14.14.4.3 Heat recovery efficiency Measure the outgoing heat recovery fluid temperature at outlet, returning heat recovery fluid temperature at inlet, and integrated flow volume or mass at inlet or outlet. Each measurement shall be taken at intervals of 60 s or less for a minimum of 3 h. If fuel is to be supplied intermittently, the data shall be collected for 20 times the interval of the fuel supply or 3 h, whichever is longer. The outgoing heat recovery fluid temperature, the returning heat recovery fluid temperature, and the difference of their temperatures shall be reported. 14.14.5 Calculation of electric efficiency 14.14.5.1 For a system without an internal battery Calculate the fuel energy input, in relation to the duration of electric demand following operation. Electric efficiency shall be calculated according to equation (63)