Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (h_ave) during the entire charging process was obtained 68 W/m²K, compared to the experimental result h_ave = 61 W/m²K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

National legal and political regulation in the field of energy efficiency is closely connected to minimizing energy consumption in buildings. Within the framework of implementing Directive 2018/844/EU on the energy performance of buildings in Europe, the practice of its application differs from country to country. This study aims to reveal the differences in the energy indicators of an energy-efficient building in European states. To that end, an analysis was made to compare the results of a single-family home model in 11 city locations with different climatic conditions (from the Mediterranean to Nordic) and appropriate national regulations in place for the past three years. The simulation was done using IDA Indoor Climate and Energy software, EQUA Simulation AB, Stockholm, Sweden. The demand for primary energy is based on primary energy factors. A comparison of overall heat transfer coefficients for walls and windows in an energy-efficient building in different locations was made to reveal the differences in applicable national regulations. The results showcase the primary energy demand depending on the different climatic conditions for building heating and cooling purposes, as appropriate, and on CO₂ emissions. The study has shown the energy demand for cooling to increase significantly—by 65% in the case of Vilnius, whereas only a slight decrease in the demand for heating. Furthermore, a Lithuanian energy class A+ building is singled out as an individual case, its energy indicators determined for a different location under analysis.

All energy processes in buildings are usually unsteady, ie time dependent. But mostly the unsteady factors influence is not taken into consideration for energy demands, microclimate changes estimating. Therefore the practical observations and theoretical investigations show an undesirable behaviour of indoor thermal microclimate and energy use, even with modern enough control systems. As a result, new methods for problem solution and investigations develop. The paper presents some theoretical aspects of unsteady heat transfer analysis based on the energy conservation law. Additionally, an experimental research made at Solar energy investigation centre in Spain ‐ Plataforma Solar de Almeria - results and its comparison with theoretical calculations are produced.

In this paper the influence of climatic parameters of building region on expedient depth of implementation of different ways of energy consumption decrease in civil buildings is reviewed. The data of multivariate calculations of power and technological efficiency of an adopted complex of energy saving measures for reference climatic zones of the terrain of Russia in modern economic conditions with allowance for discounting of costs are adduced. The analysis of the obtained outcomes is given and the guidelines are also offered at the choice of optimum combination of the solutions on a decrease of power inputs at exploitation of a building depending on the number of degree‐days of the heating season, as well as on established prices for stuffs both equipment and fares on power supplies. Santrauka Straipsnyje išnagrinėta statybos rajono klimato parametrų įtaka tikslingam įvairių energijos taupymo būdų taikymui visuomeninės paskirties pastatuose. Pateikiami energetinio ir techninio-ekonominio skirtingų energijos taupymo priemonių komplekso variantų, charakteringų Rusijos teritorijos klimato zonoms šiuolaikinėmis ekonominėms sąlygoms, įvertinant sąnaudų diskontavimą, skaičiavimo duomenys. Atlikta gautų rezultatų analizė ir pasiūlytos rekomendacijos, kaip pasirinkti optimalų energijos sąnaudų mažinimo derinį eksploatuojant pastatus, priklausomai nuo šildymo periodo dienolaipsnių ir galiojančių medžiagų, įrengimų ir šilumos tiekimo tarifų kainų.