BAU-I-3: Cooling degree days

In the three summer climate regions according to DIN 4108-2:2013-02, which is the authoritative standard for summer heat protection of buildings, the number of cooling degree days is increasing thus reflecting a significantly rising trend. Since 1999 the cooling degree days in the three regions have been consistently above the mean of the climate normal period 1961-1990. The requirements made for summer heat protection are increasing throughout Germany.

Cooling degree days

In Germany 2018 was the warmest year since weather recording began, and never before, compared to the nationwide mean were there as many hot days with temperatures of 30 °C and more. The manufacturers of air-conditioning equipment and fans were blessed with a bumper summer in terms of revenues as in many offices and homes, temperatures were clearly beyond the comfort zone.

Heat protection by means of building design is to ensure amongst other things that this type of situation remains the exception to the rule and that the interior climate of buildings remains bearable even when the external summer temperature is high. The Minimum Requirements for Protection from Heat (Mndestanforderungen an den Wärmeschutz) including heat protection in summer are described in the relevant DIN (standard) 4108-2:2013- 02 which bears the same name. In order to meet these minimum requirements at a large scale this DIN standard divides Germany into three summer climate regions, i.e. A, B and C. The summer climate region A comprises the coastal areas of North Sea and Baltic Sea as well as the upland areas of the Alps, i.e. areas which tend to be relatively cool. Summer climate region C comprises areas which tend to be warmer. This includes Lake Constance and the Upper Rhine Graben (rift valley), the Rhine-Neckar and the Rhine-Main areas, the Moselle and the Middle Rhine Valley, the Ruhr Valley and the urban regions of Leipzig/Halle and Dresden. The other regions are comprised in Region B.

These three summer climate regions make up the background for the time series illustrated for cooling degree days which were calculated according to the process developed by Spinoni et al., 2015.³⁹ The evaluation of cooling degree days was used as a basis for estimating the temporal development of cooling requirements or the extent of heat protection required in these regions in summer. The cooling degree days are a (fictional) value; in this case 22 °C, which is calculated by totalling the amount of exceedance per day for all days of the year in a weighted form. The lowest weighting is allocated to days on which the maximum day temperature alone exceeds the threshold. In this case the difference between the maximum day temperature and the threshold value is counted as a quarter. The highest weighting is allocated to days on which the daily minimum temperature lies above the threshold value. In this case the difference between the threshold value and the daily mean temperature is counted. In between are days on which the mean temperature lies above the threshold value. The data for the time series of summer climate region A were provided by the DWD stations Bremerhaven and Stötten in the Swabian Alps. For the summer climate region B the values from the DWD stations Potsdam, Essen and Hamburg- Fuhlsbüttel were used while Region C is represented by the Mannheim station.

Since 1951 all three time series have shown a significantly rising trend. A comparison shows that the cooling degree days in summer climate region C (i.e. the Mannheim station) increase faster than in the two other regions. Notwithstanding the above, a comparison with the climate normal period 1961-1990 shows that the cooling degree days in all three regions were consistently above the mean of the period 1961-1990. This means that the requirements in terms of heat protection are increasing throughout Germany. Judging by current climate projections, this development will continue for the rest of the 21st century.

In the light of this perspective and bearing in mind the necessity to further reduce carbon dioxide emissions also in respect of the building industry, it is imperative for building design circles to keep a constant eye on the increasing requirements of heat protection in the future. However, the DIN standard 4108-2:2013-02 defines only the requirements to be fulfilled by new buildings, building extensions and add-on modules such as conservatories, referring only to the climate prevailing between 1988 and 2017. This standard is currently being enhanced in order to give more adequate consideration to the projected climate warming and associated consequences, for the appropriate adaptation of minimum requirements to heat protection in summer. In the meantime it behoves developers to take adequate precautions and make appropriate provisions that go beyond the minimum requirements laid down in this standard. Starting points are, for instance, the proportion of window space, adequate window tilt and orientation, the type of nocturnal aeration and the use of solar control glass and passive cooling systems. If supported by preventative urban planning and neighbourhood-based planning practices – including the provision of appropriate aeration and adequate green space in cities – the interior climate of buildings is then able to remain in the comfort zone even if temperatures keep rising.

^{39 - Spinoni J., Vogt J., Barbosa P. 2015: European degree-day climatologies and trends for the period 1951–2011.}^{In: International Journal of Climatology 35 (1): 25–36.}^{DOI: 10.1002/joc.3959.}

Interfaces

GE-I-1: Heat exposure and Public awareness

BAU-R-1: Recreation areas

Objectives

Taking into account the adaptation to climate-related changes should be an integral part of planning a building’s design and technical equipment. […] By contrast, it will become essential in building design and technology, especially with regard to attic flats, to make provision for a more distinct adaptation to higher average summer temperatures and occasional longer heat periods. (DAS, ch. 3.2.1)

BAU-I-3: Cooling degree days | Umweltbundesamt