Thanks for straightening me out. Here’s the whole house plot. Our slope numbers are actually quite close - Both 3.6kW / CDD. And my R2/correlation is surprising better as well. But a few additional thoughts / questions.
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I’m going to need to redo if I want to match up against your results. I used CDD65 while you used CDD75, because that was the default for the website I used (partially because that’s the typical US baseline standard). That would change my intercept, but not the slope. Sorry I didn’t read your explanation more carefully earlier - I should have noticed the difference when your were showing a smaller number of cooling degree days in Texas than I saw for the CA Bay Area microclimate I’m in.
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My AC units are not that efficient - 20 year old SEER 11.5 units. But the Ecobee thermostats do turn up AC threshold when sensors tell it that we’ve been out of that part of the house for 15 min or longer.
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House is about 4000 sq feet, with reasonable insulation, but no attic fan. We keep the heating / cooling numbers at 68 degrees and 74 degrees when we are home, but we have someone home nearly all the the time.
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Our biggest cooling challenge is solar heating of roof and stucco, not air temp or humidity. That’s why we need to cool, even when the outside temperature might be below the the air temperature.
