Abstract:
The study aimed to design and model an air conditioning system for the 12 m Kayoola Electric
Vehicle Solution (EVS) bus operating under Uganda’s tropical climatic conditions. The main
objective was to develop, simulate, and validate an optimized AC system that enhances energy
efficiency, passenger comfort, and driving range. The specific objectives were: (i) to design the
AC system; (ii) to model and simulate the system thermodynamically to obtain optimum
performance parameters; (iii) to evaluate field performance in terms of thermal comfort and energy
consumption; and (iv) to assess the system’s financial viability. The research applied the HBM to
compute the total cooling load, yielding 46.245 kW, with motor heat, radiation, and metabolic load
contributing the largest share of cabin heat gains. The system was then modelled and simulated in
Engineering Equation Solver (EES) software to analyse the vapour compression cycle
performance, resulting in an optimum cooling capacity of 41.79 kW at an evaporator temperature
of 11 °C. A multi-criteria decision analysis (MCDA) guided the selection of a variable-speed scroll
compressor, brushless fans, an electronic expansion valve, and R134a refrigerant, which were
integrated into a roof-mounted commercial variable-frequency AC unit. Field tests conducted
under sunny and rainy conditions showed that the proposed system reduced specific energy
consumption to 0.926 kWh/km, compared to 1.2916 kWh/km for the existing system, extending
the driving range from 232 km to 382 km per charge. Cabin temperatures averaged 22.6 °C,
maintaining comfort within ISO 7730 standards, with 96% passenger satisfaction recorded.
Financial evaluation using the Federal Energy Management Program (FEMP) life cycle cost model
revealed long-term savings of USD 18,929.25 over 20 years despite a slightly higher initial cost.
The results confirm that a variable-capacity AC system, optimized for local climatic conditions,
can significantly improve energy efficiency, passenger comfort, and operational economy of
electric buses, supporting the advancement of sustainable urban mobility in Sub-Saharan Africa.
