ventilation systems for indoor radon mitigation in energy ... · indoor air quality. it also aims...

ECOTERRA - Journal of Environmental Research and Protection

www.ecoterra-online.ro 2015, Volume 12, Issue 3

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Ventilation systems for indoor radon mitigation in energy-efficient houses 1Alexandra Cucoş (Dinu), 1Constantin Cosma, 1Tiberius Dicu, 1Botond Papp, 2Cristina Horju-Deac

1 Faculty of Environmental Science and Engineering, Babeş-Bolyai University from

Cluj-Napoca, Cluj-Napoca, Romania; 2 Technical University of Cluj-Napoca, Faculty of Materials and Environmental Engineering, Department of Environmental Engineering and

Entrepreneurship of Sustainable Development, Cluj-Napoca, Romania. Corresponding author: A. Cucoş (Dinu), [email protected], [email protected]

Abstract. Radon inside buildings represents the main source of human exposure to ionizing radiation in the world. Studies in many countries have shown that high levels of indoor radon increases the risk of lung cancer. A current challenge in research dedicated to residential radon comes from the growing number of modern houses, well insulated with a highly airtight building envelope or conventional rehabilitated in order to reduce energy consumption. Modern trends in civil construction are based on increasing the energy efficiency of buildings in which we live. In the light of the ongoing policy to improve the energy efficiency of existing buildings, it is essential to evaluate the effect of new construction methods on the indoor radon level. Key Words: radon, indoor radon, population exposure, remediation, ventilation systems.

Introduction. Optimizing the quality of the indoor environment by monitoring and controlling population exposure to radon and other ambient pollutants in homes, reducing associated health risks by implementing preventive and remedial actions represents a global priority (Darby et al 2006; Ferlay et al 2013; Council Directive 2013/59/Euratom; www.irart.ro).

Housing is a very important sector, both from an economic and social perspective, knowing the indoor conditions being a requirement for developing habitat policies. Indoor environmental conditions of housing significantly affect quality of life, manifested by health and intellectual potential, conditions for raising and educating children, safety of daily life and demographic evolution (Pavel et al 2006).

According to the report issued in 2009 by the World Health Organization, exposure to radon in residential environments is responsible for 3-14% of lung cancer deaths. For most people, radon in indoor air is the primary source of exposure to radiation (Cosma et al 2009; UNSCEAR 2006). Reducing exposure to radon in buildings is a key priority of public health protection against radiation. Directive 2013/59/Euratom stipulates, precisely because of this, increased attention to residential radon by implementing rules in each European country since 2018 and serious approach to monitoring and mitigating actions. In many European countries significant national resources were assigned for the development of comprehensive programs to identify houses with high levels of radon and implement corrective actions to reduce radon concentration. Massive efforts have also been made to develop adequate techniques to minimize the risk of exposure to indoor radon for population. In addition, various national institutes under the auspices of European authorities (WHO, IAEA, NRPI, STUK etc.) conducted massive information campaign to increase awareness of radon problem and boost activities to reduce exposure to radon. Although there has been significant progress in European harmonization of the technical aspects provided in the monitoring methodology, mapping and radon risk remediation (European projects such as RADPAR (http://web.jrc.ec.europa.eu/radpar) or those coordinated by the EC and the IAEA) for European countries only a small percentage of the number of homes with high exposure to radon has been remedied (Holmgren et al 2013).

By the end of 2012, about 26,000 houses were remediated in 23 European countries, based on the official report submitted by each country in the RADPAR project (Holmgren et al 2013). According to current research, the number of homes at risk of exposure to radon, which are recommended to be remedied, is increasing due to the use of thermal rehabilitation technologies and modern building materials with increased



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radioactivity index or inadequate thermal insulation for energy-saving. The current situation calls for the need of an effective strategy at European level to promote remediation and prevention of exposure to radon in order to improve health and increase indoor air quality. It also aims to introduce regulations on reducing risk associated with exposure to radon in the Planning and Construction Code.

Discussion. In case of energy efficient or thermally rehabilitated houses, increased building tightness often leads to a decrease of indoor air quality. Insulation technologies must be harmonized with indoor air quality. Minimum legislative requirements recommend avoiding deterioration of indoor air quality, i.e. increasing the levels of radon and other household air pollutants after applying energy-saving technologies. Dynamic criteria of the air should be considered and applied accordingly.

In a case study conducted in the Czech Republic on a building built in 1975 was observed that after its thermal rehabilitation the indoor radon concentration increased three times. Therefore, cost reduction on energy consumption (approx. 1500 Euro/year) led to an increased risk of developing lung cancer by 125% for each inhabitant of that house (Jiranek & Kacmarikova 2014; Jiranek 2015). In this regard, ensuring air quality and a healthy indoor climate requires ventilation and fresh air supply from the outside, i.e. identifying and minimizing polluting emissions sources.

Ventilation systems in the market are based on natural or mechanical ventilation. Natural ventilation of a building involves opening windows or using special grids

mounted either in windows carpentry or on the exterior walls, but in most cases this is not enough to ensure an optimal quality of indoor air. More so, such a system is not recommended during winter. To achieve an air exchange of approximately 0.3 air changes per hour, the windows should be wide open for 5 to 10 minutes every three hours, even at night. It is obvious that this cannot be achieved in practice. A smaller exchange, for example 0.1, is not enough. By opening the windows we can also decrease the level of humidity, but as soon as they are closed the humidity increases and thus the zone of discomfort. Moreover, at excessive humidity there is the risk of mould in cold areas (i.e. in the corners exposed to the outside air). In addition, natural ventilation has an efficiency of maximum 40% in reducing indoor radon concentration. Air quality has a higher priority than energy saving and therefore must be addressed.

Mechanical ventilation, as opposed to natural, implies the use of fans, so that it can provide the exact amount of fresh air. Fans can be used for the introduction of air, its extraction or both (recommended). The ventilation solution depends on many factors, including air quality requirements, installation costs, etc. The vast majority of traditional homes use as ventilation system the air intake from the windows and mechanical exhaust in the kitchen and bathrooms. Even if natural ventilation has no initial cost, it has many inconveniences: uncontrolled air exchange rate which can lead to excessive heat loss, drafts, external noise, dust etc. A controlled mechanical ventilation system has numerous advantages (exact air flow, energy efficiency), but also has a high initial cost which can be recovered over time. In case of passive houses this type of system is mandatory to ensure an optimal air quality, without noise or drafts. Moreover, in case of natural ventilation, specific heat load required for heating the air coming in from the windows is approx. 100 W/m2 while in case of mechanical ventilation it can decrease to 10-20 W/m2.

Easy-flow mechanical ventilation. The simplest solution is the exhaust fan system that extracts polluted and damp air from the house, installed in the kitchen or bathroom. At the same time, fresh air is provided by air intakes in the facade or window frames of living areas or bedrooms. These simple systems have become standards in France; ensure indoor air quality being required by law. Although this system is simple and requires a minimum investment, it is not suitable for passive houses because the air entering through the air inlets is cold (in the winter), and requires significant energy to be heated. Moreover, the bathrooms and kitchen exhaust air is polluted but warm; evacuating it without extracting the heat from is not energy efficient.



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Dual-flow controlled mechanical ventilation. A fair distribution of fresh air throughout the rooms and dehumidification in kitchens and bathrooms is possible only through a controlled ventilation system. In this way, the air is mechanically inserted into the living room, office and bedroom, and the evacuation is done in kitchens and bathrooms where moisture and odours are more pronounced (Figure 1). This type of double-flow system associated with a heat exchanger, provides a convenient solution, both fresh air supply and discharge being ensured. In case of this type of system there is no recycled air, only fresh air. In central Europe, the Passive House standard will only work in the presence of efficient heat recovery. Such systems recover heat from the exhaust air using a heat exchanger; the transfers are made without mixing air flow - only heat exchange. At present, modern technologies allow a 75-90% heat recovery rate. This is possible due to counterflow heat exchangers and through extraction using special fans with low energy consumption, the system being very efficient and cost effective. Ventilation helps ensure air quality and eliminates air pollution (odour, tobacco, CO2, radon, etc.). In certain situations it serves also as dehumidifier, especially in wetlands. Modern fans by having moving parts can be a sources of noise for occupants, but with the new generation of engines the noise level drops below 30 dB(A). The installation of such a system is simple and can be done in a short time.

Figure 1. Double flow ventilation system with heat recovery.

Radon expert engineers from the Czech Republic developed, for rehabilitated/energy efficient houses, an air purification system for radon based on controlled mechanical ventilation, where local ventilation units are installed in bathrooms. Although power consumption is low and the reduction factor of radon concentration is high, the air flow being 80 m3/h, the main disadvantage of this system is the high cost of installation and maintenance - about 5,000 Euros (Czech Republic, NRPI-Suro).

An additional method for improving the ventilation system in terms of energy efficiency involves using heat exchangers buried in the ground - Canadian well. The system is very simple and has the great advantage of using geothermal energy which is free and inexhaustible. During cold seasons the soil temperature is higher than that of air while in the summer is lower, therefore we can use this by placing pipes in the ground through which flows the outside air, this will warm/cool the air before it reaches the



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ventilation system. We thus use heat and thermal inertia of the soil and consequently make substantial savings. This system can be seen as a natural regulator of temperature as in the summer it cools the hot outdoor air before its being introduced indoors, while in winter it preheats it. With this system it is much easier to achieve the conditions for Passive House certification, but it should be noted that in some areas it does not allow complete removal of heating or air conditioning. The system works best together with mechanical ventilation with heat recovery.

Flow ventilation system with heat recovery. In the framework of the POSCCE 586-12487 "IRART" project were implemented remediation techniques on 21 houses with high risk of radon from the uranium mining area, Baita-Stei. The implemented methods are based on active and passive pressurization and depressurization of indoor spaces (Cucoş et al 2012; Cucoş et al 2014; Cosma et al 2015). The following table presents a comparison of the main remediation methods developed experimentally and the results on the reduction factor (%) of the initial radon concentration achieved in the IRART project compared with remedial solutions implemented in 14 European countries within the European project RADPAR. Similar results can observed in terms of efficiency, but much lower costs for remedial actions implemented in Romania. All remediation methods developed and applied in the IRART project resulted in high reduction factors with an average efficiency of 81% (Table 1) (Cucoş et al 2014). The specific situation of the Baita-Stei houses with elevated indoor radon concentrations, in the order of 1000-2000 Bq/m3, entailed the need to develop effective remediation methods, at the expense of cost optimization. Among the main causes of elevated indoor radon concentrations in this area include the use of uranium waste as building (unique situation both in Romanian and European) and high levels of radon in the soil due to the specific geology of uranium ore (Cucos et al 2014). For these reasons, the methods applied in the Baita-Stei were at times highly invasive on the house’s architecture, thus leading to an increase in costs of implementation (Figure 2).

Figure 2. Installing the remediation system based on sub-slab depressurisation in one of the houses in Baita uranium mine area, in the IRART project.

From the information available to date, the 21 houses of Baita-Stei remediated, within IRART project, by members of this proposed project are the only houses in Romania for which corrective actions have been implemented in terms of indoor radon concentration. Based on the experience gained during IRART, the most effective radon remediation method applicable both on old buildings and energy efficient housesis is founded on sub-slab depressurization (Cucoş et al 2015; Cosma et al 2015). The aim of this method is to reduce the pressure under the floor compared to the one inside the house, thus avoiding penetration of radon inside the house by convection. Pressure reduction is achieved naturally due to the stack effect and wind forces or through a mechanical ventilator, most often placed on the roof. The system is composed of perforated tubes 60-80 mm in



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diameter installed in a 150 mm thick layer of gravel under the habitable rooms, which are subsequently connected to the main pipe coupled with the fan.

Table 1

Remediation techniques applied in the IRART project compared with those applied in 14 European countries within the European project RADPAR

Efficiency(reduction

factor - %) Costs

(EURO) No. Remediation technique Short description

IRART RADPAR IRART RADPAR

1

Soil depressurization

(active and passive methods)

It works by reversing the pressure difference between the space under the floor and the room above. The air containing radon is expelled through a ventilator, thus preventing its infiltration indoors. The method of coupling the radon collector with a fan is known as the active collector.

68-95 60-95 3000 5000

2 Improving

natural ventilation

Determines mixing of radon-rich indoor air with the outdoor air, thus decreasing the indoor radon concentration but also slightly increasing the pressure inside the house which helps reduces the tendency of radon to be sucked indoors.

30-59 10-50 2500 4000

3 Improving mechanical ventilation

It involves introducing air inside the house through a fan, thus creating a slight positive pressure relative to the outside air. This reduces radon entry and forces the air out through cracks, windows and other openings.

65-78 10-60 2600 5000

4

Ventilation methods

combined with soil

depressurisation

It requires installation of additional under-floor ventilation paths to force evacuate radon using an active fan. These ventilation paths are crossed by longitudinal slotted PVC pipes.

88-95 60-99 3200 6000

5

Insulation of floors and walls.

Anti-radon barrier

It prevents radon entering the ground floor from the soil underneath by isolating all entry points. The insulation material must be durable and flexible enough to accommodate future movements of construction materials. The radon barrier is based on flexible polymer membrane applied onto the internal surfaces of the floor, under flooring.

60-65 10-60 1800 2500

Moreover, the recommendations of the International Atomic Energy Agency (IAEA) on the corrective actions to reduce residential radon aimed at implementing soil depressurization system beneath the floor for houses with radon concentrations exceeding the value of 600 Bq/m3 and a ventilation rate inside the house exceeding 0.3 h-1 or installing a mechanical ventilation system if radon concentration is higher than 600 Bq/m3, but the ventilation rate is less than 0.3 h-1 (Jiránek 2015).



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In the context of the current survey worldwide, from the research conducted in the pilot study on the assessment of exposure to radon in 50 rooms located in 25 energy-efficient houses (Cucoş et al 2015) of the postdoctoral project developed within the University in Cluj-Napoca, we can conclude that the thermal insulation works, existing construction materials and air conditioning systems used in Romania contributes to the accumulation of radon in houses. The results obtained in the frame of post-doctoral researches indicate a high radon potential in all investigated houses from Cluj-Napoca, Timisoara, Sibiu, Agnita and Upper Arpaşu in Sibiu. All houses were built or insulated during the "golden age" of energy efficiency 2001-2012, most houses being single storey. Particular attention was paid to air conditioning systems, type and materials used in thermal insulation and residential behaviour, which were investigated through questionnaires. The results cleary show that 24% of the investigated houses (16% of total rooms) exceed the European reference for residential radon of 300 Bq/m3 (Tollefsen et al 2014), namely that 72% of homes (64% of rooms) have radon levels that exceed 100 Bq/m3 (Cucoş et al 2015). This value is 27% higher than the average reported by authors for conventional houses in Transylvania, Romania (Cosma et al 2013). With respect to the use of air conditioning, measured radon concentration is 1.6 times greater for 17 investigated rooms equipped with air conditioning than for rooms that do not have air-conditioning (Cucoş et al 2015). All measured values for formaldehyde (a carcinogenic chemical pollutant) exceed the limits recommended in European guidelines. The explanation for the high level recorded in furniture and flooring is new every house and high degree of tightness in the house, all the houses being built or renovated than 9 years. The mitigation sollution proposed in the present study for energy-efficient houses are generally based on an ventilation system based on the dual-flow controlled mechanical ventilation. The ventilaton recommended system is based on the sub-slab depressurization method (Cosma et al 2015; Cucoş et al 2015). The aim of this method is to reduce the pressure under the floor compared to the one inside the house, thus avoiding penetration of radon inside the house by convection. Pressure reduction is achieved naturally due to the stack effect and wind forces or through a mechanical ventilator, most often placed on the roof. The system is composed of perforated tubes 60 - 80 mm in diameter installed in a 150 mm thick layer of gravel under the habitable rooms, which are subsequently connected to the main pipe coupled with the fan. Such a proposed ventilation system presents a low energy consumption and the reduction factor of the concentration of radon very high, with the air flow of 80 m3/h. Conclusions. The conclusions of these researches prove significant health effects caused by increasing concentrations of radon and other pollutants in rehabilitated houses. In this context, a realistic scenario envisages an increase of indoor radon concentration in the future due to changes in lifestyle, the use of artificial materials with high content of radium (slag and phosphogypsum) and reducing housing ventilation during the cold seasons for economic reasons. 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. References Cosma C., Cucoş (Dinu) A., Dicu T., 2013 Preliminary results regarding the first map of residential

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ISBN 978-973-88835-2-9, 166 pp. [in Romanian]



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*** www.irart.ro. *** http://web.jrc.ec.europa.eu/radpar. Received: 21 July 2015. Accepted: 20 September 2015. Published online: 31 October 2015. Authors: Alexandra Cucoş (Dinu), Faculty of Environmental Science and Engineering, Babeş-Bolyai University from Cluj-Napoca, Fântânele Str., No. 30, 400294 Cluj-Napoca, Romania, e-mail: [email protected], [email protected] Constantin Cosma, Faculty of Environmental Science and Engineering, Babeş-Bolyai University from Cluj-Napoca, Fântânele Str., No. 30, 400294 Cluj-Napoca, Romania, e-mail: [email protected] Tiberius Dicu, Faculty of Environmental Science and Engineering, Babeş-Bolyai University from Cluj-Napoca, Fântânele Str., No. 30, 400294 Cluj-Napoca, Romania, e-mail: [email protected] Botond Papp, Faculty of Environmental Science and Engineering, Babeş-Bolyai University from Cluj-Napoca, Fântânele Str., No. 30, 400294 Cluj-Napoca, Romania, e-mail: [email protected] Cristina Deac-Horju, Technical University of Cluj-Napoca, Faculty of Materials and Environmental Engineering, Department of Environmental Engineering and Entrepreneurship of Sustainable Development, Cluj-Napoca, Romania, e-mail: [email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited. How to cite this article: Cucoş (Dinu) A., Cosma C., Dicu T., Papp B., Horju-Deac C., 2015 Ventilation systems for indoor radon mitigation in energy-efficient houses. Ecoterra 12(3):14-20.

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