Project management BBR:
Horst-Peter Schettler-Köhler horst.schettler@bbr.bund.de ,
Hans-Peter Lawrenz hans-peter.lawrenz@bbr.bund.de

Abstract

Energy saving versus summer thermal comfort? - A series of German verdicts concerning inadequate summer thermal comfort in commercial buildings has raised serious questions concerning the existing national building code's, claim to thermal comfort and sustainable building design. In this context the German Federal Office of Building and Regional Planning placed a contract to a working group of the University of Wuppertal and the Fraunhofer Institute for Solar Energy Systems to investigate the framework, the legal situation, the physical possibilities and economic aspects.

The study undertaken is based on a) a detailed analysis of the operative temperatures, mainly measured in a number of new, energy efficient office buildings applying various measures of passive cooling and b) dynamic building simulations.

To express the comfort expectations a set of national, European and international comfort standards were applied to the measured data and simulation results. This includes the new approaches with the definition of comfort classes as included in the draft prEN15251, the Dutch ISSO-74 and the ASHRAE-55.

Both, the measured data and simulations results underline, that the application of passive cooling measures such as efficient solar shading devices, solar control glass, activated thermal mass, night ventilation, earth-to-air heat exchanger, etc. result in suitable operative temperatures under a normal German summer climate. Taking the extreme summer conditions of 2003 as characteristic for a global warming scenario, comparable comfort can not be ensured: Rising ambient temperatures decrease the cooling potential of night ventilation, longer hot periods exceed the building's thermal storage capacity. Based on simulations it was found, that the demands set by the current German building code DIN 4108-2 do not ensure thermal comfort in free running indoor environments as generally expected by tenants, even in normal summers. Therefore modifications are required.

Economic considerations underline that highly selective solar control glass is the favourable measure to increase the summer thermal comfort and the robustness of buildings concerning user behaviour. The economy of heat extraction by night ventilation profits from the trend to install mechanical ventilation systems due to hygienic considerations in buildings with air tight envelopes.

The abstract is part of the German publication "Energieeinsparung contra Behaglichkeit?",
Forschungen 121, Ed.: BMVBS/BBR, Bonn 2007
ISBN 978-3-87994-453-8, urn:nbn:de:9300-FO12107229
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