Essential Flow measures effort in terms of person days.
Whether it is in the whole organization or in a part of the organization not everything that people do during the day will be considered “work”, or at least the kind of work that you are trying to use Essential Flow to manage.
Essential Flow uses the idea of Full-Time-Equivalence to address this.
Some people may only be able to devote a fraction of their day to project work. Someone who can only work four hours of an eight hour day to project work will be counted as a Full-Time-Equivalence of .5 of a person. They would have to work for 2 days to do the Full-Time-Equivalent of one days work on the project.
Questions
Would you have historical data available that would help you calculate the average effort your typical work flows demand of different persons (or groups)?
Would you be able to estimate the availability of resources (persons or groups with specific skill-sets) in the future.