Design method of multi-stage air treatment system with circulating air for high efficiency in year-round working conditions

Owing to the large temperature rise/drop during the fresh air treatment process, the multi-stage treatment systems for fresh air have good energy-saving effects. However, the energy-saving potential of multi-stage treatment systems for circulating air and the design of a multi-stage circulating air treatment (MCAT) system that operates efficiently under variable conditions throughout the year remain unclear. Therefore, this study proposed a multi-condition design method to ensure the annual energy-efficient operation of the circulating air system. Firstly, the appropriate number of air treatment stages (NUM) NUM ) and heat transfer temperature difference between air and water (Delta t) Delta t) for each single condition are determined and an appropriate heat transfer area is obtained. Subsequently, an MCAT system suitable for multiple working conditions throughout the year is designed by searching for the common values of the appropriate heat transfer area per stage. Finally, three types of buildings and six cities located in different climate zones are selected to explore the adaptability of the appropriate Delta t. The results show that (1) for each single working condition, the appropriate ranges of NUM and Delta t are 1-2 and 2-6 degrees C respectively, which can keep the system energy consumption at a low level. (2) There is generally a common range for multiple heat transfer areas per stage designed under different working conditions, and an MCAT system designed based on this common range can achieve energy- efficient operation under multiple annual conditions. (3) In an office building in Beijing, compared to the traditional one-stage air treatment system, the maximum and the annual average energy-saving rates of the MACT system designed based on the multi-condition design method are 16.1 % and 6.3 %, respectively.