Psychrometric Chart - Limitations, Inaccuracies and Restrictions.
Definition
The chart should be employed for pedagogical purposes only.
Where it occurs
Psychrometric charts are used to size air conditioning plant.
Special features
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How to draw it
Left click in the plot area to explore the thermodynamic properties for a particular (t, omega) coordinate. You can plot curves of constant dry bulb temperature, specific humidity, relative humidity, web bulb temperature or total specific enthalpy through this point of interest (POI). The POI can also be specified with the "Set POI" button. Use the nearby dropdown box to choose a pair of input properties: dry bulb temperature and relative humidity; dry bulb temperature and specific humidity; dry bulb temperature and wet bulb temperature; and specific humidity and total specific enthalpy.
Restrictions, limitations and innaccuracy.
The simulation is provided for pedagogical purposes only. It should not be employed in formal design calculations, or for summative college assessments.
All types of temperature (dry bulb, wet bulb and dew point) are restricted to the range between 0 and 40°C. The specific humidity and steam pressure are not allowed to exceed their saturation values; if necessary they are reset to the saturation value and RH=100%. Steam enthalpy and saturation pressure are computed with IAWPS 97 equations. Air properties are calculated using the ideal gas law, in particular the isobaric specific heat capacity is taken as 1.005 kJ/kg K. An iterative calculation is required and used to establish parameters from the dry and wet bulb temperatures. An iterative calculation is required and used to establish parameters from the specific humidity and total specific enthalpy.
There is no option to change scales on the temperature and specific humidity axes.
The theory
NA
Exercises
NA
Links
IAWPS Revised release .
NIST tables .