Practical Approach to Develop Low Cost, Energy Efficient Cabin Heating for Extreme Cold Operating Environment

摘要

In cold climatic regions (25℃ below zero) thermal comfort inside vehicle cabin plays a vital role for safety of driver and crew members. This comfortable and safe environment can be achieved either by utilizing available heat of engine coolant in conjunction with optimized in cab air circulation or by deploying more costly options such as auxiliary heaters e.g. Fuel Fired, Positive Temperature Coefficient heaters. The typical vehicle cabin heating system effectiveness depends on optimized warm/hot air discharge through instrument panel and foot vents, air directivity to occupant's chest and foot zones and overall air flow distribution inside the vehicle cabin. On engine side it depends on engine coolant warm up and flow rate, coolant pipe routing, coolant leakage through engine thermostat and heater core construction and capacity. The purpose of this study is to evaluate a conventional coolant type heating system and enhance its capacity to warm the vehicle cabin up to comfortable temperatures of +10℃ to +15℃ in head zone and +15℃ to +20℃ in foot zones of occupants. These temperatures are to be achieved in 15 minutes after vehicle start, prior to which vehicle has been cold soaked for 10 hours at ambient temperature of 25℃ below zero. A series of experiments have been carried out on a conventional coolant type automotive cabin heating system on a test bench to optimize the split of warm air hitting driver and occupant's chest and leg zone. Further optimization is carried out on directivity and velocities of warm air impinging on target zones such as upper and lower body of occupants. Once parameters critical to performance as mentioned above are optimized on a bench, the heating system is mounted inside a vehicle cabin. To improve overall heating effectiveness hot air leakage paths from the vehicle cabin have been identified by using a simple test rig and these paths were closed using grommets and sealant. The vehicle is tested in a cold climatic chamber at 25℃ below zero. This trial is conducted on a chassis dynamometer to simulate actual road load conditions. In this phase it is observed that the criteria for thermal comfort are met with the conventional coolant type heating system. This practical approach to meet thermal comfort requirements at extreme cold conditions, avoids the use of costly and complex auxiliary cabin heaters, which would have led to increase in energy consumption and environment pollution.