Hello,

During my recent field measurement I noticed an interesting phenomenon. On a typical winter day (meaning the interior room temperature is much higher than the outside air temperature so the heat is flowing from the interior toward the exterior), sometimes the exterior wall surface temperature is lower than the outside air temperature, which kind of makes me confused. As there is "air film" between the exterior wall surface and the surrounding air which provides additional thermal resistance ( in some literature it is called " film coefficient"), so theoretically the exterior wall temperature should always be higher than the outside air temperature on a winter day. Could anybody please explain such problem? Please correct me if I made any mistakes above.

Thank you!