Introduction and purpose of the study: The paper presents results of studies aimed to provide a rationale for the possibility of a gradual transition to hydrogen combustion in gas supply to domestic and commercial consumers without changes in the design and operation of burners. For this purpose, we have considered tasks of determining the indicators of interchangeability for natural gas and its mixtures with hydrogen. The main characteristics of combustible gases with various hydrogen content in a mixture have been studied. We have established the impact of the hydrogen content on the heat rate, emissions of harmful substances, as well as light back and flame lift phenomena. We have also analyzed the available interchangeability criteria and their applicability when using natural gas/hydrogen mixtures. The impact of the hydrogen content on the radiation heat transfer in the furnaces of gas equipment is described in the paper for the first time. Methods: The methodology of the paper is based on a critical analysis of available literature data on combustible gases interchangeability as well as theoretical and experimental studies performed by the authors. We have derived dependencies that allow us to determine the possibility of gas equipment transition to the combustion of natural gas/hydrogen mixtures. We have also developed recommendations on the permissible hydrogen content in a natural gas/ hydrogen mixture that would ensure the efficient, safe, and green use of such fuel in domestic and commercial heating units. Results: Scientific findings and practical results of the study make it possible to implement partial gradual costeffective decarbonization in the area of gas fuel utilization as an intermediate stage of transition to more extended hydrogen combustion.

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This article presents the results of experimental research on the non-stationary management of the internal climate of buildings with a non-constant stay of people. During the absence of people, a significant drop in air temperature and corresponding energy conservation in heating is possible. The effectiveness of porous building materials is shown, provided that the appropriate characteristics are selected. Daily fluctuations in the outside temperature are completely extinguished by a layer of foam polystyrene insulation. The absence of channel porosity in the structural material of the wall is a guarantee of the stability of its thermal and humidity regime. This, in turn, prevents the development of mold and mildew.

This paper presents a prototype of a thermo-hydraulic distributor for a hybrid boiler station supplying a small hotel in Koszalin. The task of the device was to balance the hybrid system with four circuits with different operating parameters, also changing in an extremely irregular manner. A prototype of a thermo-hydraulic distributor with improved internal structure was developed, ensuring the operation of the device in accordance with the temperature logic. Dimensions of the device have been calculated in accordance with the existing design principles of hydraulic distributors.