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Recently the author (Mathur, 2017) had presented a model to predict cabin carbon dioxide concentrations as a function of time, number of occupants, vehicle speed, body leakage characteristics, occupant lung capacities and concentrations of the carbon dioxide coming out from occupant’s mouth, blower position and vehicle age. The developed model was validated by the author for mid-sized vehicles (vehicles from D-segment). The simulated data was within ±11.5% of the experimental data. In this paper the author has used the developed model to predict cabin CO2 concentrations for vehicles from B, C & D segments. Or in other words, the effect of the cabin volume will be investigated on the rate of build-up of cabin CO2 concentrations. Experimental tests were conducted on these vehicles and are compared to the simulated data. Detailed results have been presented in the paper.

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.

A number of experiments were conducted to determine oil accumulation rates for a single tank laminate evaporator with the tank at the top. The tank at the top results in a U-shaped evaporator plate design at the bottom where oil can collect under extreme operating conditions. A typical 4 pass laminate evaporator was used for testing. R-134a with an oil circulation ratio of 3% was used for this study. The AC system was run for extended periods (2∼4 hours) at different compressor speeds to simulate the variation of load on the evaporator. Evaporator samples were taken off from the test stand and weighed after recovering refrigerant. The evaporators were designed such that it could be isolated by shutting off valves at the inlet and the outlet connections.

Field tests were conducted on a late full sized sedan with the HVAC unit operating in both Recirculation and OSA modes to monitor build-up of the CO2 concentration inside the cabin and its influence on occupant’s fatigue and alertness. These tests were conducted during 2015 summer on interstate highways with test durations ranging from 4 to 7 hours. During the above tests, fatigue or tiredness of the occupants (including CO2 levels) was monitored and recorded at 30 min intervals. Based on this investigation it is determined that the measured cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes (greater than 700 ppm over ambient levels) with three occupants in the vehicle. Further, the occupants did show fatigue when the HVAC unit was operated in recirculation mode in excess of 5 hours. Further details have been presented in the paper.

Experimental tests were conducted on a parallel flow condenser with HFO-1234yf as the working fluid on an AC system bench to determine average and local heat transfer coefficients during condensation of HFO-1234yf for mass flow rates that are typically encountered from idle to highway speeds (800 to 3000 rpms). A condenser from MY 2008 medium-sized sedan was used for this investigation. All original OEM parts were used with the alternate refrigerant. Same TXV set-point was used with HFO-1234yf. The magnitude of the measured heat transfer coefficient for condensation was found to be 8~12% lower in comparison to HFC-134a. The magnitudes of the pressure drop during condensation were of the same magnitude as HFC-134a system. The information from this investigation can be used to in the design of condensers for mobile air conditioning systems with HFO-1234yf as the working fluid.

Experimental studies have been conducted to determine the energy stored in vehicle's Cockpit Module (CPM) at cold soaking conditions for a MY2012 production vehicle. Detailed analysis has been done in this paper to show the influence of energy stored in various components (e.g., Instrument panel, HVAC system, heat exchanger, wire harness, etc.) contained within the CPM unit. Experiments conducted show that the instrument panel stores the maximum amount of energy at a given temperature.

Experimental studies have been conducted to determine the energy stored in vehicle's Cockpit Module (CPM) at high ambient and at high solar heat loads for a MY2012 production vehicle. Detailed analysis has been done in this paper to show the influence of energy stored in various components (e.g., Instrument panel, HVAC system, heat exchanger, wire harness, etc.) contained within the CPM unit. Experiments were conducted to show the amount of energy stored at high ambient and solar conditions.

Experimental tests were conducted on a parallel flow condenser with HFO-1234yf as the working fluid on an AC system bench. This refrigerant is being considered as an alternative refrigerant for mobile air conditioning systems (MACS) to address the global warming concerns. A condenser from MY 2008 medium sized sedan was used for this investigation. Tests were first conducted with R-134a and were then repeated by maintaining each test condition by changing the working fluid from R-134a to HFO-1234yf. The refrigerant was used as “drop-in” refrigerant in the existing system. All original OEM parts were used with the alternate refrigerant. Same TXV set-point was used with HFO-1234yf. Detailed test results have been presented in this paper.

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).

Field tests were conducted on a MY 2003 vehicle with the HVAC unit in OSA mode to monitor build-up of the CO2 concentration inside the cabin as a function of number of occupants, vehicle speed and ambient temperatures. These tests were conducted in the winter season by driving the vehicle in Detroit Metro area in city (Farmington Hills) and highway traffic conditions. Based on this investigation it is determined that the measured cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes with four occupants in the vehicle. For this investigation, one to three occupants inside the cabin did not increase the level of cabin carbon dioxide to the levels specified by ASHRAE standard. A maximum concentration with four occupants was measured at 1700 ppm. The cabin concentration level would be higher for vehicles that have lower body leakages compared to this one.

A computer program has been developed to optimize the performance of finned tube condensers. The developed program is used to predict the thermal and hydrodynamic performance of finned tube condensers. The model is based on a steady-state finite difference model. The correlations for predicting the heat transfer and pressure drop are used from the literature. Experimental test data is used to validate the developed model for a finned tube condenser with R-134a as the working fluid. The simulated performance for the condenser heat transfer is within ±7%; and refrigerant pressure drop is within 10% of the experimental data. The simulated data for the condenser coil shows that 16% of the total heat transfer area is occupied by single-phase vapor flow where the superheated vapor are cooled to the saturated conditions; 72% by condensation; and the remaining 12% is controlled by the single-phase liquid flow which results in subcooling.

A computer program has been developed to optimize the performance of finned tube evaporators. The developed program is used to predict the thermal and hydrodynamic performance of finned tube evaporators. The model is based on a steady-state finite difference model. The correlations for predicting the heat transfer and pressure drop are used from the literature. Experimental data is used to validate the developed model for a finned tube evaporator with R-12 as the working fluid. The simulated performance for heat transfer rate is within ±8 %; and refrigerant pressure drop is within ±10 % of the experimental data. The simulated data shows that 66 % of the heat transfer area is occupied by flow boiling; 23 % by the dryout region; and remaining 11 % is controlled by single-phase vapor flow. Work is continuing on predicting the performance of serpentine and laminate type evaporators with R-134a as the working fluid.

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.

In an earlier investigation (Mathur, 1997a; 1997b), the author had developed a simulation program for predicting the thermal and hydrodynamic performance of the automotive heat exchangers. The performance of finned tube condenser and evaporator was simulated and compared with the experimentally obtained data. The simulated performance for both condenser and evaporator was in good agreement with the experimental data. In this paper, the performance of serpentine condenser and evaporator is simulated by using the computer program developed earlier by the author. None of the original correlations for predicting the heat transfer, pressure drop, void fraction are changed. However, the computational methodology had to be changed as the flow in a serpentine heat exchanger is different than in finned tube heat exchangers. The working fluid used in this investigation is R-134a. The simulated performance is compared with the experimentally obtained data on the calorimeter tests.

The performance of a parallel flow condenser of a domestic vehicle was simulated by using the computer program developed earlier by the author (Mathur, 1997). None of the original correlations for predicting heat transfer, pressure drop, void fraction were changed. The working fluid used in this investigation was R-134a. The simulated performance was compared with the experimentally obtained data from the calorimeter tests. The simulated thermal and hydrodynamic performance was within ±6% of the experimental data. Detailed performance data has been presented in this paper. The performance of the same condenser was optimized by varying the number of tubes in a given pass by fixing all other variables, e.g., tube and fin pitch; tube geometry; height, length, and depth of the condenser; number of passes; and location of the inlet and outlet connections.

The thermal and hydrodynamic performance of laminate (plate type) evaporators is simulated by using the computer program developed earlier by the author (Mathur, 1997). The correlations for predicting heat transfer, pressure drop, void fraction are used from the literature. The working fluid used in this investigation is R-134a. The simulated performance is compared with the experimentally obtained data from the calorimeter tests. The simulated thermal and hydrodynamic performance is within ″9% of the experimental data. Detailed performance data has been presented in this paper.

The EPA has issued regulations in the Final Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards (420r12901-3). This document provides credits against the fuel economy regulations for various Air Conditioning technologies. One of these credits is associated with increased use of recirculation air mode, when the ambient is over 24°C (75°F.). The authors want to communicate the experiences in their careers that highlighted issues with air quality in the interior of the vehicle cabin. Cabin contamination sources may result in safety and health issues for both younger and older drivers. Alertness concerns may hinder their ability to operate a vehicle safely.

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.