Function object efficiency is included in file controlDict and configured in file: system/efficiency.fun:

efficiency
{
    type                    efficiency;
    functionObjectLibs      ( "libefficiency.so" );
    outputControl           timeStep;
    outputInterval          1;
    
    //for single region case, you can ommit this
    //for multiregion case, you need to supply region (region, where you will calculate moment)
    //inletRegion and outletRegion are optional
    region               rotor;
    inletRegion		     spiral;
    outletRegion	     drafttube;
    
    //all patches need to lie within coresponding region
    //i.e. inlet/outletPatches in inlet/outletRegion, moment patches in region
    inletPatches            ( inflow_inlet );
    outletPatches           ( drafttube_outlet );
    momentPatches           ( rotor_blade_wall rotor_hub_wall rotor_shroud_wall );
    
    //multipliers are used for periodic cases
    inletMultiplier 	     1.0; //default 1.0
    outletMultiplier 	     1.0;  //default 1.0
    momentMultiplier	     13.0; //default 1.0
    
    pName                   p;   //default p
    UName                   U;     //default U
    rhoName                 rhoInf;
    rhoInf                  1.0;
    phiName		     phi; //default phi
    log                     true; // default false
    CofR                    (0 0 0);
    machineType		    waterTurbine; // fan waterTurbine
    
    //omega and axis is read from fvOptions
}