# Dynamic Energy Consumption Modeling for HVAC Systems in Electric Vehicles
## 4 Results and Discussion
### ECE 15 Driving Cycle  
The ECE 15 driving cycle simulates urban mobility where the maximum speed of the vehicle is limited to 50 km/h, while its average speed in the cycle is equal to 18.4 km/h [13]. The powertrain of the vehicle is made up of lithium ion batteries having an electrical  
Figure 8: Thermal loads and cabin temperature obtained in the case without precooling.  
capacity 320 Ah with a discharge voltage of 50 V. The vehicle parameters, including the state of charge (SOC) of the batteries as well as the comfort conditions inside the cabin, were simulated with and without the use of the HVAC system. The main input conditions imposed in this case are reported in Table 5, while the vehicle velocity is shown in Figure 9.  
The thermal load due to solar radiation \(\dot{Q}_{rad}\) was taken as constant during the hourly simulation, and the metabolic load \(\dot{Q}_{met}\) depended on the occupancy of the passengers. The average metabolic load was set to 145 W per person according to [29]. The other thermal loads were not constant. Figure 10 shows the trend of the air mass flow rate due to infiltration s \(\dot{m}_{a,ext}\) as a function of vehicle velocity (Equation (38)).  
Figure 10: Air flow rate which enters inside the vehicle due to the infiltration.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Imposed Condition** & **Values** \\ \hline Simulation time & 3600 s \\ Outdoor temperature & \(T_{ext}\) & 35 \({}^{\circ}\)C \\ Initial inner temperature & \(T_{cab}\) & 40 \({}^{\circ}\)C \\ Relative humidity & \(\varphi_{ext}\) & 35 \% \\ Solar thermal load & \(\dot{Q}_{rad}\) & 1100 W \\ Passenger number & 2 \\ Set-point temperature & \(T_{SP}\) & 28 \({}^{\circ}\)C \\ Total distance covered & 19.8 km \\ \hline \hline \end{tabular}
\end{table}
Table 5: Main input conditions imposed in the ECE 15 case.  
Figure 9: Vehicle velocity during the regulated driving case.  
Taking into account a typical day for a metropolitan city with continental climate during the summer, solar radiation (\(Q_{\mathit{rnd}}\)) can be responsible for more than 60% of the total thermal load, while heat transmission (\(Q_{\mathit{tra}}\)) can be on the order of 20%, as shown in Figure 11.  
The results in terms of cabin temperature and thermal loads are shown in Figure 12. Fluctuations in the total thermal load \(\dot{Q}_{\mathit{lct}}\) are due to variations in vehicle velocity. In this case, 950 s after the vehicle departure, \(T_{\mathit{cab}}\) reaches the set-point value (\(T_{\mathit{sp}}\)), and 190 s later, the on-off cycle of the HVAC system starts and is repeated for the rest of the driving cycle. The average time of a single on-off cycle is about 446 s.  
The state of charge (SOC) of the batteries obtained with and without the use of the HVAC system is shown in Figure 13. As shown in the figure, the use of the HVAC system reduces the battery's state of charge of almost 7% during a driving time of an hour (without adopting the precooling phase). In terms of energy consumption, the energy required for the only propulsion is 1.815 kWh, while with the adoption of the HVAC system, the total  
Figure 11: Relative contribution of the thermal loads.  
Figure 12: Thermal loads and cabin temperature obtained for the ECE 15 case.  
energy required increases to 3.014 kWh. As a consequence, for this one-hour urban cycle, the employment of the HVAC system increases the energy consumption by about 40%.