Dynamic characteristics of a climate-adaptive radiant cooling and fresh air supply integrated system with zeotrope R290/R600a

Abstract

Enhancing climate-adaptability stands as a pivotal focus in the advancement of air-conditioning technology. The nuanced control over thermodynamic properties of zeotropic mixture emerging as a critical factor in effectively accommodating variable loads. This paper proposes a radiant cooling and fresh air supply integrated system, featuring dynamic adapting to various operating conditions by composition adjustment with zeotropic mixture of R290/R600a. By synchronizing the cooling capacities of dual cooling sources with indoor thermal-humidity load, the climate-adaptive operation is accomplished by tuning the secondary fluid of the liquid separation component. A physics-based dynamic model is constructed on the liquid separation condenser in the sequence of control volume-pipeline-path based on finite volume approach. The numerical analysis indicates the spatial distribution of mass fraction and thermophysical properties of the zeotropic mixture over time. To facilitate intuitive analysis of the climate-adaptive operation, the enthalpy humidity ratio (ε) that the system can handle is developed for evaluating the applicable scenarios and operating conditions of the dual cooling source system. The results demonstrate that the liquid separation component exhibits a rapid response owing to its low thermal inertia, lagging less than 30 s to adapt to the airflow step from 0.45 to 0.4–0.5 kg/s over a total duration of 120 s. The enhancement of convective heat transfer and reduction in heat capacity both lead to a decrease in thermal inertia, thereby shortening the response time. Increasing the airflow rate shortens the response time to 60 % of its initial duration. R290/R600a at mass fraction ratio of 0.6/0.4 exhibits the highest sensitivity to airflow adjustment. The capacities of the dual cooling sources respectively fluctuate between −55 % and 62.5 %, and −84.6 % and −0.02 %, as a result of the mass flow rates of the refrigerant varying between −60 % and 120 %, and −85.2 % and −48.1 %, with the mass fraction of R290 ranging from −20 % to −10 %, and −11.8 % to −5.9 %. The system can provide fresh air of 19 ± 16 %℃ and 12 ± 23 %g/kg and chilled water supply for the radiant terminal of 15 ± 20 %℃. The system is capable of handling air-conditioned spaces with ε ranging from 1450 to 20000 kJ/kg by adjusting the airflow rate within a range of ± 12 %, and offering an adjustable dehumidification capacity ranging from 0.2 to 2.5 kg/h. The system constitutes a promising prospect of thermal-humidity decoupling technology that adapts to various climatic conditions and personalized need.