HVAC Sizing for baseline and retrofit/new construction

[afontani]

We currently use ASHRAE 2013 Design conditions in the EPW files for an AMY run. So we are sizing to the design conditions for 2013. This might be relatively reasonable as there is a distribution of HVAC system ages. What about for upgrades? Should we use the same design conditions? Should we be using newer design conditions? What about scenarios out 30 years?

[shorowit]

Related to this, Manual J says we should be using the latest ASHRAE data. This site suggests that might be 2021? I don't know how different the 2021 data is from the 2013 data. Unfortunately no one seems to update the TMY3 EPW files with the latest ASHRAE data.

[shorowit]

FYI, I discovered that the TMY3 EPWs posted on climate.onebuilding.org include ASHRAE 2021 design conditions (as well as updated precipitation values). For example, here's a diff for one TMY3 EPW (energyplus.net on the left, climate.onebuilding.org on the right):