Here is my grandma's double door:
I had my IR thermometer with me, so I did a quick check of the temperatures. The temperature of the entry hallway was 25.5°C, the inner door's inside/outside surface temps were 26.5/27.7°C, the temps for the outer door were 28.2/30.4°C, resp., the outdoor temperature was 31-32°C.
With only ~6°C difference between indoor and outdoor, the effect of a double door does not show that much. In the winter I should get data with a 20-30°C temp difference.