# Dynamic Energy Consumption Modeling for HVAC Systems in Electric Vehicles
## 3 Validation of the Model
#### Test Conditions  
Different tests were carried out by changing the system settings (such as fan speed) and repeated for different temperatures of the climatic room. Among the different test conditions, two particular cases were chosen for the validation of the model. The first dealt with the air conditioning system start procedure: in this case, the HVAC system was turned off for several hours inside the climatic room, which had an average temperature of 32.5 \({}^{\circ}\)C. In this way, all the system components were at the same temperature as the surrounding environment. The system was turned on, with an air flow rate through the evaporator equal to 160 m\({}^{3}\)/h. The second case started just at the end of the first case, with an air flow rate of 240 m\({}^{3}\)/h. The temperature trends inside the climatic room during the two tests are reported in Figure 4. \begin{table}
\begin{tabular}{l c} \hline \hline
**Description** & **Uncertainty** \\ \hline T-type thermocouples & \(\pm\)0.5 \({}^{\circ}\)C \\ Low-pressure gauge & \(\pm\)0.2 bar \\ High-pressure gauge & \(\pm\)0.5 bar \\ Refrigerant mass flow rate & \(\pm\)0.5\% of reading \\ Volumetric air flow rate & \(\pm\)3\% of reading \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Table of experimental uncertainties. Figure 3: Schematic view of the real commercial air conditioning system: (**A**) compressor, (**B**) condenser, (**C**) fans, (**D**) receiver dryer, (**E**) TXV, (**F**) blower, (**G**) evaporator, (**H**) bypass valve. The blue points are the experimental measurements, while the black line is the interpolation. The wide range of temperature variation within the climatic room (30-35 \({}^{\circ}\)C) was chosen as an example of real variability in the atmospheric condition. The interpolating function was used as the ambient temperature input in the Simulink model. The measured relative humidity was 0.31 for the first case and 0.26 for the second case. The model developed allows us to simulate the continuous behavior of several quantities, such as the physical states of the refrigerant fluid and its mass flow rate, the mean condensing and evaporating pressure, the different powers related to the air conditioning system and the temperature and volumetric flow rate through the evaporator. Among these different variables, the most relevant to take into account for the model validation is the air temperature at the evaporator outlet. Hence, the comparison between the temperature measurements of the air exiting the evaporator and the corresponding simulated one is shown in Figure 5.  
In both figures, the dots represent the experimental measurements, while the continuous line represents the simulated trend. As is visible from the pictures, there is good agreement between the simulation results and the experimental measurements in both the start-up condition (case 1) and the maximum load condition (case 2). Figure 5 (right) shows that the variation in the air temperature at the exit of the evaporator is related to fluctuations in the air temperature at the exit (Figure 4 (right)). The time evolution obtained for the evaporating and condensing pressures is shown in Figure 6.  
The total pressure drop in the evaporator was set at 0.36 bar [17], while the pressure drop in the condenser was set at 0.6 bar. Table 2 shows the comparison between the mean simulated pressure values and the related measured ones. The table shows that the simulated data agree very well with the experimental measurements. Figure 4: Temperature trend inside the climatic chamber for case 1 (**left**) and for case 2 (**right**). Figure 5: Temperature of air exiting the evaporator. Comparison between the simulation results (lines) and experimental ones (dots) (case 1 (**left**) and case 2 (**right**)). Validation was performed for numerous boundary conditions, combining the room temperature in the range (30-50 \({}^{\circ}\) C) and the humidity in the range (30-60%). The simulation results consistently deviated from the experimental measurements by values below 10%.