Using the Real-time Radon-222 Profile to Quantify the Specific Radon Production Rate in an Air-conditioned Building

Abstract

The real-time indoor and outdoor radon-222 profiles on the fourth floor of a university library were measured through five consecutive days, with the Heating, Ventilating and Air Conditioning (HVAC) system operating on part load. The premises were served by a main air-handling unit (AHU-1) and a subordinate unit (AHU-2) of the HVAC system, but AHU-2 was shut down for maintenance. It required full operation of AHU-1 for 1.7h to reduce the radon concentration from the overnight peak down to the recommended action level (200Bq·m^-3). Clear characteristics of indoor radon profiles were observed, with the diurnal variations of indoor radon concentrations strongly coupled to the operation schedule of AHU-1. The specific radon production (value-Φ) of the site could be quantified from the characteristic profiles. This can be used to investigate the radon emission rate of a site, as well as to simulate the indoor radon concentrations at different ventilation rates. The value-Φ was 21.0Bqh^-1·m^-3, with a standard deviation of 0.6Bqh^-1·m^-3. Furthermore, it was found that a morning purge, by the fresh air intake fan operating for 2h before library opening hours, could not effectively remove the overnight accumulation of the pollutant.

Keywords

Specific radon production rate Heating,ventilation and air-conditioning system Ventilation Building material

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