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.

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The paper presents a new method to determine the sensible effectiveness and pressure loss of rotary regenerative heat exchangers using computational fluid dynamics (CFD). It is based on CFD simulations of a single thermal wheel microchannel with a small cross-sectional area and thin walls, with cyclic inlet and outlet boundary conditions. Two unique measurement set-ups were designed and built for the experimental measurement of the heat exchanger characteristics. Five different types of thermal wheels were manufactured, measured, and simulated in ANSYS Fluent. All wheels achieve an effectiveness greater than 73% under certain (air flow) conditions, which is the minimum effectiveness required by Ecodesign (in the EU). For the examined exchangers, the effectiveness ranges from 66.5% to 83.3%, depending on the boundary conditions and geometric parameters of the rotors. The highest sensible effectiveness is achieved by heat exchangers with the largest heat exchange surface Ac; on the other hand, these wheels have the largest pressure loss. The paper discusses the use of a simplified ε-NTU correlation model for the HVAC systems (typically C* = 1). The correlation model and CFD results were compared and found to be different from each other. The results of the CFD simulation were compared with measurements to prove that the proposed simulation method can predict the behaviour of the real heat exchanger as a whole. It was demonstrated that the sensible effectiveness and pressure loss of the rotary heat exchanger predicted by the CFD simulations correspond well to the measured values within the measurement uncertainty ±1.3%. The proposed method can be used for the comparison of different rotary regenerative heat exchangers before their manufacturing and for verification that they meet the EU Ecodesign requirements set by the current legislation. It reduces the cost of the initial optimisation and testing of new designs.