12.5. Logical Operators (AND, OR)
Step and ramp functions can be linked to produce logical formula profiles. There is a drop-down box that links the control action “sentences”. These drop-down lists contain the logical operators AND and OR. By linking control actions together with the logical operators, complicated control can be simply created. Consider a case where window opening is required when the internal air temperature is above 24°C but not if the external temperature is below 12°C.
To create this formula profile, first generate the internal air temperature statement: select “Room air temperature (°C)” from the first drop down list, “is greater than” from the second drop down list, and then <numerical value> and type the value “24” into the third drop down list. The first line will then read:
Controller is on if “Room air temperature (°C)” “is greater than” “24”.
Now select the logical statement AND from the third drop down list as shown below:
Then in the second control line select “Outside air temperature (°C)” from the first drop down list, “is greater than” from the second drop down list, and then <numerical value> and type the value “12” into the third drop down list.
The full description now reads: Controller is on if
“Room air temperature (°C)” “is greater than” “24”.
“AND”
“Outside air temperature (°C)” “is greater than” “12”.
This functionality can be extended further. For example, if the control action had to ensure that only cooler external air was bought into the zone, the third control line could be used with a further AND statement and if you click on the Create formula button you will see that the complete formula is now:
“(ta>24) & (to>12) & (to<ta)”.
The full description is now:
Controller is on if
“Room air temperature (°C)” “is greater than” “24”.
“AND”
“Outside air temperature (°C)” “is greater than” “12”
“AND”
“Outside air temperature (°C)” “is less than” “Room air temperature (°C)”
Further to this, the function could be ramped by adding a proportional bandwidth to each line. This would reduce the likelihood of windows being simulated to open and shut frequently when temperatures were on the limits. This would aid simulation, where too many changes within a simulated time-step can cause errors.
