Milestone 1.2. Principles of good practice to design the joints against thermal losses

Transcription

1 REPORT Milestone 1.2 Principles of good practice to design the joints against thermal losses Publisher: Felicitas Warmuth Jörg Lange Lars Heselius Task 1.1 Thermal loss in joints This report includes 5 pages. Date of issue: March 23 th, 2010

2 Project co-funded under the European Commission Seventh Research and Technology Development Framework programme ( ) Theme 4 NMP Nanotechnologies, materials and new production technologies Prepared by Felicitas Warmuth, Jörg Lange, Lars Heselius Drafting history Draft version Draft version Draft version 3 Draft version 4 Final Dissemination Level PU Public X PP Restricted on the other programme participants (including the Commission Services) RE Restricted to a group specified by the Consortium (including the Commission Services) CO Confidential, only for members of the Consortium (including the Commission Services) Verification and approval Coordinator Industrial Project Leader Management Committee Industrial Committee Deliverable D1.2 Design guidelines for good panel joints and joints sealing openings focussing on air and water tightness Due date: Month 24 Completed: Month

3 Principles of good practice to design the joints against thermal losses 1. General In the design of modern buildings, the thermal insulation plays an important role. One central point for the thermal insulation and the energy saving is the air tightness of the envelope. Due to the impervious metal sheets and the insulating core in between the sandwich technology allows constructing very tight buildings. Compared to other building techniques like masonry or concrete structures, sandwich facades have quite a lot of joints. To ensure the tightness, special attention has to be paid to them. Due to the current European and national standards, joints in the building envelope have to be sealed airtight permanently. The air tightness of sandwich constructions can be determined according to EN [1]. The majority of literature says airtight according to the state of the art. In the German standard DIN [2] the state of the art is defined by a coefficient for the air permeability of joints. The limit value for a joints is 0.1 m³/[m*h*(dapa 2/3 )]. The same value can be found in DIN 18542, which defines requirements for sealing tapes. Tightness tests within EASIE WP1 showed that modern sandwich panel joints have usually no problems to go below this limit value. In figure 1, some test results and the limit value in DIN are demonstrated. 10 air permeability in m³/(hm) 1 0,1 0,01 a-value DIN Producer A, 100 mm Producer B, 60 mm Producer B, 100 mm Producer C, 60 mm Producer D, 60 mm Producer D, 120 mm 0, pressure difference in Pa Figure 1: Tests results for the air tightness of PUR-sandwich panel joints To fulfil the limit value, some important requirements have to be considered. These requirements are depending on the core material.

4 2. Panels with core material of closed cell structure At first the geometry of the joint itself can restrict great air streams. The key and slot joints of panels have a positive influence on the tightness. In this context it is very important that the abutting ends and surfaces of the panels fit into one another very well. For a good insulation it is also important that the metal faces have as little penetration into the core as possible like it is shown in the right picture of fig. 2. A bad solution is to have the metal face bent into the core as it is done in the panel to the left in fig. 2. The problem is of particular importance for thin panels (thicknesses up to 80 mm) where there are cases where the metal faces almost touch each other in the joint. Joints always form a thermal bridge and the penetration of metal worsens this [10]. Figure 2: Examples of different joint geometries The next important point is the sealing tape. These days it is absolutely state of the art to use sealing tapes in every longitudinal joint of the panels. Different kinds of sealing tapes exist in the market [9]. The most important differentiation can be made by the cell structure. One can distinguish between open cells, partly open cells and closed cells. All of them are used in modern sandwich panels. These different structures lead to very different characteristics regarding the air permeability. Closed cell structures are practical completely airtight as soon as they have contact to the joint, whereas open structures need some compression. The required level of compression is depending on the cellular material. According to [4], the following table gives some guide values: Cellular Material Minimal compression for air tightness PUR-foam, open cells % PUR-foam, open cells, impregnated by acrylate % PVC-foam, partly open cells 30% PE-foam, partly open cells 15 % PE-foam, closed cells -

5 Impregnated open celled PUR-foam [5] Closed celled PE-foam [5] Figure 3: Examples of sealing tapes According to that information it is essential for the air tightness that the geometry of the joint allows the required compression of the sealing joint. Shadow gap Sealing joint Figure 4: Examples of longitudinal joints If the shadow gap is closed for example before the sealing joint is compressed, it will not be possible to get an air tight construction. Also the needed contact pressure plays an important role. If the necessary compression can only be reached by high pressure, the right mounting equipment has to be used. For mounting the panels an exact knowledge of the tolerable width of the shadow gap is necessary. This is the only possibility for the fitter to check the correctness of the construction and to guarantee an air tight building envelope. The tolerances have to be small enough to assure the required compression. 2. Panels with core material of open cell structure For panels with core material of open cell structure as mineral wool a different sealant solution is necessary. By these panels a sealant stripe of tight material with big flexibility shall be placed in the longitudinal joint between the metal sheets. Here it is very important to seal the joint between the sheets; otherwise an air stream through the open cell structure of the core is possible. The joint profile geometry shall be designed for this sealant stripe. Two examples are shown in figure 5. The sealant shall be placed on the warm side. In special cases, e.g. walls with high wind pressure, sealants in both faces as shown in fig. 5 (on the left) are considered meaningful.

6 Sealing lip Figure 5: Examples for a good sealing of mineral wool panels [7], [8] Also for mineral wool panels, the tolerances play an important role. They have to be small enough to assure the sealing. 3. Conclusions Principles of good practice for the design of joints against thermal losses have been presented in this document. Three points are of big interest. First, the geometry of the joint plays an important role, second the right sealing stripe is of particular importance and perhaps the most relevant item are the tolerances of fabrication and mounting. If attention is paid to all of these points it is possible to design joints with a very good air tightness. Only longitudinal joints are subject of this report. Of course, a lot other details like joints between panels and windows or panels and the ground have an influence on the air tightness of sandwich constructions. References: [1] EN 12114: Thermal performances of buildings - Air permeability of building components and building elements - Laboratory test method, April 2000 [2] DIN : Thermal protection and energy economy in buildings - Minimum requirements to thermal insulation, July 2003 [3] DIN 18542: Sealing of outside wall joints with impregnated sealing tapes made of cellular plastics - Impregnated sealing tapes - Requirements and testing [4] Galileo Kreatives Bauen mit Sandwich: Basis Info, chapter 4.9, Version D1 [5] Homepage Iso-Chemie, [7] Homepage RUUKKI, [8] Homepage Fischer,

7 [9] IFBS 4.02, Bauphysik Fugendichtheit im Stahlleichtbau, IFBS e.v., Düsseldorf, 11/2004 [10] IFBS 4.03, Bauphysik Wärmebrückenatlas der Metall-Sandwichbauweise, IFBS e.v., Düsseldorf, 03/2010