Air Exchange and PM2.5 Variation of IndoorEnvironment

樓宇換氣率與PM2.5的變化

Student thesis: Doctoral Thesis

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Award date24 Dec 2019

Abstract

In most countries, people spend more time indoors than outdoor, so indoor exposure to air pollutants is important for human-health. This dissertation uses both experimental and modeling methods to evaluate particle exchange and variations.

Indoor air quality is dependent on outdoor air pollution as air transfers indoors, and it is this process that forms the central concern of this thesis. Both natural ventilation and HVAC systems typically influence the indoor air quality. Annual measurements of indoor and outdoor PM2.5 and thermal comfort in eight different commercial buildings of Hong Kong provided a view of indoor and outdoor particles concentrations. A daily cycle of both indoor and outdoor PM2.5 concentration was observed although it showed variations with different seasons under the HVAM system. Higher PM2.5 I/O ratio was observed for unoccupied conditions under natural ventilation. When all windows and doors are closed to minimum ventilation rate, the infiltration rate and air tightness are important because they affect energy use and the rate of pollutant infiltration. Ten different residential apartments of Hong Kong are tested to measure air tightness using the blower-door measurements. Large variations in air change rate at 50 Pa (4-26 ACH) were found in the apartments dependent on their characteristics (building year, location etc).

As outdoor air pollutants influence indoor air, Chinese New Year (CNY) with a sudden peak in firework particles to provides a good example to explore how such events influence interiors. Indoor/outdoor measurement of PM2.5 in Guangzhou, from before over CNY 2019, along with CO2 concentrations (decay-rebound method) allow PM2.5 deposition to be measured and show variation due to weather conditions.

Variation of estimates from decay-rebound method, suggested a possible alternative method adopting a blower-door fan to determine particle deposition rates and penetration factors. Comparisons used indoor-outdoor PM2.5 concentrations, CO2 level and experimental conditions (temperature, RH etc.) in a detached naturally ventilated space. PM2.5 deposition rates and penetration factors were estimated under a variety of different indoor situations. Results illustrate that the blower-door method gives consistent values and detects subtle differences in penetration factors, compared to the decay-rebound method.

Real apartment is more complex than single rooms as they are connected with adjacent apartments and corridor areas. CONTAM modeling was used to simulate the indoor particle concentrations in a multistory building, under different indoor-outdoor pressure differences. Daily indoor PM2.5 concentrations under variable weather conditions and the effect of sources, gaps/cracks are investigated. The CONTAM modeling results are compared with measurements which show good agreement. Stack effects dominate the indoor particle accumulation when the sources come from floors below, high and constant pressure difference induce more particles indoors when the sources are in adjacent apartments on the same floor.