A modified Carnot analysis with finite heat exchanger (HX) sizes, counterflow HX configurations, and ideal glide matching was conducted for an air-to-air heat pump application. The purpose of the analysis was to determine the envelope of potential HX size and refrigerant-side augmentation benefits for ideal mixtures relative to pure refrigerant alternatives. The mixture coefficient of performance (COP) benefits examined are those due to exact external fluid glide-matching of idealized mixtures in more effective heat exchangers. Maximum possible mixture COP gains are evaluated for four steady-state air-to-air pump conditions. Performance improvement opportunities are found to be primarily in the cooling mode. The effects of deviation from counterflow by use of crossflow and counter-crossflow HX configurations are addressed. Refrigerant-side augmentation with pure and mixed refrigerants is examined for air-side dominant and air-to-refrigerant balanced HXs.

KEYWORDS: Heat pumps, air air heat pumps, heat exchangers, analysis, refrigerants, mixtures, coefficient of performance, steady state, cross flow heat exchangers, counterflow heat exchangers.