Laboratory for Mathematical Modelling
of Environmental and Technological Processes

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The data are obtained by software UMeas, that allows to registrate one or two het flux densities (q) simultaneously through a given buiding elment and corresponding 2 or 4 temperatures inside or outside (their difference - DT). The saved data are processed in order to obtain the heat transfer coefficient U=q/DT

Schema for registration of heat fluxes and temperature measuerments

Simple algorith of calculation by scheme U=q/DT could be used only in stationar cases at constant flux through the element and constant temperature difference. In real cases it is not so. More accurate results could be obtained by so called cumulative modelling methodology, where the registered data are averaged by scheme:
   qn=((n-1)qn-1+qn)/n, DT=((n-1)DTn-1+(Tn,1-Tn,2)/n, U=q/DT
including all previous measurement data. There are cases when the conditions are particularly unstationar or duration of mesurements is not sufficiently long. In those cases the original methodology, that includes also so called thermic time constant of the element. Here the minimisation of two argument function is performed. One of the parameters is heat transfer coefficient U, while the other one thermic time constant t).

Cummulative values of heat transfer coefficient during stabilisation

The two-argument function can be visually observed by software DataProc, that localises this minimum at first step and finds the accurate solution by iterations at next step. Therefore, not only value of heat transfer coefficient is obtained but also thermic duration constant. The last characterises the time interval in which variatrion of temperature at one side of element causes variation of it at the othetr side.

Coincidence of experimental and numerical heat fluxes during modellation

Minimum of two-argument function f=f(U, t)

Various building elements and constructions are processed by this methodology. Comparative analysis is shown in table:
Building element Heat transfer coefficient U (W/m2K) Time constant t (days)
Monolithic panel of otside wall made from ferroconcrete 0,75 0,3
The same panel with 5 cm isolating layer made from mineral wool 0,35 3,3
Panel of outside wall with improved construction with intrinsic isolation layer 0,6 1,5
Clay brick wall (55 cm) 1,2 0,5
Silicate brick wall (45 cm) 1,8 0,2