Hi GBAers! Just joined and this is my first post, and it’s a noob question from someone who’s never built a home before: how “real” are heat studies, really?
To help me understand how to build my net-zero home, I’ve created some spreadsheet-based heat studies. From my simplistic and idealistic studies, I’ve learned that with little infiltration, good ventilation with recovery, and great insulation, it appears possible to build a net-zero home here in at 4200 feet in Salt Lake City proper. 
Specifically, in a 20 feet tall, 25 feet wide, and 40 feet long house with east-west axis with 289 square feet of windows oriented primarily due south with infiltration less that 0.05 ACH50, ventilation at 0.3 ACH50 with 80% recovery, R-90 ceiling, R-60 walls, R-40 floor, and R-6 windows, the model is very close to net-zero (not including ventilation power, water heating, electrical, etc.). To heat beyond direct insolation gain, I modeled electric ventilation heating and ground-tube ventilation cooling requiring less than 3 ACH. 
From my reading, these values are extreme and on the cusp of build-able, but the PH literature aligns generally. From my reading of Building Science Corporation articles, infiltration less than 0.05 ACH50 is difficult to build; R-60 wall enclosure has significant long-term risk moisture compromise, etc.; and, yet, net-zero homes are built successfully…presumably. But how real is this really? Are these extreme values just an artifact of simplistic modeling?
Also, one specific question: to achieve the necessary cooling in the home in the month of October, the model requires about 2.7 ACH through a 53F ground-tube…which seem like a lot to me. Is 3 ACH achievable in ventilation-only designs? (I have not been able to find much on this topic, so article pointers would be greatly appreciated…)
Many thanks for your patience, and all the great information you folks dispense.