Genuine question: does old-style insulation not help? From when I was a kid I remember that a log house built using 60ies village technology (realistically probably more like 19th century technology), insulated with something stuffed in the triangles between logs and wallpaper and logs and planks (and partially eaten by mice ;)), stayed pleasantly cool on 90-degree days. And the dugout under it that we used to store potatoes and stuff like that was actually cold.
In a recent Seattle heatwave, when it was 107 outside my much poorer insulated semi-basement with direct sun shining into its large-ish windows, stayed under 85 without AC.
Couldn't people just build better / underground housing using relatively primitive technology?
This is temperature of air (big amplitude) vs temperature of ground X meters undergrounds. If you go deep enough it doesn't matter how hot it is outside - the temperature is basically constant the whole year.
I'd bet that data is from sensors with low heat dissipation. Unfortuantely, humans produce ~100W of heat each. If you're using a small underground basement as a place to escape lethal heat aboveground, or even a large underground basement with high people/m³, this added heat will steadily increase the basement's wall temperature.
The rate of temperature increase depends on physical properties of the basement walls: using the first equation here[0] as an approximation, set x to 0, set q"_o to 100W*(# people)/(basement surface area). α is the thermal diffusivity of the wall material [1].
In a recent Seattle heatwave, when it was 107 outside my much poorer insulated semi-basement with direct sun shining into its large-ish windows, stayed under 85 without AC.
Couldn't people just build better / underground housing using relatively primitive technology?