New simulations for energy evaluation

On the way to a climate-neutral building stock

Authors: Andreas Zinner, TH Rosenheim, Dr. Oliver Mayer, Bayern Innovativ GmbH (As of June 2020)

When looking at the historical course of the development of requirements for building efficiency or energy consumption of buildings in Germany, a clear trend of the regulations can be derived. Since the first legal introduction of the first heat protection regulation 1977 as a reaction to the oil crisis at that time these requirements were constantly tightened over the years.

The first heat protection regulation placed also already first requirements to the individual components of the envelope surface. A continuation of this trend at the European level is the introduction of the EPBD Directive (Energy Performance of Buildings Directive) from 2010. This established uniform standards in Europe for the first time. This directive was last amended in 2018. Since around 40 percent of Europe's energy consumption and almost 36 percent of CO2 emissions are currently attributable to the building sector, there is enormous potential for savings here. As a result of the targets of this directive, the regenerative share of energy generation is to be 35% by 2030. By 2050, moreover, a completely climate-neutral building stock is to be achieved.

New law to implement climate targets

This is now to be implemented in Germany with the introduction of the Building Energy Act (GEG). The planned implementation is to combine the existing Energy Saving Ordinance (EnEV), the Energy Saving Act (EnEG) and the Renewable Energies Heat Act (EEWärmeG) into one set of regulations. A concrete tightening of the EnEV does not take place thereby, it is equated the new building standard valid in the EnEV 2016 at present with the requirements for lowest energy buildings ([27], P. 1- 40). In addition the edition of the DIN V 18599:2016-10, which forms the computation basis for the proof guidance of the three current Regularien, valid so far, with a new version from the year 2018 is replaced. This will also be referred to in the upcoming JIT. When comparing the implementation of the EPBD Directive (Energy Performance of Buildings Directive) with other countries in the EU, differences can be identified: In general, EN ISO 13790 is used as the orientation for the calculation basis of all countries, although in Luxembourg DIN V 18599 has recently also become the assessment basis to be used. In Luxembourg and Germany, for example, a reference building with the same cubage and use, but with a specified building services equipment, is used for the energy assessment of a building to determine the permissible limit value. A positive charge by low envelope surfaces to volume ratio or energetically favorable window orientation and size are not considered thereby.

To date calculation procedures to the energy need no longer up-to-date

Before the background of the increasing requirements to the energetic efficiency of buildings (as well as to the comfort within buildings), it was examined whether the conventional calculation procedures in Germany for the determination of the energy need these requirements still become fair, since it concerns thereby procedures, which are partially based on strong simplifications and averages. The useful energy demand of an exemplary building was first determined with transient and stationary boundary conditions within a simulation program. In addition, the energy demand calculation was carried out with the monthly balance method according to DIN V 18599, which is standardized in Germany, and the results were finally compared. The building used in the work is the former library of the municipality of Feldkirchen-Westerham, which is to be extended in the course of a construction project by a connecting corridor to enlarge the library and a residential building with a cafeteria on the first floor. In the course of the preliminary planning for the building project, however, the municipality of Feldkirchen-Westerham expressed doubts about the planned use, which is why the planning and the actual building project were suspended until further notice. Thus, little or hardly any information is available, especially for the technical equipment of the planned building at the preliminary planning stage. The cubature of the building was used nevertheless for the production of this work, since particularly the constellation of the different building parts and their different envelope surface suggested interesting results.

The calculation results of the three variants were compared with each other. In the presentation of the heating and cooling energy demand, the relevant heat sinks, the available heat sources and finally the resulting useful energy demand were first presented. The three usage zones (residential, library, office) were mainly addressed, since they account for the largest share of the usable floor space of the entire model and thus significantly represent the energy demand. In summary, it can be said that the lump-sum or In summary, it can be said that the generalizations or averages, which are necessary for a stationary consideration of the actually dynamic processes in the energy balance of a building, provide comparable results to a transient calculation. Differences arise particularly when considering strongly dynamic influences such as solar irradiation or user-based interactions, which can be clearly better represented in their effects by means of thermal-dynamic building simulation. Consequently, differences arise in the solar heat supply over the heating period, which is why a detailed consideration based on structural shading or radiation data is worthwhile here, especially in the evaluation of regenerative energy generation on a solar basis.

User behavior decisive

In order to be able to consider the quite relevant influence of the user behavior on the energy consumption of buildings correctly, these must be known with sufficient accuracy with both variants. However, both calculation approaches provide the basic possibility to take these into account. A particular advantage of transient considerations lies in the possibility (apart from the purely energetic demand consideration) to make concrete predictions about room climatic parameters in their dynamic nature. Problems differentiated from the energy demand, such as room temperatures in summer or information on the indoor air quality with different ventilation strategies, can thus be solved. Also the evaluation of house-technical equipment or control strategies for the enterprise of these is possible by coupled plant simulation.

An other possibility, in order to be able to examine the correct conversion of further dynamic influences in the beginning of the stationary balance procedure of the DIN V 18599, offers itself for example by Ansetzen of the minimum target temperature after DIN V 18599-10 within the stationary simulation variant. In this way, a comparison of the heat sink or source occurring between the time of use and the time of non-use could be made in the simulation program compared to the empirical approach according to DIN V 18599. The fact that standardization is required for the regulation of the energy consumption of buildings at the state level certainly provides a solid basis for the evaluation and comparability of buildings. On the other hand, exact, dynamic illustrations by simulations are quite possible at the present state of the art. This possibility should, especially in view of the results presented in this study, be included in the development of future evaluation as well as design approaches for building planning.