Residential air‐change rates: A critical review

Abstract

Air‐change rate is an important parameter influencing residential air quality. This article critically assesses the state of knowledge regarding residential air‐change rates, emphasizing periods of normal occupancy. Cumulatively, about 40 prior studies have measured air‐change rates in approximately 10,000 homes using tracer gases, including metabolic CO2. The central tendency of the air‐change rates determined in these studies is reasonably described as lognormal with a geometric mean of 0.5 h−1 and a geometric standard deviation of 2.0. However, the geometric means of individual studies vary, mainly within the range 0.2–1 h−1. Air‐change rates also vary with time in residences. Factors influencing the air‐change rate include weather (indoor–outdoor temperature difference and wind speed), the leakiness of the building envelope, and, when present, operation of mechanical ventilation systems. Occupancy‐associated factors are also important, including window opening, induced exhaust from flued combustion, and use of heating and cooling systems. Empirical and methodological challenges remain to be effectively addressed. These include clarifying the time variation of air‐change rates in residences during occupancy and understanding the influence of time‐varying air‐change rates on tracer‐gas measurement techniques. Important opportunities are available to improve understanding of air‐change rates and interzonal flows as factors affecting the source‐to‐exposure relationships for indoor air pollutants.

Ventilation procedures to minimize the airborne transmission of viruses in classrooms

“…The uncertainty budget would be even more complex for confined spaces without mechanical ventilation where manual airing procedures, corrected on the basis of the measured CO 2 values, are put in place. Indeed, in this case, the uncertainty of the CO 2 measurements and of the CO 2 mass balance equation (“constant injection rate method” [ 33 , 50 ]) to back-calculate the corrected AERs should be included too. The effect of the CO 2 measurement uncertainty is quite straightforward: indeed, in view of correcting the manual airing cycles on the basis of the CO 2 measurement, a higher CO 2 uncertainty would undermine the back-calculation of the actual AERs.…”

“…As mentioned above, for known and steady state emission rate and outdoor CO 2 concentration, the indoor concentration is just affected by the air exchange rate of the room, and the AER can be back-calculated from the eq. (7) measuring continuously the indoor CO 2 concentration (CO 2-in ): this measurement method is known as “constant injection rate method” [ 33 , 50 ].…”

Residential cooking-related PM2.5: Spatial-temporal variations under various intervention scenarios

“…Generally, the window-open AERs were larger for single-family houses than apartments, dwellings with earlier construction years and more windows/doors, and scenarios with larger outdoor wind speeds or indoor-outdoor temperature differences [40]. levels are generally lower than 20 µg/m 3 except for certain periods, such as wildfire episodes [28].…”

“…However, the effects can be less significant when the window-open AERs are smaller due to the meteorological variations (Trial 2 of Scenario 2). Based on a recent review study [40], the residential window-open AERs varied largely with housing stock features, climate, weather, and occupancy. The reported mean AERs were ~0.5 h -1 in the lower end and ~4 h -1 in the higher end [40].…”

Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their Application to COVID-19 Outbreaks

“…λ dep for a typical furnished indoor space span 0.2-2 h -1 over this size range, with faster deposition for larger particles (50). λ 0 varies from ~12 h -1 for airborne infection isolation rooms ( 51), ~6 h -1 for laboratories,~0.5 h -1 for residences (52), and ~1 h -1 for offices (1,53). Very little ventilation data is available for many semi-public spaces such as retail, restaurants and bars or transportation.…”