Design and performance analysis of a zoned rolling strategy for thermal insulation covers in large-span plastic greenhouses

Covering greenhouses with external insulation blankets serves as a crucial regulatory approach to maintain stable thermal environments during cold seasons. It holds significant potential for reducing heating costs and enhancing the air-based heat storage performance of thermal control systems. Aiming at the insufficient thermal insulation performance and severe heat dissipation of the east-west oriented plastic greenhouse, this study innovatively proposes a zoned rolling strategy for insulation quilts, i.e., delaying the unfolding of west-facing quilts and advancing the covering of east-facing quilts. Combined field experiments and numerical simulations were carried out to quantify the influence of different operation time intervals on greenhouse photothermal environments, canopy microclimates, and enclosure heat storage. Field experimental results show that delaying the unfolding of west-facing quilts suppresses the west film temperature drop by 3.0∼4.9°C, while early covering of east-facing quilts raises the east film temperature by 4.8∼9.2°C, effectively mitigating radiative heat loss in the mornings and evenings. The synergistic application of the zoned rolling strategy and diffuse reflective film insulation skirt walls increases nighttime indoor air temperature by 11.1∼14.7%. Simulation results under winter solstice sunny conditions reveal that extending the operation interval from 30 min to 120 min boosts air-source heat gain by 0.36∼0.85 MJ/m 3 and daily effective accumulated temperature of crops increases by 4.73∼10.88%. Considering the trade-off between thermal accumulation and canopy light interception, the optimal recommended operation interval for practical production is 60∼90 min. Intervals exceeding 120 min cause severe shading on east-west skirt walls and the north gable wall, reducing soil and enclosure heat storage. The proposed zoning rolling regulation framework can be directly applied to east-west oriented and asymmetrical plastic greenhouses to optimize their light-heat balance, offering a simple energy-efficient regulation solution for winter vegetable production in northern China.