# Computational Modeling of the Thermal Behavior of a Greenhouse
## 3 Results
### Comparison with Experimental Data  
Figure 6 shows the results of the simulation interval of 28 May at 17:00 to 29 May at 16:00 for the test A1, specifically the outdoor and indoor air temperatures of the greenhouse for both the experimental and the simulated results.  
There was considered to be natural ventilation with an airflow of 0.2 ac/h without auxiliary heating for the dynamic simulation of the greenhouse in test A1. The trend of the indoor air temperature is similar in both numerical and experimental tests. However, the numerical predictions are above the experimental values during the night period, showing an air temperature difference between 7 \({}^{\circ}\)C and 10 \({}^{\circ}\)C. On the other hand, during the day the temperature predicted for the indoor air of the greenhouse is almost always above the  
\begin{table}
\begin{tabular}{c c} \hline
**Property** & **Value** \\ \hline Thickness (mm) & 0.215 \\ Thermal conductivity (W/m\(\cdot\)K) & 0.330 \\ Solar transmittance & 0.800 \\ Outdoor solar reflectance & 0.170 \\ Inside solar reflectance & 0.170 \\ Visible transmittance & 0.850 \\ Outdoor visible reflectance & 0.120 \\ Inside visible reflectance & 0.120 \\ Infra-red transmittance & 0.000 \\ Outdoor emissivity & 0.700 \\ Inside emissivity & 0.700 \\ \hline \end{tabular}
\end{table}
Table 2: Polyethylene cover properties used for the model.  
Figure 6: Experimental and simulated outdoor and indoor air temperatures in test A1.  
value measured experimentally, although the temperature of the outdoor air measured at the site is higher than that considered for modeling purposes. It reached a maximum difference of 6.5 \({}^{\circ}\)C early in the day.  
The comparison results for the period between 29 May at 17:00 and 30 May at 16:00, test B7, are given in Figure 7. This test includes an airflow rate of 12.9 ac/h and an auxiliary air heater with a set-point of 18 \({}^{\circ}\)C. The comparison shows a similar trend of the numerical and experimental indoor air temperature values. During the day, when the numerical values of the outdoor air temperature are lower than the experimental ones, a similar behavior is observed, but a temperature difference of about 10 \({}^{\circ}\)C is reached between numerical and experimental results of the indoor air temperature. This trend arises from the role of the airflow rate, which affects the indoor air temperature in both situations.  
Figure 8 shows comparison results for the period between 25 February at 17:00 and 26 February at 16:00, test C3. In this test, there was considered to be an airflow rate of 3 ac/h without auxiliary air heater. Again, a similar trend was found. The lower value of the indoor air temperature is reached at about the same time, around 06:00. During the day, the outdoor air temperature difference between the experimental and numerical models reaches a maximum value of about 16 \({}^{\circ}\)C, resulting in lower values for the predictions of the indoor air temperature by about 10 \({}^{\circ}\)C.  
Figure 8: Experimental air temperature and numerical predictions for test C3.  
Figure 7: Test B7 results for outdoor and indoor air temperatures.  
Overall, the comparison results show that the computational tool can provide a reasonable prediction of the indoor air temperature of the greenhouse. However, it must pointed out that the climatic data files used in this simulation software could significantly influence the quality of the results, as observed by other authors [28; 29; 30].