Performance of an air source heat pump integrating fan-coil window and double-layer pipe-embedded wall for ultra-low-temperature heating

The system combining double-layer pipe-embedded wall with air source heat pump has been proposed for low-temperature heating. However, such system still requires relatively high temperature water in buildings with large window-to-wall ratios (WWRs). Therefore, a system integrating double-layer pipe-embedded wall and fan-coil window with shallow geothermal energy and air source heat pump is proposed in this study for ultra-low-temperature heating. Taking a residential building as an example, the models of traditional system, reference system combining double-layer pipe-embedded wall and air source heat pump, and the proposed system are established. The heating performances of the three systems are analyzed under various WWRs and ambient temperatures in Beijing. Additionally, seasonal performance as well as economic and environmental assessments are conducted in Harbin and Beijing. The results show that compared with reference system, (1) the proposed system maintains low-temperature heating when WWR exceeds 0.35; (2) as WWR increases to 0.5–0.65, the proposed system reduces the water temperature by 5.6–10.1 ℃; (3) when WWR is 0.35, 0.5, and 0.65, the COP of the proposed system is improved by 7.9%, 10.1%, and 15.0%, with corresponding energy-saving rates of 17.4%, 23.0%, and 25.9%, respectively; (4) in Harbin and Beijing, under a WWR of 0.6, the proposed system achieves cumulative seasonal heating load reductions of 46.7 kWh/m² and 24.1 kWh/m² as well as reducing annual carbon emission reductions of 20.9 kg/m² and 7.5 kg/m² with payback periods of 0.2 and 3.6 years, respectively. Besides, compared with traditional system, under a WWR of 0.6, the proposed system reduces annual carbon emissions by 18.0 kg/m² in Harbin, and 5.6 kg/m² in Beijing. In conclusion, the proposed system demonstrates substantial potential for advancing low-carbon heating technologies.