You are tasked with designing a system to supply energy to a new block of 30 eco flats, providing heat (150 kWh per flat) and electricity (at a constant rate of 5 KW per flat) for one day (24 hours).

Heat will be delivered by an air-source cascade heat pump system, operating under the vapour-compression refrigeration cycle, between temperatures of 10C (assume air temperature is stable) and 100C, and using water as the working fluid. The cascade system has two cycles, and an intermediate temperature of 46C.

Those are the only information are given regarding the heat pump. Could you please explain to me how you got the value of mass flow rate ? and why is the efficiency is too low?!