BuildTog Bremen-Findorff

Summary of the 1st Interim Report 2018/2019


No further CO2 emissions

Since the Paris Climate Conference in 2015 it was clear that the consequences of climate change will stay within a "tolerable" range (1.5 to 2.0 degrees of global warming) if global CO2 emissions are reduced down to almost 0 within the next 30 years. A maximum of overall 600 to 800 Gt CO2 is possible to be emitted during this period. As result of largely undecided action, only 20 years are left now. The necessary fundamental change in global energy supply can only be achieved if energy consumption will drastically be reduced and if the remaining energy demand will meet from renewable sources.

Fig. 1 Paris Climate Conference*

25% of final energy for space heating

Around the year 2010, approximately 25% of the final energy (amount of energy purchased) in Germany was used to generate space heating. Because the legal regulations for heat requirements of buildings had initially developed slowly since the 1970s, the share of heat in total energy consumption was even higher before. Prior to the turn of the millennium, heating was essentially based on fossil fuels such as coal, oil or gas, which had contributed significantly to the high CO2 emissions.

CO2-neutral operation of Passive Houses

The heat demand requirement of 15 kWh/m2a for Passive Houses is much less than 10% of heat consumption in buildings constructed before the first German energy saving legislation in 1977 (1. WSVo). Necessary demand is reduced so far that the required heat can be generated close to the building without recourse to fossil fuels. The total energy consumption including hot water and household electricity has been reduced since then from over 350 kWh/m2a to around 60 kWh/m2a. The manageable electricity demand is possible to be covered completely by renewable sources. Passive Houses are easily to be operated in a CO2-neutral way. The building concept was mainly developed in Germany since the 1990s and is meanwhile adapted to many countries worldwide. It is a key element in achieving the Paris climate targets by avoiding CO2 emissions.

Thermal economy: Minimize losses and maximize gains

The functional principle of the Passive House is based on controlled heat management. The above-average interior comfort is maintained throughout the year by avoiding losses and benefiting from gains with as little energy input as possible. The components (floor, walls, roof) are very well insulated and airtightly joined together, avoiding thermal bridges. The windows, too, with their high-quality frames and triple glazing, are of a quality corresponding to the rest of the building envelope. A ventilation system ensures controlled room ventilation and allows fresh air to be filtered. By means of a heat exchanger, up to 90% of the heat (cold) from the exhaust air can be retained during the ventilation process. The movable sun protection regulates the use of solar radiation: In winter, the slats of the blinds are open and the solar heat, together with the internal gains from the waste heat from technical equipment and the heat radiation from the users, contributes up to half of the necessary heating energy. In summer, the direct incidence of light is prevented to avoid overheating of the interior. The necessary temperature compensation is so low that it can be provided by the ventilation system that is available anyway and no further active heating or cooling system is required. Usually the heat (cold) is provided by a heat pump. This simple technical system thus almost compensates for the higher investment costs for the building envelope in countries with high thermal insulation requirements, such as Germany.

Building Together

In 2008, representatives of the network of housing associations "Eurhonet" from five European countries (Sweden, England, France, Germany, Italy) founded the "BuildTog" (Building Together) working group to be prepared at an early stage for the EU's requirements for CO2-neutral buildings from 2020 on, which were already in place at that time. With the support of the renowned Parisian architect Nicolas Michelin (ANMA) and BASF's own experts for sustainable construction, they developed the typology of an apartment building, which was then adapted to 10 sites in cooperation with local planners. In the meantime, 8 buildings with more than 120 apartments have been realized and most of them have been certified as Passive Houses. Gewoba has also built a BuildTog Passive House in Bremen-Findorff and is now evaluating the operation of the building within the framework of a 3-year monitoring, with scientific support from the Passivhaus Institut in Darmstadt. The central promises of the Passive House concept are being investigated, namely maximum interior comfort with minimum energy consumption and the satisfaction of the users with their new living situation.

Fig. 2 BuildTog Passive House in Bremen-Findorff, south facade

Outdoor temperatures 2 to 3 degrees above the long-term average

The first monitoring results for the period between June 2018 and May 2019 are already available. Outdoor temperatures fluctuated between 21.7°C on average in the warmest month of July 2018 and 3.6°C on average in the coldest month of January 2019. Extreme daily averages were each about 6°C above or below the average. It is worth noting that summer was more than 2 degrees warmer than the hottest months of the last 50 years, averaging 19.6°C in July. The winter temperatures were even 3 degrees above the average of the otherwise coldest month of January, which is about 0.7 degrees. The annual average temperature was 12.4°C instead of only 10.0°C. This corresponds to climatic conditions that we had previously known from the north-western Balkans.

Fig. 3 Range of temperature curves in the observation period, inside and outside

Individually adjustable, pleasant room temperature

Even if a room temperature of 20°C would be sufficient in the Passive House in winter due to its homogeneously warm surfaces, the average internal temperature across all 16 apartments was a comfortable 21°C from November to April, in line with individual user requirements. 75% of the residential units were slightly above or below this temperature within a range of +/- 1 degree. The remaining 25% deviated only a maximum of +/- 2 degrees from the average. In summer, the spectrum of measured room temperatures was, apart from a few outliers, altogether closer together and fluctuated around the average value with +/- 1 degree. Corresponding to the outside temperature in summer, it was between approx. 21 and 25°C. It is noticeable that in hot periods at the end of July / beginning of August the mean outside temperature of approx. 27°C was for some time even significantly above the indoor temperature. The temperature spread in the rooms is not related to the location or technical equipment of the apartments. It is solely dependent on the needs and behavior of the users. The room temperature of most apartments was close to the average value. Only a few were responsible for defining the upper and lower edges of the curve.

20% below average heating requirement

Due to the introduction and tightening of energy-saving legislation, the average heating requirement of new buildings has fallen from over 200 kWh/m2a to a good 60 kWh/m2a since the 1970s. The design for Passive Houses is based on a heating (cooling) demand of 15 kWh/m2a or a heating (cooling) load of 10 W/m2. The BuildTog Passive House in Bremen-Findorff required an average of 11.9 kWh/m2a for heating in the first year of monitoring for all 16 apartments and thus remained one fifth below expectations. The lower value also corresponds to the milder winter. The spread in heating consumption appears to be mathematically quite large. It ranges between 5 and 50 kWh/m2a, which corresponds to a value of less than one third to three times the value. 6 apartments do not even need half of the calculated heat, only 2 more than double. The heat requirement of every second dwelling corresponds approximately to the average value. Here too, as with all other energy efficiency standards, user behavior alone has influenced the final energy consumption. The result is not surprising and corresponds to the positive picture from many other documented Passive House projects.

Fig. 4 Comparison of heating requirements of existing buildings to date with heat consumption per unit

80% of surveyed users on average satisfied (very or rather)

10 out of 16 tenants took part in a user survey. Although with clearly more than half of them the Passive House did not have a special value before 90% are content with it, very (50%) or rather content (40%), as many with the ventilation system (30%, 60%) and even 100% with their dwelling (60%, 40%). With exception of one tenant, all others found the humidity in winter to be pleasant (40%) or rather pleasant (50%), were satisfied with the air quality (40%), rather satisfied (30%) or partly (20%), as well as with the indoor climate (20%, 50%, 20%) and the heating (70%, 10%, 10%). In the summer, everyone felt largely comfortable, was satisfied with the indoor climate (20%), rather satisfied (70%) or partly (10%), used indoor and outdoor blinds (40%), only outdoor blinds (50%) or only indoor blinds (10%) and were satisfied with the air quality (10%), rather satisfied (70%) or partly (20%). With the handling of the existing technology 90% got along, with the heating system 40% good and 50% rather good, with the ventilation system 30% good and 60% rather good. 70% were satisfied with the water heating system and 30% partly, the ventilation system found 30% also effective against odors, 20% rather effective and 40% partly.

Fig. 5 Representation of user satisfaction with the Passive House comfort

Passive House as indispensable contribution to CO2 avoidance

A clear majority of users are obviously satisfied with the Passive House and get along well with the technology offered. The room temperature can be influenced individually at will and the heating consumption is on average below the forecasts. Clear advantages seem to be offered by summer thermal insulation, which even allows significantly lower indoor temperatures during heat waves. In view of the increasing global warming, the Passive House can therefore react in a variety of ways to changing boundary conditions and, as promised, create a significantly better indoor climate with minimal energy input. In conjunction with the use of renewable energies, which is easily possible today, the Passive House can be operated CO2-neutral. The manageable additional costs are clearly outweighed when the entire life cycle is considered in operation. If implemented on a large scale, the experience gained from the BuildTog project can help to reduce global CO2 emissions to a minimum in the foreseeable future. Numerous projects have already demonstrated that the Passive House standard can often also be implemented during refurbishment of existing buildings. Together with a decentralized energy supply based on renewable energies, entire neighborhoods consisting of existing and new buildings can be operated in a CO2-neutral manner and can make their contribution to meeting the Paris Climate Agreement.

Dramatic Climate Shift

Within the range of the evaluation of the Passive House there are no surprises related to the positive results. The most conspicuous findings can be seen in the weather records. As in the yearly process clearly more than 2 degrees higher temperatures in the comparison to the average of the last 50 years show up, the warming with 3 degrees in the coldest month affects itself more strongly than with 2 degrees in the warmest. Global warming therefore means, at least in the measured period at the Bremen location, not simply a little more pleasant warmth evenly distributed over the year, but a dramatic intensification of the extremes. The weather conditions are completely realigning themselves, which leads not to global warming only but also to a shift in climate. And this may be the far greater challenges posed by climate change.



*Source Fig. 1: Stefan Rahmstorf, Creative Commons BY-SA 4.0.