How do you determine the relative humidity of your area? Can you check any weather sites online that report it, or do you need to buy some sort of humidity reader? Maybe it's worth checking out the humidity range of my area before spending the money on an evaporative cooler. I do not live that far from the coast, so one would think it would be more humid than in west Texas.

 

Jginaz' suggestion of using a 65 oF dewpoint cutoff is a reasonable single factor, and allows us to avoid some complications. To see what US local dewpoints are today, see the second map here:

http://www.liveweatherimages.org/data/imag338.html

DAS

 

Tochatihu,
Good reference map, thanks. I'll refer to it to see when I can turn my cooler on again.

JG

 

I just clicked on that link and got the dreaded "page cannot be displayed" message. This link, OTOH, works for sure.

A word of warning: The dew point is the temperature to which the air must be cooled to reach saturation (100% humidity) without adding any water vapor. The wet bulb temperature is how low you can cool the air (reaching saturation) by adding water vapor. The wet bulb is always warmer than the dew point but cooler than the temperature (unless humidity is 100%, in which case all 3 values are the same). So evaporative cooling will at best get you down to the WB, not the DP.

 

Since the DP is the only thing the nightly weather droids give out we must depend on that for cooler use judgement. BTW in my earlier days here in PHX my first house only had evap. It would keep the house about 85 deg, but it was pretty uncomfortable in July and August.

JG

 

Does this link work OK for others? It redirects to the dew point map I had in mind

http://weather.unisys.com/surface/sfc_con_dewp.html

DAS

 

You can very easily find the wet bulb temperature by jury-rigging what us dinosaurs in the weather business called a sling psychrometer. Take a mercury type thermometer (two if you can find them), cover the bulb of one with a wet cloth, tape the thermometers to a 3' piece of string and sling them in a circle until the temp of the wet one stops decreasing. You now have the dry bulb and wet bulb temperatures. The difference (the wet bulb depression) is what is used to calc dewpoint. I'm sure if you did a google search you could find the calculator to figure dew point and rh from there. We used to use a multi-wheeled "computer" to figure it out. It's based on atmospheric pressure too.

More useless information available on request.....