Some notes on the Glaser 2d approach
Our GLASER 2D algorithm represents an extension of the classical one-dimensional Glaser method on two-dimensional configurations. Using the same model and assumptions the differential equation describing linear vapour diffusion (Fick’s law) is solved. It is therefore a straightforward and consistent extension of the well established 1d version (as described e.g. in ISO 13788), however it allows investigating more complex, but usually crucial details (such as edges, connections of windows, walls, slabs etc.). This means that the model does not include moisture storage or liquid transport processes. Consequently, the GLASER 2D method shares the same advantages as well as disadvantages of the classical Glaser (1d) method:
- The simulation basically only requires the knowledge of two constant parameters per material: thermal conductivity (known as λ) and water vapour diffusion resistance (expressed as µ or sd-value). These values are usually well known or can easily be found on test certificates or the relevant standards.
- Forming the basis of the standards for hydrothermal assessment the Glaser method is well known and proven over decades.
- It provides a conservative method to calculate if and how much condensation can be expected. The results of such an assessment are therefore on the safe side as long as vapour diffusion is the dominant process.
- The method, as well as its results, are straight-forward and graphically comprehensible.
- The method calculates the so-called stable solution of the underlying differential equation. An annual balance can still be evaluated based on stable-simulations using monthly average temperatures. Since vapour diffusion is a relatively slow process, this approach will still lead to significant results.
- In situations when strong formation of condensation occurs the method is less precise as moisture storage, liquid transport processes and moisture dependent change of material parameters are not covered by the vapour diffusion model. In such cases, the amount of condensation is usually calculated too high, whereas the evaporation potential is underestimated by the model. Again, this represents a safe side assessment that can point out the need for a closer examination.
- The Glaser-2d method can also be used to calculate evaporation of moist areas. This allows to calculate the dry-out potential of constructions. The balance between condensation amount and potential evaporation amount is a very important information to assess any condensation issues. Using HTflux this balance can be done with a two climate “block approach” (condensation period/evaporation period) or on a monthly basis.
- A more realistic simulation including liquidity transport and moisture storage would require a precise knowledge of the often complex temperature- and humidity-dependent parameter functions of all materials used. This information is often not available.
Therefore we believe that the GLASER 2D method offers an excellent and sometimes even the only practical way for hydrothermal assessment of two-dimensional details – providing precious information with little effort.