Air Change in Low- and High-Rise Apartments

Air exchange in tall apartment buildings is critical in controlling indoor environments in urban settings. Airtightness is relevant to energy efficiency, thermal comfort and air quality experienced by urban dwellers who spend much of their time indoors. While many air change measurements have been made in residential homes, fewer are available for high-rise apartments. The blower-door and CO₂ exchange methods were used to measure air change in some Hong Kong apartment buildings, for comparison with those from other parts of the world. Hong Kong apartments are often small and typical rented apartments show a median of seven air changes per hour under a 50 Pa pressure difference, similar to Mediterranean houses, though much greater than the airtight buildings of Northern Europe. Extrapolation of blower-door measurements made at 50 Pa to the natural pressure difference measured for individual Hong Kong apartments provides an approximation (within 8%) of the natural air change rate measured with a tracer. Air flow is a function of the pressure difference ∆P^nf and the exponent n was found close to the typical 0.6. There was a positive relationship between air permeability and construction age, but some of this also seems to reflect varying levels of maintenance by the building management companies. The median exchange in the apartments under naturally ventilated conditions was 0.26 h⁻¹, not atypical of some houses on the US West Coast.