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Annual performance experiments of an earth-air heat exchanger fresh air-handling unit in severe cold regions: Operation, economic and greenhouse gas emission analyses

Li, Hui, Ni, Long, Yao, Yang, Sun, Cheng
Renewable energy 2020 v.146 pp. 25-37
air, air temperature, cooling, energy use and consumption, greenhouse gas emissions, heat exchangers, heat pumps, heat recovery, land use, mass transfer, pipes, primary energy, renewable energy sources, water content
This paper proposes a fresh air-handling unit, comprising an earth-air heat exchanger (EAHE) and a heat recovery unit, to solve the problem of insufficient fresh air and save primary energy use in severe cold regions. A new construction of double-layer buried pipes was adopted to enhance heat transfer and save land use. Annual performance of system from January to December 2017 was evaluated by analyzing inlet/outlet air parameters, thermal capacity, and power consumption variation. Different operation modes were adopted to simulate use patterns of various building styles. Results show that during heating operation, the maximum temperature produced by EAHE was 22.2 °C and its maximum heating capacity was 7718 W. The average temperature drop during the cooling operation was 13.6 °C. The system can provide fresh air with sufficient temperature independently. Both heat and mass transfer exist inside the buried pipes when operated under the cooling mode. Latent cooling capacity occupied 32.1% of total cooling capacity averagely, which reveals the importance of mass transfer. From the correlation analysis, it is clear that the heating capacity and sensible cooling capacity have the strongest correlation with inlet air temperature and the latent cooling capacity reacts to the moisture content. The average annual COP¯ of the system is 8.5. Compared to an air-source heat pump handling unit, the dynamic payback period is only 2.38 years and proposed system can further provide an 82.5% reduction in greenhouse gas emissions.