Indeed, I have been speaking to this for many years. Measuring efficiency of H/ERVs is actually much more complicated than most know. That said, there is a fundamental difference between PHI and HVI/AHRI. PHI measures efficiency with the exhaust air stream as the basis, which determines the amount of energy LEAVING THE BUILDING. As opposed to HVI/AHRI which measures the incoming air stream. The incoming air stream has multiple factors that impact the perceived efficiency, such as waste heat from the motors, transfer from exhaust air to incoming air stream, energy transfer from the outside of the unit through the walls to the air stream... The PHI measurement provides a much better input for energy modeling (PHPP) that is reliable and much more realistic. I will be co-presenting with Berthold Kaufmann from PHI on this exact subject for PH2020. So I would highly recommend signing up for the conference!