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Wind chill on a car

Tom and Ray,
I have to argue with your comments that wind chill does not affect a car. Wind chill affects anything with an internal heat source; the wind blows away the heat. If it is cold and the wind is blowing, it will take longer for a car to warm up much like Tom said it will cool off faster if windy.

Also, Tom is right that the car will not get colder than the real temperature. Neither would a human.

Kriss

True, windchill affects anything with an internal heat source. So, if the car is standing still in cold weather, it would lose more heat in a wind than if there was no wind.

However, when you are driving there is no difference, since your speed is nearly always faster than the wind.

The term winchill used by weather stations more refers to the evaporation from your skin caused by the warm envelope being constantly blown away by the wind. I have walked outside at 0 degrees on a windstill sunny day with low humidity and felt OK.

What Tom and Ray meant by wind chill not effecting a car…is what MOST people get confused about. Wind chill is rate of cool…NOT how cold something will get.

If the temp is 40 degrees outside…but a windchill of 30…water will NOT freeze. Many people see the 30 degrees and automatically think that’s how cold it will get.

@MikeInNH Assuming the car and engine are warm, a windy day would remove more heat envelope from the car and presumably make the heater work harder, or take a little longer to heat up the car.

Tom and Ray are right that cars don’t feel the chill due to wind, and their temperature will stay the same. I know some folks who look at the weather channel and when it shows 25F or so chill factor while the actual temperatue is above freezing they want to put their cars inside or plug in the block heater.

"plug in the block heater"

Thats funny. Without the block heater, the car is unaffected by the wind chill, but the block heater provides the car with an internal heat source, so then the car is affected by the wind chill.

@keith That’s how some folks “reason”! Personally, I don’t plug the car in until the forecast temperature is in the low 20s. The car starts in any temperature, but it warms up muchquicker with the heater plugged in.

Wind chill is a calculation of from NOAA

"Wind chill temperature is a measure of the combined cooling effect of wind and temperature. As wind increases, heat is carried away from the body at a faster rate, driving down both the skin temperature (which can cause frostbite) and eventually the internal body temperature (which can kill). The Wind Chill Temperature index is the measure of this relationship.

Your engine has no concept of wind chill because there is no inherent temperature loss making it feel colder than it really is. It is a factor of increased cooling effect to get to a temperature, rather than the actual temperature. Your body temp is 98.6 average, wind makes you cool faster to the temp point, the engine is not under a 98.6 requirement. Sure an engine may cool faster with big winds but it will not feel below ambient temp as you may.

@MikeInNH Assuming the car and engine are warm, a windy day would remove more heat envelope from the car and presumably make the heater work harder, or take a little longer to heat up the car. - See more at: http://community.cartalk.com/discussion/2290684/wind-chill-on-a-car#latest

Agreed…And nothing I said disagrees with that statement.

40 MPH North Wind.

Car parked facing North. The air speed of the wind blowing at the front of the car is 40 mph.

Car drives North into wind at 40 mph. The air speed of the wind blowing at the front of the car is 80 mph.

Car drives South with the wind at 40 mph. The air speed of the wind blowing at the front of the car is 0 mph.

Think in terms of radiator.

CSA

I would argue that it isn’t a calculation, but rather a mathematical description of how quickly heat is dissipated from an object.

I would also argue that an “internal heat source” is a varable in the equation used to calculate the chill factor that the news warns us about, but in an automobile with the engine not running the value of that variable is simply zero. In short, a specfic mass generating X btus of heat per hour will dissipate heat in a Y mph wind at a rate of Z. With X being a lower value, Z will be higher. Etc.

Humans generate heat at a known rate. Therefore, the ambient temperature and rate of wind can be readily factored in to determine how quickly heat will be dissipated and thus, what eth equivalent ambient temperature dissipation rate would be without wind…which gives you the chill factor.

But in truth I think we’re all arguing semantics. Simply, wind has an effect on how quickly an engine reaches ambient temperature. But only if it’s passing over the engine. That’s why we always tried to park heading away from the wind in North Dakota. It helps.

@the_same_mountainbike I cannot find a definition of mathematical description, so I cannot respond to “I would argue that it isn’t a calculation, but rather a mathematical description”

I can find this "The NWS Windchill Temperature (WCT) index uses advances in science, technology, and computer modeling to provide an accurate, understandable, and useful formula for calculating the dangers from winter winds and freezing temperatures."
http://www.nws.noaa.gov/om/windchill/
Just like to make sure I state things correctly, so enlighten me, no offense intended.

@Barkydog Good chart. I remember talking to a weather man once who told me they just added the windspeed in mph to the degrees below freezing to arrive ar the chill factor.

On a more scientific basis, exposed flesh freezes within one minute at 2000 watts per square meter cooling effect. Not terribly useful.

@asecular - Wind chill is how fast something cools, not how “it feels”. It affects how quickly a car cools to ambient temperature.
@the same mountainbike - Parking facing away from the wind only matters if you plan to use the car again before it reaches ambient temperature. And it only matters if the front of the car actually gets more wind going by it than the rear (questionable). As to an internal heat source, it does affect how quickly the outside of an object cools, but it is not needed for wind chill to have an effect.

There is a mathematical formula for wind chill. It’s in the attached Excel spreadsheet. I also included a PDF version of the document. I use this table when deciding whether to drive the car to work or ride the motorcycle. Fortunately, now that I’ve moved from Jacksonville, FL to Stuart, FL, I don’t use my cold weather gear anymore.

I’m pretty sure my car and motorcycle don’t feel anything, but I sure do when I’m on the motorcycle.

I think I might be able to solve this debate with a question, to which the answer solves this riddle.

If the temperature is 35 degrees (F), and the wind chill is 30 degrees, will water that is exposed to the wind freeze, or is the wind chill something only sentient beings can experience?

In my opinion, this mathematical formula, and this table, are pretty accurate. You typically experience the coldest wind chill at 45-65 MPH. Once you go faster than that, the wind chill actually drops a degree or two. Interestingly, when you get above 95 degrees, wind speed makes the air feel hotter.

Barky, there’s no offense taken. The definition you post is saying the same thing using different words, and putting the results of the formula in a chart. Whatever works. I prefer charts.

Asecular, I respectfully disagree. Heat dissipation rate is relevant in applications all around you, including your car’s cooling system. If you think about it, that’s why the cooling fanm comes on when idling and is unnecessary at highway speeds. And the term “wind chill” is commonly used to describe the effect of the airflow on the dissipation rate even on inanimate objects.

David, I absolutely agree. However, I learned in ND that it takes a surprisingly liong time for the engine’s core temperature to reach ambient if it’s parked against the wind…and a surprisingly short time if it’s parked facing into the wind. After an 8 hour work day when the temperatures have been sub-zero, it truely makes a big difference.

Most of us are saying the same thing. Just differently.

Click & Clack get an A+ on Chill Factor.
I’m writing from Nome Alaska, where “Click & Clack” is what your car does until you get oil pressure. Oil, which is the same temperature as the outside air every morning, regardless of the wind.
I wish they would quit telling us about wind chill. It is constantly mistaken for temperature, and understandably so. It uses a scale of temperature to describe something that is NOT temperature.

Wind chill is how the wind and temperature affects the human body. It is not a measure of how wind and temperature affects vehicles. Thats not to say that vehicles are not affected by wind and temperature or that wind does not affect the cooling of vehicles, its just that wind chill by definition is the effect of wind and temperature on human bodies.

Obviously the movement of air does effect the cooling of vehicles. If it didn’t, the radiator would not need a fan attached to it.

" I wish they would quit telling us about wind chill. It is constantly mistaken for temperature, and understandably so. It uses a scale of temperature to describe something that is NOT temperature. "

YES ! I agree !

Wind chill applies to exposed flesh. I live where it is sometimes colder than parts of Alaska and I wouldn’t ever go outside in the winter with very much exposed flesh (usually only my face).

Any moron, by the time they’re a few years old knows that it feels colder outside on their face or other exposed flesh when it’s windy. Also, I ride motorcycles and snowmobiles and know that one needs clothing that keeps wind from penetrating to the flesh. Leather is a good barrier.

I don’t want to hear about wind chill and don’t need a stinking wind chill factor to tell me how to dress when I go outside almost every freaking morning to run the snowblower when it’s dark and -18*F (like it’s been this week), windy or not !

Thanks, I feel better, now.
CSA

P.S. This time of year the sun is having a greater influence on heating. It makes up for a lot of wind chill, some days. Where’s the Sun Warming Factor/Chart ?

Wind chill, although a real phenomenon, is mostly used by the media to make the cold seem more dramatic. They also use a “heat index” at the upper end. It uses the humidity to make the hot sound hotter. But, they never say what humidity they use for a baseline. (zero humidity? 20%?). Do they also factor in the wind chill at higher temperatures? We all know that a light breeze makes it feel cooler, even with high humidity!

The chart for sun warming would have to include differences for cold and materials. It’d be huge. Black absorbs more of the sun’s energy than white by a significant margin, and steel absorbs more of the suns energy than cork does by a significant margin.