## 4 Results and Discussion
### Air Temperature Distribution and Relative Temperature Deviation  
Air temperature is vital for the process of plant photosynthesis and is a crucial parameter that needs to be controlled and monitored in a plant factory. The temperature of the airflow above the crop has a direct impact on the relative humidity (\(RH\)) of the airflow and consequently affects the growth and development of the plants [15]. In subsequent analyses, the air temperature distribution above the crops in different crop areas will be investigated on the basis of \(P_{d}\) and \(ACH\). In addition, the uniformity of temperature distribution will be assessed by analyzing the relative standard deviation of temperature. Figure 9 depicts the average temperature above the crop in each layer of the cultivation tray at various planting density (\(P_{d}\)) as a function of \(ACH\). From Figure 9, the following observations can be made: (1) in the cases with crop area \(P_{d}\) > 0.5 and \(ACH\)\(\leq\) 60 h\({}^{-1}\), the average air temperature above the crops in the upper cultivation tray (layer 3 and 4 of the cultivation tray) is consistently higher than that in the lower cultivation tray (layer 1 and 2 of the cultivation tray). In the case of \(ACH\) > 60 h\({}^{-1}\), there is a phenomenon where the air temperature above the crop area in layer 2 of the cultivation trays is higher than that in layer 3. (2) In the case of crop area \(P_{d}\)\(\leq\) 0.5, higher air temperatures above the crop area in layer 2 of the cultivation tray than in layer 3 already occur in the case of \(ACH\) = 60 h\({}^{-1}\). (3) As the \(ACH\) increased, the air temperature above the crops in each layer decreased. Specifically, in the case of a crop area with \(P_{d}\) = 0.1, the air temperatures above the crops in layers 1, 2, and 3 of the cultivation trays demonstrated a clear tendency to increase and then decrease. To further understand the underlying causes of the aforementioned phenomenon, an analysis was conducted on the distribution of air temperature above the crops in the cultivation tray. Figure 10 presents the two-dimensional temperature distribution above the crops for a crop area with \(P_{d}\) = 0.3, with variations in \(ACH\). It is evident that, when \(ACH\)\(\leq\) 60 h\({}^{-1}\), the room exhibits a noticeable temperature stratification due to the combined impact of the inlet airflow and the thermal effect of the LED lamps. Consequently, the average temperature of the airflow above the crops in the upper cultivation tray (layer 3 and 4 of the cultivation tray) consistently surpasses that in the lower cultivation tray (layer 1 and 2 of the cultivation tray). When \(ACH\) > 60 h\({}^{-1}\), the effect of thermal buoyancy on the indoor flow structure is weakened due to the increase in inlet air velocity, and the inlet airflow dominates the indoor airflow pattern. The mixed flow of inlet air and indoor air affected the lower layer above the crop, resulting in lower airflow temperatures above the crop in layer 3 of the cultivation tray than in layer 2 of the cultivation tray. Similarly, air velocity above the crop increases significantly due to lower planting density (\(P_{d}\) < 0.5) and weaker obstruction of airflow by the crop (Figure 8). To further analyze the distribution of air temperature above all crop areas at various planting density, the two-dimensional temperature distribution above the crop in five different \(P_{d}\) is presented in Figure 11. These distributions are obtained under a constant _ACH_ of 60 h\({}^{-1}\). It can be observed that the air temperature above the lower cultivation tray is lower than the air temperature above the upper cultivation tray. Additionally, the air temperature above the crop in the upper cultivation tray is greater in the case of lower \(P_{d}\) than in the case of higher \(P_{d}\).