Marijke Steeman

Heat, air and moisture transport modelling in ventilated cavity walls

Cavity walls are a widely used external wall type in north-western Europe with a good moisture tolerance in cool humid climates. In this work, a cavity wall configuration with a brick veneer outside leaf and a wood fibre board inside leaf is analysed with a newly developed coupled computational fluid dynamics–heat, air and moisture model. Drying of the outside or inside cavity leaf, both for summer and winter conditions was analysed. The new model was compared with a widely used simulation tool for building envelope analysis (WUFI®) that uses a simplified modelling approach for the convection in the cavity. The study showed that the simplified model overestimated the drying and moistening rates of the cavity wall compared to the detailed model. For both models the drying of the outer leaf was mainly determined by the outside conditions, and the outside leaf dried out mainly to the outside and not to the cavity. For the inside leaf, however the cavity ventilation was of major importance in drying. The study revealed that the simplified model could not be used to evaluate the drying potential of a ventilated cavity because it overestimated the ventilation effect systematically. The simplified model would in such case indicate lower moisture contents than in reality and consequently lower risk for mould growth, wood rot or other structural damage. Only detailed modelling of the convection in the cavity, as in the new model, leads to a correct evaluation of ventilated cavity walls.

Design of Cellular Materials and Mesostructures with Improved Structural and Thermal Performances

Honeycomb mesostructures and other types of cellular material such as wood, coral, and cancellous bone have properties that make them suitable for use in many structural engineering applications. This includes not only superior mechanical behavior and lightweight high-strength characteristics, but also better thermal conductivity, electrical resistivity, etc. A good understanding of these structures and materials can help structural engineers to design lightweight building systems with, for example, improved stability combined with improved thermal and acoustic insulation. Moreover, advances in additive manufacturing methods capable of producing these cellular structures also add to the motivation. In this paper, the application of cellular materials for construction applications in the building sector is illustrated and FEM analysis is used to examine several types of mesostructures. Furthermore, we focus on optimizing the equivalent thermal conductivity and stiffness of structures with a relative density of 0.5. Special attention is given to situations for which the required properties are not necessarily equal in all directions. Results show that using multidisciplinary topology optimization methods, the structural and thermal performances of these structures can be efficiently optimized.

Earth-Air and Earth-Water Heat Exchanger Design for Ventilation Systems in Buildings

Earth-air heat exchangers are often used for (pre)heating or (pre)cooling of ventilation air in low energy or passive house standard buildings. Several studies have been published in the passed about the performance of these earth-air heat exchangers [1–8]. Often this is done in relation to the building energy use. Several software codes are available with which the behaviour of the earth-air heat exchanger can be simulated. De Paepe and Janssens published a simplified design methodology for earth-air heat exchangers, based on thermal to hydraulic performance optimisation [7]. Through dynamic simulations and measurements it was shown that the methodology is quite conservative [9–10]. Hollmuller added an earth-air heat exchanger model to TRNSYS [11]. In stead of using earth-air heat exchangers, earth-water heat exchangers are now getting more attention. In this system the ventilation air is indirectly cooled/heated with the water flow in a fin-tube heat exchanger in the inlet of the ventilation channel. The water-glycol mixture transfers heat with the earth by flowing through e.g. a polyethylene tube. In the second part of this paper a design methodology is first derived and then applied to this type of system.Copyright

Compliance, Stress-Based and Multi-physics Topology Optimization for 3D-Printed Concrete Structures

Recent advancements in Additive Manufacturing (AM) technologies have pushed the limits of manufacturability and have encouraged the design of products with increased complexity. Topology Optimization (TO) algorithms, on the other hand, have provided engineers with a tool for intelligently exploiting this design freedom by efficiently optimizing the shape of engineering structures. In this paper, three important developments of TO that might influence the manufacturing process and design of 3D-printed concrete structures are discussed. The first example shows how general structural TO problems, such as the well-known minimum compliance problem, can help to determine the optimal printing path and can discover the ideal location of the steel reinforcements. Secondly, it is considered how stress-based TO can enhance the shape of fiber-reinforced concrete components where the lack of steel reinforcements introduces a non-negligible strength asymmetry. In a third and last example, traditional structural TO techniques are extended to allow for multi-physics optimization. The thermal transmittance through a construction component is minimized, while the overall material usage is restricted. Results show the generation of very efficient (multi-material) structures that are aesthetically pleasing at the same time. The presented techniques aid in the search for more efficient structural design and might help overcome some of the technological challenges related to large-scale concrete 3D-printing.