Abstract
Light-emitting diode (LED) grow lights are increasingly used in large-scale indoor farming to provide controlled light intensity and spectrum to maximize photosynthesis at various growth stages of plants. As well as converting electricity into light, the LED chips generate heat, so the boards must be properly cooled to maintain the high efficiency and reliability of the LED chips. Currently, LED grow lights are cooled by forced convection air cooling, the fans of which are often the points of failure and also consumers of a significant amount of power. Natural convection cooling is promising as it does not require any moving parts, but one major design challenge is to improve its relatively low heat transfer rate. This paper presents a novel heat sink design for natural convection cooling of LED grow lights. The new design consists of a large rectangular fin array with openings in the base transverse to the fins to increase air flow, and hence the heat transfer. Numerical simulations and experimental testing of a prototype LED grow light with the new heat sink showed that openings achieved their intended purpose. It was found that the new heat sink can transfer the necessary heat flux within the safe operating temperature range of LED chips, which is adequate for cooling LED grow lights.
Highlights
Plants need light of varying intensity and spectral distribution depending on their growth stages
The results demonstrate that the openings significantly improve the heat transfer rate and can be used in natural convection cooling of light-emitting diode (LED) grow lights for applications to indoor agriculture, which is expected to be the generation agricultural technology
A novel heat sink design based on rectangular straight fins with openings in the base for natural convection cooling of LED grow lights is presented
Summary
Plants need light of varying intensity and spectral distribution depending on their growth stages. LEDs are solid-state devices that emit light, the wavelengths of which lie in narrow bands with high photon flux, which allows the manipulation of the spectral characteristics and intensity of the light. LED chips convert about 50–70% of the input power into light, and the remaining power is dissipated as heat, depending on the operating junction temperature and efficiency. 1 kW input power generates the equivalent of 1000–1500 W/m2 heat flux on the LED circuit board depending on the design. Since operating LED grow lights at higher temperatures significantly reduces the efficiency and reliability of the LED chips, as well as causes chip failure, proper cooling of LED grow lights is a critical design requirement to maintain the high efficiency and reliability of the LED chips [5,6]. The heat transfer must not cause the surface to exceed the maximum allowable
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