**Piotr Kolasi ´nski**

Department of Thermodynamics and Renewable Energy Sources, Wrocław University of Science and Technology, Wybrze ˙ze Wyspia ´nskiego 27, 50-370 Wrocław, Poland; piotr.kolasinski@pwr.edu.pl; Tel.: +48-71-320-23-39

Received: 9 June 2020; Accepted: 24 July 2020; Published: 2 August 2020

**Abstract:** Environmental issues are nowadays of grea<sup>t</sup> importance. In particular air and water quality should be kept at as high levels as possible. Energy conversion systems and devices which are applied for converting the chemical energy contained in different fuels into heat, electricity and cold in the industry and housing are sources of different gases and solid particle emissions. Medical data show PM2.5 dust in particular is highly dangerous for human health. Therefore, limiting the number of low-quality fuel combustion processes is a key issue of modern energy policy. Statistical data show that domestic heating systems account for a large share of the total emissions of PM2.5 and PM10 dust. For example in Poland in 2017, the share of households in the total annual emissions of PM2.5 dust was equal to ca. 35.8%, while the share of PM2.5 emission in industry (i.e., power generating plants, industrial power plants and technologies) was equal to only 23.6%. A possible way of solving this problem is by the successful replacement of old domestic furnaces by combined heat and power (CHP) or multigeneration boilers which can be used for heating the rooms and sanitary water and generating electricity and cold. Such systems can possibly contribute in the future to significant reductions of dust emissions and air pollution in urban and rural areas by limiting the number of low-quality fuel combustion processes. This article presents design considerations and experimental results related to a domestic micro-CHP unit which is based on organic Rankine cycle (ORC) technology. The main aim of the design works and experiments was therefore the analysis of the possibility of integrating the ORC system with a standard domestic central heating gas-fired boiler. The specially designed micro-ORC system was implemented in the laboratory and experiments were performed using this test stand. The main design aims of the test-stand were: low operating pressure, small working fluid flow, low price and compact dimensions. To meet these aims, volumetric machines were chosen as the expander and working fluid pump. The experimental results were positive and show that it is possible to integrate an ORC system with a standard domestic central heating gas boiler. For different heat source temperatures, the obtained expander power ranged from 109 W to 241 W and the thermodynamic cycle efficiency ranged from 4.3% to 8.8%. These positive research results were achieved partly thanks to the positive features of the different system subassemblies.

**Keywords:** air pollution; PM2.5 dust; ORC; working fluid; selection method; volumetric expander; thermodynamic analysis
