Glaser process

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The Glaser method (also known as the Glaser diagram ) is a building physics procedure that is used to determine whether and where condensation occurs in a building structure . The Glaser process is named after its inventor, Helmuth Glaser . It was developed at a time when computer-aided analyzes were not yet possible to the extent customary today, and was therefore designed as a tabular-graphic process that delivers results quickly and with simple arithmetic operations.

International standards

• In Germany, the Glaser method is standardized in DIN 4108-3 as moisture detection. (Calculation algorithm and graphic method).
• In Austria, ÖNORM B 8110 , Part 2 ( water vapor diffusion and protection against condensation ) is used.
• For Switzerland, the Swiss standard SIA 180 applies to heat and moisture protection in building construction (1999)

Basics

The Glaser method is used for the approximate determination of moisture accumulation through diffusion in building components. Standardized boundary conditions are assumed here. The climatic conditions are selected in accordance with the technical regulations so that they are a conservative approximation of the real conditions:

During the condensation or thaw period in winter (outside climate −5 ° C and 80% relative humidity / inside climate 20 ° C and 50% relative humidity, duration 90 days), a quantity of condensate accumulates in most constructions. This amount of condensation water has to dry out again during the evaporation period in summer (indoor and outdoor climate 12 ° C and 70% relative humidity, duration 90 days).

Interpretation of the results

If the amount of condensation water is less than 1 kg / m² (0.5 kg / m² for capillary non-water-absorbing layers; special regulations for wooden components) and the amount of evaporation in summer is greater than the amount of condensation water in winter, then it can essentially be assumed that the construction is free of structural damage. However, if even the smallest amount of condensation water remains in the component at the end of the evaporation period, this can add up to an amount over many years unnoticed, which will almost inevitably lead to severe structural damage due to moisture penetration.

Limitations of the procedure

The simplified assumptions do not take into account

• Moisture storage in the material (it is assumed to be unlimited).
• Water transport processes (also capillary) in materials (moisture conductivity).
• Water vapor, which can penetrate the structure through air flow in joints (e.g. due to defective airtightness levels in roof and wall structures) and condense there as additional condensation.
• The dependence of the calculated value of the thermal conductivity λ on the current component moisture, which can increase due to the water vapor diffusion flow in the component.

Due to these limitations of the classic condensation detection using the Glaser method, computer-aided simulations are increasingly used today, which also take into account the transient conditions. This is particularly advisable if a construction based on the Glaser process is to be assessed as critical with regard to condensation.

The Glaser process is a one-dimensional process in which edge influences (analogous to thermal bridges ) are not taken into account. The area of ​​the edge influences corresponds approximately to the diffusion-equivalent length of the layers involved. It is therefore not suitable for calculating a layer structure in which the edge area is larger than the area to be examined, such as B. is often the case with green roofs.

Procedure

In addition to the original graphical solution, there is also a mathematical one. Both give the same results and require the same data.

Input data

The following building construction data is required:

Construction details:

• Layer structure of the component
• the thickness of the individual component layers ... (from inside to outside) ${\displaystyle d_{1}}$ ${\displaystyle d_{n}}$

Material characteristics:

• the individual material-specific rated values ​​of the thermal conductivity of all materials used λ ... λ (from inside to outside) ${\displaystyle _{1}}$ ${\displaystyle _{n}}$
• the individual material-specific water vapor diffusion resistance figures of all materials used , ${\displaystyle \mu _{1}...}$ ${\displaystyle \mu _{n}}$

Climate boundary conditions (boundary conditions to be selected for Germany from DIN 4108-3 according to region and building type)

• Indoor and outdoor temperature θ _i , θ _e
• Relative humidity inside φ _i and outside φ _e

Information on the installation situation (derived from this and taken from the standard in tabular form):

• the heat transfer resistance inside and outside ${\displaystyle R_{si}}$ ${\displaystyle R_{se}}$

Calculation method

Details of this procedure and all relevant equations can be found in DIN 4108-3. The basic steps for estimating the amount of condensate occurring during the condensation period (winter) are:

1. Calculation of the temperature profile within the construction using the thermal resistance of the layers and the ambient temperatures.
2. Calculation of the saturation vapor pressure profile from the temperature profile (i.e. determination of the saturation vapor pressures at all layer boundaries from the temperatures prevailing there).
3. Calculation of the ambient vapor pressures on both sides of the construction (from the surrounding ambient temperatures and humidity).
4. Calculation of the vapor pressure profile through the construction with the aid of the water vapor diffusion resistances and ambient vapor pressures (i.e. determination of the vapor pressures at all layer boundaries).
5. Differentiation of different cases:
   1. The vapor pressure does not reach / exceed the saturation vapor pressure at any layer boundary → no condensate.
   2. The saturation vapor pressure is reached / exceeded at a layer boundary → condensate level.
   3. The saturation vapor pressure is reached / exceeded at several layer boundaries → condensation area.
6. If condensation occurs, the steam flow from the inside of the wall to the first condensation level is now calculated.
7. Then the steam flow from the outermost condensate level to the outside.
8. The difference between the steam flows is the amount of condensate produced per unit of time.
9. Multiplication by the duration of the condensation period gives the total amount of condensate.

After calculating the amount of condensate, the potential amount of evaporation in summer can be determined using a similar procedure. The following criteria must be observed for proof of moisture protection according to DIN 4108-3:

• The amount of condensate must be less than the potential amount of evaporation.
• The amount of condensate must not exceed a limit value (depending on the type of construction).

Graphic process

Example of a Glaser diagram

First, the component data is recorded in tabular form. A line is created for each layer, in whose columns the properties of this layer are described and calculated:

Layer no., Material description, layer thickness d in meters, water vapor diffusion resistance factor µ

The water vapor diffusion equivalent air layer thickness s _d in meters is calculated for each layer from the layer thickness and the water vapor diffusion resistance factor . This value indicates how thick a layer of air would have to be in order to offer the same resistance to the diffusion flow as the component layer with its specific dimensions and properties.

This is followed by the design value of the thermal conductivity λ as a material parameter for each layer. The quotient of thickness and thermal conductivity gives the thermal resistance R of the layer, which is entered in the column that follows. Supplemented by the heat transfer resistances R _si and R _se , the addition of the individual heat transfer resistances results in the heat transfer resistance R _T , whose reciprocal value U as the heat transfer coefficient is the so-called U-value (formerly k-value) of the component, which is used to assess the thermal protection of a component becomes.

Using the formula, the heat flow density (q) in W / m² is determined from the difference between the inside and outside temperature as well as the heat transfer resistance of the component , which can now be used to calculate a temperature profile through the component, each at the layer boundaries. ${\displaystyle q={\frac {\theta _{i}-\theta _{a}}{R_{T}}}}$

Since (in simplified terms) every temperature corresponds to a certain saturation vapor pressure, the saturation vapor pressure profile through the component can now be created with the help of a precalculated table (water vapor table) or an approximation formula , also at the layer boundaries.

The course of both profiles is drawn in a diagram; the air layer thickness equivalent to water vapor diffusion serves as the common x-axis as a hygric scale . The saturation vapor pressures are to be plotted in Pascal (Pa) on the Y-axis. ${\displaystyle P_{s}}$

In order to prove an expected loss of condensation, the partial vapor pressures determined on the basis of the relative humidity and the air temperatures are now drawn in Pa for the indoor and outdoor climate at the inner and outer boundary of the component. Since the individual material layers are not drawn in with their physical thickness but with a thickness corresponding to their value, an undisturbed vapor pressure profile in this diagram would simply result as a straight line between the two boundary values. If it is now possible to connect these two points with a straight line without the saturation vapor pressure profile being cut, the component is free of condensation. If this connection is not possible, imagine that the two points are connected with a sagging rope. Now you "tighten" the imaginary rope until it clings to the "disturbing" kink points of the profile from below and the rope sections become straight lines. At the layer boundaries or in the areas where the rope touches the saturation vapor pressure profile of the component, condensation falls out ("rope rule"). ${\displaystyle s_{d}}$

Since the inclination of the tangents in this diagram indicates the diffusion current density, the condensate mass can be estimated or determined directly from the angle between the individual rope sections.

In a second Glaser diagram with the climatic boundary conditions of the evaporation period it is shown whether the condensation can be regarded as harmless within the meaning of the standard .

Alternative procedure for moisture detection

In the case of critical constructions, such as strong internal insulation of external walls and the use of moisture-storing and conducting materials, the statements made by the Glaser method are imprecise, as moisture storage and conduction can have a positive effect on the moisture balance of a wall construction. There are various stationary and transient methods that allow a more precise estimate of moisture accumulation and drying out.

Approximation method

The COND software of the Dresden Institute for Building Climatology carries out an analytical assessment process that takes into account the storage and capillary spread of the condensate based on empirical values.

Simulation process

For more detailed considerations of critical constructions, simulation programs can be used, such as the WUFI ("Non-stationary heat and humidity") programs from the Fraunhofer Institute for Building Physics, Holzkirchen or Delphin from the Institute for Building Climatology at TU Dresden. These programs simulate heat and moisture transport processes in components through diffusion and capillary conductivity, taking into account climatic boundary conditions and offer realistic results when using appropriate material parameters.

literature

• H. Glaser: Simplified calculation of the vapor diffusion through layered walls with the separation of water and ice. In: Refrigeration. 10, H. 11, 1958, pp. 358-364 (Part 1), H. 12, pp. 386-390 (Part 2).
• OW Wetzell (Hrsg.): Wendehorst - Structural number tables. 25th edition. Stuttgart 1991, pp. 140-163.
• HM Künzel: Steam diffusion calculation according to Glaser - quo vadis? In: IBP communication. 26, No. 355, 1999. ( online , 64 KB)
• R. Borsch-Laaks: Beyond Glaser. In: the new quadriga. 5/2003.
• ÖNORM B 8110 Part 2 - Water vapor diffusion and condensation protection

Web links

• Website of the moisture measurement program COND
• Website of the Institute for Building Climatology at the TU Dresden, area building physics software
• Detailed sample invoice on the website Projekt-Baudenkmal ISSN  2509-8403