Nightcooling - Practical Experiences in Offices and the Need for Standard Implementation into Energy Performance Legislation

Night cooling is promoted worldwide as an effective tool to reduce refrigerative cooling demand. However it is clear that, as long as the potential for night cooling is not standardised and integrated into building energy performance calculations, its application will be strongly hampered. In this paper the practical experiences of night cooling in an office located in Belgium are first discussed. This case study shows that, by applying natural stack ventilation combined with different kinds of adjustable solar shading and an exposed concrete ceiling, to provide sufficient thermal mass, a sustainable summer comfort can be provided. On average, the indoor air room temperature passed 26 and 28C, respectively, for 2.5% and 0.7 % of the total yearly office hours (2250 hr). Maximum temperatures of 29 to 30C were only reached during the exceptional heat waves in the summer of 2003 and 2006, when outdoor temperatures were sometimes above 35C. As a consequence of a substantial reduction of air-conditioning and the use of efficient lighting, the electricity consumption in the office was half of that compared with similar offices equipped with full air-conditioning. This paper also reviews some features that are recommended to optimize the control system of night cooling. Secondly, it is found that, of the countries analysed, only in the French energy performance legislation (RT2005) is the effect of a night cooling system taken into account without the need of the principle of equivalence. It was found that night cooling is a proven energy friendly cooling technique. Therefore, the implementation of night cooling into energy performance legislation is discussed.