In the solar-assisted series hear pump system, coefficient of performance (
COP) can be increased by transferring solar radiation heat to the heat pump
evaporator. In the present study a method of calculating the ideal design
limit for the collector area based on the second-law efficiency is given by
using a set of experimental data on a certain design of a solar-assisted s
eries heat pump system for domestic heating during the heating season. A co
mparative study is made between the actual and ideal conditions, and a mini
mum required collector area is presented.