Hybrid ventilation in new and refurbished school buildings – the future of ventilation

More than 64 million pupils spend more time in school than in any other place except home in Europe (European Commission, 2014). The indoor air quality is often a challenge in existing school buildings and the lack of proper ventilation often leads to negative effects like increased absenteeism and sick building syndrome symptoms as well as lowered performance amongst students compared to new buildings.
For this study a comparison of automated Natural Ventilation (NV), balanced Mechanical Ventilation (MV) with heat recovery and Hybrid Ventilation (HV) with heat recovery has been made by means of detailed modelling applied to an existing school building using the simulation program IESVE. The energy demand for heating and ventilating the building using the three different ventilation methods was calculated for three key European cities; Munich, Copenhagen and London. Control strategies were set to achieve the same indoor climate for all three ventilation systems, and the indoor climate targets were set according to European Standard EN 15251 (EN15251, 2007).
The results show that the energy performance of the MV and NV systems are nearly the same in terms of primary energy, while demonstrating that HV enables energy savings of 44-52%.
Total costs of the different systems including capital expenditure (products and installation), operation (electricity and heating) and maintenance over the first year and a 20 year life cycle were calculated. This showed that in the first year MV was 2.5 to 4 times more expensive than NV. By selecting HV and taking advantage of NV reducing the load on the mechanical ventilation, 25% of the cost could be saved compared to a pure MV system, and this was similar over a 20 year life cycle.