Analyzing excess heat factors of convective/radiant terminals: Balancing beginning and steady stage

Abstract

With the improvement of living standards in China, space heating has become a focal point, where energy efficiency and thermal comfort play crucial roles in the utilization of heating devices. Addressing the limitations of existing heating systems, convective/radiant terminals have been developed to balance rapid heating during the beginning stage with sustained thermal comfort during steady stage. The convective-to-radiant unit ratio is a crucial determinant of terminal performance and a key design consideration. The excess heat factor represents the additional fraction of convective heat transfer during the initial stage. It is influenced by the excess load factor, a characteristic of building loads, specifically referred to as the excess heat factor in the design of convective/radiant terminals. This study utilized building energy simulations based on the time-series conduction transfer function by energy simulation software, considering various configurations such as enclosure structure, number of exterior walls, indoor set-point temperature, and the time required to reach the set-point temperature. Results indicate that an excess heat factor of 0.80 is technically and economically feasible based on daily operating factors and annual design factors. The research contributes valuable insights into optimizing terminal design for enhanced energy efficiency in the context of space heating. Two types of convective/radiant terminals, direct expansion, and heat pipe terminals were developed for preliminary validation, providing fundamental parameters for the specification of terminals.