Look at the code and the comments in emonLib.cpp to see exactly how emonLib works and what is needed.
The number (1480) is no longer optimal. The sampling rates, measured with a standard emonTx V3.4 (and the emonPi is the same processor) are:
calcIrms( ) - approx 5588 current samples per second.
calcVI( ) - approx 2535 pairs of voltage & current samples per second.
See Sampling rate of emonLib for more information.