Our paper presents empirical data from a laboratory experiment investigating the performance of an air-to-soil heat exchanger between July and August 2016. Measurements were performed in a laboratory of the Department of Civil Engineering and Building Engineering Physics of the University of Warmia and Mazury in Olsztyn. Empirical data were compared with the results of analytical calculations based on meteorological data for a typical meteorological year.

The article presents the results of a study aiming to select the optimal source of heat for a newly designed single-family home. Commercial software was used to compare heating and ventilation systems involving a bituminous coal boiler, a condensing gas boiler, a biomass boiler, a heat pump with water and glycol as heat transfer media. The effectiveness of natural ventilation, mechanical ventilation with a ground-coupled heat exchanger, and solar heater panels for water heating were evaluated. The analysis was based on the annual demand for useful energy, final energy, and non-renewable primary energy in view of the pollution output of the evaluated heating systems. The analysis revealed that the heat pump with water and glycol was the optimal solution. However, the performance of the heat pump in real-life conditions was below its maximum theoretical efficiency. The biomass boiler contributed to the highest reduction in pollutant emissions (according to Intergovernmental Panel on Climate Change Change guidelines, carbon dioxide emissions have zero value), but it was characterized by the highest demand for final energy. Mechanical ventilation with heat recovery was required in all analyzed systems to achieve optimal results. The introduction of mechanical ventilation decreased the demand for final energy by 10% to around 40% relative to the corresponding heating systems with natural ventilation.

For scientist, the Coanda effect has been an object of interest for a long time. All the time, some new applications of it are found although it has been more than a hundred years since Henri Coanda got a patent that was critical for that issue. Apart from aviation, it is more and more often used in ventilation systems to control the manner of air division and the design nozzles and ventilators. It is surprising, however, that a good command of that phenomenon and a need to apply it in different solutions did not entail a significant increase of the interest in the Coanda effect hysteresis, although it was mentioned for the first time by Newman in 1961. This article presents results of experimental measurements for a two-dimensional incompressible plane jet by an inclined plate. The hysteresis has been observed as a different jet behavior (a free jet or a jet attached to a flat plate) depending on the direction in which the plate deflection angle changes. The observed hysteresis area, defined by critical values for the αca attachment and αcd detachment angles, spanned from 8 deg to 14 deg. Its dependency on the Reynolds number has also been examined for Re ranging from 3500 to 26,500. Considering the Coanda effect hysteresis, a pressure distribution on the plate and the xR reattachment distance has been examined. The distribution of forces on a plate has been identified, which has facilitated a graphical mirroring of the Coanda effect hysteresis loop.

The article analyzes a ground-to-air heat exchanger (GAHE) for a mechanical ventilation system in a building. The heat exchanger’s performance was evaluated in northeastern Poland between May and August of 2016, 2017, and 2018. In spring and summer, the GAHE can be theoretically used to precool air for HVAC systems. The aim of the study was to compare the real-world performance of GAHE with its theoretical performance determined based on the distribution of ground temperature and the temperature at the GAHE outlet modeled in compliance with Standard PN-EN 16798-5 1:2017-07. The modeled values differed considerably from real-world data in May and June, but the model demonstrated satisfactory data fit in July and August. In all years, the modeled average monthly air temperature at the GAHE outlet was 8.3 °C below real-world values in May, but the above difference was only 1.1 °C in August. The developed mathematical model is simple and easy to use, and it can be deployed already in the preliminary design stage. It does not require expensive software or expert skills. However, this study revealed that the model has several limitations. The observed discrepancies should be taken into account when modeling the performance of a GAHE.

Contemporary energy-saving mechanical ventilation systems combined with Earth-Air Heat Exchangers (EAHE) can reach high energetic and economic efficiency. The necessary condition for optimisation of ventilation system functioning is the adequate design of EAHE. This requires knowledge of soil temperature distribution in the location of EAHE. It constitutes a complex problem because of the influence of different factors. The correct estimation of soil temperature for a given location can be difficult in the designing process. The designers can rely on simplified calculation models which can, however, deviate from real empirical data. The motivation to undertake this study was to compare real, empirical energy gains with handly calculations based on two different theoretical models of soil temperature distribution. The theoretical models used for comparison were European norm and semi empirical. The laboratory setting including EAHE was located at Warmia and Mazury University in Olsztyn, Poland. Thus it can reflect real condition operations of EAHE in climate conditions of central Eastern Europe. Data were gathered in a winter period between 1 October and 31 December. The results indicate that empirical data deviate from theoretical models. Models tended to overestimate the energy gains from EAHE by 23%.Keywords: earth-to-air heat exchanger, models for calculating the thermal efficiency of earth-to-air heat exchangers *