Variable load control method for magnetic cooling systems.

In this study, we demonstrate that magnetic cooling system has significant energy saving advantage when operating under part load conditions. Part load operation refers to less load under constant temperature span, or constant load with less temperature span, or a combination of both, which are common features of refrigerators and air-conditioners. To achieve high efficient operation under part load, a close loop control strategy is proposed to automatically tune the operating frequency and flow rate based on the temperature of heat source heat exchanger. The proposed control method is robust for five different load variation profiles, which can guarantee to maintain temperature within ±1K from set-point. A case study is carried out for unitary air-conditioning application, which shows over 6 times of COP enhancement from full load to minimum part load ratio conditions, and the overall energy efficiency index doubles from the nominal COP value.