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Study: Material effectiveness as a function of the installation situation of windows and doors in terms of their passive house suitability

The BBS Institute of Prof. Dr.-Ing. H.-P. Leimer from Wolfenbüttel carried out a comprehensive study into this subject for HANNO.

In the introduction to a study published recently, the Umweltbundesamt listed the following facts concerning job effects as well as the training and qualification needs in order to make buildings more energy–efficient: Buildings consume 40% of all energy consumed in Germany. If suitable measures were taken, that energy consumption level could be reduced to approximately 20% by 2020. As it is, the available options in energy-focused building refurbishment have not been exhausted by far because only about one third of the financially rewarding potential savings in building refurbishment has actually been tapped. For this reason, the German government made raising the energy efficiency of buildings one of the focal areas of attention and promised to provide financial subsidies. The availability of sufficiently trained manpower was one of the important aspects, however, it was underlined.

A fundamental question should be asked here: Are there any scientific findings on how, for example, windows and doors can be sealed permanently and in an energy-saving manner? No such findings were available in the past and so the purpose of this study was to close the gap.

To obtain sound scientific data, HANNO requested the BBS Institute of Prof. Dr.-Ing. H.-P. Leimer in Wolfenbüttel to provide answers to the following questions:

If a building is to be optimized from an energy point of view and consumption of energy is to be minimized, thermal bridges must be eliminated. How can this be achieved in window construction?

One of the critical points is the air tightness of the envelope of a building. What about air tightness under the conditions of the long-term use of the building and during temperature changes acting on the building and the joints?

The purpose of refurbishing buildings is the sustainable saving of energy. A precondition for this is that the window joints should be functioning permanently. How does a joint behave in the long term under diffusion and convection loads?

In cooperation with the manager of HANNO-Anwendungstechnik Bau, Dipl.-Ing. (FH) Björn Kethorn, expert in building damage due to heat and moisture, Prof. Dr.-Ing. H.-P. Leimer and Mr Jan Schneider of the BBS Institute developed a concept for this.

Assessment of building connection joints under energy aspects

The ift Rosenheim guideline, ift-Richtlinie WA-15/2: Passivhaustauglichkeit von Fenstern, Außentüren und Fassaden“ [2] particularly chapter 4.3. on the assessment by the BBS Institute, served as reference and on the basis of this calculations for different products of the HANNO® 3-level joint sealing system were made.

To evaluate different constructions, two constructions in annex 1 to the ift-Richtlinie WA-15/2, were chosen: a rebated wall construction with clinker and a monolithic masonry structure with heat insulation composite system. Each of these systems was assessed in combination with different sealing systems and different installation positions of the elements. Assessment criteria included surface temperature Өsi, temperature factor fRsi and length-related heat transition coefficient Ψi.

The results reveal that if the thermal bridge is planned professionally, the calculated loss by this way can virtually be eliminated completely.

Effect of the thermal conductivity of the sealing products in the same construction

Here it can be seen that when the surface temperatures Өsi  are considered, a difference of up to 0.4°C is obtained. For this reason, HANNO specifies the thermal conductivity for all sealing materials. Even decimal values can account for relevant difference. So, for example, the value for Hannoband®-3E, 0.0428 W/(m*K), which is an outstanding  λ-value for a multifunctional tape, is specified to four decimal digits.

Effect of the installation position of the building elements in different structures

In a monolithic structure with thermal insulation composite system, depending on the structure, the position has a distinct effect on the length-related thermal transition coefficient ψi. It would probably be reasonable from an energy point of view to integrate the building elements in the insulation level of the composite system. Here again, thermal conductivity is an essential factor even if more for the ambient thermal insulation, in addition to the sealing product.

Based on these findings, the Hanno®-DUO Easy flashing tape from HANNO is a system which while meeting the requirements on sealing in optimum manner does not restrict the action of the thermal insulation materials around it.

Hence: The thermal properties of all products of the Hanno® 3-level joint sealing system are suitable for passive house construction.

 

The permanent air tightness was examined in part 2 of the study.

The following question was examined: What is the behaviour of the air tightness during the permanent use of buildings and the temperature changes acting on the building and the connection joints of building elements?

Generally, building connection joints of windows should be made to be tight to driving rain and air to prevent the entry of moisture in the structure. Using a specific PVC window with a section length of 2.18 m the movements due only to temperature changes were defined and taken to be 3 mm on each joint side. Based on the assumption of 3 mm joint movement, specific test specimens were developed and 4 different sealing systems fixed to them. The joint flanks of the test specimens are made of solid wood and lime sandstone. Several test specimens were prepared from each sealing product to obtain variance of the measuring values.

Three different products were installed in the window joint:

Joint sealing tape, for which Hannoband®-BG1 was used in the test
Joint sealing tapes of stress group BG1 according to DIN 18542 of 2009 are only required to meet the requirements on external air tightness. Despite that, the tape was included in the test to see how a product open to diffusion for the outer sealing behaves with respect to air tightness under the conditions of joint movements.

Multifunctional tape, represented by Hannoband®-3E in the test.
Multifunctional joint sealing tapes are products for all three sealing levels of the window connection and therefore directly responsible for the air tightness of the joint.

Joint flashing tape, Hanno®-Duo Easy flashing tape in the test.
Flashing tapes are considered to be air-tight per se. The main point was to install a resilient material tightly, i.e., without the resilience allowance required for non-resilient systems, and obtain information on resilience.

PU-based volume adhesive, for which the product of a competitor was used for the test.

The test was to show how the products behaved under the conditions of real joint movements. The test setup for the measurements was not the one usually used for joint tests according to EN 1026 so the measuring values were not directly comparable with obtained in standard tests, but a very good comparison of the systems was possible.

Results reveal distinct differences in the extended joint

Whereas only minor differences between the sealing products were seen in the initial joint of 15 mm, the joint transition coefficient was 10 times higher in case of the PU based volume adhesive:

Finding: The tried and tested systems meet the requirements without problem. The products Hanno®-Duo Easy flashing tape and Hannoband®-3E multifunctional tape on which the air tightness was tested can be used for building construction without restriction.

The alternative system for air-tight sealing fails to comply with the requirements on the joint movement defined as normal for this test. It is not suitable for permanent air-tightness alone.

What are the consequences of this effect on the joint and its moisture balance?

To answer that question, a basic thermo-hygric simulation calculation was performed by the BBS Institute Wolfenbüttel of Prof. Dr.-Ing. H.-P. Leimer.

At first, systems with complete air tightness, i.e., with a-value = 0.0 were calculated in order to see how the systems behaved under conditions of diffusion only and to establish a reference. In a second step, the air permeability values from part 2 of the study were also considered by extrapolating the behaviour of the connection joint for a period of five years.

With this complex approach the effect of the permanent combination of diffusion and convection on the building connection joint was proved.

If only the diffusion effects are considered and a theoretical value of 100% is assumed for air tightness, none of the systems produced any harmful concentrations of moisture in the structure, as had been expected.

If the convection values are added, the systems with Hannoband® BG1, multifunctional tape Hannoband®-3E and flashing tape Hanno®-DUO EASY score excellent values and the moisture of the material in the joint even drops in comparison with the initial level. In contrast with this, the PU-based volume adhesive also tested during the study caused leaks with subsequent accumulation of moisture in the joint over the years. So this solution is not a permanent solution and therefore no alternative to an air-tight joint.