Thermal management and energy efficiency analysis of planar-array LED water-cooling luminaires in vertical farming systems for saffron

Abstract

For saffron (Crocus sativus L.) in vertical farming systems, improper design of LED lighting system may cause the variation of ambient temperature and subsequent influence of development and flowering of corms on the upper space. In the present study, blue-red (B–R) and white (W) planar-array LED luminaires were designed and fabricated with water-cooling system to solve the thermal management problem. LED modules and flow path in luminaires were calculated through the models of point heat source and non-isothermal flow in simulation software. And the temperature field distribution in saffron culture shelf system and the subsequent effect on corm developments were evaluated for the luminaires with three types of structures. The LED water-cooling luminaires without power supplies and dimming control systems (WCL-PS) demonstrated the best thermal management, because the temperature around saffron corms would not be interfered by the heat from the luminaires. Additionally, experiments were conducted to verify the simulation models, with less than 2.4 °C in the maximum deviation. LED modules were also measured as outstanding radiant performance. The photosynthetic photon flux efficacy (PPFE) was respectively 2.74 μmol J−1 for B-LED at 450 nm, 1.65 μmol J−1 for R-LED at 660 nm, as well as 2.75 μmol J−1 for W-LED at correlated color temperature (CCT) 3000 K. At last, white-LED luminaire had a higher PPFE, a lower power consumption and a better temperature field distribution in contrast with blue-red luminaire, which were more recommended for saffron in vertical farming systems.