Air exchange rates from atmospheric CO2 daily cycle

Abstract

We propose a new approach for measuring ventilation air exchange rates (AERs). The method belongs to the class of tracer gas techniques, but is formulated in the light of systems theory and signal processing. Unlike conventional CO2 based methods that assume the outdoor ambient CO2 concentration is constant, the proposed method recognizes that photosynthesis and respiration cycle of plants and processes associated with fuel combustion produce daily, quasi-periodic, variations in the ambient CO2 concentrations. These daily variations, which are within the detection range of existing monitoring equipment, are utilized for estimating ventilation rates without the need of a source of CO2 in the building. Using a naturally-ventilated residential apartment, AERs obtained using the new method compared favorably (within 10%) to those obtained using the conventional CO2 decay fitting technique. The new method has the advantages that no tracer gas injection is needed, and high time resolution results are obtained.

Exhaled CO2 as a COVID-19 Infection Risk Proxy for Different Indoor Environments and Activities

“…Then, this mixing ratio can be scaled for typical D (by multiplying it) and target P (by multiplying its ratio to 0.01%) to obtain an excess CO 2 threshold, which may be relaxed a little further depending on the local mask policy. The sum of this value and the local outdoor CO 2 concentration, the latter of which we recommend measuring regularly due to possible variations, 29 is the final recommended indoor CO 2 concentration threshold. For more complex setups (e.g., with many CO 2 meters in a company or school), a meter should be located outdoors to measure CO 2 concentration continuously.…”

Review and Extension of CO2-Based Methods to Determine Ventilation Rates with Application to School Classrooms

“…Ventilation metrics, including the VR (m 3 ·h −1 ), VR per person (L·s −1 ·person −1 ), the outdoor air change rate (A, h −1 ) and others [ 13 ], can be determined using air flow measurements [ 14 ], pulse or constant injections of tracer gases [ 15 , 16 , 17 , 18 ], occupant-generated carbon dioxide (CO 2 ) as a “natural tracer” gas [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ], and the comparison of indoor and outdoor concentrations, concentration trends, and sometimes temperatures [ 27 , 28 ]. Air flow measurements from fan pressurization tests [ 29 ] provide a related measurement, the “tightness” of the building envelope.…”

Urban Pollutant Transport and Infiltration into Buildings Using Perfluorocarbon Tracers

“…Air exchange within buildings can also be measured using gas tracers. Often CO 2 is used as a readily available tracer to measure air-exchange using the gas decay method [ 23 , 24 ].…”