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• Wall-type heat recovery units are solution for improving ventilation in refurbishment. • Assessment of air stream mixing by visualization and CO 2 measurements was conducted. • The risk of air mixing when using wall-type heat recovery units is low. • The analysis of the annual energy demand for residential buildings was conducted. • Wall-type heat recovery units are helpful in achieving low energy buildings. In the cold and moderate climates the energy demand for heating of fresh ventilation air is crucial. The mechanical ventilation systems with heat recovery are used to decrease the peak power of the heating system and to save the energy. In a case of wall-type heat recovery units there is a doubt about the possibility of mixing fresh and exhausted air in the combined intake-outtake device. In this paper experimental investigations were conducted to assess their hygienic safety. The original set-up containing test chamber and the equipment for CO 2 concentration measuring has been used. Visualization of airflows mixing with the usage of smoke is presented. The results show that the risk of the exhausted air return to the building is low. At the same time the ventilating efficiency of such systems is high. The analysis of the annual energy demand for the sample single-family and multi-family buildings has been conducted to present the possible energy benefits of usage such devices. Concluding, the wall-type heat recovery units should be considered as hygienic safe and helpful devices in achieving the standard of low energy buildings in a case of existing and refurbished ones. [ABSTRACT FROM AUTHOR]

Although the evaluation of air quality in the residential and office rooms has been significantly developed in recent decades, the issues associated with securing the air quality requirements in nurseries are still not well recognised. This study presents the results of tests regarding the physical and microbiological properties of air in selected rooms of a nursery, including the alternatively variable way of rooms ventilation. The experiment was conducted in four different rooms from the 20th of November 2017 to the 16th of April 2018. The constant measurements of basic parameters of physical air quality in rooms and outside as well as the measurements of microbiological and particulate matter contaminations were conducted in the chosen days of the analysis. The results have confirmed the unsatisfactory air quality in the rooms dedicated to small children. Modernisation of the ventilation system, from a natural one to the supply-exhaust ventilation, has lead to an improvement of physical property of the air, but it did not significantly improve its microbiological quality. Our research indicates that the controlled air flow, method of cleaning the premise and health condition of the children may have a great influence on the physical and microbiological quality of the air. • Building's indoor air is the habitat of numerous bacteria and microscopic fungi. • Source of microorganisms may be people and the external environment. • A quality of indoor air depends on the type of ventilation system. • Contamination can be reduced by the use of supply-exhaust ventilation. [ABSTRACT FROM AUTHOR]