In order to fulfil the European Energy Performance of Buildings Directive (EPBD) requirements for the reduction of energy consumption, European national requirements have been created for building envelope thermal properties and calculation methodology to determine if building energy efficiency is created. This is however not true in all methodologies. The necessity of building air tightness appears only for new A class buildings, and there are no requirements for air tightness for other building classes. Therefore, the aim of this work is to improve the methodology for the calculation of energy efficiency of buildings, while taking into account the air tightness of the buildings. In order to achieve this aim, the sum energy consumption of investigated buildings was calculated, energy efficiency classes were determined, air tightness of the buildings was measured, and reasons for insufficient air tightness were analyzed. Investigation results show that the average value of air tightness of A energy efficiency class buildings is 0.6 h⁻¹. The results of other investigated buildings, corresponding to B and C energy efficiency classes, show insufficient air tightness (the average n₅₀ value is 6 h⁻¹); herewith, energy consumption for heating is higher than calculated, according to the energy efficiency methodology. This paper provides an energy performance evaluation scheme, under which performed evaluation of energy performance of buildings ensures high quality construction work, building durability, and the reliability of heat-loss calculations.

The field study was carried out during the heating season in two Lithuanian office buildings with large glazed areas. The methodology was prepared for evaluating indoor microclimate parameters while using objective and subjective evaluation. The results show that the average temperature in all tested offices was in the range of optimal zones, but in some offices the average temperature was not in compliance with the recommended temperature for offices. During the subjective evaluation, respondents working in these offices identified complains because of too high temperatures, stuffy air and irritation in eyes. The average relative humidity measured in all tested offices was not in compliance with the optimal requirements. Such SBS symptoms as irritation in eyes, cough and dry skin of the hands were identified as the most frequent symptoms in the second tested building. Main indoor microclimate problems arising in buildings with large glazed areas were related to overheating indoor spaces because of the direct sun and improper ventilation. Santrauka Straipsnyje nagrinėjamos patalpų mikroklimato sąlygos pastatuose esančiuose biuruose, turinčiuose didelius įstiklintus plotus. Didelių skaidrių atitvarų plotų įrengimas pastatuose ne tik didina energijos sąnaudas pastatams šildyti, vėsinti ir orui kondicionuoti, bet ir sukuria mikroklimato sąlygas, kuriose dirbantys žmonės dažnai patiria šiluminį diskomfortą, nors aplinkos parametrai atitinka normų reikalavimus. Natūriniams patalpų mikroklimato tyrimams sukurta patalpų mikroklimato tyrimo metodika, kuri sieja objektyvius ir subjektyvius tyrimo metodus patalpų sąlygoms optimaliai įvertinti. Patalpų mikroklimato sąlygos tiksliausiai įvertinamos pagal patalpų mikroklimato parametrų matavimo, papildyto subjektyvaus mikroklimato sąlygų įvertinimu, apibendrintos analizės rezultatus.

Windows, which have a U-value that is governed by an insulating glass unit (IGU) U-value, must be a building’s only enclosure element, which has no design value concept. The declared U-value, which is calculated or measured with 0 °C of external ambient temperature, is used instead of the design value. For most of a building’s elements, its thermal transmittance with a decrease in the external temperature diminishes a little, i.e., improves. However, for modern window IGUs with Low-E coatings, it is the opposite: the thermal transmittance with a lowering external temperature increases. Therefore, for calculating the peak power for the heating of buildings it is necessary to pay attention to this phenomenon and, therefore, it would be wise to introduce the concept of design U-value for windows, recalculation rules, or affix their declared U-values. This is especially the case in modern times with the prevailing architectural tendencies for enlargement of transparent building elements. For IGUs with Low-E coatings and inert gas fillers, the thermal transmittance depends on the temperature difference between warm and cold environments. When the external temperature is −30 °C instead of 0 °C, the thermal transmittance of the IGU can increase by up to 35%. This study presents the thermal properties of windows’ IGUs depending on the changes in outdoor temperatures by using guarded a hot box climate chamber and presents the proposed simplified methodology for determining the thermal properties of windows’ glass units. The accuracy of the composed simplified methods, comparing the calculated thermal transmittances of IGUs with those measured in the “hot box”, were up to 1.25%.

Slow population growth has limited the construction of new schools, leading to the renovation of existing buildings to achieve energy efficiency goals. While improvements are made to thermal insulation, heating and ventilation systems often remain outdated, presenting challenges in maintaining indoor air quality (IAQ) in schools, where children spend a significant amount of time in densely populated classrooms, and whose health is more affected by IAQ than that of adults. Therefore, this study assessed the possibilities to achieve IAQ requirements in schools ventilated by opening the windows by monitoring the carbon dioxide (CO₂) concentration, temperature, and relative humidity (RH) fluctuation. The results of the study have shown that it is not feasible to achieve the defined IAQ parameters in classrooms through window opening alone. The measured CO₂ concentration during lessons in many cases exceeded the limit value of 1000 ppm and did not decrease to ambient levels when the windows were opened during the break. Additionally, the internal air temperature dropped below the normative when lessons started, and RH was significantly below the recommended minimum value on all days. It was also found that the use of thermal energy decreases evenly because of inefficient air change leaving no direct economic leverage for the installation of efficient ventilation systems.

The European Union has adopted legislation aimed to increase the use of renewable energy and improve the effectiveness of conventional-form energy use. Additional structure insulation helps to decrease heat energy loss. Airtightness of the building envelope (building airtightness) is an additional factor that determines comfortable and energy-saving living environment. The conformity of heat energy loss with the object’s design energy class is one of the mandatory indicators used in the obligatory building energy performance certification procedure. Optionally, the objects to be certified are the entire buildings or separate units (flats). There is an issue of concern whether a flat assessed as a separate housing unit would meet the requirements of design energy class depending on the location of the unit in the building. The study is aimed to determine the change in heat loss of end units in terraced houses (townhouses) as a result of various factors, leading to uneven airtightness of the building envelope. The non-destructive assessment of building airtightness was implemented through the combined use of methods, namely Blower Door Test (around 200 measurements) and Infrared Thermography. The hollow clay unit masonry showed ca. 7–11% less airtightness than the sand–lime block masonry structure. The end units were up to 20% less airtight compared to the inside units.

The paper considers the velocities of air movement in the ventilated air gaps of walls and focuses on pressure fields in both wall models arranged in a climatic chamber and exploited houses. The article investigates the influence of air movement on heat transfer through walls applying numerical modelling methods and conducting experiments in the climatic chamber. The thermal effects of air flows have been described with reference to the Nusselt number defined as the ratio of average convective and conductive heat fluxes and heat flux through still air