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The article presents the methodology for calculating the optimal insulation thickness that is related to the quality of energy supply and fuel prices. Assuming that the total cost following renovation is the sum of the costs of heating and thermal upgrading, it was shown that when calculating the optimal insulation thickness, the thermal resistance of the outer walls should be taken into account. Such calculations, in addition to the characteristics of the heat source, should be carried out taking into account local weather conditions. The study presents the results of such calculations for the building heated with gas and the air-source heat pump. The results of the investigations are referred to the mean climatic conditions recorded in the last 10 years. It was found that for thermal upgrading with the use of foamed polystyrene having the optimum thickness, total investment costs are almost the same, regardless of polystyrene thermal properties. The same also refers to energy costs. The article also provides sample calculations for plaster, the main ingredient of which is perlite. In the case of internal thermal upgrading of the historic buildings, such isolation is recommended in order to prevent moisture problems inside the envelope.

Abstract. The paper presents the research methodology, the test facility and the results of investigations into non-isothermal surfaces in water boiling at atmospheric pressure, together with a discussion of errors. The investigations were conducted for two aluminium samples with technically smooth surfaces and thickness of 4 mm and 10 mm, respectively. For the sample of lower thickness, on the basis of the surface temperature distribution measured with an infrared camera, the local heat flux and the heat transfer coefficient were determined and shown in the form of a boiling curve. For the thicker sample, for which 1-D model cannot be used, numerical calculations were conducted. They resulted in obtaining the values of the local heat flux on the surface the invisible to the infrared, camera i.e. on the side on which the boiling of the medium proceeds.

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