INDOOR RADON EXPOSURE IN ENERGY-EFFICIENT HOUSES ...

ENVIRONMENTAL PHYSICS

INDOOR RADON EXPOSURE IN ENERGY-EFFICIENT HOUSES FROM ROMANIA ALEXANDRA CUCOŞ (DINU)1, TIBERIUS DICU1, CONSTANTIN COSMA2 1

Faculty of Sciences and Engineering, Babes-Bolyai University, 30 Fântânele Street, RO-400294, Cluj-Napoca, România, E-mail: [email protected] 2 Environmental Radioactivity and Nuclear Dating Center, Babeş-Bolyai University, Cluj-Napoca, România Received April 30, 2015 Modern trends in civil construction are based on increasing the energy efficiency of buildings in which we live. But unfortunately efficient insulation of buildings and the introduction of air conditioning systems and other architectural and energyefficient technologies lead to elevated indoor radon levels and other chemical pollutants. In this paper the assessment of population exposure to radon in energy efficient buildings was studied. To investigate indoor radon levels in the modern buildings the measurements were performed in 25 energy efficient houses constructed in the last decade by using mostly solid concrete or gas-concrete blocks, by using nuclear track detectors CR-39 exposed for 6–7 months on inhabited area of dwellings, according to the NRPB Measurements Protocol. The overall concentration levels of the indoor radon in the 50 studied rooms varied from 18 to 593 Bqm−3 with a mean of 160 Bqm−3. This value is 27% higher than the average reported by authors for conventional homes in Transylvania, Romania. Key words: energy efficient houses, indoor radon, population exposure.

1. INTRODUCTION

Exposure to radon and radon decay products in homes and at workplaces constitutes one of the greatest risks from ionizing radiation. Risk estimations show figures in the rank of thousands of deaths per year from cancer caused by exposure to radon and especially to its decay products [1–3]. Modern trends in civil construction are based on increasing the energy efficiency of buildings in which we live. But unfortunately, efficient insulation of buildings and the introduction of high-performance windows, air conditioning systems and other architectural energy-efficient concepts reduce the air permeability of the building envelope and can cause elevated indoor radon and other pollutants levels [4]. A significant impact of house thermal retrofitting and the air conditioning system usage on radon levels have been already reported [4–6] and the conclusions of these studies prove considerable health effects caused by increasing population exposure to radon and other pollutants in modern homes. Rom. Journ. Phys., Vol. 60, Nos. 9–10, P. 1574–1580, Bucharest, 2015

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Indoor radon exposure in energy-efficient houses from Romania

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A realistic scenario envisages an increase of radon concentration in dwellings in the future due to changing lifestyles, the use of artificial materials with high content of radium and economic reasons for reducing the ventilation housing in cold seasons. In this paper the indoor radon exposure in 50 rooms of 25 energy-efficient houses was evaluated and discussed. An actual priority at European level [7] is to identify potentially risks induced by radon levels to population exposed in such houses and also to evaluate the impact of modern trends in construction and retrofitting thermal insulation to indoor air quality.

2. MATERIAL AND METHODS

The studied houses were selected from the Romanian regions where previous indoor radon measurements reveal elevated levels: Cluj (Cluj-Napoca, Floreşti), Sibiu (Sibiu, Agnita, Arpaşu de Sus) and Timiş (Timişoara) Counties. All houses were built or thermal insulated in the period 2001–2012, in the era of energy-efficient houses, majority of the houses with one floor. Special attention was paid to air conditioning systems, type of thermal insulation and building materials, which, along with residential behavior were investigated through questionnaires. Indoor radon exposure was measured by using CR-39 nuclear track detectors exposed for 6–7 months in 2 different seasons on inhabited rooms of dwellings, at 1–1.5 m above floor level, in compliance with quality assurance and control programs according to the HPA-NRPB Measurements Protocol [8]. The measuring protocol, the placement of detectors and processing of the results has already been detailed in previous works [9, 10]. The accuracy of these measurements was periodically checked by participation in international intercomparison exercises [9–14]. The annual average of radon concentration, expressed in Bqm-3, was calculated from the results for radon concentration measured in each room over two consecutive 3-months measurements. The measured radon concentration value was corrected for seasonal variations, depending on the time when detectors were exposed [8, 14]. The statistical analysis has been performed with GraphPad Prism 5.0 (GraphPad, San Diego, USA) and the comparison between samples was made with t-test, for the natural logarithm of the radon concentration. The significance level was chosen at α = 0.05.

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3. RESULTS AND DISCUSSIONS

Table 1 illustrates a summary statistics of the indoor radon levels in 50 different types of rooms from 25 energy-efficient residential buildings located in Cluj and Sibiu Counties and also Timişoara. As can be seen from Table 1, the exposure of indoor radon in the 50 studied rooms from energy efficient houses involved in study varied from 18 to 593 Bqm−3 with an annual average (AM) of 160 Bqm−3. The obtained value is 27% higher than the average reported by authors for conventional homes of Transylvania, Romania [9, 11]. Table 1 Descriptive statistics for indoor radon measurements in monitored energy-efficient dwellings of Romania County

No.

AM (Bqm−3)

SD (Bqm−3)

Cluj Sibiu Timiş Total

30 16 4 50

128 170 352 160

114 144 37 133

GM GSD Min (Bqm−3) (Bqm−3) (Bqm−3) 97 134 351 119

2.0 2.0 1.1 2.1

18 49 301 18

Max (Bqm−3) 593 588 385 593

No. (%) > 300 (Bqm−3) 2 (7%) 2 (13%) 4 (100%) 8 (16%)

For Cluj County the results are slightly higher than those obtained previously (112 Bqm-3) for conventional houses [15], while for energy efficient homes in Sibiu County the measured average annual value is 79% higher than the value reported previously (95 Bqm-3) for conventional homes [11]. The highest average annual radon concentration (352 Bqm-3) was calculated for two houses located in Timişoara, thermal insulated in 2006 and with air conditioning system operating usually. About 24% of investigated houses and 16% of investigated rooms exceed the European reference level of radon gas in dwellings air of 300 Bqm−3 [7] and that indoor radon exceeded 100 Bqm−3 in 32 (64%) of these rooms respectively 18 (72%) of these houses (Table 1). The distribution of radon concentration measurements in 50 rooms of the surveyed areas are represented in Fig. 1 by the quantile-quantile (qq-plot), which should be a straight line for a normal distribution. In our case, the initial data were ln-transformed and plotted. A small deviation can be observed in the low concentration end of the qq-plot due to the measurement errors. The variability of radon concentrations among surveyed houses and rooms could be related to a series of factors, such as the type of building, type of thermal insulation, the behavior of the occupants, various air exchange systems and age of construction [4]. In the field of the protection of houses against radon, several factors that could control the source and the behaviour of radon in air inside building should be carefully studied.

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Fig. 1 – Normal qq-plot of the indoor radon concentrations in 50 surveyed rooms.

Six factors that may affect the indoor radon concentration, such as the season of measurement campaigns, the influence of the floor where is located the investigated room, the presence or absence of cellar under studied rooms, the type of room, the age of building and the air conditioning systems usage were also examined. Indoor radon levels in relation with some of these factors are presented in Table 2. Table 2 Indoor radon levels in relation with variable influencing factors within 50 rooms of energy-efficient dwellings from Romania Factor

Type

No.

Measurement Campaign*

1st 2nd Ground f. 1st floor Yes No Bedroom Living Kitchen Yes No

50 50 36 14 15 21 22 25 3 17 33

Floor Cellar Room A.C. *

AM (Bqm−3) 118 192 139 117 131 211 166 160 112 212 133

SD (Bqm−3) 104 164 139 71 104 167 150 125 82 161 109

GM (Bqm−3) 87 143 105 95 104 157 122 123 77 153 105

Min (Bqm−3) 13 23 22 18 22 37 48 22 18 37 18

Max (Bqm−3) 460 792 593 263 426 593 588 792 170 593 588

Measurement Campaign: 1st reefers to the period August–October 2015 and 2nd to the winter season November 2014–February 2015.

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The expected temporal variations were confirmed, the average for the measurements performed in winter (2nd campaign) being 1.6 times higher than in the warm season (1st campaign) (Table 2). The difference between the means of the indoor radon concentrations in the two campaigns is statistically significant (p < 0.001) by applying paired t test. The statistical analysis of radon levels among floors indicate that the highest indoor radon values were measured at the ground floor (Table 2). With reference to the existence of cellar below studied rooms, the radon level is 1.6 times higher in houses without cellar compared to those with rooms above the cellar. A similar situation related to the influence of the cellar’s presence on indoor radon variations was found in our previously study [9], where radon concentrations in bedrooms without cellar was 1.4 higher than in bedrooms above the cellar. This variation can be related to the architectural design of buildings, which allow several air circulation patterns in cellars. Concerning the type of surveyed rooms within dwellings in Table 2, the higher indoor radon levels occur in bedrooms, although in particular the highest value of radon concentration was found in a living room (792 Bqm−3). Regarding the usage of the Air Conditioning Systems (A.C. in Table 2), for 17 investigated rooms equipped with air conditioning measured radon concentration is higher by 1.6 times compared to the rooms and homes that do not have air conditioning. Thereby it can be concluded that the Air Conditioning Systems can affect radon concentrations by changing the pressure of a space and thus may conduct to elevated indoor radon levels. Referring to building materials, 24 analyzed houses were built of brick and concrete and one house was built of stone. With respect of the year of construction, the mean values of radon concentration in the group of buildings constructed in the last decade are well greater than the average indoor radon level measured in previously studies in the framework of national and international projects [9–14] in buildings constructed during 1940–1990 in the same municipalities, brings evidence that new energy efficient technologies or rehabilitation works have an influence on radon accumulation levels in dwellings. Our results are consistent to that of other several studies that have been carried out related to the importance of monitoring radon levels inside the new modern buildings. Recent research shows that additional risk of lung cancer increased by 125% in classical conventional homes thermal rehabilitated compared to the previous situation [6]. The results of a Swiss study comparing the radon concentration in 163 housing analyzed before and after thermal insulation [16] show that the average radon concentration increased by about 26% after isolation. Another study conducted in Russia on 20 newly built homes compared to homes built between 1950 to 1989, confirms that new technologies and construction materials increases the level of radon in the buildings environment [17]. Considering the air conditioning systems usage, an evaluation of indoor radon

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levels in 7 energy efficient multi-storey buildings equipped with air conditioning systems from Ekaterinburg (Russia) showed that the mean radon level in the group (133 Bqm-3) exceeds the city average radon concentration by a factor of 3 [18]. The high levels of radon concentration related to the energy efficient reconstruction can be reduced by natural or mechanical ventilation. Although it is one of the possible techniques, which effectiveness is amply studied, it is advisable to put emphasis on the energy impact on loss of thermal comfort conditions. 4. CONCLUSIONS

In this study, we found that the annual average radon concentration in 50 investigated rooms of 25 newly energy-efficient constructed homes was 160 Bqm−3 and that indoor radon exceeded 100 Bqm−3 in 32 (64%) of these rooms respectively 18 (72%) of these houses. The obtained value is 27% higher than the average reported by authors for conventional homes of Transylvania, Romania. The usage of the Air Conditioning Systems leads to increase of indoor radon levels by 1.6 times compared to the rooms and homes that do not have air conditioning. In conclusion, the energy-efficient techniques including the Air Conditioning Systems used for modern insulation of buildings can lead to the accumulation of high levels of radon indoors. The investigations clearly show that not only needs for energy saving but also indoor environmental quality should be carefully planned in thermal rehabilitation process of buildings. In the light of sustainable development and the policy to improve the energy efficiency of buildings, it is recommended to find an optimal solution to maintain a reasonable level the energy efficiency need for modern houses and also the indoor air quality. Acknowledgements. This paper is a result of a postdoctoral research made possible by the financial support of the Sectoral Operational Programme for Human Resources Development 2007–2013, co-financed by the European Social Fund, under the project POSDRU/159/1.5/S/133391 – Doctoral and postdoctoral excellence programs for training highly qualified human resources for research in the fields of Life Sciences, Environment and Earth. The work was also made possible with the financial support of the project RAMARO No. 73/2012.

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