Research on Heating Characteristics of Radiant and Fresh Air Composite Systems Based on Frequency-Domain Resistance-Capacitance Model

Based on the analogy of the resistance-capacitance (RC) model and frequency-domain transformation theory, a transfer function of the RC model coupling the air conditioning system and the room was established. During the modeling process, the unit efficiency method was employed to simplify the equivalent treatment of the water supply coil in the radiant terminal, and the core temperature layer theory was introduced to hypothetically simplify the complex internal structure of the prefabricated trench plate. Finally, the accuracy of the model was validated through a constructed radiant experimental platform, and the effects of the thickness of the prefabricated trench plate and the spacing of the coils on the heating performance were analyzed. The results indicate that reducing the thickness of the trench plate increases the floor heat flux by 10% and enhances the effective heat dissipation capacity of the radiant surface. In contrast, increasing the coil spacing leads to a 13.6% decrease in air temperature and a 20.1% decrease in floor temperature, with significant reductions in both the water-side and floor heat fluxes. These findings provide a theoretical basis for optimizing the design of radiant and fresh air composite systems.