Unconditioned space anomalies. Or not?

Dear community, I faced with strange thing.
I have several unconditioned spaces where internal temperature has to be studied. I made calculation for summer period and everything seemed to be close to reality. But after simulating all of the year I noticed that at the days with the lowest external temperature (even minus 17) the internal one starts to grow and reaches almost 40 Celsius.

Any ideas why is it happening? I believe I made something wrong.
GH file is attached. Thank you.
Olsztyn_Test.gh (494.1 KB)

No GH file attached.

1 Like

Sorry, my mistake. Changed my first message.