Experimental study on spatiotemporal variation patterns of thermal environment in the large-span insulated greenhouse

• Spatiotemporal characteristics of greenhouse environment are clarified. • Insulation projection and external climate lead to increased heterogeneity. • Low enclosure wall improves microclimate heterogeneity. • Attaching aluminum foil diffusion film increases photothermal utilization. • Partitioned operation strategy for external thermal blankets is proposed. Large-span plastic greenhouses face serious challenges of insufficient insulation performance and uneven thermal environment distribution, which would weaken the heat storage and release performance of active/passive environmental control systems. The research problem is thus the spatiotemporal characteristics of large-span externally insulated greenhouses yet to be quantified and energy-saving strategies for facility retrofitting still need to be addressed. The objective of this study is to analyze the greenhouse microclimate under the different insulation schemes, weather conditions and ventilation managements. The novelty of the work is that we introduce a low enclosure wall positioned at the bottom edge of transparent roofs to reduce the greenhouse heating load. Moreover, the aluminum foil diffusion film applied to the wall surface further improves the photothermal utilization. Main results of this experimental study are that horizontal microclimate heterogeneity is primarily affected by the fixed insulation projection and outside temperature, and low enclosure walls mitigates the difference in energy demand between the east and west cultivation zones. The construction of low enclosure walls effectively elevates the average night-time temperature by 1.4–3.3 °C, while attaching aluminum foil diffusion film can again raise it again by 1–2 °C. The incorporation of passive thermal storage media is useless for low enclosure walls, since the intercepted radiation at the wall surface accounts for only 12.3 % of the cumulative intensity of solar radiation. For the renovated greenhouse structure, we assessed the dehumidification and cooling effects of different ventilation scenarios. The partitioned operation strategy for east–west external thermal blankets was specified to avoid condensation heat loss.