## 5 Conclusions  
In this research, the computational fluid dynamics (CFD) model has been developed to investigate heat/moisture transfer and fluid flow in the agriculture plant factory. The CFD model has been used to analyze and understand the distribution characteristics of airflow, temperature, and relative humidity. The effects of planting density (\(P_{d}\)) and air change rate (\(ACH\)) on the air velocity, temperature, relative humidity distribution, and uniformity above the crop in a plant factory, have been investigated with an accompanying comprehensive analysis and discussion. The purpose of the present work was to understand how \(P_{d}\) and \(ACH\) influence the airflow patterns and microclimate conditions within the plant factory, particularly within the region of crop plants. The following main conclusions were obtained:  
After carefully varying \(ACH\) and crop planting density (\(P_{d}\)) in CFD simulation cases, uniformity of air velocity distribution above the crop was confirmed in the range between 48% and 76%.  
1. In the cases of identical \(ACH\), airflow velocity above the crop in areas with low planting density becomes higher than that with high planting density. This was essentially due to the fact that lower resistance of the sparse planting crops was presented to the airflow fields.
2. Smaller planting density (\(P_{d}\)) and larger \(ACH\) promote a greater uniformity of air velocity distribution. However, it is important to note that excessively small planting density (\(P_{d}\)) of crop area and overly large \(ACH\) do not necessarily result in a more favorable airflow distribution uniformity. This is because a very small planting density (\(P_{d}\)) of crop area and an extremely large \(ACH\) could lead to excessively high air velocity above the crops in the bottom cultivation trays. As a result, this could expand the deviation from the optimal air velocity (\(U_{0}\) = 0.4m\(\cdot\)s\({}^{-1}\)) and consequently reduce the value of \(OU\) in the entire room.
3. Air temperature and relative humidity above the crop area of each cultivation tray layer are significantly influenced by different categories of \(ACH\) and planting density (\(P_{d}\)). In the case of a smaller \(ACH\), thermal buoyancy generated by the indoor LED lights has a more pronounced or sensible effect, resulting in significant thermal (temperature) stratification in the room-space. As a result, the relative deviation of temperature (\(RSD_{T}\)) in the room becomes higher, which in turn leads to a higher relative deviation of relative humidity (\(RSD_{RH}\)).
4. As \(ACH\) increases, both the relative deviation of temperature (\(RSD_{T}\)) and relative deviation of relative humidity (\(RSD_{RH}\)) of the air above the crop decay in any discussed cases of crop area planting density (\(P_{d}\)). Moreover, smaller planting density (\(P_{d}\)) values result in smaller values of \(RSD_{T}\) compared to \(RSD_{RH}\) for the air above the crop.
5. It should be especially noted that excessive increment in \(ACH\) and decay in \(P_{d}\) did not have a significant effect on \(\theta\), which was influenced by a combination of \(OU\), \(RSD_{T}\), and \(RSD_{RH}\). Therefore, a more appropriate combination of \(ACH\) and \(P_{d}\) could be needed in the design to balance energy use and crop yield. To enhance the uniformity of air velocity, temperature, and relative humidity above the crops, joint effects of crop planting density and \(ACH\) could be further optimized.  
This research has uncovered the roles of crop planting density and air change rate on the microclimate above crops in plant factory. These findings could serve as a valuable reference for designing modern agricultural systems with the aim of boosting the productivity of crop production in plant factories.