How does "Temperature Difference Between Cutout And Setpoint" affect Unmet Hours?

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In your example, Setpoint temperature is 70F, and Cutout temperature is 72F. EnergyPlus tries to heat the zone so that the zone temperature doesn't drop below 70F. If Temperature Difference Between Cutout And Setpoint is not implemented, Setpoint temperature is 70F, and Cutout temperature is 70F. EnergyPlus tries to heat the zone so that the zone temperature doesn't drop below 70F. They are the same in terms of heating unmet hours. I'm still not convinced why the former is considered "incorrect". In reality, all HVAC systems operate with deadband. The former is rather more accurate.

Do you think we should NOT use Temperature Difference Between Cutout And Setpoint for ASHRAE90.1 Appendix G compliance?

FYI, ASHRAE90.1-2016 Performance Rating Method Reference Manual Section 3.5.1 asks us to model Building Zone Thermostat Throttling Range as designed with a default of 2°F.

If you look at your plots for zone temperature vs setpoint for 0 delta C and 0.5 delta C, you can see that when the heating coil or cooling coil is on and delta is 0 C, there are no unmet hours during that time period, because ZMAT = setpoint. When the equipment is cycling (0.5 delta C) you could have unmet hours because ASHRAE 90.1 defines an unmet load hour as "an hour in which one or more zones is outside of setpoint + OR minus 1/2 temperature control throttling range." Does ASHRAE 90.1 make the distinction of heating vs cooling unmet hours?

@sashadf1

When the equipment is cycling (0.5 delta C) you could have unmet hours

No, we don't have unmet hours. I have already visualised the relationship between ZMAT and unmet hours in my question. We have unmet hours when ZMAT (the thick black line) is above the orange line during cooling or below the orange line during heating.

You misunderstand the definition of unmet load hours. It is an hour in which one or more zones is outside of setpoint plus 1/2 temperature control throttling range during cooling OR minus 1/2 temperature control throttling range during heating.

Ok, that definition of unmet load hours is more specific than ASHRAE 90.1, makes sense. In that case, you don't have any unmet hours when the coil is on, regardless of what Temperature Difference Between Cutout And Setpoint is set to.