Download Psychrometric Chart User`s Manual

Psychrometric Chart User's Manual
Modeling Tips
Identify boundary conditions:
A helpful first step in building a model is to identify the boundary conditions. These are the points
where moist air is entering or exiting the system. They are not dependent upon other points on
the chart. Entry points usually represent boundary conditions.
Identify process points:
It is helpful early on to identify the process points. (Any points that are dependent upon another
point in the model.) Then determine the defining parameters for these points. (The properties
that best represent the process being modeled.) Often these properties relate directly to
equipment capabilities, specifications, or operating parameters. Often these should be delta
properties (properties that describe a change from a previous condition or point).
Using a negative mass:
In a more complicated model it may be desirable to represent an exit point that is not the final
point of the process. A bleed stream is an example, and can be represented by creating an entry
point with a negative mass and mixing it with a process stream. By using the advanced process
point options, a process point can also be used to represent an exit point in a model.
Ambient Conditions:
In many model it is useful to create an ambient conditions point early in the definition of the
model. This point can then be referenced by multiple points later on using the advanced options
features. The model can then easily be used to evaluate a complex process or model under
various ambient conditions by editing the values for a single point.
Splitting a Stream:
A stream can be split by referencing a single point multiple times from following points and
assigning appropriate proportions of that point to the points that reference it. A split stream can
later be mixed again using a mix point.
Using a point above the saturation curve:
In many cases it is useful to create an intermediate point that lies above the saturation curve,
even though such a point can not really exist. Then define a process that returns to a realistic
condition. For example: It is possible to inject steam into an air stream knowing it’s specific
enthalpy and obtain a point above the saturation curve. By adiabatically moving to the saturation
curve the resultant air conditions and condensation rate can be determined.
Define complex or abstract units:
It is possible to define unit conversions that perform more complex or abstract calculations. A
simple example would be to define a unit conversion that translates kilowatt hours into energy
costs.
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