Because buildings are responsible for 40% of energy use and 36% of Greenhouse Gas (GHG) emissions in the EU, energy efficiency in buildings has become a priority to drastically reduce the energy use in buildings. Consequently, a number of policy measures have been implemented in European Member States to drive the market towards Nearly Zero-Energy Buildings, including the Energy Performance of Buildings Certificates (EPCs), which are the most visible instrument of the Energy Performance of Buildings Directive (EPBD).

There have been many new sensors introduced on the market claiming that they can perform accurate measurements of Indoor Air Quality. Many of them are low-cost sensors that can be applied at the mass scale. The subsequent question is what is and should be considered to be the metric of Indoor Air Quality. No consesus on this matter has yet been achieved. Few metrics have been proposed in the past including most known CO2 and TVOC concentrations but actually only CO2 concentration has been widely used in the applications related to built environment and HVAC.

Building airtightness tests have become very common in several countries, either to comply with minimum requirements of regulations or programmes, or to justify input values in calculation methods. This raises increasing concerns for the reliability of those tests.

There are four key sources of uncertainty in airtightness testing:

The European market for residential ventilation is highly driven by energy performance regulations. In new buildings the share of balanced ventilation with heat recovery is increasing as a result of more severe energy performance requirements (NZEB). The energy labeling for residential ventilation units and the ecodesign requirements for ventilation units may be drivers for a more wide-spread application of heat recovery ventilation in new buildings.