Indoor temperature Doesn't drop below heating setpoint

Hi there

First post on here. I have been starting to play around with Honeybee Energy and getting to know the tool. I’m trying to do some basic analysis on an empty industrial hangar, first looking at how the indoor temperature changes within a closed envelope without any internal loads, conditioning or ventilation. After this I want to analyse how building insulation, HVAC and other strategies could contribute to keeping the temperatures between 15 ad 25ºC.

I believe to have modelled everything correctly and seem to be getting realistic results. However, I noticed that indoor temperatures do not drop below 15ºC at any point, which is impossible during winter months in an unheated hangar. Conversely, in summer temperatures do exceed the 25ºC setpoint.

Could anyone help me find out where this fixed 15ºC come from and how i could fix/improve the model? (I tried uploading the file but it seems I am not allowed…)

Thank you very much in advance!
Erik