Journal of Building Physics

Computational fluid dynamics (CFD) technique is well-known for its powerful capability of modelling the cross-ventilation. CFD is broadly coupled with energy simulation programmes, such as EnergyPlus, to expand its application in building energy calculation. During the coupling process, iterative calculation is required to improve the accuracy of the coupling method, which means the scale of the model should be designed with extra care so that the simulation can be practical in terms of computational cost. A coarse-resolution mesh (here denoted as CFD_c) cannot properly represent the required local environment to study the underlying physics. However, a fine-resolution CFD microclimate model (here denoted as CFD_f), which includes both indoor and outdoor spaces, always requires a large number of cells to capture the complexities of environment; this makes the coupling procedure a challenging problem. This study aims to propose an innovative, high-resolution and computationally cost-effective CFD_f-CFD_c model to overcome this gap. The full-scale CFD_f works in an off-line manner at the preliminary simulation stage and generates detailed flow parameters at the interfaces for CFD_c. At the dynamic stage of the simulation, CFD_c participates in the coupling procedure with the other tools, for example, building energy simulation (BES) tool (e.g. EnergyPlus). The coupling of CFD_f-CFD_c-BES is about 200 times faster than an ordinary coupled CFD_f-BES method with a significantly quicker and more stable achievement in the convergence.

Excess moisture in concrete structures is a major problem in building industry. It is claimed that degradation of the finishing materials of concrete slabs is the largest source of volatile organic compound in the building stock in the Nordic countries. Considering concrete wall panels, the choice of the insulation material influences concrete drying considerably and causes a risk for moisture accumulation on the interior surface, if vapor tight finishing materials are used or if finishing materials are installed prematurely. Mineral wool insulation, which has predominately been used in Finland, is a vapor open material. However, vapor tight plastic foam insulation materials are nowadays more commonplace. Here we show that the overall rate of drying of the concrete panel with a vapor open insulation material is higher in comparison to the concrete panel with vapor tight insulation materials. However, relative humidity distribution near the inner surface of the concrete panel at the end of the drying phase is almost identical irrespective of the insulation material and the water vapor resistance of the interior surface material has a greater impact on the relative humidity level on the inner concrete surface. Moisture behavior of concrete panel walls is studied under a certain building schedule in Finnish environment and building conditions by numerical simulation. The model for drying of concrete is calibrated based on laboratory measurements. According to our study, self-desiccation and changing diffusivity due to the hydration process of the concrete cannot be ignored when evaluating the moisture behavior of the concrete wall panel structure with a low water binder ratio (w/b < 0.5). Measurements indicate that the early age humidity drop is by up to 10 percentage points.

In building design, the decision-makers should not focus only on energy efficiency as a single objective but indoor environmental quality indicators, such as thermal comfort, daylight usage and so on, should also be considered as a part of building performance. The building performance can be ensured by determining the proper performance indicators and the variables during the design. In this context, a weighted (among the objectives) multi-objective cost function was proposed, for the optimisation of energy, thermal comfort and daylight usage of a case study archetype design, through the selected design variables, considering the base architectural design principles as well. A typical social housing archetype design was determined as the case study to apply the proposed approach. The window sizes are optimised for each orientation simultaneously, for a temperate-humid climatic region. The results were evaluated in terms of improvement potentials of energy, thermal comfort and daylight performances, and the dominant values for the window sizes for each facade. According to the results, the optimised scenario achieved an 11.42% reduction in primary energy use equivalent to 181.24 kWh/m²a, a 4.52% reduction in a predicted percentage of dissatisfied with 9.12%, and a reduction in lighting energy of 4.94% equivalent to 21.17 kWh/m²a. These reductions verify the possibility to achieve higher performances on each criterion.

Nowadays, latent heat storage is becoming an imperative in building sector since it plays a crucial role in conserving energy through controlling the thermal comfort level. In this field, different storage systems based on phase change material show great performances in terms of energy saving, leading to a significant improvement of occupant thermal comfort. In this work, the thermal behavior and energy efficiency of a residential house incorporating various phase change materials (RT18HC, RT21HC, RT25HC, and RT28HC) in Mediterranean climate region were investigated via numerical simulations. EnergyPlus software was used to analyze the thermal performance of phase change materials applied to the interior wall surfaces of a simplified building model in El Jadida city. The integration of different single and double phase change material layers has been evaluated based on various concepts such as the average temperature fluctuation reduction and the monthly energy saving. The study showed that low melting point phase change material outperforms in terms of heating load, while phase change material with high melting temperature favors the cooling performance. Moreover, the results show that double-layer systems formed by two distinct phase change materials exhibit higher performance than a single phase change material layer throughout the whole year. The annual energy saving rate reaches 41.42% and 55.41% when using single and double phase change material layers, respectively. Finally, we opted for an optimum double-layer system for lower energy consumption in the selected city.