The intermediate temperature optimization for cascade refrigeration system and air source heat pump via extreme seeking control

The cascade refrigeration system and cascade air source heat pump have both been a well-known advanced technology for providing cooling and heating under certain circumstances. The intermediate temperature has been proven as a key factor in affecting the operating performance for both the refrigeration and heat pump system. However, the optimal intermediate temperature varies along with the change of the ambient temperature, cooling/heating demand. So achieving the real-time optimal intermediate temperature in a realistic operating circumstance is critical for improving the performance of cascade refrigeration or heat pump system. In this paper, the extreme seeking control strategy is proposed to optimize the coefficient of performance via seeking the real-time optimal intermediate temperature. A cascade refrigeration system model and a cascade air source heat pump water heater model are built based on Modelica, and the ASHP water heater model is validated by experimental data. The simulations are conducted under fixed and variable operating conditions to validate the effectiveness of the proposed strategy.