## 4 Results and Discussion
### Uniformity of Air Velocity Distribution
In contrast, when \(P_{d}\) \(\leq\) 0.5 in the crop area, the crop exhibits less resistance to airflow, causing the air velocity above the crop to increase significantly as \(P_{d}\) decreases (Figure 8). This indicates that lower planting densities result in a substantial increase in the \(U_{0}\) value with increasing \(ACH\). Furthermore, at the same \(ACH\), the \(OU\) value is larger at smaller planting density (\(P_{d}\)\(\leq\) 0.5) compared to larger planting density (\(P_{d}\) > 0.5). It is apparent that, as \(P_{d}\) decreases in the crop area, particularly when \(P_{d}\) < 0.5, the air velocity above the bottom cultivation tray increases significantly, surpassing the optimal air velocity \(U_{0}\) = 0.4 m\(\cdot\)s\({}^{-1}\). This phenomenon is attributed to the positioning of the air inlet at the bottom. Consequently, this is also reflected in the decrease in \(OU\) values in the indoor scenario with \(P_{d}\) = 0.1 and \(ACH\) = 100 h\({}^{-1}\). In summary, a smaller value of \(P_{d}\) in the crop results in a higher \(OU\) value in the room. Specifically, when \(ACH\) is further increased (\(ACH\) > 80 h\({}^{-1}\)), the average air velocity above the crop area of the lowest cultivation tray becomes excessively high, leading to a decrease in the overall \(OU\) of the indoor in the case of crop \(P_{d}\) = 0.1. Figure 6: The objective uniformity (\(OU\)) as a function of \(ACH\) for all different planting density cases. Furthermore, it can be observed that the air velocity above the crop in the cultivation tray near the outlet side is higher compared to the cultivation tray on the inlet side. This discrepancy is attributed to the heat generated by the LED lamps, which results in a higher air temperature at the outlet compared to the air temperature at the inlet. As a result of the thermal buoyancy force induced by the heat dissipation of the LED lamps in the room, the air with the higher temperature near the exit side tends to flow upwards. Therefore, based on the variation in OU with \(ACH\) depicted in Figure 6, it can be concluded that increasing \(ACH\) or decreasing \(P_{d}\) generally results in higher \(OU\) values. However, it should be noted that the combination of higher \(ACH\) and lower \(P_{d}\) does not necessarily imply greater \(OU\)  
Figure 8: The velocity distribution of the airflow above the crop at each \(P_{d}\) at \(ACH\) = 80 h\({}^{-1}\) is presented in two dimensions. Figure 7: Indoor air velocity at \(P_{d}\) = 0.5.  
values, as observed in the case of \(P_{d}\) = 0.1 and \(ACH\) = 100 h\({}^{-1}\). This occurs because, when the \(ACH\) is too high, the excessive air velocity at the inlet of the indoor ventilation system causes the air velocity above the cultivated tray crop near the inlet side to become too high. As a result, the air velocity deviates significantly from the optimum velocity (\(U_{0}\)), leading to a decrease in the overall \(OU\) value of the room. Hence, in situations where the planting density of the indoor cultivation tray crop area is high, increasing the \(ACH\) value can enhance the overall uniformity of the airflow rate above the indoor crop area. Conversely, when the planting density of the indoor cultivation tray crop area is low, a smaller \(ACH\) value can be utilized, potentially reducing energy consumption related to the ventilation system while still ensuring improved airflow uniformity over the crop area.