Incomplete condensation may occur for zeotropicmixtures used. Experiments for two zeotropic mixtures were conducted and the variation of heating capacity and COP with the increase of water flow rate in a condenser was obtained to confirm the possibility of incomplete condensation. Moreover

an incomplete condensation criterion

a maximum flow rate discriminant

was used for calculation and was verified by the maximum flow rates measured. The difference between experimental and theoretical results was analyzed. It is suggested that pressure drop of zeotropic mixture in a condenser

temperature difference between zeotropic mixture and heat transfer fluid

and other forces during heat exchange should be considered in the criterion.