By on August 8, 2014

icevest

It’s always nice when you come across an answer that addresses a question that you’ve wondered about? When I saw that Vox, a relatively new site that says it has “the smartest thinkers, the toughest questions” to “explain” our confusing world to us, was running a post on which uses less fuel, running the A/C or opening the windows, I figured I could put the question to bed. While I did find out about the windows down vs air conditioning thing, I also found out that the smart thinkers over at Vox may not be as smart as they think they are.

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The article, by Joseph Stromberg, answered my question in the headline, “Why rolling down your cars’ windows is more fuel efficient than using AC”, perhaps in line with that explaining thing. Stromberg’s primary source is a study published by the Society of Automotive Engineers in 2004, “Affect of Windows Down on Vehicle Fuel Economy as compared to AC load“. My first inkling that Stromberg wasn’t completely in command of his sources was when I checked out the study’s presentation. Vox’s writer said “In 2004,the Society of Automobile Engineers tested a full-size V8 sedan and SUV on a desert track and in a wind tunnel, with outside air temperatures around 86°F.” While the SAE indeed published the study, which bears an SAE logo on the title page, on that same page there is a GM logo. Most of the research that the SAE publishes is done by members for their employers, the SAE functions as a clearinghouse to disseminate the information to other engineers. If that logo didn’t make the study’s origin at GM obvious enough, it says that wind tunnel tests were done at GM’s aerodynamic wind tunnel facility according to GM’s internal program and that the road tests were done at GM’s desert proving grounds. A quick search on the lead author, William Hill, also shows that he’s an HVAC engineer at GM.

acwindows4

Okay, so maybe the guy doesn’t cover the automotive beat much and isn’t familiar with the SAE. Well, then there’s the question as to whether the Vox post accurately conveys what it says in the study. Stromberg writes, concerning the fact that running the A/C consumed more fuel than driving with the windows down (at least when the ambient temperature exceeded the A/C settings by at least 15-20 deg F), “The difference was very small for the sedan, and the gap did close even further at high speeds, but it didn’t disappear. For the SUV, the difference was much bigger, and actually increased at high speeds.” While the graphs for the two vehicle types indeed showed those differences between the sedan and SUV, the authors of the study concluded that the differences weren’t significant, not “much higher” as Vox has it: “Penalty of AC ON at higher ambient as compared to windows down is not significantly different for SUV or Sedan [5-10%]”.

acwindows1

Finally, there’s Stromberg’s suggestion, and I can’t tell if he’s being serious or not, that if you really want to save fuel, you should emulate what some hypermilers do. Since it’s true that cars and SUVs are more aerodynamic with the windows closed, some hypermilers will keep the windows up at all times, even in broiling heat, and stay cool by wearing vests with pockets for ice packets. He even links to places where you can buy them. Now using ice to stay cool is not unheard of in the automotive world. I’ve seen ice cubes poured into the racing suits of NASCAR drivers and many race cars today have cooling systems for the drivers, so maybe it’s not such a silly idea. Something the author says about how that ice is made, though, makes me believe that he doesn’t quite understand how energy works.

Some of the best hypermilers wear ice vests to stay cool without windows or AC. They’re not cheap, but you can get a good ice vest for a few hundred dollars, and it’ll pay for itself over the course of a few years of saving gas.

Instead of draining your fuel efficiency, its cooling power is drawn from the freezer you already have running in your house. So if minimizing gas use is your thing, forget about this silly debate, and slip on a vest filled with little ice packs that normal people use to keep food cool at a picnic.

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Stromberg couches his suggestion in the context of concern over climate change. He seems to understand that running a refrigeration system in your car takes energy and that the bigger the cooling load, i.e. the greater the difference between the ambient temperature outside and the temperature that the car’s A/C is set to, the more fuel it takes to run the A/C compressor. However, at the same time he doesn’t seem to understand that the freezer in your home works on the same principles. While it’s not as silly as suggesting running the A/C off of a hood mounted windmill with a generator or other perpetual motion-like concepts there’s still no such thing as a free lunch and when you put those unfrozen ice packs, at room temperature, into your freezer that actually increases the load on the freezer’s compressor system. It’s pretty basic science. When I asked a scientist friend who does thermodynamic problems for fun if putting a jug of water in a freezer increases the electrical consumption of the compressor, he said, “Of course, that heat has to go somewhere, why would you ask?”, as though it was too simple to ask about. You might be saving fuel in your car, but you’re using more electricity at home. Overall, you might not really be saving any energy, or money (that would depend on how much you pay for fuel and electricity) at all and still end up wearing a cold soggy vest while you’re at it, with possibly no impact on climate change.

acwindows

Either way, if it’s more than about 78 or 80 degrees outside and I’m driving, I’m going to have the A/C on, often with the temperature at its lowest setting, the fan at its highest setting, recirculating the air (or, as some car companies labeled the switch back in the early 1970s, Desert Air), just as the good Lord intended Schreiber men to do so, unless I’m running low on fuel.

Charts courtesy of the SAE.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can get a parallax view at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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110 Comments on “Vox Explains: Don’t Use A/C – Roll Up Windows & Wear an Ice Vest to Save Gas...”


  • avatar
    sportyaccordy

    There could be savings using the ice vest rather than the car’s A/C.

    For starters, the compressor in your fridge isn’t subject to the wildly changing speeds of a car’s engine.

    More importantly though, the A/C in your car is trying to cool the whole car. It’s trying to remove all the heat pouring in from the poorly insulated exterior surfaces, as well as your body heat, to try and keep you comfortable. The ice vest just works as a reservoir for your body heat.

    Ice vest kind of makes sense but there’s two obvious issues to me. 1, you only really save energy if you perfectly match your ice sizing to your loads. I.e. the last ice crystal should turn to water once you pull into your parking spot, otherwise you are wasting energy. 2, the condensation. That alone makes me wonder what the hell these hypermilers are doing.

    Ideal hypermiler setup would probably be some kind of ice cartridge that would allow air to flow through while removing heat. Kind of like a replacement for the evaporator coil.

    • 0 avatar
      bigdaddyp

      “Ideal hypermiler setup would probably be some kind of ice cartridge that would allow air to flow through while removing heat. Kind of like a replacement for the evaporator coil.”

      You can make an ice chest air conditioner. Basically a cooler full of ice and a fan that pushes air into the cooler, across the ice and out an exhaust port. I’m thinking about making one for my work truck. Most of the time, working in and around Atlanta, I don’t feel comfortable leaving the windows down when parked. It gets stupid hot in the cab even if the windows are open an inch or so.

      • 0 avatar
        KixStart

        Wouldn’t the air from your “ice chest air conditioner” be fairly humid?

        • 0 avatar
          bigdaddyp

          As long as there is ice and the air coming into the cooler is cooled, you should get a net reduction in moisture. In theory, once the heat sink is nearing exhaustion you would them start to pick up moisture. I’m going to try using several 2 liters with filled with water and then frozen. A swamp cooler relies on the evaporation of water to cool, that does add moisture and would do nothing in Atlanta’s muggy environment.

          If it can keep the cab 15 degrees cooler for about 6 hours, 2 hours at a time then I would consider it worth the effort. Since I love to tinker and have some extra coolers I am going to give it a shot. Even if it doesn’t work it will still be an amusing experiment. I suspect that it will work but I’m not so sure for how long.

    • 0 avatar
      Russycle

      Good points. Also, the energy used to power your freezer is generated much more efficiently than the energy used to power your car’s air conditioner. ICE’s generate a lot of wasted heat.

      Regarding issue 1, it’s not that simple. Suppose it takes 10KwH to freeze the ice in your vest, and it lasts for an hour. You take a half hour trip, and “waste” half that energy, 5 KwH. But if running your AC for half an hour uses the equivalent of 20 KwH of electricity, you’re still 10 KwH ahead by using the vest.

      That said, it’s hard to draw any firm conclusions due to the lack of any numbers on the y-axis of those graphs. If we assume they start from zero, the first graph implies that the SUV running AC at 110 kph uses 3 times as much fuel as it does with no AC and windows up. Clearly, that’s not the case, but we have no idea how that axis is weighted.

      • 0 avatar
        319583076

        ICE thermal efficiency is about 20%, steam-tubine generated electricity thermal efficiency is about 30%. Both processes generate a lot of waste heat.

        • 0 avatar
          KixStart

          319,

          You sure? I thought steam power plants were pushing up towards 60%. There’s some more losses on the way to your freezer, of course.

          “Wate heat” is a relative term, of course. Here, the Twin Cities, 9 months of the year, there’s no such thing.

    • 0 avatar
      319583076

      “you only really save energy if you perfectly match your ice sizing to your loads. I.e. the last ice crystal should turn to water once you pull into your parking spot, otherwise you are wasting energy.”

      A false statement. Heat transfer between source and sink is a function of the temperature difference between the two. Furthermore, the heat transfer properties of water and ice are not equivalent. The final phase transistion from ice to water doesn’t represent anything meaningful in this scenario.

      Even more fundamentally, according to the 2nd Law of Thermodynamics, entropy increases. Any action on your part can thus be interpreted as “wasting energy”.

      • 0 avatar
        sportyaccordy

        The transition from ice to water does much of the heavy lifting as far as the heat transfer goes. I.e. it takes 80 times the energy to thaw a gram of ice than it takes to heat a gram of water 1 degree Celsius. Not sure what your point about enthalpy is either.

        And yes, any ice that is melting that isn’t acting as a reservoir for your body heat is ice that is being wasted. OK, the break even point for the ice vest vs your car’s AC can probably allow for a good amount of wasted ice. But why bother with the ice vest and not size your ice to your load if the goal is to save energy?

    • 0 avatar
      Scoutdude

      If this vest were a one time disposable type of thing then the idea that it was fully melted at the end of the single use could potentially have some merit. However if you are going to reuse it then keeping it in the ice state would be more cost effective. If you are going to put it in a freezer then you’ll need to remove the heat that it has gained. So if it gained X BTUs then you’ll have to remove X BTUs to prepare it for its next use. That is excluding the energy required to go through a state change. Water and Ice can both exist at the phase change temp of 32 degrees but you’ll have to remove some heat to get that 32 degree water to change into ice. The same thing applies on the change of state from liquid to gas or vice versa. In that case the amount of energy required to make the change of state is known as the latent heat of vaporization and is the principle behind why AC works.

  • avatar
    chuckrs

    “It is not even wrong”, attributed to Wolfgang Pauli (possibly apocryphally) comes to mind about the Vox article.
    Oh, and regarding the ice vests, Heinlein’s TANSTAAFL also applies.

    • 0 avatar
      bunkie

      ” Heinlein’s TANSTAAFL also applies.”

      Since everyone is in a “let me correct you” sort of mood, let me just say that I seem to remember this as the oft-said quote by Von Rijn, Poul Anderson’s galactic trader character featured in many of his stories.

      • 0 avatar
        krhodes1

        Heinlein and Anderson were very much contemporaries – The Polesotechnic League books started about the same time as Stranger in a Strange Land and it’s decedents. I certainly was introduced to TANSTAAFL through Heinlein, but I can’t recall the FIRST work of his that first used the term. It’s in a LOT of his work. Heinlein was a good bit older, and started writing well before Anderson though.

        As to the premise here, and the testing. Myth Busters tried this out on their show, also with results of a wash. But like the study quoted, they used V8 SUVs at relatively low speeds on a not that hot day. Well, duh, using the A/C or not didn’t make any difference. You have an unaerodynamic vehicle that is already highly inefficient with a huge motor that doesn’t even notice the added load of the compressor. Try again with a very aerodynamic car with a small motor on a really hot day. Opening the windows and sunroof on my BMW wagon on the highway feels like hoisting a sail, whereas with a modern variable displacement A/C unit, you can’t even tell if it is on or off, and there is no cycling.

        The things people will do to possibly save a thimble full of gas! Count me in with Ronnie, the A/C is cranked in my car, and house, from April to September. In MAINE. You could hang meat in my bedroom. I don’t care what it costs, if anything.

        Here’s an idea though to REALLY make this pay. Why use your refrigerator to make the ice? Back in the day, Maine had a HUGE industry harvesting and storing ice and shipping it around the world. Pack it in sawdust and it keep quite well. So here is the plan – cut down your own trees to make sawdust in the winter – it will keep you warm! Harvest ice off the pond yourself! Free! Use the ice to keep cool all summer and profit! Of course there might be an added cost to the extra food to keep you going through all that hard work, but most Americans need the exercise anyway. Bonus!

  • avatar
    petezeiss

    As a sufferer of hyperhidrosis I’ve long dreamed of an A/C suit. I had hoped thermoelectric cooling would advance to a wearable solution for dangerously hot job environments that I could repurpose for merely surviving summer outdoors.

    But tiny, refrigerated gel packs distributed throughout a vest would at best be a 20 minute remedy. This plan is not just automotively stupid.

  • avatar
    danio3834

    Energy transfer debates aside, I think most people would be fine taking a 1-2 mpg penalty instead of wearing a stupid ice vest. It’s really a joke to mention it as a solution, but the author doesn’t appear to be joking.

    You’ll recoup the cost of the vest over a couple years? Maybe if you live in the South and use your A/C the majority of the days of the year. Even then, you have to take the time to prepare and wear an ice vest every day…

    • 0 avatar
      johnny_5.0

      I live where it is beastly hot. So I’d have to wear this ridiculous thing on my commute to work, after all the wife sure as hell won’t be seen with me in one, let alone wear one herself on this icy energy saving adventure we call life. I look like I’m worried about drowning inside my own car, but no biggie since I don’t carpool, nobody to laugh at me! Now I exit my vehicle and wear the vest into the office? Security would tackle me for the lovely postal shoot ‘em up appearance. Take it off and carry it? Then I’d have to put it in one of the freezers at work. I can just imagine the hilarity that would ensue as I push some people’s frozen meals around to make room for that sucker. The idea that this could be a workable solution in mainstream life is laughable for so many reasons.

  • avatar
    Vulpine

    Something doesn’t fit here. For almost four decades we’ve been told that AC-on, windows-up is more efficient than AC-off, windows-down. This “study” seems to say the exact opposite, despite the fact that ACs are much more efficient than they used to be and rolling the windows down DOES increase drag significantly. The only part of this chart that makes sense is the AC-off, Windows-up configuration as I have used this in nearly every vehicle I’ve owned whenever possible–though I admit I cheat slightly.

    Rather than rolling the windows ALL the way up, I leave them down from one inch to three inches from the top. This lets air circulate through the cabin without the added heating effect of catching it as it comes over the engine compartment through the ventilation system. With the windows mostly up, you still get a relatively clean flow of air around the vehicle, no matter the type, which improves fuel mileage. I did this back in 1980 with a Dodge coupe on I-40 with a 318c.i.d. V8 under the hood and managed 25mpg through Arizona, New Mexico and Texas, dropping to 23mpg through Oklahoma and Arkansas. It wasn’t until I entered Tennessee and passed Nashville that I was forced to turn on the AC–at which point mileage dropped to 18 for the rest of my trip.

    Now, I’ll grant that this is anecdotal evidence, but it IS personal experience and I DID calculate my fuel mileage at every fill up. My own experience gives the lie to the charts above.

    • 0 avatar
      strafer

      So you got 25mpg on flat states, and got worse as you got closer to the Appalachians.
      Don’t you think gravity was the likely culprit?

      • 0 avatar
        Vulpine

        Nope. That 25mpg was going essentially downhill for a big part of it, albeit at a very shallow slope. Oklahoma and Arkansas across the portions I drove were more flat and I didn’t start climbing again really until I reached Nashville–which is when I turned south. That’s also where the humidity jumped and I was forced to turn on the AC. Had I not had to turn on the AC I would have probably managed right at 20mpg for the last leg of the trip.

        The point is that by running with the windows almost closed, I clearly got better gas mileage than I would have with them open and clearly got better than I DID running the AC.

        But that again returns to the question of when did cars start getting better fuel mileage with the windows down than with the AC on? Practical experience has proven to me that the AC does not create as much parasitic drag as windows-down creates aerodynamic drag.

    • 0 avatar
      redav

      Here’s what’s wrong with it: Every car has different aerodynamics, and aerodynamic drag is sensitive to speed. That means anyone who makes a general, universal statement about one being better than the other is flat-out wrong and should be ignored.

  • avatar

    whether AC or open windows provides more efficiency for the car at various speeds is an interesting question for those of us who take a geeky interest in such things. But it doesn’t account for the benefit reducing humidity has on human comfort.

    Ice vests are very helpful for people with MS who have the symptom where they feel hot all the time, especially since heat reduces their nerves’ ability to conduct much more dramatically than it does for the rest of us. I wish I had known about them when my late mother was still alive.

    Stromberg is, of course, welcome to drive around wearing an ice vest if he wants, along with the hypermilers.

  • avatar

    Both of my cars are black paint.
    Until now I’ve had silver cars.
    I can feel the temperature difference. In winter I don’t need the heat as much – when it’s sunny – and in summer I have to drive with AC at full power.

    Ventilated seats on “high”!!!

    Cooled cup holder activated to keep my charging cellphone cool.

    If you truly can’t afford to be comfortable in your car then you shouldn’t be driving it.

    • 0 avatar
      petezeiss

      My car is white, my wife’s is black. The difference on a hot, sunny day is immediately obvious. I couldn’t believe she chose that color (maintenance), she adores it. But she’s vastly more heat tolerant than I.

      She also doesn’t worry about keeping it clean; she knows I’ll cave and wash it before she has to.

      • 0 avatar
        VCplayer

        A good man knows to always cave in that situation.

      • 0 avatar

        I love hand washing my cars. My girlfriend keeps cars cluttered. It’s annoying. I just through her stuff in a garbage bag and return the interior to pre-purchase standards.

      • 0 avatar
        Sky_Render

        California, at one point, kicked around the idea of outlawing dark-colored cars because of increased A/C demand and thus fuel consumption. They commissioned a study, which found that the color of a car has little to do with how hot it gets inside, since most of the heating of the car’s interior comes through the WINDOWS.

        • 0 avatar

          I think all of us understand that dark colors absorb heat more than lighter colors.

          The BEST selling paint colors are WHITE, SILVER and Black (in that order) for a reason.

          I would like to take 3 Toyota Camry with those colors and do my own test. Leave all three in a parking lot for Summer, Winter, Spring and Fall and take their cabin temps at the same time and record the data.

          My hypothesis is that the Black car will be the warmest.

          Maybe I could do this by just taking thermometers to a Toyota dealer?

          • 0 avatar
            krhodes1

            They have been quite a few studies on this – as I recall, in the long run color makes very little difference to the ultimate temperature. A Black car heats up a little faster, but it doesn’t really get much hotter. As someone already mentioned, the glass is a much bigger issue than the paint. Interior color made more difference than exterior color.

            My last wagon was a white on white Saab, my current one is a dark green on dark red/brown BMW, I don’t notice much difference, as long as the sunroof shade is closed. The BMW’s panoramic roof is 3x the size of the Saab sunroof, and even though it is fairly heavily tinted, it makes a HUGE difference to the sun load in the car.

    • 0 avatar
      darkwing

      Nope — Fiat just saved a few lira by giving you crappy A/C.

      My last two cars have been black on black. The old one, 74 and auto in the summer, even on 90+ days in the city — barely noticeable. The new one, 75 and I have the vents half closed, it’s so good.

  • avatar
    Demetri

    On a Mazda3, a car with a rather weak compressor, I’ve observed very little penalty to using the AC, 1 MPG maybe, certainly nothing to sweat it out over, especially when you’re already getting 40+ mpg.

  • avatar
    Rod Panhard

    Stromberg? Like the carburetor most sensible people toss into the bin and replace with a Weber?

    Hey, I got an idea for you Stromberg. It’s that if I try to fit an ice vest into the freezer part of my refrigerator, there’s no room left for stuff like, uh “food” and “ice.”

    So to accommodate the cooling needs of the ice vest, I have to buy an extra freezer. That’s about $250, plus the $50 per year to run it.

    Now, if my car gets 2 mpg less while using the a/c, then the extra $50 in running the freezer still doesn’t offset the loss of MPG. So basically, your freezer vest is about as useful as the craperators that share your name. Sorry.

    • 0 avatar
      strafer

      That’s what I was thinking.
      Also, what about the passengers?
      They suffer while you are all nice and cool? So you gotta buy 4 more ice vests so you may have to upgrade to a $500 freezer.

    • 0 avatar
      CRConrad

      Naah, Stromberg as in the guy who wants to start humanity over in under-water habitats, and wants to de-populate the above-surface world by starting a nuclear war between the Unied States and the Soviet Union.

  • avatar
    Volt 230

    Better yet, reusable ice packs in your pockets, crotch and an ice bag on your noggin’

  • avatar
    balreadysaid

    energy is energy. all the extra work you do to drive with your vest, all the sweating and stress you put yourself under will make you burn more energy and eat more food. you can replace things in certain ways and save pennies on the dollar by doing things like this but your brain has to think of all these things and you will burn energy. and your adding stress. LOL who ever spends 200 on a vest like that to drive to work in is in need of some guidance!

  • avatar
    OneAlpha

    This isn’t just a ridiculous idea, it’s a ricockulous one.

    One can just imagine telling some Cockney about this and him asking you if you’re ‘avin’ a Turkish.

  • avatar
    Macca

    Ah yes, the geniuses at Vox (the “smartest thinkers”) have brought us stories including a Gaza-West Bank bridge (that doesn’t exist), strangely incorrect maps, blatant geographical errors (claiming the UK has provinces) and an editor who posted his pondering as to why Miami abruptly ends to the west as if it was a brilliant observation of urban development patterns.

    Most of their glaring errors wouldn’t be so egregious if they didn’t pitch themselves as brilliant minds breaking down the news for us mouth-breathers. These guys aren’t even proficient with Google or Wikipedia.

    It really boggles the mind as to where along the way these guys became convinced of their own brilliance and to their stunning lack of self awareness and inability to thoroughly research any given topic. It would certainly make sense if this was just some random blog.

    At least they provide some good entertainment as they are routinely schooled via Twitter by folks who take them to task for their asinine errors.

    • 0 avatar
      Toad

      Vox seems to be populated by smart writers that are handicapped by having no adult experience actually doing anything. Vox shows the peril of going from school directly to dispensing knowledge without building up any “boots on the ground” encounters with reality.

      Getting information from Vox about any subject is equivalent to getting sex advice from a virgin; lots of theoretical knowledge but no real world experience.

  • avatar

    It didn’t fit in the post, but the U.S. military has paid for research showing that people can tolerate more extreme levels of exercise and endurance as long as their extremities, their heads, hands and feet, particularly their hands, are cooled. In other words, you can run farther and faster with refrigerated gloves and shoes. So, in racing, keeping the driver cool isn’t just a matter of comfort and convenience, it can affect performance.

    These guys at Stanford appear to be trying to commercialize the concept:

    http://news.stanford.edu/news/2012/august/cooling-glove-research-082912.html

  • avatar
    Scoutdude

    There are way too many variables for a one size fits all answer to this question.

    What is the difference in drag for a given vehicle of windows down vs windows up? In general the more aerodynamic a vehicle is the greater the increase in drag for windows down.

    What type of AC system does it have? Clutch cycling systems engage and disengage the compressor to maintain the pressure in the evaporator and are more efficient that systems that use a thermal expansion valve.

    What is the efficiency of the compressor? Different compressor designs have different HP requirements. Many if not all serious hybrids us electric compressors and they run the compressor at the necessary speed to meet the current demand meaning over the long run they require less HP to run particularly at higher speeds.

    What is the sun load? Cars with a lot of solar gain which unfortunately is most cars to day thanks to the sloping curved windows will place more demand on the AC system.

    What is the overall average demand on the AC system sure when you start out with a parked car you’ll need more cooling but once the temp has stabilized there will be less cooling needed and if you’ve got a clutch cycling system the compressor will need to run at a much lower duty cycle.

    I’ve seen many other studies that showed that AC on is more efficient than windows down once you exceed a certain speed that because of all the factors above can be as low as 25-30mph.

    With my Wife’s 10 Fusion Hybrid there is a significant increase in MPG once the average ambient temps start getting into the 60’s and there is no statistically significant increase when the average temps climb above that. It is pretty consistent at ~41mpg from Mar/April until Sep/Oct. It then falls off partially due to the fact that it gets agressive snow tires that aren’t LLR instead of LRR touring tires in the summer.

    • 0 avatar

      Also, the GM tests were done 10 years ago. A lot has changed in 10 years with both aerodynamics and HVAC systems. Now we have hybrids, stop-start systems, soon maybe even supercapacitors that help run the car’s systems when the combustion engine isn’t running. All that would affect the results of windows down vs A/C. Speaking of which, would battery EVs perform differently, particularly if the test cycle included standing still as opposed to steady state speed testing?

      It’s all a great question, with many variables poorly served by Vox.

      I don’t want to go on a kids get off of my lawn rant, but the declined standards of our educational system makes me worry for the future. I see young adults today, smart kids with impressive educations, that have junior high writing, debating, and thinking skills, and I’m not talking 4.0 GPA level junior high work.

    • 0 avatar
      bball40dtw

      Re: your Fusion Hybrid

      I experience has been the same with my C-Max. I do notice that I can stay in EV mode longer with the A/C off, but its seconds of difference. I’m sure if I drove 65 instead of 80 on 696, which is impossible, it would be much more statistically significant when it comes to increasing fuel economy.

    • 0 avatar
      OneAlpha

      “There are way too many variables for a one size fits all answer to this question.”

      That’s the problem. There’s no such thing as a one-size-fits-all answer to anything.

  • avatar
    VCplayer

    If you’ve really convinced yourself that the difference between AC on and windows up is environmentally significant, you need some serious lessons in perspective. If every car driver in the world did AC off and windows up all of the time, it would have essentially zero impact on anything. Not to mention the environmental strain of producing millions of ice vests.

    Sweating out your drive isn’t going to save the world. Neither is that Tesla being charged by coal-produced electricity. Practical physics needs to be a required high school course.

    • 0 avatar
      bunkie

      Due to the nature of the power grid, it’s practically impossible to run any electrical device on power generated from a single source at any give time. Just as you can’t take the same glass or water out of river downstream from where you poured into said river.

  • avatar
    KixStart

    Sometimes, maybe all the time, “Hypermiler” is roughly equivalent to “obsessive-compulsive.”

    As for the efficiency… out here in the Real World we have found that driving at highway speed with the windows open makes it difficult to listen to “Car Talk*.” The windows, therefore, will remain closed.

    * – Or anything else, for the matter of that. But Car Talk is the best way to pass the time.

  • avatar
    redav

    The point that usually gets ignored here is that the question ASSUMES opening the windows provides cooling. Throughout much of the south, if you open a window, it’s hot and sticky, not to mention all the pollen & other allergens. If the air is nice enough to provide actual cooling, then it feels fine inside the car with the windows up & no AC.

  • avatar
    chuckrs

    Imagine a world where the government mandates ice vests and weak ACs (more like dehumidifiers) like it now does seat belt usage. What is the cost of Mom and Dad’s vests plus the various ice packs plus a whole spare set so you always have frosty ones available. Now add some vests for their 2.1 little nippers, who outgrow them every couple of years, plus the attendant properly sized ice packs. Now add the price of small chest freezer chest to put in the garage. Now try and keep said nippers in their vests. Were he still alive, Jean Shepard could have a good time with that – family road trips with ice vests….

    The Vox article could only sound reasonable to childless and carless urban dwellers whose last science course was in the ninth grade.

  • avatar
    WaftableTorque

    On a hot day, I’ll drive with the windows rolled down AND the A/C on.
    [/confession]

    It’s like the yuppie’s rolling coal.

    • 0 avatar
      danio3834

      Nice. You could probably bottle all the water coming out of the evaporator drain.

    • 0 avatar
      krhodes1

      A friend of mine constantly drives his Miata with the top down and A/C on, and I have to admit, it works wonders! I was able to do this in Dallas in a rented Chrysler 200 convertible and be comfortable, but only at night. Of course it was 95F at 11pm.

  • avatar
    APaGttH

    But I thought through greater technology efficiencies (not in actually cooling, mechanical improvements) that in a modern car running AC on versus AC off the impact is negligible.

    I also thought that on a growing number of cars the AC compressor may come on as the climate control dictates, and that the operator has literally no way of turning off the AC compressor – even if they wanted to.

    Wouldn’t that make all of this debate kind of moot?

  • avatar
    tankinbeans

    A number of years ago I remember reading that the A/C compressor in your car is strong enough to cool a moderately sized McMansion, I can’t recall exactly how large that would have been, because it has to combat the greenhouse effect of heat coming in through the windows and being trapped with nowhere to go.

    I can’t recall the source or what the context was, but I’d be curious if it were even true.

    As for A/C versus windows down, I’ll do whatever I damn wall want to do. This summer has been nice because it’s been relatively free of humidity and the temps have stayed low. I hate heat and prefer to be a walking iceberg. The penatly in my car is about 2 mpg which adds up to peanuts over the course of a tank.

  • avatar
    S2k Chris

    Best driving: Top down, A/C on max (with recirc pushed, it’s like boost for the A/C), and the engine screaming away clubbing 9000 baby seals per minute.

    I work too damn much to worry about the extra $.00006 I could save not running A/C or with windows up or whatever. Insert Peter Griffin’s “OMG who the Hell cares?”

    • 0 avatar
      This Is Dawg

      It’s amazing how fast I switched from caring about it when I got a steady job, but when I couldn’t afford to fill up my tank every time I needed to, it was windows down always for me.

      Hilariously, I’ve got a friend who makes enough money to not care, but whines about people riding in his Mustang GT because then he has to turn the air on and not have “FULL POWAH!” Bro, when you live in Texas and are overweight no one is impressed that you treat the A/C button like a self destruct trigger.

  • avatar
    Meko_Suko

    Look at it from a health perspective.

    With the windows down, and in an urban or semi-urban area, you’re soaking/breathing in far more CO2. You’re likely also hurting your hearing with wind shutter/noise etc…

    I would think this conversation is pointless based on the fact that (1) The savings are marginal, and (2) You’ll live a healthier life if you drive with the AC on and windows up!

  • avatar
    55_wrench

    I grew up in the generation where A/C was not on 90% of the vehicles out there.

    For years several of my daily drivers had cable actuated footwell vents that pulled air from the windshield cowl.

    or as in the case of my old Mercedes W123, you drop the right rear window about an inch and crack the sunroof about the same amount, and you would get prodigious amounts of air coming thru the car with no wind buffeting whatever.

    Why can’t we have the footwell vents again?

    I realize they were not much good in 105 degree heat, but in many cases the huge amounts of ambient air that came through those vents were more than enough to stay comfortable if you wanted to not run the AC..or if it wasn’t working in the first place.

  • avatar
    punkybrewstershubby aka Troy D.

    “OK, kids. Seat belts, check. Doors locked. check. Ice vests on, check. Ok, lets go!”

  • avatar
    kkop

    Cooling vests are fairly common in the motorcycling world, although there they are of the evaporative type: add cold water to the vest or soak the vest in water, and let the evaporation of that water cool you down.

    • 0 avatar
      redav

      I have something known as a “Cool Vest” that uses a chemical that freezes at ~60 deg. Because of the wonders of chemistry, a substance stays at a constant temperature while changing phases, despite high heat transfer (latent heat). The end result is that the vest stays at a constant 60 deg until the chemical has fully melted.

      It’s much better than ice because it’s just a cool temperature instead of cold, and the body doesn’t react to it by shutting down blood vessels in the skin.

  • avatar
    dal20402

    And… in the excitement over being able to criticize a website that is typically opposed to his political leanings, Ronnie completely misses the obvious tongue-in-cheek tone of the article involved.

    • 0 avatar

      Vox has a political stance? You mean it’s not impartial? To be completely honest, it was the first time I was at the site and this is the only article there that I’ve read so I really can’t speak to their political leanings.

      As I said in the post, it’s not clear to me if Stromberg is serious or not about the ice vest thing.

      Now, if you’ll excuse me, I have to finish the article that I’m doing about the GM’s Parade of Progress Futurliner buses from the 1930s and figure out a way to work in blaming FDR for prolonging the Depression.

      • 0 avatar
        mcs

        >> I have to finish the article that I’m doing about the GM’s Parade of Progress Futurliner buses

        Awesome. Looking forward to it! Maybe a “swamp cooler” article as a companion to this post next?

  • avatar
    stevelovescars

    I wrote an article about this subject 6 years ago referencing the same SAE study but with a bit more logic behind it, I hope. I didn’t think of ice cubes… seems like a silly, and wet, idea.

    http://stevelovescars.blogspot.com/2008/07/staying-cool-and-saving-gas-ac-or-open.html

    To confound the question, the aerodynamic drag of windows down vs. not depends on the relative aerodynamic efficiency of the vehicle with which you’re starting. If you drive a Hummer, you simply won’t notice a fuel efficiency drain with the windows down since you’re driving a big brick anyway.

  • avatar
    April

    I have a friend that is in the Anthropomorphic (Furry) Fandom who wears a cold vest under his fursuit. He swears by them.

    If they can keep someone in a full suit cool I’m sure they would work well in a non air conditioned automobile or truck.

    :)

  • avatar
    Sigivald

    Am I the only one noticing that those graphs (and God, that report is terrible – bad English, bad Powerpoint) *have an unlabeled vertical axis*?

    We don’t know what the baseline number is. We don’t know what the top is. Thus we can’t even guess at the actual magnitude of the effect.

    This is making the baby Edward Tufte cry.

    • 0 avatar
      matador

      That’s what I thought. The graph suggests that the fuel usage is a lot higher with the A/C. But, the open window could be a insignificant difference, with A/C not that expensive.

  • avatar
    matador

    Now, what if I drive around with the windows down, the A/C on, and wear an ice vest?

    Any graph that doesn’t illustrate that cannot be relied upon.

  • avatar
    Hummer

    This is fine and all, but I’ll keep myself feeling however I want.
    Besides it doesn’t really cause much stress to turn an air compressor on a 6L gas engine.

    Windows down, A/C on max or however I want it.

  • avatar
    petezeiss

    Let’s take this opportunity to give thanks for that most effective preventer of violence, stink and disease humanity has ever conceived:

    Ladies and Germs, three cheers for Mechanical Air-conditioning!

    I should think the American South would have erected a Freon Tower somewhere by now.

    • 0 avatar

      Alan Trammell and Lou Whitaker should be in the Baseball Hall of Fame and Willys Carrier should have been given a Nobel Prize.

      I believe that the widespread use of air conditioning in homes also reduced the frequency of urban riots. When it’s so hot that you can’t sleep, it makes for frayed nerves. People have literally chilled out.

      • 0 avatar
        petezeiss

        “Willys Carrier should have been given a Nobel Prize.”

        Completely agree except for their having given one to that skinny-ass tent preacher. I’d hate to demean Mr. Carrier by association.

  • avatar
    wibigdog

    My head hurts.

  • avatar
    George B

    The author at VOX misunderstands what air conditioning does. Humidity reduction is just as important as temperature reduction. Wearing ice is going to leave your clothes all wet. Opening the windows is inadequate when the environment outside the car also feels like a sauna.

    • 0 avatar
      Drzhivago138

      >Implying you’re wearing the vest on your bare skin
      >Implying the ice isn’t contained
      >Implying it’s not dry ice or some other chemical

      I normally don’t post rebuttals 4chan style (I really need to stop going there), but here I couldn’t help myself.

  • avatar
    Mandalorian

    If you want a car with a powerful a/c get something popular in the middle east. My Q7 has a beast of an air conditioner.

    • 0 avatar
      Vulpine

      The AC in my Jeep Wrangler is surprisingly strong. Even with a soft top it keeps the interior comfortable once you blow out the overheated stale air. And it’s strong enough to actually flex the top, meaning it manages to pressurize the cabin even with all the “built in leaks” of a Jeep soft top.

    • 0 avatar
      Drzhivago138

      If you want a car with a powerful A/C (or heater, for that matter), buy a modern regular cab pickup. Since the vast majority of pickups sold in the last ten years are extended or crew cabs, the A/C has to be heavy enough to make that larger cab space tolerable. It’s the same HVAC regardless of cab, though, so a regular cab (like our ’08 F-350 V10 5-speed) cools off or heats up in literally less than a minute.

  • avatar
    Drzhivago138

    Here in the land of eternal winter and 1 month of hell (aka Minnesota), I would probably have to run my car nonstop with the A/C cranked to even begin to see the same MPG penalty I normally see from October to March.

  • avatar
    mcs

    Here’s an old method of cooling cars and houses. It predated a/c:

    http://www.youtube.com/watch?v=aHbQYajfGqM

    The downside is that it doesn’t work well in humid air.

    • 0 avatar
      Drzhivago138

      Ah, the “swamp cooler”. There were a few aftermarket kits for cars, and CC did an article about them a month ago:

      http://www.curbsideclassic.com/blog/cc-capsule-firestone-thermador-car-cooler-swamp-cooler/

  • avatar
    JimC2

    “Affect[sic] of Windows Down on Vehicle Fuel Economy as compared to AC load.”

    *Effect*, not affect. Not your error, Ronnie, but the error of the authors and editors of that report. Sheesh, how does a professional organization allow such sloppy written communication?

    I’ll remove my spelling and grammar curmudgeon hat, step back now, and continue to watch the downfall of society.

  • avatar
    FormerFF

    My car has an electrically driven A/C compressor, and a readout that tells me how much electricity it is using. If I have to cool the car after it’s been sitting in the sun and is heat soaked, the climate control will consume as much as 4 kW while bringing the interior down to a habitable level. If the car is in the shade, the cooldown draw is more like 1.2 kW. Once the interior is down to temperature, the draw drops to someithing like 500 – 600 watts. If you want to reduce your A/C unit’s energy use, don’t let the car heat soak.

  • avatar
    tankinbeans

    Serious question, does it matter how many windows are open and how much? Is there a point at which the max drag will be exerted on the vehicle and any further opening wouldn’t matter?

  • avatar
    Power6

    Ronnie seems like you are grasping at straws here, does seem like the
    Vox peice does take too strong a stance for the data but thats a pretty common affliction of online publishing.

    The author pretty plainly stated the idea of the ice vest was to save gas at the cost of whatever electricity it takes to freeze the ice.

    Also nice quip about the “desert only” setting that was only on AMC cars and it was not a recirc setting it was a constant on compressor setting (it was otherwise evap temp sensor driven) which gave max output without the fear of freezing the core as desert=dry air, hence the “desert only” moniker, warning one not to use it ion humid weather and risk freezing up the evaporator.

    “Max A/C” in most any other car like a GM was a recirculation setting in American cars in the days before there was a seperate button for that function.

    You are usually way knowledgeable on this stuff, this just happened to be something I know about!

  • avatar
    Hemi

    Wtf who is that cheap? Also the vest would probably wrinkle all your clothes. Would work well while you take your date dumpster diving.

  • avatar
    th009

    It’s pretty easy to test this on your own car these days if you have an instantaneous fuel economy readout (which measures fuel flow), cruise control and a relatively empty (and flat) stretch of the road.

    In my car, at around 25C ambient and an 80 km/h (50 mph) cruise speed, I see about a 5% drop in fuel consumption by opening the front windows and switching off AC. Switch AC back on, wait 30 seconds (for the compressor to settle down), and it’s back up by the same 5%.

    Higher speeds will be different. Higher ambients will be different (but at 35C I won’t enjoy opening windows much, either). Different cars will be different.

    Do your own test and make your own decisions. Me, I enjoy the breeze at 25C more than I do the cooled AC cocoon.


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