Drøbak Montessori lower secondary school is Norway’s first plus-energy school and also the first school built after the Norwegian Powerhouse-concept, www.powerhouse.no. This concept implies that the building shall produce more renewable energy during the lifetime of the building, than used for materials, production, operation, renovation and demolition.
To achieve the energy ambitions for the project there has been a high focus on obtaining an effective and low-pressure ventilation system. The chosen solution is a concept with relatively tall rooms with displacement ventilation that varies between fully mechanical and hybrid ventilation depending on the time of the year. The extract air is removed from the rooms by overflow to adjacent areas. During summer the exhaust air is directly let out through an opening in the top of the centrally placed atrium. In the heating periods the exhaust air is driven mechanically through the air handling unit for heat recovery.
The school has an all-air HVAC-system where all the heating and cooling demand for the building are covered by the ventilation system, no additional heating sources is installed in the building. Room heating only provided by ventilation is not something new, but is often combined with mixed-flow ventilation. At the Montessori school in Drøbak the heating with ventilation is combined with displacement ventilation. To avoid a short circuiting of the supplied fresh-air when the occupants are present, the air is supplied with a lower temperature than the surrounding air. During night time the system switches to heating mode when necessary, depending on recorded indoor and outdoor temperatures. When in heating mode, the supply air is recirculated and heated to a supply temperature higher than the surroundings. The supply air temperature depends on the outdoor temperature and the airflow is demand-controlled based on temperature and CO2.
To ensure that the chosen solution provides a satisfactory thermal indoor climate and to provide input to the tuning and optimization of the control strategies, simulations with a two-zone model, advanced simulations in IDA-ICE, laboratory tests and field measurements has been performed.
This paper will present the analysis, results and conclusions from the above mentioned two-zone model compared to the results from the field test. The results from the advanced simulation in IDA-ICE and the laboratory tests will not be presented in this paper.
The results from the two-zone model and the field test show promising results when it comes to achieving thermal comfort by using displacement ventilation for heating. The results also shows good consistency between the 2-zone model and the measured data from the field test. This research will provide useful knowledge for future projects when it comes to minimizing the energy use, costs and complexity for HVAC-installations in buildings where displacement ventilation is suitable.