.
Both technologies utilise latent heat storage, allowing large amounts of cooling energy to be stored within a relatively small volume.
Key results
Using operational data collected at Rørosmeieriet, the project quantified the refrigeration demand and evaluated the performance of the different storage concepts.
The results demonstrated that thermal energy storage can significantly reduce the required refrigeration capacity:
- Without storage, the refrigeration system would need approximately 161 kW of cooling capacity to cover peak demand.
- With thermal storage, the required refrigeration capacity could be reduced to approximately 33 kW, corresponding to a reduction of around 80%.
Among the investigated alternatives, the ice slurry system delivered the best overall performance.
Key findings include:
- Higher energy efficiency compared with the pillow-plate alternatives.
- A calculated system COP of 2.48, compared with 2.29-2.39 for the pillow-plate systems.
- Moderate storage volume requirements of approximately 16 m³.
- The use of water as the primary storage medium.
- Improved ability to operate the refrigeration plant closer to its optimal operating point for longer periods.
The pillow-plate systems were found to be technically feasible today and may offer advantages where installation space is limited, but their performance depended strongly on operating temperature, storage material properties, and available heat-transfer area.
Main conclusions
The study shows that thermal energy storage is a promising strategy for adapting dairy cooling systems to warmer summers and increasing production demands. Rather than continuously enlarging refrigeration plants, dairies can improve energy efficiency and system flexibility by storing cooling energy and using it when demand is highest.
For the case studied, ice slurry technology emerged as the most promising solution due to its combination of high energy efficiency, compact storage requirements, and operational flexibility.
Next steps
The project represents an important first step towards implementation of advanced cold thermal energy storage in the dairy sector. Further work should include detailed assessments of investment and operating costs as well as validation under full-scale production conditions.
A pilot-scale demonstration of an ice slurry system is considered a particularly relevant next step to verify the predicted benefits under real operating conditions and to support wider adoption within the food-processing industry.