## 6 Results and Discussion
### Short-Term (3-Day) Performance  
Figure 3 presents the time evolution of four key system outputs--biomass, internal CO\({}_{2}\) concentration, temperature, and relative humidity--over a 72 h simulation for six NMPC configurations (C, CW, P, PW, I, IW). The biomass plot shows similar growth patterns among all controllers, indicating comparable crop development. The CO\({}_{2}\) concentration plot reveals that C and CW maintain higher and more stable daytime CO\({}_{2}\) levels, supporting enhanced photosynthetic activity, while the other configurations regulate CO\({}_{2}\) more conservatively. The temperature and humidity plots demonstrate that all controllers keep these variables within safe bounds, with some fluctuations corresponding to environmental changes and control actions. Overall, this figure highlights the ability of all NMPC configurations to maintain suitable conditions for crop growth, with clear differences in resource management and environmental stability.  
Figure 4 illustrates the control signals generated by the NMPC controllers for CO\({}_{2}\) injection, ventilation, and heating during the same simulation period for the six configurations. The C and CW controllers apply CO\({}_{2}\) in large, stable pulses, while the predictive configurations (P, PW, I, IW) use smaller, more frequent, and dispersed doses to optimize CO\({}_{2}\) usage. Ventilation signals show that C and CW often adopt an on/off approach, whereas the predictive controllers adjust ventilation with higher frequency and smaller amplitude to more precisely regulate the internal climate. Heating is activated in cycles, mainly during cooler periods, with predictive controllers exhibiting more frequent and flexible power adjustments. These results demonstrate distinct control strategies, where C and CW focus on maximizing growth, while P, PW, I, and IW prioritize efficient resource utilization and operational cost savings.  
Table 6 summarizes the short-term performance (first 72 h) of all six NMPC controllers. Final biomass after 3 days is highest for NMPC-C and NMPC-CW controllers (7.489 and 7.490 g/m\({}^{2}\)), slightly higher than for the predictive (P, PW: 7.369 g/m\({}^{2}\)) and ideal controllers (I, IW: 7.347, 7.348 g/m\({}^{2}\)). Total constraint violation (\(V_{total}\)) is similar across all controllers (\(\approx\)8.7%). The average solver time is substantially reduced in warm-started controllers (CW: 0.299 s, PW: 0.404 s, IW: 0.302 s) compared to their non-warm-started counterparts (C: 0.489 s, P: 1.188 s, I: 0.897 s). Furthermore, for each pair of controllers with and without  
warm-start, the output values are nearly identical, as visually confirmed by the almost overlapping trajectories in Figures 3 and 4, and quantitatively reinforced by the summarized data in Table 6, where performance metrics such as biomass, constraint violations, and profit differ by less than 0.1% between each pair. This demonstrates that, under the tested conditions, the use of warm-start mainly improves computational efficiency without significantly affecting the control quality or agronomic outcomes. For subsequent full-cycle analysis, only the warm-started controllers (CW, PW, IW) are visualized for clarity.  
Figure 4: System control signals for all six NMPC controllers over the first 3 days of simulation.  
Figure 3: System outputs for all six NMPC controllers over the first 3 days of simulation. Gray dashed lines indicate operational bounds for CO\({}_{2}\), temperature, and RH.