Potential for free-cooling by ventilation Cristian Ghiaus a,b, * ,1 , Francis Allard a a Laboratoire d’Etude des Phenomenes de Transfert Appliques au Batiment (LEPTAB), Universite ´ de La Rochelle, Av. M. Cre ´peau, 17000 La Rochelle, France b Technical University of Civil Engineering, Bd. P. Protopopescu, Bucharest, Romania Received 24 November 2004; received in revised form 31 May 2005; accepted 31 May 2005 Available online 29 September 2005 Abstract Natural ventilation is one of the most effective techniques for cooling. Its potential for cooling may be assessed by using a method based on the indoor–outdoor temperature difference of the free-running building, the adaptive comfort criteria and the outdoor temperature. It is demonstrated that the free-running temperature may be used instead of the balance temperature in energy estimation methods. The indoor–outdoor temperature difference of the free-running building becomes a characteristic of the thermal behavior of the building which is decoupled from comfort range and outdoor tem- perature. A measure related to the energy saved and the applicability of free-cooling is given by the probabilistic distribu- tion of the degree-hours as a function of the outdoor temperature and time. Weather data for this method are available in public domain from satellite investigation. The method can be applied when buildings similar to existing ones are con- structed in a new location, when existing buildings are retrofitted or when completely new buildings are designed. The method may be used to interpret the results of building simulation software or of the field measurements. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Natural ventilation; Energy; Building design; Free-running temperature 1. Introduction The most important decisions that affect the ther- mal performance of buildings are taken in the initial stages of design (Holm, 1993; de Wilde et al., 2002). Design evaluation may be supported by the results of building simulation, by simplified guidelines or by expert advice based on experience (deWit and Augenbroe, 2002). Building simulation programs are based on first principles and require as inputs the geometry of the building, the comfort criteria and even the specification of the HVAC technology. These prerequisites make simulation more adapted for evaluations in the final stages of design rather than a support for decisions when the building is sketched (Clarke, 1985; Shaviv, 1998; Al-Homoud, 2000; Hong et al., 2000; Olsen and Chen, 2003; Clarke et al., 2004). In the initial design, the archi- tects have many important issues on which the pro- ject is evaluated and investing more in thermal design would make them less competitive. The ther- mal analysis is done usually by engineers after the 0038-092X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2005.05.019 * Corresponding author. Address: Laboratoire dÕEtude des Phenomenes de Transfert Appliques au Batiment (LEPTAB), Universite ´ de La Rochelle, Av. M. Cre ´peau, 17000 La Rochelle, France. Tel.: +33 5 4645 7259; fax: +33 5 4645 8241. E-mail address: cristian.ghiaus@univ-lr.fr (C. Ghiaus). 1 ISES Member. Solar Energy 80 (2006) 402–413 www.elsevier.com/locate/solener