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In last 10 years or so, a number of OEMs are designing vehicles with start-stop function to save energy and to reduce pollution. For these systems, the situations in which air-conditioning systems are used have been changing with a significant increase in adoption of idle-time reduction systems (no idling-system). Blower fan remains operating at idle condition while compressor stops in most cases for these systems. In this case, the air temperature at the vent outlets increases. The increase in the air temperature under range of thermal boundary conditions around the evaporator causes a concern of odor to occur. This paper describes and explains experimental studies on changes in heat and humidity at the air outlets according to the switching operation of compressor and root cause analyses of odor coming from air-conditioning system for vehicles with start-stop function.

In recent years, start-stop systems have been implemented by many OEMs for improvement of fuel economy. When the engine stops, the occupant comfort typically deteriorates. Hence, the climate and fuel economy engineers are struggling to combine the passenger comfort and fuel economy. Especially in a vehicle cabin where the thermal environment becomes unsteady and highly non-uniform due to a start-stop. It is difficult to adapt any comfort evaluation index that have already been well established for a stationary/uniform space in building type environment in comparison to a vehicle cabin interior. The existing standard of ISO-14505-2 does not consider this for vehicle cabin interior condition. Hence, the authors have developed the occupant’s comfort prediction method under highly non-uniform condition and unsteady conditions and have established a new methodology [1].

To improve fuel consumption, hybrid system, turbo-charged engine, and clean diesel engine vehicles have been developed. These new systems require additional heat exchangers which reduces air flow rate within the heat exchangers of an engine cooling module. Consequently, power of cooling fan is increased. CalsonicKansei (CK) has developed a new cooling module “SLIM” (Single Layer Integrated cooling Module). This consists of a current condenser which is air-cooled and a new water-cooled condenser. This water cooled condenser is specifically designed to bring superheated refrigerant vapor to saturated conditions. The water-cooled condenser is located inside of the sub-radiator tank. The operation of the sub-radiator is to provide cooling to charge air cooler (CAC) and to water-cooled condenser. The switch of the operation is done automatically without any valve and any actuator.

The current investigation is focused on enhancing the mobile air conditioning performance by improving the air management for the front end. The following enhancing strategies were investigated: air guides, seals between the condenser and radiator and the seals on the hood. The following are the major conclusions from this study: A study of 12 current production vehicles revealed that the majority of the vehicles did not have good front end designs for optimum performance. Significant amount of air bypasses the condenser and radiator in the current production vehicles that has a major impact on the performance of the air conditioning and engine cooling systems. For a typical current production vehicle 15% bypassed the condenser; 24% bypassed the radiator; and 9% bypassed between the condenser and the radiator. This is the first paper in the literature that presents this information.

The current investigation focuses on the heat pick up by the air as it flows into the cowl from one end to the blower unit intake. Tests were conducted on a number of current production vehicles. The following are the major conclusions from this study: 1 A study of 8 current production vehicles revealed that the cowl surface were significantly heated resulting in an increased air temperature as it flows into the blower intake through the cowl. 2 Based on the wind tunnel data, the sheet metal cowl channel is heated up to 50∼63 °C at highway speeds and up to 85 °C at idle. 3 Hence, in OSA mode the ambient air is heated up by the hot channel surface as it travels from the cowl inlet to the blower unit that result in increasing the evaporator loads by significant levels, thereby, increasing the vent outlet temperature. 4 Tests were conducted by removing the cowl cover to determine the maximum potential of improvements (to prevent air from being heated up in the cowl channel).

In this paper a methodology is presented to predict the water drop trajectories at a given fan operating condition (i.e., face velocity), coil height and for a range of water drop diameters. Water drop carry over horizontal distances have been calculated as a function of evaporator coil height, water drop diameters, and face velocities for an evaporator unit. The simulated data has been compared with the experimental data. Initial results have shown that the model can predict the water drop trajectories fairly well. The developed model can be used to calculate the maximum horizontal distances the water drops will be carried over with the airstream for a range of water drop diameters. This is very important information to the design engineers for properly designing the evaporator units.

The efficiency of thermal systems (HVAC, engine cooling, transmission, and power steering) has improved greatly over the past few years. Operating these systems typically requires a significant amount of energy, however, which could adversely affect vehicle performance. To provide customers the level of comfort that they demand in an energy-efficient manner, innovative approaches must be developed.