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This Post is Scientifical

I don’t know what it is about many men that makes them so sure they’re always right in all matters involving broad scientific principles.  By the same token, I don’t know what it is that makes so many smart women defer to their judgement (note correct spelling) even when it’s obviously full of shit.

Of course, I’m over-generalizing here, but as a broad pattern, it does hold true.

What prompted me to write about this are the recent hot temperatures we’ve had here, and the three – count ’em, three – separate conversations/debates I’ve had with three different men regarding the relatively simple concept of how to cool down the interior of a car that’s been parked in full sun all day.  All three of these men insisted that the best way to cool the car off is to get in, crank it, and turn the a/c to full blast while leaving the windows completely rolled up.

This is retarded, so if you’re a man (or a woman) who suffers from this delusion, let me explain the reasons why:

  1. A car that’s been parked in full sun all day is going to be at least 20 degrees hotter on the inside than the broiling temperature outside.
  2. The hotter something is, the longer it takes to cool it down, unless you’re Mr. Freeze.  Your car’s a/c unit is not Mr. Freeze; like all a/c units, it can at most effect and maintain a temperature differential of around 20 degrees. 
  3. The initial blast of air that comes out of an auto a/c unit when it is turned on is also going to be at least 20 degrees hotter than the outside air, for the simple reason that the air blasting out has been sitting in the blower ducts under the hood and baking all day.
  4. Given #2 above, does it make more sense to expect the a/c to cool the car interior down to a reasonable 80 degrees more quickly if it’s working to cool down air that’s 120 degrees, or if it’s working to cool down air that’s 100 degrees?

Those are the broad principles involved.  Clearly, we’re going to have better results if we get in the car, crank the a/c and roll the windows down so the a/c can blow the hotter air out of the car before trying to actually cool it down.  The added benefit being that the air that’s been baking in the supply ducts under the hood all day can also escape.

Here’s another dumbass thing one of the guys told me:  you get quicker cooling by not only leaving the windows up, but by setting the a/c to “recirculate” immediately.  Again, see #2 above.  Recirculating 120 degree air, rather than putting the a/c unit to work on cooling down 100 degree air pulled from outside just means you’re more likely to get sweaty balls before the car reaches a reasonable temperature.  Because I don’t have balls, at least not the actual kind, I can only imagine what it feels like when they sweat – but I imagine that it’s not pleasant.  So don’t do boneheaded shit like setting the a/c to “recirculate” right away.

This last bit I can’t prove, but it stands on solid logic and from my experience, it seems to work:  after letting the a/c run a minute with the windows all the way down to blow the hotter air out of the car, roll the windows up about halfway.  As the car begins to cool, roll them up further.  The cooler air sinks; as it displaces the hotter air in the car (which rises), the hotter air can escape through the partially-open windows.  Once the car is noticeably cooler at chest level, roll the windows all the way up; after another minute or so you can set the a/c to recirculate and it will actually do some good.

Consider this a public service.  And ladies, those of you who have to deal with a husband or significant other who insists on making you cook in a 120 degree car interior while the a/c unit struggles to lower the temperature to the refreshing 100 degrees it is outside – and I know some of you do have to deal with this – sit him down and have him read this post.

Either that, or continue to deal with the pungent aroma of ball sweat.

  1. July 2, 2010 at 2:13 am

    Having been forced to visit Arizona (It’s a “dry heat,” as if that makes any difference when it’s 110 to 120.) several times one summer by corporate interests, I can advise you (& the bullheaded, “macho” “Run it loud & fast” cretins you mentioned) that after a car’s been sitting in the sun for eight hrs., Arizonans open all the doors & wait about five minutes before they even get in the damn things.

    • jennofark
      July 2, 2010 at 9:53 am

      Yes, on the really hot days I’m also a practitioner of said strategy. You can actually look down at the pavement and see the shadows of the heat waves rising out of the car through the open door.

  2. July 2, 2010 at 1:15 pm

    The problem (IMO) is that d00ds are all NUMBERZ!

    Your average mid-sized automobile has 110 cubic feet of interior space (apologies for the bullshit units, but that’s what the info is available in. I blame Obama) which works out to about seven (wince) pounds of air. A typical automobile AC unit is coming in between 10 and 15 (shudder) MBTU/hr. Heat capacity of air, although a function of temperature, can be roughly approximated at about a quarter (ugh, kill me naow) BTU per pound per degree Fahrenheit.

    Basic math tells us that on recirculate, the air temperature is going to drop 20 fahrenheit degrees in about 10 seconds – therefore recirculate is the best solution. Especially considering that even in the permafrosted wilds of LEAFS SUCK, 10 seconds is an amazingly short time to get the car down to a manageable temperature.

    Except that the math ends up being totally wrong. After 10 seconds and judging only by the air coming out of the car vents, you’re probably still wondering if you turned on the heat or the AC.

    Because the car itself is still ridiculously hot and acts as a massive heat battery pumping BTU’s into the air the entre fricking time – something that anyone who has gripped a blistering steering wheel is well aware of. And the heat capacity of a car is not an easily look-up-able thing, especially if you count the tons of assorted junk strewn all over the seats and floor.

    IOW, using the numbers available closed windows-recirculate-AC is the best option – unfortunately the available numbers only account for a tiny fraction of the issue.

    Anyways, from an engineering perspective – the greater the delta T (difference in temperature between the car and ambient air) the more sense leaving the windows down/doors open makes.

  3. B^4
    July 2, 2010 at 2:07 pm

    You silly liberals and your science. You know how to cool the car? You pray. That’s right, you pray because Jesus was way cool.

    • jennofark
      July 2, 2010 at 4:49 pm

      Fucking thermodynamics – how do they work?

  4. July 2, 2010 at 9:36 pm

    Heat transfer is theft.

  5. herr doktor bimler
    July 3, 2010 at 7:13 am

    What do the Mythbusters have to say?

  6. Bilo
    July 9, 2010 at 8:51 pm

    Opinions! Theories!

    Er, any numbers? Data? Testing?

    I’m a fan of:
    Reflecto windshield shade
    windows cracked
    sunroof cracked, if possible
    and doors opened for a minute or two before I get in at the end of a day.

    But I’ve been living without A/C for a long time.

    Recirc is something to reconsider at some point, when you’re desperate for cold now. But the first minute or two, yeah, I lean towards just blow that air out, drive a bit with windows open.

    Most Americans are just very offended at the Things Not Cold Right Now condition and their urge/goal is to start that process ASAP.

    • jennofark
      July 9, 2010 at 11:24 pm

      Numbers, data, and testing are for FAGS, as any teabagger can tell you.

      These are all worthy suggestions; back in the day when I had a sunroof, it was a godsend for venting the heat while the car was parked all day. But this is about how to get the accumulated heat OUT of the car; not about how to keep it out in the first place. The most obvious solution to that issue is PARK IN THE SHADE. Which is unfortunately rarely possible in a parking lot.

      Agreed on the HULK SMASH!! attitude many of us seem to have about Not Cold Right Now, though.

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