Passive cooling by night ventilation is one of the most promising approaches to reduce cooling energy demand of office buildings in moderate climates. However, the effectiveness of this system depends on many parameters. Some of them are related to characteristics of building (percentage of glass in building envelope, shading devices, accessible thermal mass of partitions, height of building), some to installed ventilation (type of ventilation, cross-section of ducts, location of air intake and exhaust) and finally some are related to use of building (profile of occupation, heat gains form lighting and equipment, required indoor parameters etc.).
The existing case-study buildings with night ventilation indicate that close to optimal performance of night ventilation requires detailed analysis performed at very early design stage when change of some input parameters is still possible. That is typical for concept of integrated design of buildings.
The paper describes simulations of night ventilation for the office building (floor area 3640 m2 for approximately 400 persons) located in Warsaw, Poland. The calculations were performed with utilisation of quite simple but satisfactory accurate method 6R1C that is a modification of simply hourly method described in EN ISO 13790 (Energy performance of buildings - Calculation of energy use for space heating and cooling).
Achieved results confirmed big impact of night ventilation intensity and thermal capacitance of building on energy use in office buildings. Taking into account integrated design of buildings the paper provides also basics of methodology for selection of the optimal level of thermal capacitance and optimal intensity of night ventilation.