Wind chill applies to only people, animals

The wind chill formulas account for the loss of heat from something, such as a human body, by warm air around the body being replaced by colder air. It does not consider how well the person is dressed, whether the person is exercising or sitting, or whether the sun is shining. It also does not take into account how hard the person is breathing. Rapid breathing can be a major cause of heat loss since the body has to warm up the cold air that's taken in, and then exhale warmed air.

You'll note that at low wind speeds, the wind "chill" temperature turns out to be warmer than the actual temperature. When the air is still, your body heat warms the layer of air touching your body. Since the air is not moving, this layer of warmed air acts like an insulator, protecting your skin from the colder air farther away from your body. This makes the temperature feel warmer than it actually is. If you are running or walking briskly on a calm morning, the temperature would feel a little colder than if you were standing still. This is because you are wiping out the insulating layer of warm air around your body by moving.

Another important point is that wind chill is an attempt to measure the effect of combinations of low temperature and wind on humans - or animals. When we say the "wind chill is 18 degrees" we are not saying that the chilled object is cooled to 18 degrees. A wind chill temperature is not some different kind of temperature.

Wind chill does not repeal the Second Law of Thermodynamics, which says, that heat cannot "flow" to a warmer object. What this means in practical terms is that if the antifreeze in your car's radiator is good to 10 degrees Fahrenheit and the temperature drops to 20 Fahrenheit you don't have to worry, even if your car is out in a 20 mph wind that drops the wind chill to minus 10 degrees. As long as the actual temperature is 10 degrees, the fluid in your car's radiator and engine block will not cool below 10 degrees no matter how hard the wind blows. You could leave the car's hood open and it wouldn't make any difference. The only difference is that the fluid in you car's cooling system will cool to the 10-degree air temperature quicker on the windy night than on a calm night. But it won't drop below the actual temperature.