## 37.4. Comfort Factors

There are expressions for calculating Mean Radiant Temperature and Resultant Temperature for use in HVAC simulations. Resultant Temperature is a comfort factor defined in [92]. Two options are available:

- Derive the factors during postprocessing, as user scalar variables.

  A CFD-Post macro is available for this purpose, and is accessed using the Macro Calculator from the Tools menu. This is the most common approach. For details, see Comfort Factors Macro in the CFD-Post User's Guide.

- Compute them as run time Additional Variables.

  This method is best used when the control system depends upon a derived comfort factor. The approach involves using the `comfort-factors.ccl` library file in CFX-Pre.

Most users are likely to prefer the first option, but sometimes the second option will be required, for example when the model simulates a ventilation system in which the control system depends dynamically on derived comfort factors.

The model library template creates two Additional Variables: `PMV` (Predicted Mean Vote) and `PPD` (Predicted Percentage of Dissatisfied), which are comfort factors defined in [93].

A User Fortran routine named usr_pmvppd.F has been developed for computing the values of `PMV`, and can be found in the `etc/model-templates/` directory of your ANSYS CFX installation. The template contains a CCL definition for the user routine named `pmvppd`, which calls the Fortran routine. Values for U, V, W, temperature and radiation intensity are passed to the routine and the dimensionless value of `PMV` is returned. The value is then used to calculate `PPD` based on the formula:

| (37–1)

Only a fixed value for humidity for `PMV` and `PPD` can be used at the present time. The values should be supplied as partial pressure of water vapor.

Radiation and the ISO tables for metabolic rate and clothing thermal resistance are included in the template file, which can be accessed by opening the following file in a text editor:

<CFXROOT>/etc/model-templates/comfort-factors.ccl

You can also use customized values pertinent to your simulation. Full details are given in the template file itself.

Compiling the routine requires the use of the `cfx5mkext` utility. For details, see Creating the Shared Libraries in the CFX-Solver Modeling Guide.

An absolute Library Path must be set for the User Routine. For details, see User CEL Routines.

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