The work reported in this paper extends previous work on the feasibility to characterise air leakage and mechanical ventilation avoiding intrusiveness of traditional measurement techniques. The feasibility to obtain the air renovation rate itself, as well as the possibilities to express it as function of other variables (such as wind speed, atmospheric pressure, etc.), are studied. Tracer gas measurements based on N2O have been used as reference. Experimental relations between air renovations and wind speed, indoor-outdoor air temperature difference, and atmospheric pressure have been analysed. The reliability of an alternative method based on the evolution of metabolic CO2 using wall mounted sensors of CO2 concentration is evaluated. Two full size buildings are considered as case studies. First a very simple single zone building, without mechanical ventilation, is considered. Afterwards, rooms in an office building have been studied with and without mechanical ventilation. One month test campaigns have been used for the reference test campaigns based on tracer gas measurements using N2O, in both buildings. Longer periods are available for the analysis based on CO2 concentration.
The following conclusions are extracted from the tests when mechanical ventilation is not active: Significant correlation between air renovation rate and wind speed has been observed in both buildings. The agreement between the values obtained using N2O and the evolution of metabolic CO2 increases when the starting value of CO2 concentration increases.
The following conclusions are extracted from the tests when mechanical ventilation is active: Large variations have been observed among the different values obtained along the test campaign using N2O tracer gas. However these values don’t show any correlation with any of the considered boundary conditions. Consequently the observed spread has been used to estimate an uncertainty of the air renovations rate. The measurements based on CO2 concentrations don’t show good agreement to the values obtained using N2O tracer gas. This issue will be further investigated, but in principle it is attributed to the low level of CO2 measured along the analysed test campaign when the mechanical ventilation is active. This explanation is in agreement with previous works carried out regarding the air renovation in the same building.