Ventilation systems for indoor radon mitigation in energy

Transcription

ECOTERRA - Journal of Environmental Research and Protection
Ventilation systems for indoor radon mitigation in
energy-efficient houses
1
Alexandra Cucoş (Dinu), 1Constantin Cosma, 1Tiberius Dicu,
1
Botond 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
www.ecoterra-online.ro
2015, Volume 12, Issue 3
14
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.
15
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
16
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 subslab 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
17
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
No.
Remediation
technique
1
Soil
depressurization
(active and
passive methods)
2
Improving
natural
ventilation
3
Improving
mechanical
ventilation
4
Ventilation
methods
combined with
soil
depressurisation
5
Insulation of
floors and walls.
Anti-radon
barrier
Short description
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.
Determines mixing of radonrich 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.
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.
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.
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.
Efficiency(reduction
factor - %)
IRART
RADPAR
Costs
(EURO)
IRART
RADPAR
68-95
60-95
3000
5000
30-59
10-50
2500
4000
65-78
10-60
2600
5000
88-95
60-99
3200
6000
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).
18
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.
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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 ClujNapoca, 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 ClujNapoca, 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.
20

Ventilation systems for indoor radon mitigation in energy

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