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Since decades, indoor aerosol models have been introduced to understand the behaviour of indoor aerosols. However, studies about model validation in multi-zone form are very rare because of the lack of high quality and well-controlled measurements. We utilized state-of-the-art measurement and modelling approaches to validate the Multi-Compartment and Size-resolved Indoor Aerosol Model (MC-SIAM) inside a two-zone apartment with natural ventilation. According to the MC-SIAM simulations, the ventilation rates ranged from 0.06 to 0.31 h–1 during closed windows and it was as high as 2.1 h–1 when a window was open; compared to the tracer gases analysis results, the ventilation rate was as high as 0.26 h–1 (closed windows) and 1.7 h–1 (open window). The internal airflow predicted with the MC-SIAM ranged from 9.3 to 11 m–3 h (tracer gas analysis 7.6–15 m–3 h) when the door between the internal rooms was opened. The methods utilized in this study have proven that indoor aerosol models such as the MC-SIAM are valid to describe the behaviour of indoor aerosol particles inside multi-zone dwellings with the assumption of well-mixed indoor air inside each zone. The next step in indoor aerosol models development should include re-suspension and new particle formation processes.

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The current regulation of European Commission No. 1253/2014 regarding Ecodesing requirements for ventilation units, which classified them based on the Specific Fan Power (SFP), has been driving the innovation in the sector of air-handling systems. The required energy saving can be met by applying modern and energy efficient Electronically Commutated (EC) motor which, at the same time, significantly change the internal geometry of the fan unit. The paper deals with design of a new type of modular fan unit ALTEKO Alton with EC motor and unhoused backward curved impeller. The design development and optimization of the fan unit leading to the reduction of generated aerodynamic noise, lower pressure loss and better outflow characteristics is supported by the Computational Fluid Dynamic (CFD) simulations, which enables visualization of air streamlines, velocities and pressure contours within the unit. Such a design is an iterative process between CFD specialist and construction team, where, based on the simulated results, the critical spots are identified, the geometry is improved and again verified throughout the CFD simulation. The paper describes in detail the individual steps of the optimization study, starting with the import of the detailed geometry from the design CAD software and its necessary simplification for the use in the CFD study, meshing of the model and consequent simulation. The methods of the fan rotation approximation are discussed as well. Additionally, the optimum position of heat exchanger in front of the fan unit is addressed. The presented work is a part of a project supported by the EU under the Operational Program Enterprise and Innovation for Competitiveness.