Effects of dry ice jet cooling on LED light and carbon supplementation for crop growth in plant factories

Heat generated by light-emitting diode (LED) light sources in plant factories must be dissipated in a timely manner to guarantee the performance, service life and reliability of LEDs. In this study, a dry ice jet cooling and carbon supplementation system was designed. Dry ice jetting was adopted to achieve high-efficiency cooling of LED light sources, while carbon dioxide gas produced via dry ice sublimation was recycled for carbon supplementation to support plant growth. The cooling performance of LED light sources under different fluid inlet velocities and the effects of supplementary carbon dioxide on lettuce growth were investigated.The thermal performance of the LED module was assessed at dry ice fluid inlet velocities from 0.005 to 0.007 m/s under a constant input power of 100 W. Results demonstrated that the surface temperature of the LED module remained consistently below 60 ℃ with uniform distribution over the surface. Compared with conventional water cooling, dry ice jet cooling reduced 10 ℃ in the central region temperature of the LED light source, indicating the superior efficiency of localized heat dissipation. The CO₂ released during dry ice sublimation was utilized for carbon enrichment in lettuce cultivation. Morphological and physiological analysis revealed that the multiple growth indicators were improved substantially, followed by carbon supplementation. Average plant height increased by 4 cm, stem diameter by 1.6 mm, and leaf number by three leaves per plant. Biomass accumulation was significantly enhanced, with fresh weight per plant increasing by 132.87 g and dry weight by 11.21 g. Biochemical assays demonstrated that there was an increase in the pigment concentrations, including chlorophyll a (0.2 mg/g), chlorophyll b (0.052 mg/g), and carotenoid content (0.057 mg/g). Nutritional quality parameters also shared marked improvements, with soluble protein content rising by 1.39 mg/g, vitamin C content by 49.99 µg/g, and reducing sugar content by 7 mg/g. The carbon supplementation via dry ice sublimation effectively promoted lettuce growth and nutritional quality. Economic analysis was compared with conventional water cooling. The dry ice cooling incurred lower equipment investment and operational costs, indicating a net economic benefit of 33.93 yuan per square meter per month. Water circulation components were eliminated to add value for the high crop productivity and quality. Two challenges remained on thermal management of high-intensity LED lighting and atmospheric carbon enrichment for optimal photosynthesis in artificial light plant factories. Waste heat dissipation was converted into a natural resource for crop production. This finding can provide a promising framework for dry ice cooling and carbon supplementation in the more energy-efficient and productive controlled-environment agriculture. Research directions can be expected to optimize the injection parameters for various crop species, the scaling system for commercial applications, and long-term impacts on both LED lifespan and crop performance over multiple growth cycles.