Belgium

Heat recovery ventilation (HRV) is one of the usual techniques (next to demand controlled) to reduce the energy impact of ventilation in buildings. For a given air change rate, the energy savings of HRV are in the first place dependent of the heat-exchanger efficiency, usually measured in standardized laboratory conditions. However, many other factors can have an impact on the overall system performance in practice.

Ventilation systems play an important role in providing a good indoor air quality in dwellings. Mechanical exhaust ventilation systems implement natural vents, also called trickle vents, to supply outdoor air to the dwelling. The airflow through these natural supply vents depends on the natural driving forces, i.e. wind and the stack effect, which vary in time.  

Ventilation is critical in interpreting indoor air quality (IAQ), yet few IAQ assessments report ventilation rates; even when they do, the measurement method is often not fully described. Most ventilation assessments use a tracer gas test (TGT) to measure total air change rate. In a TGT, the indoor air is marked with an easily identifiable gas (tracer) so that the air change rate can be inferred by monitoring the tracer’s injection rate and concentration.

This paper discusses two particular points of the buildings airtightness measurement method (ISO 9972) in relation with the pressure difference: (1) the nature of the pressure tap and (2) the place of the pressure tap outside. 

Uncertainties in airtightness measured using fan pressurization test should not be defined by the scattering of the points around the line defined using ordinary least square method anymore. Its definition requires first to know the uncertainties in pressure and airflow measurements. This works aims at quantifying one of the component of the envelope pressure uncertainty: the uncertainty in zero-flow pressure approximation due to short-term fluctuation of wind speed and direction.

This overview focuses on model based control strategies for ventilation in nearly zero energy buildings (nZEB) where slower reactions towards disturbances are expected as a result of high insulation and air tightness of the building envelope (Killian and Kozek 2016). Furthermore, internal heat gains have a higher impact in these kind of buildings. In addition, occupancy pattern can be variable (e.g. in office- and school buildings) and HVAC control is consequently more challenging.

In school and office buildings, the ventilation system has a large contribution to the total energy use. A control strategy that adjusts the operation to the actual demand can significantly reduce the energy use. This is important in rooms with a highly fluctuating occupancy profile, such as classrooms and open offices. However, a standard rule-based control (RBC) strategy is reactive, making the installation 'lag behind' in relation to the demand. As a result, a good indoor climate is not always guaranteed and the actual energy saving potential is lower than predicted.

From a product point of view, today’s state-of-the-art ventilation boxes for residential buildings are generally reliable, efficient and silent according to formal European and national product standards. Ongoing development projects are focussing on making the products even better, but because of the maturity level of today’s solutions, breakthrough revolutions should not be expected. 

Mixed-mode ventilation uses intelligent switching between natural and (partly) mechanical ventilation modes to find the best possible balance between indoor air quality, user comfort and energy consumption. It applies demand-control at the level of the operating mode depending on the constraints imposed by the building, its users and its surroundings. Although mixed-mode ventilation is said to have the potential to achieve a comfortable and healthy indoor environment while achieving significant energy savings, it is rarely used in practice.

This study is a first large-scale analysis of the performance of a cloud connected and smart residential mechanical extract ventilation (MEV) system based on field data. About 350 units were analysed over a period of 4 months from December 2018 up to March 2019, corresponding with the main winter period in Belgium. Half of the units were installed as a smartzone system which means additional mechanical extraction from habitable rooms as bedrooms.