What is the degree of glazing
Avoiding overheating in summer is one of the most important aspects for future building planning. Modern construction methods, such as lightweight construction methods or a high proportion of transparent elements, increase the risk of overheating in hot periods. Global warming is causing these heat spells to be more frequent and intense, and urban areas in particular are affected by aggravating microclimatic impacts known as the Urban Heat Island Effect. The planning of new buildings, building extensions and building renovations therefore requires reliable methods that can be used to determine whether there is a risk of overheating in summer. The present work compares the Austrian normative methods with a common dynamic thermal simulation method. There are significant differences with regard to the resolution of the input and output data, complexity and applicability of the methods. The simplified normative proof is based on elementary calculations with only a few input parameters and is mainly used in the context of the generation of energy certificates for residential buildings. The detailed normative verification already requires more complex input data in somewhat more complex calculations. However, according to the current legal situation, this is not mandatory and is therefore only rarely used, but should also be included in the official building guidelines in the future. The dynamic simulation requires special know-how due to the large number of required input data and possible calculation settings as well as the operation of the special software required for the complex calculation algorithms. This also leads to large differences in terms of the number and resolution of the output data. In order to be able to carry out a practical comparison of the methods as well as an analysis of the results, a case study and a parametric study based on it were carried out. In the case study, four specific designs for an attic extension with residential use in Vienna were evaluated. Critical prerequisites such as low thermal mass and high degree of glazing showed in particular the limits of the normative methods. Among other things, it turned out that rooms that are classified as safe from overheating according to the simplified method, nevertheless have room temperatures beyond the comfort range in detailed calculations and simulations. In the parametric study, 48 different design variants were evaluated using the detailed method and dynamic simulation. On the one hand, it was shown that the results of the two methods largely correlate despite the different resolution. On the other hand, there were deviations due to special design elements or the use of future weather data, both of which can only be taken into account by means of simulation. In general, the results show that avoiding overheating in summer could become much more difficult in the near future and that the current normative methods and criteria for this need to be rigorously developed.
Summer overheating avoidance is considered to become one of the most critical building performance aspects in upcoming years. Design specifications, such as contemporary construction methods, the usage of materials with low thermal mass or a high ratio of transparent elements, increase the tendency of overheating during hot periods. Global warming triggers higher frequency and intensity of those hot periods. In particular, urban areas are affected through microclimatic implications known as Urban Heat Island effect. The planning of new buildings, building extensions, such as rooftop extensions, and building retrofit thus require robust methods that are capable to determine if a building design is in risk of summer overheating. This contribution compares the Austrian normative methods with a common dynamic thermal simulation method. There are major differences regarding the complexity and usability of the methods. The simple normative method is based on elementary calculations with only a limited set of input parameters. It is mainly used in the course of the mandatory energy certification for residential buildings, based on the Austrian building guidelines. The detailed normative method processes more input data and features more advanced calculations. It is not stipulated by building regulations and therefore it is rarely used. However, future changes in the regulations intend to incorporate this method into the official building guidelines. Dynamic simulation requires special know-how due to the variety of possible input data and the operation of the specialized software tools to be able to utilize these powerful but complex calculation algorithms. This also leads to major differences regarding the resolution and appearance of the output data. As such, a direct comparison of results from the different methods is not possible. For the practical comparison of the methods and the analysis of their outputs a case study and a parametric study have been conducted. The case study evaluated four specific designs of a roof top extension for residential use in Vienna. Critical preconditions such as low thermal mass and high glazing ratio particularly illustrated the limitations of the normative methods. Some results even suggest that simple normative calculations would specify specific rooms as safe against overheating, while the more advanced normative procedures and the thermal simulation point towards overheating tendencies. The parametric study evaluated a set of 48 design variants with the detailed method and the dynamic simulation. Despite their different resolution, the results of the two methods showed mainly correlation regarding overheating evaluation. Moreover, occurring divergences due to special design elements or the use of future weather data for the simulation were analyzed. Generally, the results show that the avoidance of overheating will become more challenging in close future. As such an update of the normative methods and the used key performance indicators is highly recommended.
Summer overheating; normative procedures; thermal building performance simulation; parametric study; key performance indicators
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