An extensive sensitivity study explores the various possible configurations described further up (5760 combinations), as well as some alternatives with non-efficient solar protections. They are

analyzed by way of classified illustrative tables (not presented here), in terms of overheating

duration and peak temperature (free-floating case) as well as in terms of auxiliary thermal cooling

energy and peak load (back up cooling at 26.5°C). Synthetic conclusions are as follows:

• It is shown once again that in terms of energy efficiency, good solar protections is the fundamental measure for reaching of acceptable summer comfort or for reducing of cooling energy. In comparison, all the other building parameters (thermal mass, insulation, orientation) are of secondary importance.

• That being, it is easier to obtain a good summer comfort with a well insulated building. In other words, and contrary to a hasty judgment, there is total compatibility between the winter and summer objectives. That is the case because for a comfortable administrative building, the internal temperature during occupation is lower than the outside temperature, the effect of insulation turning out to be positive. This can in principle be extended to residential buildings, insofar as when at night the differential is reversed, opening of the windows allows for adequate heat exchange.

• Internal loads also play a central role and have to be kept as low as possible. In this respect, the study on the other hand did not approach the effect of management by the occupants of opening, blinds, lighting and other apparatuses, management which was supposed to be correct.

• At climatic level, significantly different results are obtained for an urban or a rural site, or for a normal or an extreme summer (of type 2003).

• For a normal summer, a rural site, a building with efficient solar protection and modest internal loads (10 W/m2), a good comfort can be guaranteed by simple night ventilation, with an air flow equivalent to the minimal hygienic rate (1.3 ach). In all the other cases, guaranteeing of the comfort (less than 100 h above 26.5°C) without auxiliary cooling is only possible with passively cooled air and higher ventilation rates.

• In this respect, evaporative cooling not only brings about the highest potential, but also the best stability in respect to summer conditions of type 2003. The effective water consumption for evaporation (in most cases less than 50 liter/m2 per summer) remains sufficiently weak not to be a concern. Not tackled in this study, the question of hygiene and moisture however should be addressed carefully.

• As an upstream complement to evaporative cooling, but in some cases also as an alternative, day/night storage systems (buried pipes or phase-shifting) often make it possible to gain to gain 1-2 additional degrees on the peak summer temperature, respectively to harvest the few tens of hours of comfort that are missing, this even for an extreme summer. Such is particularly the case when these storage systems are set up in alternate mode with direct night ventilation.

• For an 8-18 h occupation, the storage system providing with the best result clearly is the 8 h phase-shifting device. That being, the choice between a buried pipe system or a phase-shifting device will also depend on other than thermal questions: available space, intervention possibilities, costs, maturity of technologies, electric consumption, etc.

• In all the cases, the question of increased airflow requires a detailed attention regarding charge losses and electric consumption, which was not tackled in this study. In this respect, air distribution in the building usually plays a more important role than the proper storage device.

• In the case of high internal gains (>30 W/m2), auxiliary cooling turns out necessary. Implementation of above strategies then allows for considerable reduction in cooling energy, and to a lesser extent to peak power. In several cases the cooling system (especially distribution and emission) could be simpler and of less expensive than with traditional stand-alone air­conditioning, possibly allowing for moderate temperature sources, available in the environment (lake, ground).

References

[1] Ineichen P. (2006) M-ete-O, donnees climatiques estivales dans la region genevoise, valeurs moyennes et extremes. Geneve, CUEPE, Universite de Geneve (Rapports de recherche du CUEPE n° 7).

http://www. unige. ch/cuepe/html/biblio/detail. php? id=387

[2] Hollmuller P. (2002) Utilisation des echangeurs air/sol pour le chauffage et le rafraichissement des batiments : mesures in situ, modelisation analytique, simulation numerique et analyse systemique.

Geneve, Universite de Geneve, Faculte des Sciences (These, Section de physique et Centre universitaire d’etude des problemes de l’energie).

http://www. unige. ch/cuepe/html/biblio/detail. php? id=$179

[3] Hollmuller P., Lachal B. (2008) Air-soil heat exchangers for heating and cooling : dimensioning guidelines, in: Eurosun 2008, 1st Internationla Conference on Solar Heating, Cooling and Buildings, Lisbon, 7-10 October 2008. Publication prochaine.

[4] Hollmuller P. (2003) Analytical characterisation of amplitude-dampening and phase-shifting in air/soil heat-exchangers. International Journal of Heat and Mass Transfer, vol. 46, p. 4303-4317.

[5] Hollmuller P., Lachal B., Zgraggen J. M. (2006) A new ventilation and thermal storage technique for passive cooling of buildings: thermal phase-shifting, in : PLEA 2006, 23rd Conference on Passive and Low Energy Architecture, 6-8 September 2006, Geneva, Switzerland, Universite de Geneve, Vol. 1, p. 541-546.

http://www. unige. ch/cuepe/html/biblio/detail. php? id=397

[6] SIA (2007) Norme SIA 382/1 — Installations de ventilation et de climatisation — Bases generales et performances requises, Zurich, Societe suisse des ingenieurs et des architectes.

2004 2003

Fig. 1: Dry and wet bulb temperature, dynamic over a hot summer weak.

Buried pipe Thermal phase-shifting

Fig. 2: Thermal storage, dynamic over a summer week (top) and dimensioning data (bottom).

Without evaporative cooling	With evaporative cooling
Fig. 3: Ventilation strategies and building response over a summer week (2004, urban situation).