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Energy-optimal ventilation strategy outside of the operating time for passive house office buildings in cold climates

Per M Holth, Mads Mysen, Axel Cablè, Kari Thunshelle , 2014
thermal inertia | cold climate | heating by ventilation | office building | low heat demand
Bibliographic info: 35th AIVC Conference " Ventilation and airtightness in transforming the building stock to high performance", Poznań, Poland, 24-25 September 2014
Languages: English

The GK environmental house is the first office building in Norway built according to the passive house concept. In such buildings, it is crucial to develop a ventilation strategy to reduce the energy use outside of the operating time. An optimal operating strategy has been developed for cold days, when the outdoor temperature falls well below 0 °C, which is presented in this paper. Indeed, these conditions correspond to the largest heat loss.

The building is mainly heated with warm air supplied through the ventilation systems, with power poles down in each area for peak load. The air handling units(AHU) can be turned into a recirculation of the indoor air mode by night, when there is no need for fresh air since there are no person presents. Data from the active supply air diffusers and AHU’s are logged in a central control and monitoring system.

The approach followed in this paper, was to develop different models for running the AHU by night in the building. Energy consumption for the AHU are then downloaded from the central control and monitoring system after each test. Tests at Environmental house GK is then used as foundation for verifying calculations, by comparing the logged data and calculations.

Room temperature data from the supply air diffusers, were used to calculate the building time constant. The latter describes the thermal inertia of the building, and represents the relationship between the heat storage and heat loss capacity. The NS 3031 standard (“Calculation of energy performance of buildings – Method and data”) was used as a foundation to create a dynamic model for the building. This model enabled to see the temperature development in the building and find the time constant corresponding to the measurements.

The tests are showing that turning the AHUs in recycling mode by night, enables to easily maintain the temperature throughout the night and also save energy. The results show that the studied building with very low heating demand has a long time constant compared with conventional buildings. Therefore, even for low outside temperatures, the drop in inside temperatures is slow. This makes it possible for intermittent operation without compensating for the heat loss in the off mode.

The developed strategy provides a good example of how to reduce the energy use in in office buildings with very low heating demand in a cold climate.

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