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Hi @ben

Using "HVACTemplate:Zone:IdealLoadsAirSystem" would be a right way to assess the heating and cooling loads. I just looked at the weather file "USA_OH_Dayton.Intl.AP.724290_TMY3". The ratio of HDD to CDD appears quite different for the two baseline temperatures which might partly explain your issue.

- 1794 annual (wthr file) cooling degree-days (10°C baseline)
- 1532 annual (wthr file) heating degree-days (10°C baseline)

-  538 annual (wthr file) cooling degree-days (18°C baseline)
- 3197 annual (wthr file) heating degree-days (18°C baseline)

I never worked on a project in this area but if have experience in this area and if you think the ratio of heating loads to cooling loads is too skewed, you should possibly find a way to fix that based on the thermostat set points and thermostat schedules.

I suggest taking a closer look at your thermostat set points and schedules and see if they are correctly modeled. For similar issues, I typically look through the .Zsz file to look at the peak heating and cooling loads (last row in the .zsz file) for each thermal zone to identify if the issue is caused by any particular zone.

Hope that helps!

Raghu