Abstract
Greenhouse models are important tools for the analysis and design of greenhouse systems and for offering decision support to growers. While many models are available, relatively few include the influence of supplementary lighting on the greenhouse climate and crop. This study presents GreenLight, a model for greenhouses with supplemental lighting. GreenLight extends state of the art models by describing the qualitative difference between the common lighting system of high-pressure sodium (HPS) lamps, and the newest technology for horticultural lighting - the light-emitting diodes (LEDs). LEDs differ from HPS lamps in that they operate at lower temperatures, emit mostly convective heat and relatively little radiative heat, and can be more efficient in converting electricity to photosynthetically active radiation (PAR). These differences can have major implications on the greenhouse climate and operation, and on the amount of heat that must be supplied from the greenhouse heating system. Model predictions have been evaluated against data collected in greenhouse compartments equipped with HPS and LED lamps. The model predicted the greenhouse's heating needs with an error of 8–51 W m −2 , representing 1–12% of the measured values; the RMSE for indoor temperature was 1.74–2.04 °C; and the RMSE for relative humidity was 5.52–8.5%. The model is freely available as open source MATLAB software at https://github.com/davkat1/GreenLight . It is hoped that it may be further evaluated and used by researchers worldwide to analyse the influence of the most recent lighting technologies on greenhouse climate control. • Model for lighting in greenhouses, including HPS and LED lamps, was developed. • Model was evaluated using data from a greenhouse with HPS and LED top-lights. • Model evaluates energy requirements of the greenhouse with an accuracy of 1–12%. • Model predicts indoor temperature and humidity with an RRMSE of 6–11%. • Model is publicly available in free open source format.
Highlights
Greenhouse climate models are a useful tool for the analysis, design, and optimisation of greenhouse structures and climate control
High pressure sodium (HPS) lamps are the main source of assimilation lighting in greenhouses (Marcelis, Costa, & Heuvelink, 2019; Virsile_, Olle, & Duchovskis, 2017), and their efficacy, measured in mmol of photons of photosynthetically active radiation (PAR) per joule of input, can reach values of around 1.7e1.8 mmol JÀ1 (Nelson & Bugbee, 2014)
Light emitting diodes (LEDs) are gaining interest as a useful source of assimilation lighting in greenhouses (Dutta Gupta, 2017; Mitchell et al, 2015), especially since surpassing high pressure sodium (HPS) lamps in efficacy, and reaching as much as 2.5 mmol JÀ1 (Bugbee, 2017), and even a reported 3 mmol JÀ1 (Horticultural lighting qualified products list, 2020)
Summary
Greenhouse climate models are a useful tool for the analysis, design, and optimisation of greenhouse structures and climate control. Such models have been in use for several decades, and are continually being extended and developed (Lopez-Cruz, Fitz-Rodrıguez, Salazar-Moreno, Rojano-Aguilar, & Kacira, 2018). Light emitting diodes (LEDs) are gaining interest as a useful source of assimilation lighting in greenhouses (Dutta Gupta, 2017; Mitchell et al, 2015), especially since surpassing HPS lamps in efficacy, and reaching as much as 2.5 mmol JÀ1 (Bugbee, 2017), and even a reported 3 mmol JÀ1 (Horticultural lighting qualified products list, 2020). The efficacy of LEDs is expected to continue to rise, the current and potential efficacies strongly depend on the spectral output of the lamp (Pattison, Hansen, & Tsao, 2018)
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