I am in the process of choosing a compressor for a low temp. condensing unit I am having installed. I am being given the choice of a Copeland Scroll or Semi-Hermetic compressor. With similar btu ratings (29,000 at -25C), the scroll has an EER of 5.8 vs 4.6 for the other, but has a mass flow of 349 (lb/hr) compared to 585 lb/hr for the semi-hermetic. I am a bit confused which is the better choice in terms of energy efficiency and actual cooling capacity.