Turn it up: Researchers optimise air conditioners to prevent drivers losing their cool

Monash University
  • Truck drivers across the world could have access to in-cabin temperature control that reduces windscreen condensation and improves comfort.
  • Optimum anti-dewing, occupant comfort and energy efficiency were met when relative humidity was between 20-60 per cent and temperature ranged from 19°C-25°C.
  • Findings of this study are expected to influence the design of automotive air conditioning systems.
  • Truck drivers globally could soon have access to state-of-the-art temperature control in their cabins that reduces windscreen condensation and improves comfort.

    An international research team involving Monash University, Zhejiang University (China) and the University of Pennsylvania (USA) have spent the past two years investigating the air inlet mode, temperature, relative humidity and flow speed of ventilation of air conditioners in truck cabins, and how this impacts dewing and driver comfort.

    The study, published in Applied Thermal Engineering, found highest anti-dewing efficiency was achieved when the air conditioning airflow was set to speed above 0.6 metres per second, a relative humidity of 20 per cent and temperature above 320 Kelvin (46.85 Celsius) within 200 seconds.

    However, the optimal zone – where the combined requirements of occupant comfort, energy efficiency and safety were met – was when the relative humidity was within the range of 20-60 per cent and the temperature was between 292K-298K (19°C-25°C).

    Researchers have collaborated with automobile manufacturers in Australia and China on thermo-fluid problems, such as vehicle aerodynamics, drag reduction, and thermo-fluid flows in engines. Findings from this study could influence the future design of automotive air conditioning systems.

    “The other interesting finding is that the optimised settings can effectively and efficiently control the flow velocity and temperature distributions of the window surfaces and inner cabin space,” Dr Jisheng Zhao, Research Fellow in the Department of Mechanical and Aerospace Engineering at Monash University, said.

    “These findings should provide us with a basic design guideline for the air conditioning system in trucks when considering the combined requirements. The airflow velocity and temperature distributions should also help locate comfortable positions in the cabin.”

    The problem of vehicle window dewing not only affects the occupants comfort, but also interferes with the driver’s sight and potentially threatens the safety of driving as well as electronic equipment in the vehicle.

    Vapor condensing is caused by the differences in temperature and relative humidity (moisture) in the air. The problem can be resolved by adjusting the inside temperature to avoid the dewing point and reducing the relative humidity through the ventilation system.

    But, in order to reach maximum defogging capacity, cabin temperatures could soar to nearly 50°C – making drivers extremely uncomfortable and distracted while on the road.

    In order to #CHANGEIT, researchers, led by Professor Yuqi Huang at Zhejiang University, simulated 33 different working conditions of air conditioners – including temperatures, humidity and flow velocities – to improve cabin defogging and maximise driver comfort in a retrofitted truck cabin.

    Results showed that reducing humidity could not only effectively control condensation, but also optimise the distribution of the internal airflow and increase the heating effect.

    “On the other hand, low cabin pressure affects the occupants’ thermal comfort, whereas high temperatures will increase the content of water vapour in the cabin, thereby worsening the problem of condensation,” Professor Huang said.

    To satisfy the comfort, efficiency and safety requirements simultaneously, the research identified that automobile air conditioners could be controlled with the relative humidity range of 20-60 per cent, and a temperature range of 292K-298K (19°C-25°C).

    Dr Zhao said the findings were significant, especially for vehicle batteries, which could see losses of up to 50 per cent of the total driving distance due to the energy consumption of air conditioners.

    “Trucks play an important role in our freight transport system, carrying more than 70 per cent of the freight across land. The need for energy reductions and environmental compatibility of truck design, by improving aerodynamic performance for example, is now a worldwide priority,” Dr Zhao said.

    Professor Yuqi Huang at Zhejiang University led the study, with research support from Dr Jisheng Zhao (Monash University) and Yue Yang (University of Pennsylvania).

    /Public Release.