A novel cabin air distribution strategy for automotive applications

Abstract

This report looks at the current state of the art for air distribution methods in particular, personalized ventilation (PV) type of air distribution. PV systems have been widely used in the buildings applications and lately, in the development of new aircraft cabin air distributions. Air distribution in vehicles has had a few new cooling methods like spot cooling being researched on. PV systems have the aim of providing effective cooling with increased comfort providing better quality air to the occupant. The solar heat load on a vehicle was studied. It was shown that the peak heat load in the vehicle does not occur when the sun is at its peak, but only when the sunlight is able to penetrate most of the windows at about 2 pm. There are also various methods to lower the direct solar radiation coming into the vehicle and one of them is via geometry. The best geometrical compromise to minimise solar radiation, and yet not affect the aerodynamics of the vehicle too drastically, is to position the windscreen at an angle of 40o from the vertical plane. This gives a reduction of about 15% in terms of solar loading compared to an angle of a conventional car at 57o. The most effective way of heat reduction is to prevent the solar radiation from entering the vehicle directly. If the peak cooling load and the energy usage for cooling were to be reduced from the cooling down phase after parking, some effective methods would be to allow for natural or forced ventilation of the ambient air during parking or lowering the thermal capacity of the materials in the cabin. Both methods can lead to a decrease in energy requirement by 27%. A PV system for vehicles was introduced. This design was developed from prior designs which had various issues with airflow being affected by the warm air in the vehicle. The PV seat allowed for the individual cooling of a passenger. A series of simulations were conducted using StarCCM and Theseus FE. Three cases were ran, one being the full conventional air conditioning system with a mass flow rate of 0.1 kg/s, the next is a conventional air conditioning system but only with mass flow rate of 0.025 kg/s and focused entirely on the driver, and lastly the PV seat with the driver seated inside. The same mass flow rate was used for the PV seat case. All cases used an inlet air temperature of 8℃. Comparing to latter 2 cases, the PV seat was able to produce a better comfort index score compared to the conventional seat with an improvement of about 0.7% to 50%. This was done with a reduction of air inlet velocity of 110%. The streamlines also showed that the airflow was more effective and much of the air did not flow into the back seat area reducing the cross contamination between passengers. Taking reference from breathing region at the back seat, measuring the spread of contaminants from the front, the PV seat case had 32% less contaminants compared to the convention air conditioning layout. Most importantly, although not proven via simulations, it can be deduced that potential energy savings are possible for a comparable comfort between the 2 types of cooling systems.