The temperature of the gas pipe, which is welded to the flange whose temperature is measured by TC4, depends both on the ambient air temperature (which is stable at 25 °C) and on the convective heat exchange coefficient with the ambient air, the value of which, on the contrary, is by no means constant, because it varies considerably with the air speed, which in turn depends on the ON-OFF status of the AC unit.
Thermotechnic is far outside your area of expertise. Even farther than kindness and fairness
Ascoli65, in order to better understand your point, can you provide a numerical exercise such that would allow, to those who disagree with you, to better visualize the magnitude of the potential error in the calorimetry that could, as you point out, be induced by this heat exchange coefficient variation caused by the AC air circulation?