Investigation of the Effect of Series and Parallel Line Designs on Temperature and Flow Rate Distribution in Bus Cabin Heating Systems

The aim of this study is to improve cabin temperature homogeneity by comparing serial and parallel coolant line configurations in Anadolu Isuzu’s new midibus model. A one-dimensional hydraulic model was developed in KULI using supplier-provided pressure drop versus flow rate curves for the preheater, defroster, convectors, and pumps. Pipe lengths and inner diameters were obtained from the CATIA vehicle layout. The model was assessed against physical flow rate measurements for both configurations. The maximum deviations were 11.6% for the serial layout and 6.2% for the parallel layout. KULI was used only for coolant flow rate prediction; all temperature results were obtained from physical vehicle tests. At the 30th min, the measured left–right convector outlet temperature difference decreased from 6.6°C in the serial layout to 1.0°C in the parallel layout. For the investigated vehicle and operating condition, the parallel configuration provided a more balanced flow distribution and improved outlet temperature homogeneity.