measurements

In recent years, naturally ventilated glass façades have become a common feature in the design and retrofit of large-scale non-residential buildings, integrating architectural aesthetics and energy efficiency. These façade systems are complex and multifaceted. Thus, introducing them in buildings poses many challenges from economic, engineering, health and behavioural perspectives that can reduce optimal building performance. Building occupant behaviour and preferences are important contributors to the gap between the predicted and actual building energy performance.

The content presented comes from the paper under review “Quantitative correlation between buildings air permeability indicators: statistical analyses of about 500,000 measurements” (Moujalled, 2023a).

With the constant evolution of the French EP-regulations, good building airtightness has become mandatory to reach required energy performance. More than 60,000 airtightness tests are performed each year since 2015. Each measurement performed by a qualified tester must be recorded in a national database that is therefore growing fast (more than half million in 2020).

In Switzerland, 70 % of building refurbishments are realised in stages. When only a window replacement is done, the new airtight windows can lead to a reduced infiltration air exchange and subsequently there may be moisture issues, e.g. mould. The integration of passive window ventilation openings (PWVO) with additional exhaust fans in the kitchen and bathroom(s) can ensure a user-independent basic air change rate. PWVO can be defined as small air inlets integrated in or near the window frame.

The test lecture rooms of KU Leuven Ghent Technology Campus are one the demonstration cases of IEA EBC Annex 62: Ventilative Cooling. This nZEB school building is realised on top of an existing university building and contains 2 large lecture rooms for maximum 80 students with a floor area of 140m² each. An all air system with balanced mechanical ventilation is installed for ventilation, heating and cooling.

This paper summarizes the most recent results of the French database of ductwork airtightness. This database was created in 2016. It is fed through measurements performed by qualified testers according to a national scheme regarding ductwork. Measurements are mainly performed in building applying for the Effinergie + label which requires class A for ductwork airtightness. Therefore, results discuss in this paper only apply to the buildings of the database and cannot be generalized to all new buildings in France.

The French database of building airtightness has been fed by measurement performed by qualified testers since 2006. In 2015 and 2016, the database was enriched by 63,409 and 65,958 measurements respectively, which is 74% more than in 2014, making the total number of measurements about 215,000. However, residential buildings (multi-family and single dwellings) account for almost all of measurements, only 4% of tests are performed in non-residential buildings. Indeed, since 2013 the French EP-regulation requires a limit for airtightness level for all new dwellings.

In France, the current regulation on the energy performance of buildings (RT 2012) does not require ductwork airtightness measurement when the default-value is used in the regulatory EP-calculation. Thus, measurements are only mandated when a specific airtightness level is used in EP-calculations or required by a voluntary certification scheme. In such case, measurements have to be performed according to a national scheme regarding ductwork airtightness measurement.

There are several methods for measuring air tightness that may result in different values and sometimes quite different uncertainties. The two main approaches trade off bias and precision errors and thus result indifferent outcomes for accuracy and repeatability.  To interpret results from the two approaches, various questions need to be addressed, such as the need to measure the flow exponent, the need to make both pressurization and depressurization measurements and the role of wind in determining the accuracy and precision of the results.

Ventilation’s historical goal has been to ensure sufficient air change rates in buildings from a hygienic point of view. Regarding its potential impact on energy consumption, ventilation is being reconsidered today. An important challenge for low energy buildings lies in the need to master airflows through the building envelope. Data collected from controls in 1287 recent dwellings shows us that 68 % of the dwellings don't respect the French airing regulation.