All the previous examples involve a numerical comparison: the formula tests whether a simulation variable is greater or less than a numerical value. Many practical control functions involve comparisons of one variable with another. This can be also achieved with formula profiles.
If a particular action is required when the internal air temperature is greater than the external air temperature this can be achieved using either a step or a ramp function. Select “Room air temperature (°C)” from the first drop-down list, “is greater than” from the second drop down list, and “Outside air temperature (°C)” from the third drop down.
If you now click on the Create formula button you will see the formula “ta>to” appear in the Formula profile box. The dialog will then look like this:
Note that only meaningful comparisons can be set up in the formula profiles dialogue. A comparison between (say) wind speed and temperature will not be allowed. A formula profile that compares two variables using a Ramp function can also be created, by entering a value in the “Subject to a proportional band of width” box.
