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Design of ventilation systems in Belgium is currently based on the Belgian Standard NBN D 50-001:1991. This regulation is more than 25 years old, and is not anymore suited to new technologies developed in the frame of increasing energy performance of buildings and its associated ventilation systems. This standard defines four classic ventilation systems, going from A (natural ventilation) to D (double-flux ventilation eventually with heat recovery). One of its main shortcomings is that it does not consider demand controlled ventilation (DCV) systems. For example, there are no requirement in the current standard on the type of detection appropriate for the living spaces. Carbon dioxide (CO2) is usually considered as a good tracer for human occupation.
This paper presents the experimental and numerical investigation that have been performed in a pre-normative project whose objective is to evaluate the relevance of detection based on humidity for DCV systems in the living spaces.
Experimental measurement have been carried out in 26 dwellings in Belgium during more than 1 year. Temperature, humidity, CO2 concentration have been monitored with a 5 minutes time step in 4 rooms and outside for each building. Measurement also took place in several meeting rooms in office buildings.
The analysis of the data showed no evident link between CO2 concentration, usually considered as reliable indicator of human occupancy, and relative humidity. Same analysis has been performed with absolute variables (volume and mass concentrations). When considering the difference in absolute humidity between inside and outside, correlations are stronger. They are even stronger when looking at time derivatives of humidity and CO2. On basis of this dataset, the direct correlation between CO2 and RH does not seem sufficient to consider it as a relevant detection mean for DCV systems in living spaces. However, the analysis of the variations show that there is clearly a link between the two.
Next to experimental data analysis, DCV strategies have been evaluated through simulation with CONTAM software. The target was to compare RH based detection systems with CO2 detection systems and constant flow systems. Various strategies and control algorithms have been tested. At equivalent air quality, direct control on the RH level does not achieve significant flow reduction compared to a constant flow ventilation. An alternative algorithm based on 24h moving average of RH shows significant flow reduction compared to constant flow or direct RH regulation while keeping high IAQ. This is only a theoretical demonstration, and should be demonstrated and/or fine-tuned in practice.