Development of a methodology to characterize radon entry in dwellings

Transcription

1 ROOMS 2016 Concarneau, France Development of a methodology to characterize radon entry in dwellings Friday 7 th October 2016 E. Powaga

2 Context MAIN RADON ENTRY PROCESS > Convection generated by depression between soil and indoor environment > Airflow from ground depends depression, soil permeability and basement permeability HIGH VARIABILITY OF INDOOR RADON CONCENTRATION ALONG TIME DIFFICULTY TO ASSESS ANNUAL AVERAGED INDOOR RADON CONCENTRATION In France, radon screening normalised: > 2 months measurement during heating period > Protocol used in regulation for public building and working places > Difficult to use this protocol in existing dwelling (real estate transaction, occupant behaviour,...) Text < Tint P- P+ P+ Radium (solid) Radon (Gaz) Diffusion Convection Source CSTB 2

3 Goal General objective : to find an alternative or complementary technique to assess radon potential of a dwelling DEVELOPMENT OF A METHODOLOGY FOR THE CHARACTERIZATION OF THE RADON ENTRANCE IN DWELLINGS > Based on previous works undertaken by M. Sherman, W. Ringer, A. Fronka > Protocol developed on a preliminary study (CSTB, IRSN) : instrumented house during one year > To define experimentally a potential of radon entrance for a given building (entrance law) > To assess averaged annual indoor radon concentration using entrance law with mathematical or numerical tools 3

4 Protocol - Principle Depressurization of dwelling using a blower door 1. FOR A GIVEN DEPRESSURIZATION ( P) AND MECHANICAL EXHAUST AIR (AR) : > Measurement of indoor Rn concentration at exhaust > F Rn = C Rn asympt x RA 2. TEST AT DIFFERENT DEPRESSURISATION LEVELS ( P) > Convective flux of radon from ground > Rn entrance law F Rn = K DP n C Rn asympt. F Rn time DP 4

5 Protocol - Steps REALIZATION OF 2 OR 3 DEPRESSURISATION LEVELS ( P) > Depressurization of dwelling using a blower door > Continuous measurement of Rn Concentration using Alphaguard device DWELLING AIR-TIGHTNESS MEASUREMENT > Using a blower door DWELLING VENTILATION SYSTEM CHARACTERISATION > Using a hot wire anemometer 5

6 Exemple of realization of several P levels > Each P levels lasts 2 to 3 hours > Stabilization of the signal on 5 to 6 points > Purge between each level More ΔP More F Rn More RA C Rn asymp ~ Opposites effects 6

7 Exemple of determination of Rn entrance law > 3 F Rn for 3 P > 4 interpolations laws possible WHICH ONE USE? F Rn (Bq/s) > All interpolations laws compared with screening measure INTERPOLATION LAWS BETWEEN THE TWO EXTREMES POINTS GIVES BEST RESULTS 7

8 Radon entrance potential - Definition Bq/s Bq/s Bq/s/m² F Rn = 13,6 x (DP) 0,6 example of Rn entrance law determined experimentally F Rn (4 Pa) = 13,6 x (4) 0,6 Radon flow entrance for a 4 Pa P P Rn4 = Q Rn (4 Pa) / Soil surface Radon entrance potential > Potential reflecting the amount of radon entering the building by m² of heated floor and for a depressurization level of 4 Pa > Potential depending only on characteristics of the building > The greater the potential, the more there is a risk of exposure to radon 8

9 Tested dwellings Characterization measurements tested on 28 dwellings ( ) > Distributed in 5 regions : Auvergne, Limousin, Bretagne, Languedoc-Roussillon and Rhône-Alpes > Old buildings (18th century) to very recent (2010) > Very air permeable (I 4 = 7.7 m 3 / h / m²) to very airtight (I 4 = 0.34 m 3 / h / m²) > Different ventilation systems > Exposure to radon low to high (from 50 to 7000 Bq / m 3 ) 9

10 Radon entrance potential - Compared to radon screening data PRn4 < 0,25 Bq/s/m² C RN < 400 BQ/M 3 0,25 < PRn4 < 0,65 Bq/s/m² 400 < C RN < 1000 BQ/M 3 PRn4 > 0,65 Bq/s/m² C RN > 1000 BQ/M 3 Characterization of radon potential globally consistent with radon screening 10

11 Assess averaged annual indoor radon concentration Numerical model SIREN Unsteady Ventilation model INPUT DATA > Dimensions and orientation of the dwelling > Air-tightness of dwelling > Ventilation system > Annual local weather (Wind, Text) > Rn entrance law (F Rn = K DP n ) RESULTS > Depressurization of the building throughout the year > Air exchange (RA) > Indoor concentration of radon (CRn) 11

12 Assess averaged annual indoor radon concentration Compared to radon screening data GOOD PREDICTION WHEN: > Few wind (< 2m/s) > ventilation system correctly dimensioned > House relatively air permeable I 4 > 1.7 m 3 / h / m² LESS GOOD PREDICTION WHEN: > Strong wind (> 2m/s) > No ventilation system > House relatively airtight I 4 <1.4 m3 / h / m² Characterization of radon potential globally consistent with radon screening 12

13 Conclusion LIMITATIONS > Protocol to set up in calm weather conditions (wind average < 5 m/s) > Prediction models don t take into account the occupation of the building (frequency and windows open time) annual average concentration prediction higher compared to reality. RESULTS OBTAINED PROMISING > Housing classification proposal > In most cases consistent results STRENGTH OF THIS METHOD > Characterization performed on one day, in every season > Could be used in radon management complementarity in buildings PUBLICATIONS > Development of a methodology to characterize radon entry into dwellings. Collignan B., Lorkowski C., Améon R. Building and Environment 57, , November 2012 > Procedure for the characterization of radon potential in existing dwellings and to assess the annual average indoor radon concentration. Collignan B, Powaga E. Journal of Environmental Radioactivity, 2014 Jul 7;137C: doi: /j.jenvrad

14 Thanks for your attention Merci pour votre attention