Radon distribution in space

Pao Yue-kong Library Electronic Theses Database

Radon distribution in space

 

Author: Ho, Wai-lan Janice
Title: Radon distribution in space
Degree: M.Eng.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Indoor air pollution
Radon -- Environmental aspects
Department: Dept. of Building Services Engineering
Pages: xvii, 119 leaves : ill. (some col.) ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b1810012
URI: http://theses.lib.polyu.edu.hk/handle/200/5455
Abstract: In order to maintain an acceptable indoor air quality (IAQ), policies, strategies and guidelines on achieving the required IAQ have been developed worldwide. In Hong Kong, the Environmental Protection Department (HKEPD) has launched an indoor air quality (IAQ) certification scheme to promote an acceptable IAQ in workplaces. For practical IAQ measurement, it is proposed that the required number of sampling points is related to the total floor area. However, the associated uncertainties and measurement efforts have not been detailed for practical measurement in indoor spaces. In this study, indoor carbon dioxide (CO2) concentration was selected as an indicator of the indoor air quality to investigate the probable errors and measurement efforts in different sampling schemes regarding the sampling point density. In particular, a one-year measurement for sample-spatial average indoor CO2 concentration at 17 sampling locations in a typical large office (floor area - 1200 m2) has been used to evaluate the probable errors of the sample-spatial average concentrations using different sampling point densities. The results show that the measured concentration at a single sampling point could not be representative for the space and more than one sampling location would be required in order to increase the measurement accuracy. Mathematical expressions for the sample-spatial average concentration at a confidence level at certain sampling point densities are proposed in this study. When doubted the required measurement points, it was found that the probability of obtaining a measured CO2 concentration at the confidence level of 95% could be increased from 70% to 90%, as compared with the current sampling practice. It is recommended the measurement uncertainties be specified in future codes so that effort for IAQ measurements in indoor spaces could be determined for practical strategies.
For the consideration of IAQ measurement, there are numerous indoor air pollutants which will pose health hazards to the building occupants; and radon is classified as one of the twelve IAQ parameters in the HKEPD guidelines. Although radon is not related to sick building syndrome, it can lead to lung cancer due to its radioactive characteristics. It is classified as a significant indoor air pollutant, especially in Hong Kong. However, it is not valuable to measure the indoor radon concentration directly since it is very specialized, labour intensive and time consuming. Also, the radon measurement equipment is very expensive, so it is not possible to carry out the measurement directly. In order to determine the possibility of using indoor air velocity as an indicator of the indoor radon concentration level, both the air velocity and radon concentration in the environmental chamber have been measured continuously for different ventilation conditions to evaluate their relationship. The results show that the air velocity is a good indicator of the indoor radon level and the ventilation rate is an important parameter for their relationship since the indoor radon level increase with the air velocity when the ventilation is insufficient to compensate for the radon generated indoor and vice versa. Mathematical expressions for the sample-spatial average radon concentration with different air change rates at certain indoor air velocity are proposed. For the measurement of the environmental chamber, the ventilation rate of the chamber is greater than 50%, the indoor radon level can be totally compensated by the outdoor air and the relationship between air velocity and radon concentration varies with the ventilation rate. With the findings in this story, it is recommended the indoor radon level be determined by measuring the indoor air velocity with the specification for measurement uncertainties.

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