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The last several days it's been hot here in Indiana with temperatures going above 90&deg;F (32&deg;C) and virtually no wind.  I spent one of these days tending the smoker on the previous post about ribs.  It's not extremely hot compared to other parts of the world, but for Indiana, it's hot.  The humidity levels haven't been bad with dew points just above 70&deg;F, resulting in relative humidity of 42%.  Good conditions for a misting fan.  The comfort range for relative humidity is between 40% and 60%.  Below 40% and it's too dry and above 60% we start to feel muggy.  I can remember what felt like for weeks during the summer growing up in Alabama it was 95&deg;F with more than 90% humidity, this is bad.

Misting fans cool the surrounding area by evaporating water into the air.  When one pound of water is evaporated approximately 1100 Btu of energy is absorbed to convert the liquid water into water vapor cooling the surrounding air.  The lower the relative humidity the more effective misting fans are.  Even with higher relative humidity, a quick stop in front of a misting fan can feel good on a hot day.

This misting fan uses about one half gallon of water per hour, generating a cooling effect of over 4500 Btu if all the water is evaporated.  This is equivalent to a small window air conditioner that might be used to cool a single room.  If you put five of these fans together it can generate the cooling of a one ton air conditioning unit that could be used to cool a complete house.

Given the condition of high temperature, low humidity and low winds, misting fans can lower the surrounding temperature about 10&deg;F.  Being able to create your own little local environment that is 82&deg;F instead of 92&deg;F can feel good on a hot day that you want to be outside.  Misting fans won't work everywhere, but if you're in a location with the right conditions it's a great way to keep cool on a hot afternoon.