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Friday, July 03, 2020

Explained: Why ‘extreme heat wave like conditions’ are created inside parked cars

As global temperatures rise, it will be crucial to model cars specifically to decrease levels of thermal discomfort within.

Written by Chahat Rana | Updated: June 25, 2020 2:41:48 pm
heat wave conditions in cars As mercury rises, heat gets trapped inside parked vehicles through the green house effect creating “heat wave like conditions”. (Express File Photo: Jasbir Malhi)

A recent study by doctors from the Department of Community Medicine at the Post Graduate Institute of Medical Education and Research (PGIMER) observed how extreme “heat wave like conditions” are created inside parked vehicles. The study observed that the mean radiant temperature in parked cars in the summer exceeded 62 degree Celsius, when the acceptable radiant temperature should be less than 35 degrees Celsius, according to the standards prescribed by the Indian Society of Heating, Refrigerating and Air Conditioning Engineers. The Indian Express explains the reasons behind the study and its results

What is the purpose of the study?

Thermal discomfort in buildings and other indoor spaces have been extensively studied in the past, but very few studies assessed it in standing vehicles. As mercury rises, heat gets trapped inside parked vehicles through the green house effect creating “heat wave like conditions”, which are much worse than the atmospheric temperature outside.

This study used different models of cars to capture the extent of heat wave like conditions and thermal discomfort experienced by passengers in the micro-environment of the vehicle. “Such conditions are known to have adverse effect on health. Apart from heat exhaustion, irritability and difficulty in concentration, it can lead to major issues such as a heart attack or even a stroke,” says Ravindra Khaiwal, one of the authors of the study. “With temperatures rising and people spending more and more time commuting in their vehicles, it is essential that the cars are designed to reduce such thermal conditions in the future,” adds Khaiwal.

How was the study conducted?

The study was conducted in a parking lot inside PGIMER, Chandigarh, where the ambient conditions inside and outside three models – a sedan, an SUV and a hatchback – were recorded on different days in the summer of 2018. Devices to record relative humidity, air temperature and pollution levels were placed in the front of the car, the back and outside on the top of the car. These parameters were further used to calculate Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD). Both PMV and PPD are measurement scales devised to calculate the thermal comfort experienced by individuals. PMV records the level of discomfort faced by an individual and PPD predicts the percentage of individuals who will be dissatisfied by the thermal conditions. Parameters including clothing insulation and metabolism rate of individuals are also incorporated into the PMV-PPD calculation.

What were the results of the study?

It was observed that the mean radiant temperature remained more than 62° C in all cases inside all three cars monitored in the study, while the ambient temperature outside remained between 30 to 40°C. This is much above the standards of minimal thermal discomfort in asymmetrical structures as prescribed by the Indian Society of Heating, Refrigerating and Air Conditioning Engineers.

Further, temperatures recorded in the front area of cars was always higher than the back, and the temperature inside the cars was at its peak in the evening. “This is because the cars get continuously heated up and don’t lose that heat at all so the temperature inside keeps rising,” says Khaiwal. The study also states that the sedan recorded highest ambient temperature despite the atmospheric temperature outside being lower on the day it was monitored as compared to the days on which the study was conducted inside the SUV and the hatchback. “The sedan was black in colour, which could have been why it retained more heat,” says Khaiwal.

The PPD was 100 per cent in all cases, which means that under all circumstances observed, it was predicted that individuals will be highly uncomfortable. The PMV levels calculated were also much higher than the recommended levels of thermal discomfort at all times.

How can vehicles be modelled differently to curb thermal discomfort?

As global temperatures rise, it will be crucial to model cars specifically to decrease levels of thermal discomfort within. “We can’t just rely on air conditioning, because the sudden blast of AC can make us even more sick. The point is that the designs of cars should be made keeping in mind strategies to curb heat wave like conditions within,” explains Khaiwal.

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To mitigate conditions, Khaiwal and his team suggests developing sensors for monitoring thermal discomfort parameters within the car and installing an alarm system based on artificial intelligence which “advises passengers to exit the car or wait for a specific time interval before entering the car cabin in case of poor thermal comfort”. “Less complicated factors such as the material of the car and even just the colour scheme of cars can make a lot of difference in controlling thermal conditions. One can even just begin by using thermal shades when their cars are parked in the heat for longer periods of time,” says Khaiwal.

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