Travis Jordan wrote:

"What happens is through cooking and the opening and closing of windows,
the interior adjusts to a temperature that is comfortable to you,"

Yeah, sure. Uh huh.

Why not, with enough insulation? The deep ground temp in Seattle is 52 F
and an average house uses 800 kWh/mo (3800 Btu/h) of electricity, so
a 2300 ft^2 house with 6000 ft^2 of exterior surface could stay 70 F if
3800Btu/h = (70F-52F)6000ft^2/Rv, with Rv = 28 ft^2-F-h/Btu walls.

The yearly average sun on the ground is 1050 Btu/ft^2 per day, and 820 falls
on a south wall, so a house with lots of insulation and thermal mass could
stay 70 F with no indoor electrical usage with A ft^2 of R2 skylights with
80% solar transmission if 24h(70-52)((6000-A)/Rv+A/2) = 0.8x1050A, ie A
= 6000/(1+1.44Rv) = 201 ft^2 with R20 walls or 100 ft^2 with R40 walls.

With a long time constant, the indoor temp changes slowly, so there's no need
for a thermostat :-) My neighbor raised the temp of his PA underground solar
house from 70 to 72 F every year by closing windows over 2 weeks in November.

Why are the homeowners only shooting for 55-60 F and how can the house be
"sixty feet under" 50 tons of soil?

John Hait's 1983 "Passive Annual Heat Storage" and Mike Oehler's
"$50 and Up Underground House" books are related...

Nick