Fish products are frozen to preserve quality and extend shelf-life. However, freezing processes in the industry are typically very energy demanding and seldom optimized with regard to energy usage. During freezing, the operating conditions for the refrigeration cycle, as well as the driving temperature difference over the product changes significantly from start to finish. A complete transient model including a refrigeration plant, an air blast freezing tunnel and food products has been built, based on the Modelica programming language. The product model is discretized into uniform layers, described with equations for temperature dependent properties such as thermal conductivity and heat capacity.