Optimal temperature setpoints for greenhouse lettuce

Optimal Greenhouse Cultivation Control: Survey and Perspectives

“…All co-state trajectories show a decreasing trend towards zero in about 20 days, equally suggesting that initial investment in dry matter production is worthwhile. This amounts to on average higher greenhouse temperatures at the beginning of the growing season, and lower ones later on, consistent with the findings of Seginer et al (1991). As shown by De Graaf (2006) in a study on optimal control of nitrate in lettuce, the actual optimal on-line greenhouse temperatures are fluctuating quite heavily throughout the season, as driven by the actual weather, which is consistent with the findings of Gal, Seginer, and Angel (1984), who state that the temperature set-point should depend on the actual weather only.…”

“…As shown by De Graaf (2006) in a study on optimal control of nitrate in lettuce, the actual optimal on-line greenhouse temperatures are fluctuating quite heavily throughout the season, as driven by the actual weather, which is consistent with the findings of Gal, Seginer, and Angel (1984), who state that the temperature set-point should depend on the actual weather only. Even though this may be the case, the results of Seginer et al (1991) suggest that in lettuce there is not much difference in economic result between dynamic temperature set-points and an optimized fixed set-point. The effect of spacing strategies on the optimal control policy for nitrate in lettuce is studied in Ioslovich and Seginer (2002) Van Henten (2003) investigates the sensitivity of the optimal control solution to parameter uncertainties and model errors.…”

“…Co-state trajectories for a two-state lettuce crop, where the states are biomass and leaf area ratio, using smoothed nominal synthetic periodic weather, are presented by Seginer et al (1991). Results suggest that in the beginning it makes sense to achieve canopy closure as soon as possible.…”

An Optimum Light Environment Design of Double-Stack Bed System by using Genetic Algorithms

“…Net photosynthesis is obtained from gross photosynthesis after subtraction three respiration terms; light respiration and growth respiration, which are assumed to be proportional to gross photosynthesis; growth respiration, which is assumed to be proportional to total dry weight. The rate of dry-weight accumulation can be expressed as (Seginer et al, 1991 ). CO2 concentration is assumed to remain constant at the normal atmospheric level.…”

“…(1), R is the rate of maintenance respiration of a unit dry matter of tissue, and N{W} represents the effective dry mass of the crop. Simplified forms of G, M, R and N are as follows (Seginer et al, 1991):…”