Hi Antonio,
I replied to you on jEPlus forum but just in case you haven't seen an answer I'll repeat it here.
For a clarification, you mentioned you use jEPlus+EA. In this case you have an opportunity to do automatic postprocessing within jEPlus+EA by specifying mathematical operations in rvi (or rvx) file (you can do postprocessing by including python script as well).
Total building area can be extracted from sql. If you choose to output simulation results to sql file (by adding Output:SQLite, SimpleAndTabular; object) you would be able to extract the total building area by using SQL query. From top of my head the SQL query should be:
SELECT Value FROM TabularDataWithStrings Where RowName = 'Total Building Area'
However, if I'm wrong, you'll have to check and update the sql query. YouTube video tutorial can be found here
Having the total building area extracted from sql, you'll be able to calculate normalised energy consumptions and use them as optimisation objectives. For example, if your Heating:DistrictHeating output [in J] is c2, and total building area [in m^2] is c4, the normalised heating consumption would be:
Heating; kWh/m2; c2/c4/1000/3600.
Cheers,
IK
@Antop Just for clarification, are you using EnergyPlus?