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The vehicle's AC system should not be operated in recirculation mode for extended periods of time due to build up of CO2 inside the vehicle cabin. This is the CO2 that is exhaled by the occupants of the vehicle. This CO2 is then inhaled by the occupants that goes into their blood streams which results in a negative impact on health. This becomes critical when a number of people are sitting inside the vehicle. Field tests were conducted on a MY 2003 vehicle in recirculation mode to monitor the build-up of the CO2 concentration inside the cabin as a function of number of occupants, vehicle speed and ambient temperatures. The vehicle was driven in Detroit Metro area in city and highway traffic conditions. Based on this investigation it is determined that the cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes in first 5 minutes of driving with only one occupant in the vehicle.

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.

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 author has developed a model that can be used to predict build-up of cabin carbon dioxide levels for automobiles based on many variables. There are a number of parameters including number of occupants that dictates generation of CO2 within the control volume, cabin leakage (infiltration or exfiltration) characteristics, cabin volume, blower position or airflow rate; vehicle age, etc. Details of the analysis is presented in the paper. Finally, the developed model has been validated with experimental data. The simulated data follows the same trend and matches fairly well with the experimental data.

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.

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.

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.

Carbon dioxide exhaled by occupants remains within the cabin during operation of HVAC unit in recirculation mode. The CO2 inhaled by the occupants goes into their blood stream that negatively affects occupant’s health. ASHRAE Standard 62 specifies safe levels of carbon dioxide in conditioned space for humans. The CO2 concentration limit per ASHRAE is 700 ppm over ambient conditions on a continuous basis. In a recent investigation the author had developed a model to predict cabin carbon dioxide concentrations for recirculation mode 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. This developed model has been modified to simulate cabin airflows from 100% recirculation mode to 100% outside air mode, i.e., for any percentage of partial recirculation.

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.