Annex 59 – Heat Pumps for Drying

Drying is generally understood to be the removal of liquid from a dry material or product. This can be done either mechanically or thermally by using energy. If possible, mechanical drying should be used, as these processes only require about 10% of the energy input of thermal processes. Drying processes are widely used in industry and commerce (food industry, paper industry, chemical industry, ceramics industry, laundries etc) as well as in household applications (white goods, tumble dryers, dishwashers) in various forms and contribute significantly to energy consumption. (10-25% of industrial energy consumption is used for drying processes). In thermal drying, processes can be distinguished by the form of energy input, such as convection drying, contact drying, radiation drying or electrical drying. The moisture (e.g. water) extracted from the material to be dried is in most cases released into the environment in pure gaseous form or with a drying medium (e.g. air, steam). This exhaust air contains high amounts of energy, which is currently only partially used by heat recovery. Heat pumps can make a significant contribution to heat recovery by lowering the temperature level below the dew point to recover the latent energy of water vapor. By integrating heat pumps, energy savings of up to 80% can be achieved in the drying process. Heat pumps can either bring heat back into the process or make it available for further use (heating, hot water etc.). As many of the processes have to run at certain temperature levels, the use of high temperature heat pumps (up to 200°C) in industrial environments is of great interest. Annex 59 – Heat Pumps for Drying aims to structure and describe the numerous possibilities and advantages of heat pump integration in dryers. Both state of the art and innovative solutions in industrial, commercial and household applications will be investigated and described.