Evaluation tool of climate potential for ventilative cooling

The new initiatives and regulations towards nearly zero energy buildings forces designers to exploit the cooling potential of the climate to reduce the overheating occurrence and to improve thermal comfort indoors. Climate analysis is particularly useful at early design stages to support decision making towards cost-effective passive cooling solution e.g. ventilative cooling. As buildings with different use patterns, envelope characteristics and internal loads level do not follow equally the external climate condition, the climate analysis cannot abstract from building characteristics and use.
Within IEA Annex 62 project, national experts are working on the development of a climate evaluation tool, which aims at assessing the potential of ventilative cooling by taking into account also building envelope thermal properties, internal gains and ventilation needs.
The analysis is based on a single-zone thermal model applied to user-input climatic data on hourly basis. The tool identifies the percentage of hours when natural ventilation can be exploited to assure minimum air change rates required by state of the art research, standards and regulations and the percentage of hours when direct ventilative cooling is useful to reduce overheating risk and improve thermal comfort. The tool also assesses the night cooling potential and highlights other useful climate performance indicators such as the day-night temperature swing.
Furthermore, the analysis method has also been devised to provide building designers with useful information about the level of ventilation rates needed to offset given rates of internal heat gain.
The paper also presents several analysis performed on a reference room in a case study (Aarhus town hall office in Denmark) in order to validate the analysis method development. Specifically we analysed the influence of using dynamic loads, building thermal mass and ventilation control in the heat transfer model and on the calculation method for the heating balance point temperature of the building.
Finally, the ventilative cooling potential tool outputs are compared with the predictions of a state of the art building performance simulation model of the reference room, highlighting several possible improvements in the evaluation criteria.