Endothermic-salt cooling for greenhouse climate control: Techno-economics, Hazard assessment, and Life-cycle screening

As temperatures continue to rise in the hot arid regions, the demand for sustainable greenhouse cooling solutions is becoming increasingly urgent. This study presents a comprehensive thermodynamic and techno-environmental screening framework to identify endothermic salts that can serve as passive cooling agents and be regenerated using solar energy. Drawing from thermodynamic literature, a database of over 170 salts was compiled and filtered through six key criteria: minimum cooling density (>= 100 kJ per liter of water, sufficient to meet typical 10-15 degrees C greenhouse cooling gaps), adequate thermal stability (melting or decomposition point above 100 degrees C), low specific heat (< 2 kJ/kg & sdot;K), affordable cost (< 1 $/kJ for first-cycle use), acceptable safety rating (NFPA hazard index <6), and low environmental impact (global warming potential under 10 g CO2-eq/kJ). This rigorous screening process narrowed the list to five promising and widely available salts, including CO(NH2)(2), NH4Cl, NH4SCN, KNO3, and KSCN. A multi-criteria sustainability index, integrating cooling performance, cost, safety, and environmental footprint, was applied under five different stakeholder weighting scenarios to identify the best fit candidates for varying priorities. The results show that CO(NH2)(2) consistently excels across most cases, while NH4Cl is most cost-effective in first-cycle use. Incorporating multi-cycle regeneration (10-100 cycles) reveals that CO(NH2)(2) maintains robust performance, whereas NH4SCN improves substantially with reuse, outperforming NH4Cl and KNO3 in long-term operation. These findings highlight their potential as low-carbon, cost-effective alternatives for space cooling in water and energy-constrained regions. Future studies should focus on validating the durability of repeated regeneration under real-world conditions.