Assisted drying of internal building components
Water damage caused by burst pipes or flooding is never easy to deal with. Apart from the inconvenience (and cost) of having to replace damaged furniture, it can also have more serious consequences. For the infiltration of water into structural elements of a building such as floors, walls and ceilings can affect their stability and reduce their thermal resistance. The increased humidity also encourages the growth of mold.
Insurance companies in Germany process 3000 claims for water damage on average each day, or up to 1.1 million such cases every year, resulting in annual compensation costs of around 2 billion euros (source: GDV). Common causes of water damage include old leaky pipes, burst pipes due to the freeze-thaw cycle, and badly installed plumbing. All too often, the problem goes unnoticed for quite some time and doesn’t become visible until damp patches start to appear on the wall or ceiling or until trickling water forms puddles on the floor. By then, the dampness may already have spread to other parts of the building. Extreme weather events with heavy rainfall and flooding can also cause substantial water damage to buildings. Another non-negligible source of damp, typically encountered in newly built homes, is the residual moisture in building materials such as floor screeds, wall plaster and concrete, which contain large quantities of water when they are mixed at the building site.
It is therefore all the more important to know and be able to evaluate how water infiltration affects the hygrothermal behavior of building materials and entire building components, so that suitable drying methods can be developed to restore them to their original state after flooding or other types of water damage. Damp treatment companies increasingly have to deal with new challenges because of the wide diversity of building materials used in all possible combinations – including vertical-core blockwork with and without integrated insulation, solid bricks, aerated concrete blocks, and different types of damp-proof membrane. Wide-ranging specialist knowledge is required to choose the right treatment method in each case, so as to obtain the optimum drying result without excessive use of energy.
In recent years, the Fraunhofer Institute for Building Physics IBP in Stuttgart has carried out a large number of experimental tests to investigate the drying behavior of wall, floor and ceiling structures with artificially induced water damage. A large climate simulator in the institute’s laboratory complex in Stuttgart provides the ideal conditions for such tests. With a chamber measuring seven meters in length, six meters in width, and six meters in height, it can accommodate diverse components, complete building shells, roof structures, and individual test setups. The controlled environment enables ambient conditions during the tests to be maintained at the optimum level.
On behalf of industrial customers, researchers from the institute’s Hygrothermics department have investigated numerous different construction materials and building components with respect to their drying behavior. To conduct many of these tests, they set up complete rooms consisting of different types of floor, wall and ceiling structures. A floor might, for instance, be made up of a concrete slab, an insulating layer of a material such as EPS, mineral wool, or perlite, and a top layer of screed. Materials used to construct the walls included vertical-core blockwork with and without integrated insulation, aerated concrete blocks, gypsum wallboards, solid bricks, and lightweight wall panels, either with or without a tiled or plaster finish. In other experiments, the researchers investigated the drying behavior of ceiling structures consisting of wooden beams and planks with an insulating system of clinker or clay pellets. The test setups were equipped with a multitude of measurement sensors to track every detail of the water infiltration and drying processes. Various humidity and temperature sensors were installed in the flooring layers, inside the wall and ceiling structures, and also used to monitor the ambient air. Before beginning the actual experiments, the test setups were inundated with water for several days to artificially induce the effect of water damage for the purposes of the simulation. In the case of wall and floor structures, the water was introduced at floor level (Fig. 1), while in the case of ceiling structures the water was introduced from above. This was followed by a drying period lasting several weeks. In some experiments to investigate drying behavior, the test setups were left to dry out naturally in the climate simulator, at a constant temperature and relative humidity. In other experiments, different types of specialized drying equipment were used to assist the drying process.
The equipment used included, for example, sub-screed drying systems with adsorption dryers, infrared heating panels to dry walls, floors and ceilings, and adsorption dryers directed between walls and a covering of plastic sheeting (Fig. 2). In the case of wooden plank ceilings, drying was assisted by turbines to create an underpressure between the joints (Fig. 3). The mechanical drying process was tested in both continuous mode and with alternating on/off intervals. The results of some of the tests carried out in the laboratory were verified using the WUFI® simulation tool, which computes the coupled heat and moisture transfer in building components.
The measured data enabled the researchers to acquire extensive knowledge concerning the drying behavior of different test setups and materials in connection with different drying methods. The use of different types of sensors enabled a detailed analysis of the drying rates of different structural layers, allowing the drying method to be adapted accordingly. The results made it possible to evaluate the efficiency of the various drying processes and optimize the choice of appropriate drying methods. It was also found that, in certain cases, an alternation between natural and assisted drying produced the best results. As part of these tests, the experimental setups were also checked for the possible development of mold.
The lab facilities available to researchers at the Fraunhofer Institute for Building Physics IBP and their in-depth knowledge of the drying behavior of building materials are a great asset when it comes to testing and evaluating different drying methods for complex structures containing many different components. By simulating many different structures and drying methods, complemented by mathematical simulations using the WUFI® software tool, it is possible to predict the drying behavior and the duration of the drying process for each case.