The overheating risk in apartments retrofitted to energy efficient standards has been identified by previous studies as one that is particularly high. With climate change and rising mean temperatures this is a growing concern. There is a need to understand the kinds of practices,
This article analyses the connection of the two types of floors on the ground (floors on joists and self-supporting floors), with the external wall made of a hemp–lime composite for the occurrence of thermal bridges. Several factors that may affect the heat transfer in the junction were taken into account: the level of the floor on the ground, the wall thickness, the thermal conductivity of the composite, and the location of the timber frame construction. The technology of using hemp and lime is relatively new, and there is a lack of such analyses in the literature. The two-dimensional (2D) heat-transfer in the described construction joints was analyzed based on the finite-element method with the use of the THERM 7.4 software. The results were presented as averaged and linear thermal transmittance coefficients dependent on the above mentioned factors. The possibility of surface condensation was also checked. The differences in the values of the thermal transmittance of the junction between the two variants of ground floors reached around 0.13%–1.67% and the values of linear thermal transmittance factor reached approximately 2.43%–10.13%. The junctions with the highest floor level showed a decrease in the thermal transmittance value by about 3.00%–5.77% and in the linear thermal transmittance, by about 21.98%–53.83%, compared to the junctions with the lowest floor level. Calculations showed that almost all analyzed junctions are free from surface condensation causing mould growth, because the minimum temperature factors f0.25 were higher than 0.78 (except for junctions with the lowered floor levels). The junction with a floor on the timber joists showed better thermal parameters than the junction with a self-supporting floor in each of the analyzed variants. By increasing the level of floor insulation, it is possible to limit the thermal bridges and improve the thermal properties of the junction.
Thermal bridges increase heat losses in buildings and reduce the temperature of the internal envelope surface, causing moisture condensation and mould growth. This is an important issue for building materials based on organic components such as a hemp-lime composite, as they are particularly susceptible to biological degradation.The hemp-lime composite is used as a filling in timber frame construction. The increased cross-section of wooden elements together with the geometry change in the construction joints can form thermal bridges. The paper presents numerical analyses of temperature distribution in the area of construction elements connections, taking into account several variants of junctions: external walls, corners, and window placement in a wall. The thermal parameters of hemp-lime composites used in the analyses were obtained from the authors’ own research.Despite relatively good insulating properties, timber elements have a noticeable influence on the local increase of the heat transfer in hemp-lime composite structures, forming thermal bridges in the partitions themselves and in the construction nodes. However, the linear thermal transmittance coefficients in the presented joints were not very significant (in the range of 0.026 ÷ 0.092 W/(m·K) depending on the type of connection), proving the usefulness of this type of construction in energy-efficient buildings.
The paper discusses the possibilities of using passive greenhouse systems, such as glazed balconies, in an example residential building. The analyses were carried out for five localities in Poland, different in terms of external air temperature and insolation. Typical meteorological years were used as the source of climatic data needed in calculations. Two types of balcony’s casing were evaluated, with high and low thermal insulating properties. Demand for heating and cooling in a flat was determined with the use of dynamic computer simulations, and the outcomes were compared with the energy performance of a flat with an open balcony. Additionally, the number of hours with the internal operative temperature exceeding 26℃ was taken as a measure of overheating the apartment when natural airing by opening windows was included in simulations. The calculations showed diversification in the effectiveness of greenhouse systems resulting from climatic conditions, and allowed areas which are the most suitable for the passive use of solar radiation to be identified. Practical application: Analyses present energy savings in a typical dwelling achieved thanks to glazed balconies, and allow to choose the most efficient type of balcony’s envelope taking into account the heating and cooling demand, and the risk of overheating. The results are diversified in respect of building’s location, showing the areas of Poland where the passive use of solar energy would be most beneficial. The calculations may become the basis for further economical evaluation of greenhouse systems effectiveness.
A typical meteorological year (TMY) for Poland was developed in 2004, on the basis of climatic data collected from 1971 to 2000. Due to the observed tendency of global warming, the buildings’ energy performance obtained with the use of TMY may differ from the actual heating and cooling demand. This research compares energy demand calculated using TMY and climatic data collected from 2001 to 2012. Calculations were made by means of a simulation computer program, designed for dynamic analyses of buildings and installation systems. The analyses concerned typical living quarters in a multifamily residential building located in Warsaw. According to the results, TMY is useful for estimating the heating demand of existing buildings. Cooling demand calculated with the use of TMY was, however, up to 37% lower in comparison with the mean cooling demand for subsequent years. This may distort the energy needs and indoor environment conditions in summer, and create discomfort while using existing and new buildings. Practical application: The paper presents comparison between energy demand calculated with the use of typical meteorological year (TMY) based on the climatic data from the period of 1971 to 2000, and real climatic data from subsequent 12 years, 2001–2012. There is substantial difference in the results presenting cooling demand in buildings evaluated with the use of both datasets. Unless national energy certification procedures are updated, this may cause serious faults in building design, due to incorrect assessment of internal conditions in new and existing buildings, and higher than expected energy use in summer.
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