EDEN - Developement of a structured data and preparation documentation with a minimized error-proneness for energy performance cerificates.
Starting point / motivation
The main target of the herein presented research efforts was approaching/improving the quality of energy certificates for buildings in Austria. A major problem that can be found in everyday practice regarding energy certificates is the lack of reproducibility due to incomplete documentation or erroneous calculation input data assumptions. Energy certificates have a validity of maximum 10 years, and – in Austria – the first ten year period is now coming to an end. For this period a wide range of different styles and manners of issuing certificates by different practitioners can be observed, which results in a severe lack of comparability between different certificates / different buildings. Moreover, the calculation methods have been constantly further developed and changed, so that differences can be caused by the change of method as well. Furthermore, in between close to all buildings require an energy certificate to be issues. A crucial aspect is that subsidies for thermal retrofit and increased thermal quality of new buildings are directly depending on the results of energy certificates, which seems critical, given the deviations in the certification results caused by different input data assumptions, different issuer's approaches and methodologies, and erroneous input data assumptions.
Contents and goals
The main goal of this research work was the development of easy-to-use methods for input data documentation. Such a documentation – given the negligible result differences between different energy certification tools – should ensure an increased reproducibility of the certificates. Given the legal meaning of energy certificates, such documentation could help to reduce uncertainties and increase the quality of certification in general.
The development of the input data documentation was performed based on the following
- Collection of national and international guidelines, laws, and standards, as well as a collection of best and worst practice examples.
- Establishment of a building database encompassing a wide range of different buildings. This database should be used to extract sample buildings for in-depth examination.
- Issuing of energy certificates of the sample buildings, and documentation of experienced input data uncertainties.
- Utilization of scientific methods from mathematics and statistics to assess the impact of input data deviations on the results of energy certificates.
- Derivation of a comprehensive and convenient input data documentation routine, which can be used for generic buildings and their energy certification.
The different parts of the project all were worked on carefully: The collection of sample buildings for a database of buildings, for instance, resulted in 85 buildings (including 149 thermal zones) and their plan documents, input data documentation and (in part) existing energy certificates. Thus it was well suited to act as a base for the derivation of sample buildings which were worked on in detail: Building samples were chosen based on key data of the buildings, such as Usage, Size, Age, and others. 16 buildings were chosen and examined in detail. During the work it turned out that the manual change of input data parameters not only is very time-consuming, but rather error-prone. Therefore, the original conception of the project was extended by a software tool which helped to better understand the dependencies between independent (input) variables and the dependent KPIs (Key performance indicators). For the heating demand ("Heizwärmebedarf") a script was developed in the parametric scripting language grasshopper, which allowed changing several input variables and dynamically seeing the change in the results. In this fashion, the identification if a input variable can be considered as strong or weak regarding the influence on the result was facilitated.
Uncertainties were categorized based on previous experiences, the calculation of sample buildings in the project and a repetitive analysis approach. The uncertainty categorization is illustrated in the Figure (right side). To better assess the uncertainties regarding their impact, methods regularly utilized in other fields of science, such as the elasticity (known from economics) and the ABC-portfolio analysis (which is used in stock broking and production logistics a lot), were adopted and used on the input and output datasets.
Prospects / Suggestions for future research
It is important to reconcile on the background of this research. The European efficiency goals (20 percent reduction of primary energy usage within the EU until 2020) focus – amongst others – on buildings. This resulted in the EU guideline 2012/27/EU. The Austrian national energy efficiency program NEEAP 2014 mentions energy efficiency measure in buildings, especially in deep renovation programs, as of highest strategic importance. Subsidies and incentives toward retrofit are coupled with building energy efficiency calculations. Therefore, the goals and results of the EDEN project can be considered as important for this playing field.
The results do not only encompass a input data documentation approach, but also offer a wide range of improvement ideas and concepts to in future increase both the reliability and comparability of energy certificate calculations for buildings.
Arch. DI Bernhard Sommer, Department of Energy Design - University of Applied Arts Vienna
Project or cooperation partners
Department of building physics and building ecology - TU Vienna