Numerical Analysis of Hybrid Ventilation Performance Depending on Climate Characteristics

This study, which formed part of the Annex 35 Hybrid Ventilation in New and Retrofitted Office Buildings project, was completed at LEPTAB and supported by the French Research Ministry and the ADEME (Agence De lEnvironnement et de la Matrise de lEnergie). It consisted of modelling a typical classroom and comparing different control strategies to estimate the performance of a hybrid ventilation system for different climates. The intention was that investigated classrooms were assumed to be on the middle level of a three-storey building, oriented South and surrounded by other classrooms subjected to the same conditions. Two mechanical ventilation systems were taken as references. These were : a mechanical exhaust system with a low consumption fan and without heat recovery, and a balanced mechanical ventilation system with two fans and some heat recovery. The hybrid ventilation approach investigated was a fan assisted natural ventilation system incorporating a demand control strategy based on indoor air temperature and CO2 concentration. The performance of this hybrid ventilation system was analysed in terms of energy consumption, indoor air and dry resultant temperatures, and CO2 concentration level. Simulations of specific weeks in the year were performed for ten French cities and gave quite detailed patterns of behaviour. The study was extended to include yearly mean values of energy consumption. The results for both short and long time periods showed the potential of this specific hybrid ventilation system according to climate and control strategy. Hybrid ventilation is shown to provide improved air quality. Also, in relation to delivered energy, energy savings are possible but, except for Mediterranean cities, are not as much as with a mechanical system with heat recovery.