# Wind chill

Discussion in 'Electronic Design' started by Howard Eisenhauer, Jan 29, 2005.

1. ### Howard EisenhauerGuest

Anybody know of a circuit to measure wind chill? I'm guessing the
best/simplest/cheapest way would be to measure how much current it
takes to keep a resister at certain temperature while exposed to Ma
Nature's little tantrums but I really don't feel like getting into a
yadda project on this. Something I could get built & calibrated
before next summer would be nice- by next week would be fantastic .

Thanks,

Howard.

2. ### Leon HellerGuest

A temperature sensor and anemometer connected to a suitable MCU should do
what you want. You could use a lookup table based on this:

http://www.nws.noaa.gov/om/windchill/index.shtml

Leon

3. ### Rene TschaggelarGuest

IMO, machines don not feel windchill. It appears to be
connected to evaporating moisture from a surface.
As close a machine could come would be measuring
temperature, wind and moisture content of the air.

Rene

4. ### Fred BloggsGuest

Wind chill cannot be measured directly, the assumptions of core body
temperature and heat diffusion through facial tissue are statistical and
it would make no sense to simulate this with analog electronics when it
can be computed, also, it appears that the extrapolation of wind speed
measurement at a standard height of 10m to a 1.5m average by
multiplication by ~2/3 assumes an orographical surface roughness factor
of ~0.1m, which again is another statistical artifice. The purpose of
wind chill estimation is to obtain a probabilistic risk assessment of
frostbite and is therefore not really a physical measurement in the
ordinary sense. Why don't you just buy a weather station and use a chart
or something.

5. ### GarethGuest

Yes, but a heated resistor will loose heat faster in moving air compared
to still air. In fact it is quite common to measure wind speed by
measuring the rate of heat loss from a heated coil or thermistor
(hotwire anemometer).

It seems reasonable, to me, that measuring the heat loss from a heated
resistor could enable you to calculate windchill in the way the OP
suggested.
Temperature and wind speed yes, but surprisingly, humidity has very
little effect on windchill. See:

http://www.nws.noaa.gov/om/windchill/windchillglossary.shtml#13

Gareth.

--

6. ### MacGuest

Wind chill is very close to being a bogus idea. To the extent that it is
meaningful, it is meant to assess how much faster a person will cool down
in a moving stream of air than in a still stream of air of the same
temperature. So it is mostly about heat transfer under convection
conditions.

I think you are right that what the OP should do is focus on measuring
air speed and temperature, and possibly humidity. The wind chill could
then be looked up or calculated or whatever. I don't know exactly how they
calculate it.

--Mac

7. ### Fred BloggsGuest

If you don't know anything about it, then why are you posting an opinion
about what the OP should do?

8. ### Guest

Because this is Usenet.

HAAHAH

10. ### Mike DiackGuest

Twc=33 + (T-33)(.474+.454sqrt(S)-0.0445 S) {siple (1945) }
T=ambient temp Celsius
S=Windspeed m/s
Holler if you need a version of this rendered down to 8051 assembler (needs
a 16 bit math package)
M

11. ### MacGuest

There is a difference between "not knowing anything about" wind chill
(your words) and not knowing "exactly how to calculate it," my words.

You sure are a surly one. ;-)

--Mac

12. ### Guy MaconGuest

And it has to be a naked person. It was developed by the military
to act as a baseline for cold-weather gear. Anyone wearing clothes
will find that a 10 degree wind chill is much warmer than a real
10 degrees.

So why is it so popular? It makes the weather report on your local
TV station more exciting. A REAL correction factor that tells you
how cold it will seem while you are wearing a good coat would be
far more useful, but instead they give the bogus numbers.

Trivia: Inb the military tests, females complained about the cold
sooner but could tolerate a colder environment without having it
disable them.

(This spot reserved for Rich Grise so he can insert a joke about
frigid naked females...)

13. ### Jim ThompsonGuest

You misspelled "Shirley" ;-)

...Jim Thompson

14. ### James MeyerGuest

That's been my take on wind chill from the beginning.

Jim

15. ### Fred BloggsGuest

In your case a much more literal measurement of WCT is required: paste a
temperature indicating strip to your forehead and stand outside for an hour.

16. ### Jim ThompsonGuest

Eh? Never been in Detroit this time of year have you ?

...Jim Thompson

17. ### Spehro PefhanyGuest

The US and Canada switched to a new formula for calculating wind chill
in the fall of 2001. The difference between dry bulb temperature and
wind chill temperature is not as great with the new formula.

Best regards,
Spehro Pefhany

18. ### Spehro PefhanyGuest

I took the dog for a walk at night a week or two ago- the wind was
~20-30mph and temperature -22°C (-8°F). Taking a glove off to use my
Maglite and bag the leavings, I wasn't across an open field diagonally
before all the feeling was out of my little finger in that hand. Wind
chill is real enough!

A few miles in that sort of environment without proper clothing and
you could be dead. It's not nearly as bad without the wind.

A comfortable -1°C (30°F) and sunny today.

Best regards,
Spehro Pefhany

19. ### Jim ThompsonGuest

I always seem to have business back east at the worst-weather times of
the year... Pittsburgh on Wednesday :-(

It's cold here today... a cold front with rain came thru yesterday
afternoon... it's only +60°F, +15.5°C, here ;-)

...Jim Thompson

20. ### John WoodgateGuest

I read in sci.electronics.design that Spehro Pefhany <[email protected]
Just hold the bag. Your canine friend provides you with a lovely squishy
hand-warmer. (;-)