## 6 Results and Discussion
### Discussion of Trade-Offs and Controller Selection  
The comparative analysis conducted in Section 6.2 clearly reveals a fundamental trade-off inherent in the selection of NMPC strategies. On one hand, feedback-only controllers (C, CW) excel at maximizing final yield and profit by aggressively managing CO\({}_{2}\) enrichment and overall climate conditions to consistently favor robust plant growth. However, this approach inherently leads to higher CO\({}_{2}\) consumption and a greater tendency for the system to operate at or occasionally slightly beyond predefined operational constraint boundaries (Figures 8 and 9). Heating expenditures for these controllers are generally lower, as they do not proactively compensate for future environmental changes (Figure 7). On the other hand, predictive controllers (P, PW, I, IW) demonstrate superior performance in minimizing constraint violations and reducing CO\({}_{2}\) costs (Figures 7 and 8). This enhanced efficiency and constraint safety is achieved through more cautious and anticipatory control actions, supported by access to future disturbance information, albeit typically involving a modest sacrifice in maximum potential yield, and consequently, net profit (Table 7). This observedtrade-off between productivity and strict constraint adherence is a common challenge in greenhouse climate control, as highlighted by recent studies [15; 20].  
The choice of an optimal NMPC strategy should therefore be guided by the specific operational priorities and economic context of the greenhouse. If maximizing output is paramount and the system can tolerate minor deviations from setpoints, NMPC-CW presents a compelling option due to its high yield, profitability, and computational efficiency. This aligns with recent research emphasizing yield optimization in horticulture [20]. If, however, strict adherence to climate setpoints, energy conservation, or CO\({}_{2}\) emission reduction is the primary concern, a predictive strategy such as NMPC-PW may be more suitable, offering a favorable balance between proactive control, resource savings, and computational feasibility. The ideal preview controllers (I, IW) serve as important theoretical benchmarks, highlighting the potential gains from perfect foresight. The results also suggest that while the economic weights in the NMPC objective function influence the trade-off between productivity and resource use, the penalty factors for constraint violations predominantly determine the overall degree of constraint violation and play a crucial role in ensuring system safety. With appropriately tuned penalties, all evaluated controllers maintained the greenhouse environment within broadly acceptable limits for lettuce cultivation.  
To evaluate the practical implications of measurement uncertainty, we conducted a sensitivity analysis examining how a \(\pm\)10% error in final biomass (\(B_{f}\)) estimation impacts net profit calculations for each NMPC controller. Our findings, summarized in Table 8, show that while net profit is linearly related to \(B_{f}\) (Equations (14) and (15)) and, thus, fluctuates directly with measurement error, the relative ranking of controller performance remains robust. This indicates that our main conclusions are valid even under realistic measurement uncertainties in crop yield, reinforcing the robustness of the proposed NMPC strategies for practical application.