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Comment by temporaryvector | Hacker News Reader

I live in a pretty hot city (My car's outside thermometer showed 48°C yesterday at midday).

The extended range is nice and all, but if somebody makes a car that can run the AC without running/draining the battery while it's parked, even if it's just a little to keep the car interior at 35°C or so, I would, without exaggeration, buy it the day it's released here. Hell, I'd consider it even if it would just keep the fans on to vent the hot air out.

Parking in the sun while doing errands, which often involve multiple short trips where the car's AC doesn't get enough time to cool it down, seems to be a very common cause of heat-stroke among white-collar workers here. I've had to go to the ER twice about it this summer alone.

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> The extended range is nice and all, but if somebody makes a car that can run the AC without running/draining the battery while it's parked, even if it's just a little to keep the car interior at 35°C or so, I would, without exaggeration, buy it the day it's released here.

Tesla's dog mode does this. Draining the battery isn't really something to worry about; AC uses <300 watts over long periods (turns on and off at <1 kW). Leaving it on for 8+ hours you're talking about <5% capacity loss, at a cost of <50 cents. For short trips you could leave the AC on full blast without even noticing a drop.

It looks like the Hyundai Kona EV has a Utility Mode that works similarly (the headlights are off, the vehicle is locked in park, and you can run the AC indefinitely.)

However, based on this thread, utility mode requires the key fob, so someone could just break a window and steal the car. I wish manufacturers other than Tesla would think about these use cases:

https://www.insideevsforum.com/community/index.php?threads/u...

It was mentioned later in that thread, but the Kona EV also lets you control the AC remotely via its mobile app without leaving the keys in the car. I don't know if it'll run indefinitely, though; my old Chevy Volt would turn off remotely started climate control after 15 minutes or so, and I haven't tried in the Kona yet.

That said, even if it is time-limited, 15 minutes is usually enough to cool down the car without leaving the AC on all day.

Any time limit defeats the point. An electric car isn't just a car without gas, it's a climate-controlled room you can put anywhere.

As global temperatures rise, there are places becoming increasingly uncomfortable to live in. There may be cases where it's cheaper to wait out the hottest days in your car, instead of retrofitting a cooling system onto a building.

I'm not sure how true that would be in extremely hot weather, but it is probably the only reason I'm considering a Tesla if it ever comes to my city, my commute is really short so even if it cut 200 miles off the range it'd be worth it for me.

Having a car with remote start alleviates the problem a little bit, but I'd rather not run an ICE engine while I'm not in the car for obvious reasons.

Even on constant full blast with the smallest battery Tesla sells, it's only gonna use ~2-3% per hour. Over 8 hours that would be 44 miles off the 220 mile range.

> but it is probably the only reason I'm considering a Tesla if it ever comes to my city

Hmm, Telsa should be pretty reachable. Perth and El Paso look like some of the only neglected hot cities.

I don't live in the US, as far as I'm aware there's only one Tesla store in my country and it's nowhere near me.

I figured- Perth is in Australia. If you're in Mexico you're pretty screwed, as is... South America, Africa, and most of Asia. You can check the map if you like!

https://www.tesla.com/findus?v=2&bounds=67.51085725091038%2C...

Mexico. I'm actually surprised there's one charging point in my city. I'd expect there to be none.

I'm pretty hopeful that we'll either get Tesla in a couple of years or other manufacturers will come out with something.

It seems that they deliver, if I'm reading the pages right. Not sure what being further away means for servicing though.

What do you mean by 'if it ever comes to my city'?

Yeah, can't you drive Teslas anywhere?

I wouldn't want to own a car that can't be repaired locally.

Sure, I mean they float, right?

Wouldn't chucking a bucket of water over the car with the evaporation help cool the car down quicker initially? Along with least reducing the amount of time needed to run idle for cooling.

Though this would depend upon the humidity, would not work in high humidity and equally work better in low humidity.

Sure, but for that to work you have to carry around buckets of water.

Not in the morning when you're at home.

This definitely makes Teslas more attractive to me. About half the homes on my (short) street have Teslas. I didn't know how little hot weather affected the battery usage. I had mistakenly assumed that A/C would have a greater negative impact on range.

It will on an older Leaf with a smaller battery. In Norway, you might be forced to turn of the heating in winter if traffic gets bad. But with double-digit kWh of battery capacity as a normally-unuser buffer, it won’t be much of a worry, if at all.

> Tesla's dog mode does this.

Dog mode is the main thing keeping me from trading in my Tesla for something else.

Tesla also has the milder "Cabin Overheat Protection" that can be turned on in settigns to keep the car interior from going over about 100 degrees fahrenheit.

You can also just turn on the AC from your phone 10 minutes before you leave. Or, have it learn your schedule so it prepares your car for you before you go.

In hot climates, even when the air temperature returns to tolerable levels, radiant heat from the various surfaces is no joke.

It helps that a Tesla battery can basically power a house for several days.

2015 and later variants of the Prius already have this via the solar roof option: https://www.jpauleytoyota.com/blog/how-does-the-toyota-prius...

“If you want to activate the solar powered ventilation system before you get out of the vehicle it is a simple process. On the left side of the steering column, you will find a small square button with a car and fan on it. Press this button before you turn off your vehicle and you are all set. Next time you get in your Toyota Prius it will be nice and cool.”

Edit: apparently it’s limited to running the fan, there’s also a remote a/c option that’ll run for a few minutes off of battery before you get to the car.

I did not know that, and neither did the salesman when I was choosing my current car. They really should put that feature front and center, at least locally. Maybe that option isn't available in this market.

The solar roof for running a fan has been around since the 2010 prius.

I had a 2010 Prius with the solar roof. It does work, but it just reduced the temperature from unbearable to quite hot, it did not make it cool. It's somewhat nice to have on very hot days, but is not really a killer feature.

Even just running the fan on a 45c day should have a huge impact on the internal temperatures of the car.

You can easily hit ~85c (+/-) in very little time then; sadly lots of children / pets are killed all the time as people are just dumb, ignorant, or forgetful.

Someone mentioned dog mode in a Tesla, but that’s not the only feature that does this. Dog mode or Camping mode is for keeping the interior at something around 20c or whatever you set.

from reading your comment it sounds like you just don’t want the interior to ever get over 35c, which is exactly what the Cabin Overheat Protection mode is. Basically this is a set it and forget it setting that ensures the inside will never go over 100F. You can choose to use ac which kicks it on and off every so often using minimal range, or you can choose for it to only use outside ambient air, granted it if it’s 48c then you are only getting as cold as that.

check out this article and video https://insideevs.com/news/340230/how-much-does-cabin-overhe...

My old car had a sunroof that could also tilt up. That took the edge off and let excessive heat escape. Combined with a reflective windshield shade it worked reasonably well. Not chilly but more practical and env friendly than running AC for 8 hours a day.

I keep the AC on in my Tesla a lot during the summer. Costs a couple miles per hour of range. Totally worth it.

Toyota Prius had (has?) something similar. They had this add on where they install a 100W panel on the roof to run the car fan to vent outside air in and inside air out. One of my coworkers had it and the car temperature was significantly lower during the summer days during lunch.

«somebody makes a car that can run the AC without running/draining the battery while it's parked»

Temperatures could be reduced significantly with a car modification that uses very little energy: a small fan to circulate and replace all inside air with outside air, and a one-piece reflective foil cover on top of the car, covering the entire windshield + roof + sides + rear windshield.

It hits these temps in Phoenix; huge market for Tesla's. They have cabin overheat protection plus you can start the AC from an app on your phone. Really nice!

A couple of the old Priuses used to have a solar powered fan. I can’t find any good info on it at the moment but IIRC it was basically a computer fan coupled to a small solar panel so don’t think it was too effective.

https://priuschat.com/threads/solar-powered-fan-is-it-workin...

In theory, the solar roof should absorb ~30% of the rays a cars is exposed to, so it won't heat up as much. Not sure if the effect would be significant, though.

It would help but the glass windows (greenhouse effect) are probably a bigger factor.

Good window tints (with IR and UV blockers) help big time keeping the car cool.

We need integrated pop up solar car awnings that provide energy and shade. They actually make funky pop up car awnings, but a sleeker, solar option would probably take hold in hotter climates.

How does that compare the the fraction reflected by a white paint scheme?

You can have your cake, eat it and get icing on top by using a coating that

a) has a transmission window in the range that's useful for PV b) has high emissivity in the atmosphere's IR window c) has high reflectivity in the rest of the spectrum

That’s awesome. Either we don’t have those materials nailed yet, or the demo version pictured has the cells showing for presentation purposes, or both.

Edit: third possibility described by the interesting reply below: there could be an out of visible band reflective coating over the panels.

Cells with such a coating would still appear dark to the human eye because the visible spectrum contains the peak of sunlight's energy distribution and you want to convert that to energy (you could optimize around the UV/violet range since the excess photon energy gets converted to heat there). But there's a broad limb of IR in the distribution that is useless because it's below the bandgap of most PV materials, that's the part you want to reflect. But then again inside the IR range there's the IR window, where you don't want to be reflective to increase emissivity to shed heat into space.

I have read research papers about such coatings, but I don't know whether they're in commercial use.

Tesla will keep your car at 105F or less while parked unless your battery is too low.

Electric car or not, a very low tech but effective approach is to use a decent sunshade. Quick to set up, and have been shown to lower the internal temperature 20 degrees or so.

I had this feature on my old 2007 Audi A6, which replaced the moon roof with a solar sun roof, which powered a fresh air fan when parked in the sun. I purchased it off-lease, and it was pretty much maxed out on features. I never saw another A6 with the solar option - I think it had to be special ordered from the factory. A shame, it was really handy in the Texas heat.

Now I have a tesla which can just run the AC at will, which is even better :)

It would also be cool, pun intended, to add windows with liquid crystals that can darken when parked to keep additional heat out.

I've wanted this for a while, in combo with a head-tracking cabin camera. That way the windscreen would tint in specific areas over the sun, oncoming headlights, and glare.

You can't use LCs, as they don't have a real "clear" mode- they always block a very significant amount of light. You'd have to use electrochromatic paint or similar, as some trains and airplanes do. It's expensive and a chipped windscreen would be awful. You also can't get great resolution. I still wish somebody would do it.

Wouldn't darkening just absorb more heat? How about turning white, or a reflective coating? (Maybe not something liquid crystals could do, but a car with mirror shades would look cool.)

Probably true that white or reflective coating would be better, but even with black there would be much less green house effect inside the car. The windows would heat up though and would be cooled by the air outside.

I believe the reduced interior heating comes from the windows absorbing heat instead of the interior surfaces. Those hotter windows may radiate some inside, but they'll radiate a lot outside that never got into the interior.

Smart film/tint/glass on a car window: https://www.youtube.com/watch?v=c7xEcI1oSVs

Great idea! Much of this cooling can probably be accomplished by better sun shading and airflow. I always thought this[1] type of privacy glass would be a great idea in a car. Put it in park and the windows automatically tint.

http://www.smartglassinternational.com/electric-switchable-g...

> I would ... buy it the day it’s released

Sounds like this “dog mode” does exactly what you’re wanting. I see a new Tesla in your future :)

Electrically adjustable tint for windows would be a better option if it existed. Keep the heat out instead of dealing with it after it heats up the interior.

Just regular tint would be good too. I'm not sure if there are tints which block depending on the angle of the sun.

My gasoline Volvo has a feature where you can run the ac/heater remotely from a watch and phone app. It is limited to 15 minutes, but I find 5 minutes at full blast makes it very nice when I get in.

I believe hybrid Volvos can do this while using the battery.

Seems like a specialised window AC unit could work, run it off solar panels on the dash board. Maybe not safe for insecure areas but a controlled work car-park .. but then you could probably just leave your windows open in 'safe' places.

Actually, in Tokyo I noticed it's common for drivers to wait for their clients for hours, sleeping in the car with the air conditioner on with the engine running, hopefully this is one step closer towards solving that issue!

Many modern Hybrids run the AC off battery so would it be sufficient to buy a hybrid with an app that can do "remote start" so you can turn on the car an hour before you leave work?

Just an idea but maybe you shouldn't run errands at noon anymore? Twice to the ER from running errands seems extreme.

In the meantime, maybe roll your windows down when you get in the car?

> My car's outside thermometer showed 48°C

In case you wanted to feel like you were in a blast furnace instead of an oven?

how much power does an AC use (say on medium settings) ?

Wikipedia says 3kW https://en.wikipedia.org/wiki/Automobile_air_conditioning#Po...

It also says that the most efficient photovoltaics yield 175W per square meter. (Though I've seen figures as high as 200W.) https://en.wikipedia.org/wiki/Solar_panel#Efficiencies

That's for a belt-driven A/C, tied directly to the engine RPM. They're inherently much less efficient because they have to work over a wide range of speeds. A motor-driven A/C will be 1-2 kW.

That's also the peak power, and a motorized A/C will instead be turned on and off leading to a much lower power draw that also depends less on the peak power. Typically a 50-30% duty cycle, so 200-300 watts very roughly. More depending on the insulation, sun, and outside temperature.

And if instead of getting into a sweltering 330K car, if 300W was enough power to cool it to a reasonable 300K, that's still a win. Happy to start car to cool it down to a comfier 295K.

This man is using Kelvin... why do you use Kelvin?

yeah forget it, 3kW is small house scale

the best bet with solar panel AC... is to cover all windows with them so sunlight doesn't heat the inside of the car when parked. :cough:

Window units range from 700 W to 2+ kW. The Model 3 has a pretty powerful one, at least 1 kW. That's peak draw, and it'll turn on and off intermittently[1]. Average draw should work out to 200-300 watts for medium.

[1]: Like a fridge. Refrigeration systems are most efficient at full power. IIRC it's due to the restrictor plate separating the hot and cold radiators- it's designed to work at a certain rate of flow, so you'll get gas and liquid mixing at lower power.

Not sure on medium but I think ev A/C like Tesla's are 15,000 btu units. A 15k btu a/c should be between 1000-1600 watts depending on efficiency.

This probably isn't the most reliable source, but the infotainment screen on my VW estimates the hourly gas consumption for the climate system.

Running on Max A/C, the screen reads just under 1/8 gal/hr. With the A/C on and with the fans at 50%, consumption is a little less but still around 1/8 gal/hr. Consumption drops too low to get a reading when A/C is off with fans 50%.

I'm actually not sure in terms of car AC. Local wisdom says that on hot days your AC will sap up to 10 HP from your engine. Not sure how accurate that is.

Looking around on Telsa forums and the like, I'm seeing numbers between 1 and 3 kW. My house's mini split AC unit draws around 9 amps (according to documentation, anyway), so around 2 kW. Actual numbers seem to be closer to 3 kW in the summer.

I currently have my Tesla plugged in to my 6kw home charger, with the AC blasting, and the range isn’t increasing, leading me to believe that the AC running 100% takes around 6kw.

hmm, gets me wondering if that's why my car can't climb hills when on AC.

That may be part of it. Most (all?) newer cars will automatically cut off the AC pump under heavy acceleration.

"Hang on, I'm hitting the turbo button." (turns off AC)

Every car with voice control should recognize “divert life support to propulsion" as a command to turn off engine-driven AC.

Oh man passenger reactions would be so awesome. Suddenly the driver just says "divert life support to propulsion" - and the passengers are like "WAIT WHAT LIFE SUPPORT?!"

as an 80s kid you don't know how much I love your idea..

Yeah I'd want that in a normal ICE car.

Why would you want this feature knowing that is burning gas that you paid for while idle? Would you be happy about the car releasing toxic gases like CO and NOX while parked?

Because of the “going to the emergency room twice with heat stroke” thing, I’d guess.

But it seems that "dying of CO poisoning while staying cool from the AC" would be worse?

Yes, and solar roof would prevent that...

Presumably you park the car outdoors when it's running, where it exhausts into the atmosphere like usual.

If the gas-powered car has a solar roof that's not a problem.

That's exactly why I want the feature of a solar roof to power AC - so I don't have to burn gas while idling and release toxic CO and NOX just to stay cool.

This comment confuses me. The electric energy isn't free, and depending on the source its possibly emitting the same gases (but hopefully at a lower rate due to efficiency gains).

I'm all for EVs but I find these types of comments distracting and underscoring a fundamental misunderstanding

Parent article is about a solar roof, parent comment wishes such a car to keep AC on while parked. Solar roof = no emissions.

Where is the misunderstanding?

You're right, misunderstanding was on my end

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