Improvement of thermal efficiency for isobutane refrigeration system could match well with the building requirements of low-carbon, and sustainable development. The electric radiant heater (ERH) is widely used for the freeze and cold storage (FCS) system, but it has problems of high electric consumption and high freezer compartment temperature rise (FCTR) as a result of low heat-transfer efficiency under defrosting. Therefore, a novel FCS system with an additional electric radiant heater (AERH) based on the heat required for frost melted and synchronous defrosting is proposed. The defrosting consumption and the FCTR of the novel FCS system are comprehensively evaluated by a novel evaluation method. Besides, the effect of the thermal parameters (i.e., the defrosting pause temperature, the position, and electric power of the AERH) on the heat transfer characteristics are compared and optimized by the experimental method. Finally, a novel method is presented to predict the optimum thermal conditions. The results show that the optimum system thermal performance is obtained, the defrosting duration and defrosting consumption are reduced by 44.02 % and 37.03 %, and the defrosting efficiency and energy efficiency could be increased by 17.92 % and 9.96 %, respectively, as compared to the conventional FCS system. The proposed FCS system has better economic performance and heat transfer efficiency. Meanwhile, 30.54 kg of CO2 emissions could be avoided during the annual operation period, and the environmental benefits are also considerable. This study not only reaffirms the benefit of using the AERH for defrosting in the FCS system but also provides a reference for the promotion and application of efficient heat transfer technology in building refrigeration engineering.