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Finding humidity variables
Finding humidity variables
Example: T=20°C and Tw=12°C
Step 1: Calculate the wet bulb depression (Twd = T - Tw)
Twd = 20°C - 12°C = 8°C
Step 2: Use the Psychrometer Chart to find the dewpoint temperature (Td).
Step 3: Get the saturation vapor pressure (es) from the column left of the T value.
Step 4: Get the actual vapor pressure (e) from the column left of the Td value.
Image Description: Getting Values from the Psychrometer
Take the Wet Bulb Depression (Twd ) starting at 8C, and rise up towards the 20C Dry Bulb (Temperature) value.
The values on the far left list approximate es values associated with each temperature.
§ See how the 20C temperature lines with the 23.2mb es value
Starting where Wet Bulb Depression (Twd ) and Dry Bulb (Temperature) meet, follow the diagonal lines to the end of the graph. The value of the Dry Bulb now represents the Dew-Point Temperature (Td).
§ The values on the far left list now approximate e values associated with each temperature.
See how the 5C dew-point temperature lines with the 8.7mb e value
Step 5: Find Relative Humidity (RH, in %)
Compute RH using es and e from the Psychrometer chart:
e = 8.7 mb
es = 23.2 mb
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