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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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