Integrated CO₂ refrigeration and heat pump systems for dairies

Production facilities in the food industry are large consumers of electricity and thermal energy due to energyintensive processes such as steam production, cleaning, sanitising, refrigeration and drying. Furthermore, there is often a considerable thermal demand for heating the building and for air‐conditioning purposes. Dairy plants require both heating and cooling at various temperature levels to process the different dairy products. The thermal demands in these plants have traditionally been covered by separate systems, such as fossil fuel burners or electric boilers for the heating processes and various refrigeration systems for the cooling processes. In recent years, there has been an increased focus on integrated energy systems for dairies as a measure to reduce the overall energy consumption of the plant. This strategy involves integrating all functions to serve the thermal demands into one centralised energy system.
This paper describes the energy system for a dairy plant in central Norway. A CO₂ refrigeration system serves the various cooling loads in the production process. The energy system in the dairy is mapped and the thermal loads have been identified. Based on the current configuration of the cold side of the CO₂ refrigeration units, proposals for improvements are made. Using thermodynamic calculations, the modifications are evaluated in terms of COP improvement and the annual reduction in energy consumption. The calculations show that the energy consumption can be reduced by 12 % to 21.2 % depending on the alteration of the system.