A. Wagner, Building Physics and Technical Building Services, University of Karlsruhe; S. Herkel, Fraunhofer ISE, Freiburg; G. Lohnert, sol id ar Planungswerk — statt, Berlin; K. Voss, Building Physics and Technical Building Services, University of Wuppertal.

Within the funding programme1 "Solar optimised building — SolarBau" projects of commercial buildings are subsidised, if the predicted primary energy de­mand for all technical building services does not exceed 100 kWh m-2a-1. Main objective of the demonstration buildings is the combination of high workspace quality with a low energy consumption. An accompanying research programme is evaluating the buildings with a two-year data acquisition campaign. The pa­per summarises some of the results and experiences.

Towards lean building concepts

In contrast to the established low energy and passive house standards in the sector of domestic dwellings there is only little consciousness of the energy consumption of commercial buildings — neither by their planners nor by owners and users. Numerous office buildings of the eighties and nineties show a very high energy consumption due to the fact that they have been designed without any respect to the interdepend­ence between outdoor and indoor climate. As a result the thermal and visual comfort in office rooms can only be guaranteed by extensive technical building services for heating, ventilation, air-conditioning and lighting (HVACL). High investment costs and a space demand of about 20 — 30 % of the building volume for HVACL equipment characterise a large amount of commercial buildings. The electricity consumption is dominated by HVACL facilities and not by office equipment.

Despite internal heat gains caused by the electric energy consumption, there is still a high demand of heating energy due to the high proportion of glazing and high air ex-

German Ministry for Economy and Labour / Deutsches Bundesministerium fur Wirtschaft und Arbeit

change rates. The left graph in figure 1 qualitatively shows the energy consumption of a normal office building as a function of the ambient temperature. The base load is caused by office equipment and the idling consumption of building services facilities. The waste heat associated with this base load affects the position of the balance temperature.

Figure 1: Qualitative end energy consumption of a conventional office building (left) and a lean office building (right). The dependence of the total consumption (HVACL and office equipment) on the ambient temperature is shown based on daily average values.

A higher common consciousness of resources, an increasing awareness of operation costs of buildings and the preference of users towards individual control of the indoor climate have led to a new trend in architecture: buildings with moderately glazed fa­cades, a high amount of daylight at the workspaces and the option of natural ventila­tion through windows that can be opened. However, a combination of integrated measures for "passive cooling" is a pre-requisite to ensure summer comfort without actively cooling or dehumidifying the inlet air.

Due to the reduced HVAC equipment these "lean" building concepts show a different performance (figure 1, right graph). Energy efficient office equipment, lower air change rates and a higher daylight autonomy reduce the base load and better insula­tion results in a lower balance temperature. Above this temperature the indoor condi­tions remain within the comfort range only by passive cooling measures. Although the indoor climate will vary more than in a completely air-conditioned building, this does not necessarily affect the perceived comfort negatively. Only extreme outdoor condi­tions may lead to short periods of discomfort.