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Old 14th May 2024, 10:33   #1
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Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Superheated glasshouses
The superheated interiors of the car glasshouse is a well known curse for us Indians.
Anyone could figure out that it was dangerously hot but i was curious on the numbers - how hot in Celsius, how much energy just to cool this to the acceptable levels.

While it was quite easy to figure out the interior temperatures, a simple no-contact thermometer to the task.
The energy used up for the cooling, was almost impossible to accurately figure out, atleast with the ICE’s. No consumption figures in liters of fuel or electrical units in KWh.
So could never figure it out, till we got the EV’s.
Almost all EV’s come with energy meters and this is what helped. The energy consumed in KWh’s by the AC was clearly indicated. (The reason why this post is in the electric cars section!)

So, down to the experiment.

This experimentation was all at Chengannur with a dry bulb temperature of around 35 deg Celsius but with humidity of 70% or higher, so that results in a heat index (felt air temperature) of around 50 deg Celsius. The body will sweat like anything but does not cool down.
Unfortunately the interiors of my car were dark grey with leather seats so you can imagine the discomfort (compared to, if it had lighter interiors with fabric seats).


To keep it simple, i will let the pictures do most of the talking

Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-under-sun-glass.jpg

Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-under-sun-interior-without-cover-last-reading.jpg

The temperature quickly overshot 60 degree Celsius, this was the temperature limit of the infrared thermometer i had, I do not know how high the temperature finally was!

At these temperatures, the car is intolerably hot. So it usually comes down to a full blast of AC, to make the car comfortable again.
Since that is quite inefficient for the experiment’s sake, I tried the slower and more time consuming process to see what would be the minimum energy required to cool the cabin down. Set temperature to 24 deg Celsius and fan at medium so that the entire cabin, including the rear seats get cooled).

The AC struggled to cool the cabin within 10 mins even while drawing more than 3 times the energy. Moreover the seats and the surface temperatures of the interior were still not comfortably cool. It took more than half an hour before the interior was cool enough and the AC load came down to around 0.6KW.
Compare this to, if the car was parked under shade – the AC starts off as low as 0.6KW and it's immediately cool.
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-ac-cons..jpg
Result: The savings definitely are not substantial around 0.7 to 1 KWh; it is more about the degree of comfort and degradation of the interiors that counts.
Though for a mileage counter like me this another venue for savings.


So, as the designated driver, it was important for me to find a solution. After all it was my job, to cool down the car before others could comfortably enter.
A strong enough motivation, as it is not always easy to find a shaded spot - every time the car gets parked (although my brain is usually on overdrive when hunting for a parking spot).
The bonus, saving the precious unit of energy to cool down the superheated interiors.

Reflective half covers
And it was this hunt that finally led to something known as Reflective half covers. Initially it was used only at charging stops, but thanks to the heat wave we are facing nowadays, it just goes up every time the car is stopped for more than 30 mins.
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-half-cover.jpg

This has now become my final solution after trying all the other options available on the market:
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-alternatives.jpg
- Sunshades (magnetic & suction cup ones): Cheap and mildly effective with vehicle running. Felt useless in parked vehicle
- Reflective sunshades: - Could find only for front and while it was moderately effective, the glass still got hot (more than 60 degree Celsius) as this was placed inside. So when we get back in, the first few moments we can still feel the radiated heat.
And it is always a hassle if dashcam's and mobile mounts are on the dash.
- Sun films: - Quite effective as long as the car is running and makes a world of a difference. But leave the car parked for more than 10-15 mins and it's as if the film never existed.
Reason - When the vehicle is running the glass gets cooled by air flow, the sun film does the job of limiting the incident Infrared from entering the cabin. But when the vehicle is stopped, within 10-15 minutes the glass heats up and in turn heats up the cabin.

I finally realized that all of these touted solutions, are inside the glass. So they cannot prevent the glass from heating up, which in turn heated up the cabin.(temperature above 60 degrees Celsius).

- So, finally I tried carrying the bulky car cover:. Yes, i did carry it and tried putting it up under a blazing sun, in a burning parking lot, with folks watching me struggle, considering me to be nut case, which actually felt true at that moment ). It worked , the car was cooler. The unmanageable pain of putting it up, just made it impossible as the “on the go” solution.

And that’s how i ended up with these reflective half-cover’s

The most important points about these half - covers
- Best part, its compact and takes around a minute or two, to just throw this blanket over and strap it on to the vehicle(may not be as easy but got the jest of it after a few rounds).
- Temperature reduction’s almost like 20 degree Celsius.
- This material runs even cooler than the standard silver colour cover the car comes with.
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-reflective-vs-stock-cover.jpg
Cons
- Not rain / waterproof
- Does not seem as thick/sturdy as the standard covers.
- Possibility of damage/tearing due to the stubby antenna

And as usual, i ended up even testing these covers.
Testing under the sun:
The comparison
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-under-sun-interior.jpg
It was suffocating hot without the cover.

Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-under-sun-seat.jpg
The Hot seat – burning through even thick jeans.

While testing with cover i let the car stay out under the sun longer.
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-under-sun-interior-cover-last-reading.jpg

Result
It manages to keep the car “substantially cooler”.

There was another interesting observation , this reflective cover managed to keep the car almost 5 degree Celsius cooler than if the car was parked under shade without cover (thick tree canopy on one side and cool winds from the large irrigated paddy fields on the other side)
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-shade.jpg

Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-shade-interior.jpg

A 5 degree Celsius difference makes it noticeably cooler.
Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?-cover-test-shade-seat.jpg

I literally did not need the AC or the ventilated seats, whenever the car was covered. I could start driving, without even starting the AC for preconditioning.

The cover manages to keep the interiors dark enough, to keep it cooler. My guess - it prevents even the reflected infrared radiation, from ground and surrounding structures, entering the cabin and heating the dark interior of the car.

The absolute relief of not stepping into a burning oven, has now made it worth carrying it in the boot regularly.

Details of the product that i tried:
- Official Company Link
- Amazon Link

Disclaimer: Not associated with the company in anyway. Found it, tried it, experimented with it and now just sharing about it
Infra red thermometers are not accurate with glossy or reflective surfaces with incident light, hence relied mostly on interior temperatures.

Last edited by EV Fan : 14th May 2024 at 10:35. Reason: Reduced the usage of the smiley's
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Old 14th May 2024, 11:25   #2
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Thanks for the experiment. Little bits add up in the long run and energy savings is always great.
Regarding the energy consumed, I see the car shows instantaneous KW and we need to compute Kwh. Did it ever go down as it cooled down ?
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Old 14th May 2024, 13:08   #3
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Is it possible in your car to turn ON the car fan remotely with external ventilation without turning on the AC?
Did you also try solar powered fans/car ventilators that get installed on the window edge and provide ventilation.

2 KW peak load is too high because my 1.5 tons ac's peak power consumption is less than 1.5 KW. Do these figures match with the percentage of battery drop?
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Old 14th May 2024, 13:09   #4
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Good stuff. Car covers seem to gather more dust and sand than the sahara desert, end up with the texture of sand paper in short time. is this thing more resistant?
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Old 14th May 2024, 20:54   #5
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Quote:
Originally Posted by PreludeSH View Post
Regarding the energy consumed, I see the car shows instantaneous KW and we need to compute Kwh. Did it ever go down as it cooled down ?
Instantaneous KW X Time = KWh.
Basically just used it to roughly come to 1KWh.

AC load actually came down sometime after 30 mins, but the seats and other surfaces were still warm so waited almost 20mins more till it actually felt cool "to touch" also.

Usually we just blast the AC at full for 5-10mins, this slow cooling was just for the experiment.

Quote:
Originally Posted by ishekk View Post
Is it possible in your car to turn ON the car fan remotely with external ventilation without turning on the AC?
Kona has a time based preconditioning in the MID, no wireless or app based controls. It is something that i use if i know exactly when i will be back like at charging sessions.

Problem is it needs to be pre-programmed on the infotainment - works like clockwork. Get delayed to return and the AC cooling would have worn off.

Quote:
Originally Posted by ishekk View Post
Did you also try solar powered fans/car ventilators that get installed on the window edge and provide ventilation.
Had tried them long back on another car. It somewhat managed to reduce the hot air blast that we get when we step in initially. but the glass and interiors were super hot, so it's more or less the same.
Also they seemed flimsy- Broke pretty quickly.
Interestingly the moment sun films were put on the car's windows, the solar panels which were mounted inside, were rendered useless. So basically ended discarding them.

Quote:
Originally Posted by ishekk View Post
2 KW peak load is too high because my 1.5 tons ac's peak power consumption is less than 1.5 KW. Do these figures match with the percentage of battery drop?
I have seen it as high as 2.4KW in the Kona. EV's have a pretty strong cooling system especially since they need to cool the battery.

Quote:
Originally Posted by ballkey View Post
Good stuff. Car covers seem to gather more dust and sand than the sahara desert, end up with the texture of sand paper in short time. is this thing more resistant?
Yet to see how it fares, on longevity. It's just been a few months but is being used daily. Seems to be holding well for now.
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Old 15th May 2024, 09:59   #6
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

That is why I am a strong opponent of this Sky Roofs and Full length Sunroofs etc. especially in North India. Sunroof's are NOT practical for North India. Period. And people in Delhi NCR realise that sooner than later, in our summer heat, how tormenting it can be. Manufacturers and car buyers need to get their head around this fact.

Another useless feature, especially in North India, is Cruise Control and ADAS. I could never use cruise control on my Superb for more than 5 minutes in one go, even on the latest Delhi-Meerut Expressway, it is so crowded most of the times. And with ADAS, I am more likely to cause an accident than any convenience.

Maybe this RANT deserves a new topic.

Cheers...

Last edited by dkaile : 15th May 2024 at 10:00.
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Old 15th May 2024, 10:11   #7
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

I have a Nexon EV Max #Dark edition so this is particularly useful for me! A few questions:
1. Will it fit the Nexon? One of the Amazon reviews says it doesn’t, hence curious.
2. Does it tend to scratch the paint from your experience?

As a side note, I find the Nexon EV Max cabin cools faster than my earlier Civic after being in the sun. I suppose this comes down to two reasons:
1. The Civic glass area is humongous - especially the windshield
2. The sun roof on the Nexon - I open it in tilt mode and hot air escapes readily through convection (the cool a/c air settles down for the same reason)
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Old 15th May 2024, 10:15   #8
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Quote:
Originally Posted by dkaile View Post
That is why I am a strong opponent of this Sky Roofs and Full length Sunroofs etc. especially in North India. Sunroof's are NOT practical for North India. Period. And people in Delhi NCR realise that sooner than later, in our summer heat, how tormenting it can be. Manufacturers and car buyers need to get their head around this fact.

Another useless feature, especially in North India, is Cruise Control and ADAS. I could never use cruise control on my Superb for more than 5 minutes in one go, even on the latest Delhi-Meerut Expressway, it is so crowded most of the times. And with ADAS, I am more likely to cause an accident than any convenience.

Maybe this RANT deserves a new topic.

Cheers...
On the contrary, opening the sunroof in tilt mode, without sliding the cover below, creates a chimney effect that sucks out hot air from the cabin in a jiffy. I use it a lot more than actually retracting the sun roof fully, which of course lets the direct sun in and roasts you more
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Old 15th May 2024, 10:28   #9
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

More than the experiment and the product, I'm more amazed with the temperature in your city.
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Old 15th May 2024, 10:30   #10
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Quote:
Originally Posted by navinmra View Post
On the contrary, opening the sunroof in tilt mode, without sliding the cover below, creates a chimney effect that sucks out hot air from the cabin in a jiffy.
Strongly disagree. The same job is done more easily by just opening the windows. And without the added advantage to get baked by the sunroof in the first place.

Cheers..
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Old 15th May 2024, 10:52   #11
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Great experiment! Thanks! Surprised to see so much effect of the cover!

Quote:
Originally Posted by dkaile View Post
Strongly disagree. The same job is done more easily by just opening the windows. And without the added advantage to get baked by the sunroof in the first place.

Cheers..
Sunroof is in tilted mode and has a cover. So you donít get the sun inside. Hot air will rise, so opening the roof in tilt mode is the most effective. Most likely recommended in the owner manual as well.


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Old 15th May 2024, 11:00   #12
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Never owned a car with a sunroof but wouldn't opening the sunroof slightly aid in cooling the cabin faster, with hot air rising up and all?

This strategy could help cool a superheated car.

Step 0: Install 99% IR Rejection VKOOL film on the Sunroof glass. (less heat enters through the sunroof)

Step 1: Open the sunroof 10%. Hot air now has a place to escape.

Step 2: Start the aircon at full blast / reasonable temperature depending on how soon cooling is required.

Step 3: Wait for the car to reach the required temperature.

It is time someone does a calculation on how much forex the nation is wasting in cooling cars with the sun film removed vs installed. With EVs, the extra energy required can be measured easily. Just 8x the energy cost and you have your number for the amount spent in Petrol terms. This can be easily extrapolated for all cars in the country and we could easily get a number in couple of thousand crores per year or about 0.x% of GDP. The same money that could have been spent on installing y GW of capacity in solar every year contributing another z amount in energy generation or 0.q% of GDP.

It is also time OEMs mandate IR cut glass to boost efficiency with aircon. The latter probably won't happen till ARAI does not conduct their test outside in the real world in the summer heat to meet CAFE norms.

The latter is impossible till there is change in regulation. But the former is up to someone enterprising among us. Maybe someone has done this kind of research in the developed world. Need to figure that one out.
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Old 15th May 2024, 11:07   #13
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re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Quote:
Originally Posted by Jeroen View Post
Sunroof is in tilted mode and has a cover. So you donít get the sun inside. Hot air will rise, so opening the roof in tilt mode is the most effective. Most likely recommended in the owner manual as well.
Agreed to an extent IF you have a sunroof and there is no way out. But Sir, my humble submission was that sunroof, as a product feature, in itself is useless for us in Delhi NCR, especially the panaromic ones, when the temperature is touching 45 degrees here in Meerut. I have seen people here packing their Sunroof gaps with thermacole sheets (kindly refer to the Skoda Kodiaq thread - a car with a panaromic sunroof), just to be able to drive in these months and have a effective AC. If we need to resort to such measures for the peak summer months, then that product feature is clearly not designed for the Indian Climate. Maybe that is why Maruti was so late in introducing sunroofs in their cars, because even they knew it was impractical here, but had to bow to public pressure (read their Children, who especially like to stick their necks out ). India really survives on 'jugaad', we have got one for everything .

A big fan of your threads, btw.

Regards and Cheers...
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Old 15th May 2024, 11:18   #14
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Re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Quote:
Originally Posted by antz.bin View Post
Never owned a car with a sunroof but wouldn't opening the sunroof slightly aid in cooling the cabin faster, with hot air rising up and all?
The additional safety feature of sunroof in Nexon --- when you lock it the sunroof closes -- means that you cannot lock the car and leave the sunroof in tilt mode .

I do not know how it is for other cars.
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Old 15th May 2024, 11:32   #15
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Re: Experiment: Parked car under the sun | How many kWh to cool the superheated cabin?

Regarding cooling, it's always better to tilt the roof during initial drive, due to the pressure differential and venturi effect, the air inside the cabin will be sucked out immediately, add AC to circulation mode and the temperature would be lowered fast. The aerodynamics of the sunroof are made that way, even if you keep it tilted during rains, it won't come inside, as long as the car is moving.

Quote:
Originally Posted by electric_eel View Post
The additional safety feature of sunroof in Nexon --- when you lock it the sunroof closes -- means that you cannot lock the car and leave the sunroof in tilt mode
In my opinion that's a neat and much wanted feature. Keeping it open in stationary position is anyway a hazard and you might never know what kind of insects would be waiting for you during the next drive.

Quote:
I do not know how it is for other cars.
My car gets locked irrespective of the condition of the sunroof, in fact at times I have noticed it next day that the sunroof was tilted, a downpour during the night would have definitely created havoc. And we get sand storms quite often, I would never want my sunroof to be open while not driving or being parked.

Last edited by NomadSK : 15th May 2024 at 11:34.
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