Who are we kidding? A variable that is not directly measured cannot be directly controlled. This is the simple fact of HVAC system airflow measuring/monitoring/controlling. It’s always good to pause to ponder if the way the airflow is being measured/monitored/controlled can indeed be defended in court if the design intent is not achieved. The cost of saving a few dollars on first cost can be far offset if shortcuts are taken when attempting to utilize and rationalize the use of indirect methods.
There are many types of indirect methods one may pursue to ensure the required airflow is being delivered or removed from a space or a building; however, are they all defendable, repeatable, and accurate all the time in all conditions? Of course it is possible to have algorithms within building automation software programming to calculate airflow based on temperature sensors using mixed flow calculations; however, this adds a greater degree of inaccuracy depending on the accuracy of the sensor at any given point in time. What risks are being taken to not measure/monitor/control airflow directly, and who is at risk?