Hi Soner - You could have a look at this paper Article Novel Anthropometry-Based Calculation of the Body Heat Capac...

which seems to be based on body composition and measurements. Another angle to try is looking at the work of air conditioning/refrigeration engineers such as here https://pp.bme.hu/me/article/download/1440/844/

I hope this will be useful. Philip

The gold standard method is direct calorimetry, which is costly in terms of the initial equipment set-up. Indirect calorimetry provides a reasonable substitute.

Thanks a lot Philip. That's exactly what I'm looking for.

Thanks a lot Gordon.