Workshop Exercise: Psychrometric Charts

City: Chattanooga, Tennessee. 35 Degrees North, 85 Degrees West. Elevation 688ft.

Chart Basics:

– If the temperature is 80 degrees and the Relative Humidity (RH) is 40% the dew point is 53 degrees.

-The humidity ratio would decrees by .01 if a space was cooled from 90 degrees, 60% RH to 68 degrees, 50% RH.

-The RH is 8% when the dry bulb temperature is 78 degrees and the wet bulb temperature is 50 degrees.

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Climate Response:

-Chattanooga is a humid temperate climate that is extreme, it is HOT is the summer and COLD in the winter.

-Chattanooga sits on the Tennessee River at the base of Lookout and


Signal Mountain with Missionary Ridge to the East. This means that downtown Chattanooga is in a valley type situation.

-Chattanooga is most in the Comfort zone during April, May and September, with most of the days falling in May.

-High Thermal Mass (Night), Natural Ventilation, Internal Heat Gain, Passive Solar and Sun Shading are passive design strategies that work well in Chattanooga.  Internal Heat Gain is most effective.  Evaporative Cooling does not work well in Chattanooga.

Screen shot 2013-10-08 at 2.43.02 PM

– Chattanooga can move from an 11% comfort level to a 59% comfort level using only passive design strategies.  The biggest issues are on the winter months when it is very cold and the summer months when it is hot and humid.  During these months air conditioning must be used to maintain the “comfort level”.

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