A PROPOSED METHOD AND CASE STUDY OF WASTE HEAT RECOVERY IN AN INDUSTRIAL APPLICATION

Waste heat recovered from a refrigeration machine is associated with the double benefit of generating cold and heat with just one unit. Additional energy is required in most cases to achieve these benefits. To evaluate the efficiency of waste heat recovery, two novel efficiency indicators are described. The Overhead-COP describes additional electrical power required to raise the temperature to make waste heat useable. The Coefficient of Savings describes power reduction when condenser heat is fed into a cold district heating network instead of exhausting it to high temperature outside air. Results are reported from a case study in a food logistic center with high cooling demand in Isny, Germany. Waste heat at this facility was previously released unused to outside air. We describe how this waste heat can be used to supply sustainable heat supply to a new residential area. During the design phase, it is difficult to choose the best operating temperature for district heating networks (DHN). The novel indicators are used to value the effort to make waste heat useable. Whereas a sup-ply temperature of 20 °C has no disadvantages for the operator, a supply temperature of 40 °C is associated with an increase in electricity consumption. Resulting OCOPs are above 5.0 even under unfavourable conditions and exceed the theoretically calculated [1,2] and measured [3] COPs for air-sourced heat pumps. Although using waste heat is not free, it is beneficial when overall efficiency is considered.