THERMAL COMFORT: THE IMPORTANCE OF THE “U VALUE” IS JUST ONE FACTOR!
The degree of insulation of a material is expressed by the thermal transmittance, also known as U value, expressed in watts per meters squared Kelvin, or W/m²K.
The thermal transmittance is the rate of transfer of heat through one square meter of a structure divided by the difference in temperature across the structure, considering stationary thermal conditions. The lower is the thermal transmittance, better the insulation. Well-insulated parts of a building have a low thermal transmittance whereas poorly insulated parts of a building have a high thermal transmittance.
Recent tests carried out by Polytechnics of Zurich on Biohabitat solid wood walls has shown that the U value is just one factor that had influence on the thermal behavior of the wall and that at least other three factors determine the behavior itself:
1 – thermal lag, i.e. the capacity of the wall to react very slowly to the external temperature variation;
2 – the capacity of the wall to accumulate heat, reaching values very close to those of the environment;
3 – the thermal perception of persons, influenced, inter alia, by the temperature difference between the internal surface of the walls and of the environment.
The comparison of the temperature variation between the Biohabitat solid wood walls, masonry structures and platform frame structures with the same U value, has shown that, in period of large external thermal excursion, the Biohabitat walls present more constant temperature values.
The Biohabitat wall reacts very slowly to the external temperature variation. The thermal lag value is higher than those of a masonry wall or of a platform frame wall.
The excellent thermal behavior of Biohabitat walls, combined with their breathability, is a guarantee of optimal living comfort.