Enhanced Vapor Injection (EVI) is the engineering feature that separates capable cold-climate heat pumps from standard units. By injecting refrigerant vapor mid-compression, EVI compressors achieve two key benefits:
Higher discharge temperature: Enables delivery of 60–80°C water even at -20°C ambient, without staging.
You assumed 0°C? They solved it at winter temperatures most of Sweden sees.
Any COP above 1 eventually pays off, as long as it does so before the equipment is due for replacement you're good.