Hardware in the loop evaluation of a hybrid heating system for increased energy efficiency and management

This study presents the tests of a hybrid heating prototype, designed for retrofitting thermal treatment plants like pasteurization, to use hot water and steam in controlled ratios. In the food industry, steam with a temperature above 140 °C usually supplies the thermal production processes. The majority of processes require temperatures below 100 °C and could be supplied more efficiently by cogeneration, heat recovery or heat pumps. These low temperature heat sources can only be combined with the rigid steam system if the demand structure is changed to a hybrid use of hot water below 100 °C and steam. The hybrid heating system (H2S) increases the energy efficiency by integrating the highest possible amount of low temperature heat and responds to sudden changes in the supply structure, like demand response strategies on intermittent renewable energies and the changing availability of hot water and steam. The technical implementation is realised by a hydraulic interconnection of heat exchangers and valves. A smart algorithm controls the integration of hot water and steam into the thermal process. For reasons of food safety and product quality defined process temperatures have to be met. Prerequisite for functional verification on a laboratory scale is a simulation of the process heat demand and potential of hot water during the entire production cycle. The load profiles and relevant process parameters are passed in real time to a hardware-in-the loop (HIL) test-bed and returned to the simulation respectively. Two scenarios, hot water integration from heat pump and demand response management with a gas engine CHP and an electrical steam generator, were evaluated and the functionality of the H2S was proved. Up to 78 % of the final energy demand can be reduced by the H2S based implementation of a heat pump. The control response of the system, even with fluctuating hot water potential and temperature, met the requirements of the dairy industry.

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