Hybrid ventilation – the ventilation concept in the future school buildings?

Hybrid ventilation (HV), as a combination of automated natural ventilation (NV) and balanced mechanical ventilation (MV), provides opportunities to use the advantages of both ventilation systems during the seasons in order to reduce energy demand and at the same time obtain comfortable indoor climate.
For this study a comparison of NV, MV and HV systems applied to an existing school building has been made by means of detailed modelling in the widely adopted simulation program IESVE. The energy demand for heating and ventilating the building in the different ventilation modes was calculated for three key European cities; Munich, Copenhagen and London. Control strategies were set to obtain the same indoor climate for all ventilation systems, and the indoor climate classification was made according to EN15251 [4].
The overall ambition in the study has been to make a very realistic modelling of state-of-the-art MV and NV systems and apply these systems to an existing school building renovated to fulfill expected energy performance requirements for 2015 buildings.
It is noteworthy that the results show that the energy performance of the MV and NV systems are nearly the same in terms of primary energy, while it is showed that HV enables energy savings of 44-52% compared with MV and NV. This corresponds to a total primary energy consumption for the NV and MV of 18-21 kWh/m² per year in all three locations, while the HV consumption was only 9-10 kWh/m² per year.
Calculation of the total investment of the different systems including maintenance, operation (electricity and heating) and capital cost (products and installation) showed that in the first year MV was found to be 2.5 to 4 times more expensive than NV. By selecting HV 25% of the total investment could be saved compared to a MV system. The differences between the systems were found to be the same in a 20 year timeframe