How is HSPF measured and can units really be compared by the rating?

I'm looking at a pamphlet that lists SEER and HSPF for some 1991 units. The systems in question were top shelf at the time for ratings but a bit bare bones for fault protection. I'm looking at three configurations in this old pamplet. They are not in the AHRI database for comparision anymore. One is HSPF 7.9, Seer 12.85. The second is HSPF 8.5 and SEER 12.8. The last is HSPF 8.5 and SEER 12.8. What caught my interest is the heating peformance numbers are consistently higher than the new equipment of similar SEER, say SEER 13. That lead me to wonder if they are measured against the same conditions.

I'm comparing these to new gear to calculate payback. In the higher end equipment the ratings are HSPF 7.8 through HSPF 9.0 and SEER 13-15 depending on the blower-coil selected.

Are performance numbers published in 1991 directly comparable to numbers published for other units in the AHRI directory today? Were they measured with the same procedures and same seasonal environment?

ARI 210-240-2006: Performance Rating of Unitary Air-Conditioning & Air-Source Heat Pump Equipment


I don't know where you could find revisions of the standard but for the most part it's the same. Look through the standard and notice how the SEER rating is weighted......HSPF and EER are much better indicators of performance than SEER in most cases....although SEER can be used for small % for accurate assessment.