decay method

The COVID-19 pandemic has raised concerns about indoor ventilation conditions worldwide. Monitoring CO2 concentrations in rooms has been widely used, but its relationship with outdoor air ventilation rates and ventilation performance is uncertain. Several uncertainties must be quantified, including the location and rate of CO2 sources, sensor locations, and the dynamics of the surroundings, as well as limitations of existing simulation models, such as well-mixing assumptions.

By 2050, the European council proposed to achieve total decarbonization in buildings. In this way, building energy models are key factors to predict the energy consumption in the design, use and retrofit stages. However, these models may present a relevant gap between predicted and measured energy performance, which should be minimised by cutting uncertainties with real data. Air leakage is one of the main uncertainties and causes of increasing building loads by renovating the indoor air in an uncontrolled way.

The air renovation of a building should be controlled in order to ensure a proper level of indoor air quality while minimize heat losses. It is a crucial point for the future energy efficiency goals. However, air infiltration rate in buildings is a complex parameter which is influenced by several boundary conditions. Although a detailed dynamic analysis could be used to properly characterize the phenomenon, estimated values can be obtained from experimental methods, as Blower Door test and gas concentration-based approaches.

Air change rate is often used as an important characteristic of indoor environmental quality, which significantly impacts human health. However, easy, effective, real-time and low-cost air change rate measurements in naturally ventilated resident buildings are still a huge challenge. This paper presents a method based on the release of a stable rate of the tracer gas CO2 given off by solid CO2 (dry ice) in an insulated box.  In theory, the dry ice will sublime at a constant rate as long as there is sufficient dry ice in the box.