Comparison of various dual-temperature zones space heating systems based on energy cascade utilization principle

The high efficiency heating system is crucial in ensuring both residents and buildings remain comfortably warm during cold seasons, providing not only a comfortable living environment but also contributing to health, productivity, and overall well-being. Based on the energy cascade utilization principle, three multi-temperature zone space heating systems were introduced firstly, namely warm air (WA), radiator combined with fresh air (RA + FA), and floor combined with fresh air (FL + FA) in this research. The detailed energetic and exergetic models of these space heating systems were developed to investigate and compare the system performance under various operated conditions, including the fresh air, supply air, radiator, and floor temperatures. The results showed that the energy efficiency ratio (EER) value increased first and then decreased with the supply air temperature increasing for the WA, while the EER of the RA + FA and FL + FA decreased with the floor and radiator tem-peratures increasing. The maximal EER for the WA, FL + FA, and RA + FA system were 2.96, 3.52, and 3.43 under selected conditions. Besides, the WA system outperformed the RA + FA system in terms of exergy efficiency, and the WA system exergy efficiency ranged from 22 to 28% under selected conditions. Lastly, for the FL + FA system, the system exergy loss increased by approximately 0.016-0.018 kW/degrees C for the floor temperature, and the values were 0.024 kW/degrees C for fresh air temperature.