nice post!This is something that I have found as well - our first Geothermal install also happened to be a foam insulation job (house fire rebuild). Of course, the homeowner didn't tell me that during the design phase, and the plans didn't specify so my load calcs and equipment sizing were based on conventional insulation, etc. Well, they sprayed the underside of the roof (cathedralized?) and made the attic a conditioned space so the interior volume went up by another 25% or so. I was a little nervous at startup because 1) it was my first Geothermal and I was trusting my training and calculations and 2) I had sized a 4 ton geothermal where we probably would have installed an 80k BTU furnace. When the system first started up it was middle December and below freezing outside. Thankfully, the HO had been keeping things warmish with a kerosene torpedo heater so I wasn't trying to come up from too low, but without resorting to the auxiliary heat it took a while to chip away at those degrees.
The lesson I learned is that an appropriate sized system will do a great job of keeping the space at temperature, but extreme recovery is another story. New startup in the middle of record high temperatures? A few days at the very least before getting worried.
We had a similar issue with our service side last month - record highs for a few weeks and lots of broken down systems. The house would be 90 degrees inside when we got the system running again and the customers would be calling 2 hours later complaining that it wasn't 70 degrees in the house yet. I told all of them to call back 24 hours later if it wasn't the temperature they wanted - I didn't get any calls.