Year-round energy-efficient multi-stage fresh air treatment system utilizing lake water as energy source

Supplying fresh air is crucial for indoor air quality but significantly increases energy consumption. To enhance energy efficiency, switch-type energy source systems and multi-stage air treatments utilize natural energy sources. Few studies have explored using lake water as a natural energy and bypassing heat exchangers and filters to reduce fan power consumption. This paper proposes a multi-stage fresh-air treatment system using lake water. Low-grade fresh air is pre-treated with lake water, while two-stage lake-water source heat pumps handle the remaining load. Heat exchangers and filters can be bypassed. Experimental results demonstrate the feasibility of using various water temperatures for air treatment and significantly reducing fan energy consumption. In a case study, the proposed system's annual performance is compared with traditional systems. The main conclusions are: (1) The system can adjust air dampers to reduce airflow resistance and fan power consumption by 91.5 % and 76.5 %, respectively. (2) It treats low-, middle-, and high-grade fresh air loads accounting for 16 %, 38 %, and 46 % of annual loads in Beijing. (3) Compared to traditional systems, the proposed system saves 56.5 % and 31.1 % of fan and compressor power consumption, achieving total energy savings of 32.2 % and increasing the system COP from 3.6 to 5.5.