This thesis focuses on the heat dissipation by night ventilation. However, the whole passive cooling system has to be analysed in order to ascertain the night ventilation efficiency. For this investigation, the realised passive cooling systems are analysed in four low-energy office buildings. Using the wide data pool from a two years’ monitoring, the night ventilation concepts are analysed comparatively. Short-term measurements in each building complement the information and are used for the thermodynamic models.
As the energy demand of new office buildings has been reduced during the last years, there is a rising interest for heating and cooling systems based on renewable sources of energy. While conventional office buildings requires complex technical devices which associate a high energy demand, the reduced energy demand of low-energy office buildings can be supplied mostly by natural heat sources in winter or heat sinks during the summer. Low-energy office buildings can successfully use passive cooling concepts in order to achieve a comfortable indoor climate during the summer, without a high energy demand for air-conditioning. However, not every office building can be passively cooled. Cooling and building concept has to complement one another. Passive cooling concepts for the Mid European summer minimise the solar and internal heat gains and utilise the building’s thermal inertia. The reduced and smoothed heat gains are counterbalanced only by natural heat sinks, i.e. earth-to-air heat exchanger, concrete slab cooling or night ventilation. Different techniques for data analysis are applied to the monitored data. A building simulation provides an explicit thermodynamic model of the building. As the simulation deals with a vast number of input parameters and variables, the determination of separate effects is difficult. A parametric model reduces the influences to a concise number of parameters and variables. Proceeding, the energy balance summarises the results to the bare minimum. However, the energy balance can only be drawn, if all input parameters and influences are known.
The realised passive cooling systems are analysed based on the same thermodynamic model. Besides the separate conclusions from the data evaluation in each building, universal conclusions concerning the night ventilation efficiency are drawn: Night ventilation operates well, if the passive cooling concept is accurately designed and sufficiently operated. However, a passive cooling system cannot ensure that the room temperatures meet the comfort criteria everytime.
This thesis aims to enhance the design and operation of passive cooling concepts. A comprehensive data analysis shows not only the night ventilation potential in realized buildings, but also how design tools should be used in order to accurately design and how to operate the passive cooling concept with night ventilation. The use of statistically distributed input parameters enhance greatly the significance and clarity of simulation results. A precise realisation and an accurately implementation of the concept are essential for the proper operation of night ventilation and the functionality of the passive cooling system.