New insights to boost the application potential of Chinese solar greenhouses in cold desert regions: System design and implementation

Traditional designs of solar greenhouse heat storage and release structures are difficult to maintain a stable thermal environment in cold desert regions. To maximize the utilization of solar energy, thereby increasing the adaptability in harsh environments such as deserts, a heating strategy that integrates surplus air heat (SAH) energy with shallow geothermal energy (SGE) within greenhouses was proposed. An efficient active heating system of air-source heat pump combined with buried water pipe (HP-BWP) for greenhouse heating was designed. Based on the energy balance method, the mathematical model that coupled greenhouse heat load with optimal heat transfer of water pipe was constructed to design the size parameters of water pipe, so as to maximize heat transfer efficiency while minimizing costs. The system was tested on the spot to verify the design theory and evaluate the heating performance of the system. After heating with HP-BWP system, the minimum temperature of indoor air and soil at night increased by 6.3 °C and 2.9 °C, respectively. The heating power at night could reach 37 kW on average. The system coefficient of performance (COP) reached an average of 4.92 and a maximum of 7.86. The energy saving rate of the system reached 76.0 %. The investment payback period of 1.7 years proved the satisfactory promotion and application value. The life cycle analysis of the heating system's carbon footprint demonstrated strong potential for sustainable development and significant environmental contributions.