Ventilation in European dwellings: A review

Building and Environment 47 (2012) 109e125

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Building and Environment journal homepage: www.elsevier.com/locate/buildenv

Ventilation in European dwellings: A review C. Dimitroulopoulou University of West Macedonia, Dept of Mechanical Engineering, Sialvera and Bakola, Kozani, Greece

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 February 2011 Received in revised form 15 July 2011 Accepted 17 July 2011

Adequate ventilation is essential for the health and comfort of building occupants. This review examines, first of all, why residential ventilation is an issue of concern in Europe and how is related to the human health. A review of the current status of residential ventilation standards and regulations in Europe is also provided, as a reference. Finally, a review of measurements of ventilation rates in European dwellings is provided, where the compatibility with the European standards/regulations is examined. The review shows that ventilation is increasingly becoming recognised as an important component of a healthy dwelling. Ventilation requirements receive major attention in building regulations, across Europe. However, ventilation measurements across Europe show that ventilation is in practice often poor, resulting in reduced ventilation rates (lower than 0.5 h
1, which is currently a standard in many European countries), increased concentrations of indoor pollutants and hence exposure to health risk. Surveys showed that although occupants generally think that ventilation is important, their understanding of the ventilation systems in their own houses is low, resulting to under-ventilated homes. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Ventilation Rates Regulations Health

1. Introduction Ventilation is the means by which ‘fresh’ air is introduced and circulated throughout the building while contaminated or ‘stale’ air is removed or diluted. The primary purpose of ventilation is to create optimal conditions, in terms of air quality and thermal comfort in indoor environments, for people living or working there, taking into account their health, comfort and productivity [1]. The role of ventilation in residential buildings is mainly to maintain good air quality by diluting air pollutants. This process is described in more detail in AIVC Publications (e.g [1,2]). More specifically, the steady concentration of a pollutant, with a given emission rate, depends on the ventilation rates. As the ventilation rate increases, the ultimate steady state pollutant concentration is reduced. However, this includes an energy penalty. Therefore, the dominant pollutant needs to be identified in order to reduce the steady state concentration to at or below an acceptable ‘comfort’ and ‘safe’ concentration. In such a case, the needs for less ventilation and hence less energy will also be satisfied. However, the removal of pollution sources is a more effective way to control indoor air quality than diluting the pollutant concentrations by ventilation. Therefore, indoor sources should be avoided and eliminated wherever is possible (e.g. by use of low emitting materials and products) [3]. Today there is a variety of ventilation strategies in various European countries. In some countries, uncontrolled air infiltration E-mail address: [email protected]. 0360-1323/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2011.07.016

and window opening is often the only ventilation, while in others, passive stack ventilation systems are more or less used. In countries with colder climates, mechanical systems have been installed, which are either exhaust only or balanced, with or without heat recovery units [4,5]. Each system has its advantages, disadvantages and applications. The choice of ventilation system ultimately depends on indoor air quality requirements, heating and cooling loads, outdoor climate, cost and design preference. The choice is often predetermined - in moist, temperate climates, such as Britain’s, the structure of houses used to be so leaky that mechanical ventilation was not considered to be economic. However, in colder climates (e.g. Scandinavian countries), houses need to be as airtight as possible to conserve heat. In this case, natural ventilation is often unable to provide adequate ventilation for odour or contaminant removal and mechanical ventilation is necessary to achieve minimum ventilation rates. This is also stands for the warmer regions, where buildings are airtight in order to reduce energy consumption during cooling rather than heating periods [6]. Apart from northern Europe, the dominating European ventilation system is natural ventilation. The natural ventilation systems are driven by wind and thermally (stack) generated pressures. Designing for natural ventilation is concerned with harnessing these forces by the careful sizing and positioning of openings [7]. The infiltration of air through the fabric of the building, which occurs if the building is not airtight, may lead to energy waste and sometimes discomfort. It is important, therefore, to achieve

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a balance between indoor air quality, energy conservation and the necessary ventilation requirements for the wellbeing of occupants in buildings [5]. The impact of energy reservation on ventilation rates started in 1973 in the States with the Arab Oil Embargo, which led to increased costs for energy, and thus for the heating of buildings. This had as a result the tightening of building envelopes and reduced ventilation. The decrease in ventilation rates coincides in time with the increase in allergic diseases, since the prevalence of asthma was increased during the past decades in the industrialised countries [8,9]. A comprehensive review based on epidemiological studies [9], of the indoor factors in dwellings that influence the development of asthma in children concluded that, the most consistent findings are exposure to environmental tobacco smoke, to traffic related pollutants that penetrate indoors, and to dampness in homes with visible moulds. He recommended that more research is needed to understand better the potential risk for exposure to volatile and semi-volatile organic compounds due to renovation, painting activities and floorings, to phthalates and chlorine due to the frequent use of cleaning chemical agents and, to emissions of damp mould components. Finally he pointed out that in order to prevent asthma onset in children, measures that need to be considered is to avoid or reduce the source and to increase ventilation. To reduce levels of indoor pollutants, modest improvements in construction practice and living conditions should aim to eliminate first the sources, by applying mitigation techniques and supply simultaneously with adequate ventilation [10,11]. Improved ventilation may be advisable even when source control measures have significantly reduced the indoor concentrations of contaminants since adequate ventilation is essential for the health, safety and comfort of building occupants [12]. This review examines, first of all, why residential ventilation is an issue of concern in Europe and how is related to the human health. A review of the current status of residential ventilation standards and regulations in Europe is also provided, as a reference. Finally, a review of measurements of ventilation rates in European dwellings has been carried out and the compatibility with the European standards/regulations is examined. 2. Residential ventilation and health Ventilation has a significant impact on several important human responses [13,14]. Low ventilation rates may result in increased concentration of indoor generated pollutants, which may be associated with:    

Sick building syndrome symptoms; Comfort (perceived air quality); Health effects (inflammation, infections, asthma, allergy), and Productivity.

A review of the human responses to ventilation [15] pointed out that, regarding ventilation in residential buildings, little information is available on the health effects of measured ventilation rates. Following that review, a few conclusive studies were found regarding residential ventilation and its association to health effects of vulnerable groups (children and elderly people). In these studies, the value of 0.5 air changes per hour (h
1), which is frequently used in national standards/regulations in Europe (see Section 3), is reported as a threshold below which associations may occur (see the next sub-Section). However, this value should not be considered as a recommendation for the minimum ventilation level, based on health criteria. On-going research funded by EU DG Sanco (HealthVent project) aims at

developing health-based ventilation guidelines, considering both health and energy impacts. 2.1. Ventilation and children’s health Asthma is a complex chronic inflammatory disease of the airways, which has a characteristic of the reversible airway obstruction. The clinical diagnosis of asthma is based on the medical history of the patient, a physical examination and the exclusion of other diseases with similar symptoms. However, this diagnosis methodology cannot be used in epidemiological studies dealing with large population samples, since the reversibility of airway obstruction can only be tested by repeated medical examination [9]. Thus, there is no commonly accepted set of criteria to identify asthma in epidemiological studies. It should also be noted that studies on asthma, especially in early life (<6 years old), have a high risk of misclassification, since there is no harmonised diagnosis of asthma, worldwide. As a result, the disease may not be effectively predicted or prevented (e.g [16]). Finally, due to the lack of harmonisation, asthma may be overdiagnosed in some developed countries, given that there is also an increased tendency to diagnose asthma in patients with respiratory symptoms [17]. In the above review [9], it was followed the definition used in observational studies of “asthma onset” for incidence and prevalence studies using ‘doctor’s diagnosed asthma and wheezing with and without asthma medication. So the results of some of the studies discussed below should also be seen under this light, keeping in mind, however, all the above considerations. In two Nordic studies (Sweden and Norway), no direct association was found between home ventilation rates and asthma and allergy among children ([18,19], Sweden [20];, Norway). However, in both studies, ventilation rates greater than 0.5 h
1 were reported. More specifically, the Swedish studies [18,19] examined the impact of building characteristics and indoor air quality on recurrent wheezing in infants (4089 children) in Stockholm, during their first 2 years of their life. The mean ventilation rate was 0.68 h
1. They found out that the age of the building, certain types of buildings (e.g. relatively new apartment buildings and singlefamily homes with crawl space/concrete slab foundation), and indoor air humidity (>45%) were associated with recurrent wheezing in children up to the age of two. The results from this study should be seen keeping in mind that a reliable diagnosis cannot be achieved under the age of six. A strong correlation between indoor and outdoor humidity levels were also found during the winter months, which shows that indoor humidity was influenced by that outdoors. A weak association was found between ventilation rates and NO2 levels in homes with no NO2 indoor sources. In the Norwegian study, 63% of the homes had rates greater than 0.5 h
1 [20,21]. In this study, it was hypothesised that bronchial obstruction among children was associated with exposure to phthalates from PVC materials and with dampness and that this association became elevated at a low ventilation rate (below 0.5 h
1). However, the hypothesis regarding the potential role of phthalates exposure to asthma was severely criticised [22,23]. The former [22] concluded that there are no reported chemicals in indoor environments that promote development of allergy by adjuvant effects (in agreement with [24,25]). Indoor dust was associated with allergy-promoting effects in humans, although further research is required. Exposures to dampness and combustion particles (e.g. [26]) may also be associated with the promotion of asthma and asthmatic symptoms, but not the phthalates. Insufficient ventilation has recently been associated with the observed increase in allergic diseases among children. The relation

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between IAQ and asthma/allergy was studied in a Swedish investigation comprising 11,000 children [27,28]. Detailed chemical, physical, biological and medical measurements were performed in 200 homes with asthmatic children (cases) and 200 homes with healthy children (controls). In contrast to the previous studies with higher ventilation rates, the single-family houses had a mean rate of 0.36 h
1, whereas the multi-family house had a rate of 0.48 h
1. The results showed that allergic symptoms were related to ventilation. Cases with doctor-diagnosed rhinitis and eczema lived in single-family houses where the ventilation rates in the child’s bedroom (0.35 h
1) were lower compared with controls (0.51 h
1). However, no association was found between ventilation rate and doctor-diagnosed asthma. The lack of an association indicates that there are no immunological mechanisms involved. Instead, a low ventilation rate could be considered as a risk factor for irritation. The effects of different types of buildings to cases and controls were also examined [28]. Regarding single-family houses, cases were more likely than controls to live in houses that had mechanical exhaust ventilation, were constructed in the period 1961e1983, had a concrete foundation, and were one-storey buildings. In multi-family houses and row houses, there were no significant effects to the cases and controls, given also the higher ventilation rates measured there. Adequate ventilation is important to reduce indoor air humidity. This is confirmed by the negative correlation between ventilation rate and the indoor humidity found in another study [19]. Indoor air humidity increases the risk of dampness in dwellings and of infestation with house dust mites (HDM). Excess moisture on indoor materials leads to microbial growth, i.e., mould, fungi and bacteria, which subsequently emit spores, cells, fragments and MVOCs into indoor air (e.g. [29e32]). Sufficient epidemiological evidence from different studies and under different climatic conditions show that the occupants of damp or mouldy houses are at increased risk of respiratory symptoms, respiratory infections and exacerbation of asthma. Some evidence suggests increased risks of allergic rhinitis and asthma (e.g. [33e37]). For instance, damp housing was one of the factors associated with wheeze ever, significantly associated with recurrent wheeze and strongly associated with severe wheeze in a study of Dutch infants (1115 questionnaires), in their first year of their life [38]. Observations and measurements were carried out in a nested caseecontrol study of 198 children with asthmatic and allergic symptoms (cases) and 202 healthy controls, in Sweden [39]. These were performed by inspectors, and the children were examined by physicians for diagnoses of asthma, eczema, and rhinitis. They found an association between mouldy odour along the skirting board (which can be a proxy for hidden moisture problem inside the wall construction or in the foundation construction) and allergic symptoms among children, mainly rhinitis. They pointed out that the highest odds ratios for case children were found in homes with a low ventilation rate (below the median of 0.34 h
1) and the strongest association was found for rhinitis. They did not find any associations with any of the allergic symptoms for discoloured stains, floor dampness or a general mould odour in the rooms. Furthermore, in a subsequent study, no association could be found between the spore concentration in indoor air and asthma/ allergy in the children [36]. Exposure to HDM is a well-known risk for sensitisation and symptoms among sensitised persons (e.g. [40,41]). For dwellings in a Nordic climate, the EUROVEN group concluded that ventilation rates above 0.5 h
1 decrease the risk infestation of HDM [14]. Based on the results of theoretical modelling, a study in the UK suggested that although in most cases 0.5 h
1 is required to avoid mould growth, significantly higher ventilation rates (0.8 h
1) may be required to control mites’ growth [42]. Although there is evidence

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that mechanical ventilation in combination with improved thermal insulation of walls and windows reduce indoor RH and HDM allergen burden (e.g. [32,43]), the clinical effects of mechanical ventilation remained unproven. The hypothesis that, domestic mechanical heat recovery (MHRV), in addition to allergen avoidance measures can improve asthma control, was recently tested in half the homes of 120 adults with asthma in the UK, allergic to Der p 1 [44]. They did not find any effect of MHRV on mite allergen levels, but indoor relative humidity (RH) was improved and evening peak expiratory flow of the MHRV group also improved compared to the control group. This suggested that improved ventilation may need to be considered in the bedrooms of asthmatic children. Furthermore, another study was carried out to test the hypothesis that targeted low-cost interventions in homes of asthmatic children improve asthma symptoms [45]. The major interventions were HVAC servicing, dehumidification, and improved air filtration. The most effective intervention types at reducing breathing problems were HVAC servicing (p < 0.05) and dehumidifiers (p < 0.05). Coughing was significantly reduced (p < 0.005) for homes with one of the three interventions and for homes receiving all interventions. Wheezing was slightly but not significantly decreased for all interventions and increased or stayed the same when dehumidification and room air cleaners were evaluated alone. Although a few intervention studies are available, their results show that remediation of dampness problems can reduce adverse health impacts [37]. According to WHO guidelines, well-designed, well-constructed and well-maintained building envelopes can prevent and control excess moisture and microbial growth. Control of temperature and ventilation distributed effectively throughout spaces are required to avoid excess humidity, condensation on surfaces and excess moisture in materials. Finally, home ventilation can modify the risk of asthma/allergic symptoms among children due to exposure to outdoor traffic penetrating indoors. Increased ventilation rates may have a negative effect on indoor air quality. Thus, in homes with no indoor sources, a positive correlation between indoor and outdoor NO2 levels was reported (e.g. [19]). However, homes with air-conditioning can have reduced ventilation rates and hence smaller exposure to indoor pollutant levels of outdoor origin. A cross-sectional study of 2994 children living in homes without any other risk factors [46], reported that for preschool children sleeping in non-air conditioned homes, there were strong associations between asthma and rhinitis symptoms studied; however, there were no associations for children sleeping in air-conditioned homes. 2.2. Ventilation and elderly A survey of 96 subjects was carried out between the ages of 60 and 95 years, living close to Paris in a social collective habitat [47]. Their results suggest that the lifestyle and the behaviour of elderly people (e.g. long hours of gas-cooking, overuse of chemical cleaners, increased time spent in the kitchen instead of the living room, drying clothes in the living room) cause indoor air pollution. However, they point out that the principal risk for health problems is inadequate ventilation (e.g. unclean screens, blocked air vents and closed windows), which increases the concentration of indoor pollutants. These risks are amplified by ignorance or negligence about the hazards of indoor pollutants and inadequate ventilation. 2.3. Ventilation and perceived IAQ The “sick building syndrome” [48] involved a set of symptoms which office workers have reported, although today attention is

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given on single symptoms [49,50]. However, there is not much information on how common these symptoms are among the occupants of dwellings and whether the occurrence of the symptoms is related to the home environment. A study in the Helsinki Metropolitan Area [51] was performed among 473 occupants of 242 dwellings (houses and apartments), with different ventilation systems, in order to evaluate the occurrence of “sick building syndromes” and the perception of poor indoor air quality among the occupants. Simultaneously, a twoweek period of indoor air quality monitoring was performed between November 1988 and April 1989. Their main conclusions were as follows:  The most common perception was stuffiness;  22% of the occupants perceived that the ventilation rate of the bedroom was often insufficient;  46% of the occupants felt the bedroom air was sometimes or often stuffy in the mornings during the two weeks;  40% of the occupants felt the bedroom air was usually too dry in winter-time;  At least one day over the two-week period, B Half of the occupants reported that they had had sneezing (51%) and/or nasal congestion (50%); B One third of the occupants expressed nasal discharge (34%), nasal dryness (33%), dryness or itching of the skin (36%), headache or migraine (31%) and lethargy, weakness or nausea (35%); B 25% of the occupants reported that they had had cough and 19% dryness, irritation or itching of the eyes, whereas 6% of the occupants expressed breathlessness on at least one day during the two weeks. The occupants of the apartments reported systematically more symptoms and perception of poor indoor air quality than the occupants of the houses. Furthermore, the occupants of the naturally ventilated houses reported eight out of ten symptoms and complaints more commonly than those in the houses with balanced ventilation. However, the measurements of ventilation rates in the different types of dwellings did not provide a clear answer regarding the differences in the occurrence of symptoms and complaints, since the measured air change rates were on average higher in the apartments (0.64  0.30 h
1) than in the houses (0.45  0.22 h
1). Reduced ventilation flow in dwellings below the value of 0.5 h
1 may cause a perception of impaired air quality. A one-year crossover intervention study [52] was carried out in 44 subjects in a multi-family building, to determine if seasonal adapted ventilation (i.e. a 25e30% reduction of outdoor ventilation flow during heating season) influenced sick building syndrome (SBS) and the perception of the indoor environment. Their measurements showed that reduced ventilation slightly increased the relative air humidity by 1e3% in the living room and 1e5% in the bathroom, during heating season, increased the room temperature slightly by 0.1e0.3  C, and the mean CO2 concentration in the bedroom. The indoor air quality was perceived as poorer, whereas there was a significant increase of stuffy odour. However, there was no significant influence on SBS symptoms or specific perceptions such as draught or air dryness. 3. Regulations on ventilation in European dwellings On European level, there are two directives that relate to ventilation, but in an indirect way: the Construction Product Directive (CPD, 1989), and the Energy Performance of Buildings Directive (EPBD, 2002). Thus, CPD requires construction product

standards that relate to hygiene, health and the environment to be aligned within the member countries, whereas EPBD mentions that energy “requirements shall take account of general indoor climate conditions, in order to avoid possible negative effects such as inadequate ventilation”. The European Committee for Standardization (CEN) is the body responsible for most of the standards relating to ventilation. Many standards have already been published and others are in development [53]. Table 1 summarises the standards/regulations related to the whole building and room by room ventilation rates in European dwellings. These derived from AIVC Annotated Bibliography 13 [48], a review paper on ventilation regulations [54] and other individual sources ([55] for Portugal [56]; for Czech Republic). 4. Measurements/modelling of residential ventilation rates Measurements of ventilation rates as well as modelling work have been carried out in several European Countries with emphasis given in the Nordic Countries as well as the North European. Recently, ventilation measurements were also reported in the Mediterranean countries. The ventilation conditions of dwellings in a number of European countries are discussed in this Section. The results from monitoring or modelling studies for all the countries are reported in Table 2. 4.1. Belgium Building regulations in Belgium have recently been in place. The regulation on the Energy Performance of Building (in place since 2006 in Flanders, since 2008 in Brussels Region and foreseen in 2010 in the Walloon Region) requires that new buildings fulfil certain ventilation requirements (standard NBN D 50-001). No legal requirements are in place for the airtightness of buildings. In consequence, it is expected that new constructed building will become more and more airtight and the ventilation rates are expected to decrease. Given the absence of regulation, there are no reported measurements of ventilation rates in the open literature. However, modelling work has been carried out using CONTAM to determine the air change rates in a model detached house, for various conditions and systems of ventilation, under fixed conditions for airtightness, and for compliance with the standard NBN D 50-001 [57]. The parameters used in the simulations are briefly summarised below.  Building model house with 4 façades, floor space of 153.7 m2 and volume of 379.7 m3.  Dynamic simulations during the heating season (from 28/9 to 15/4) using Contam.  Ventilation: B System A standard I (natural ventilation), according to NBN D 50-001; B System C standard I (natural supply and mechanical exhaust), according to NBN D 50-001; B System D standard I (mechanical ventilation), according to NBN D 50-001; B System "D low energy", characterised by a lower operation flow (about 50% for the flow of fresh air) and an air recycling from 2 bedrooms to the living room; B System "D occupancy” the ventilation system operates on occupant demand (assuming an occupancy profile).  Airtightness of the building envelope: B 3 m3/h/m2 for the System D low energy; B 12 m3/h/m2 for all the other systems.

Table 1 Ventilation standards/Regulations in European dwellings. Country and Standard/ Regulation reference

Whole building ventilation rates

Belgium (NBN D 50-001 1991)

Finland (NBC e D2)

France (Arreté du 24.3.82)

Germany (DIN 1946 Part 6, DIN 18017, VDI 2088)

0.5 h
1

0.5 h
1

> 0.4 h
1 General rule: Outdoor air flow should be at least 0.35 l/s.m2 (1.26 m3/h.m2) Min air flow for dwellings, according to number of habitable rooms (R) 1 R: 105 m3/h 2 R: 120 m3/h 3 R: 150 m3/h 4 R: 165 m3/h 5 R: 210 m3/h 6 R: 210 m3/h 7 R: 210 m3/h

<50 m2, up to 2 occupants, Nat. vent: 60 m3/h Mech. vent: 60 m3/h 50e80 m2 up to 4 occupants Nat. vent: 90 m3/h Mech. vent: 120 m3/h >80 m2 up to 6occupants Nat. vent: 120 m3/h Mech. vent: 180 m3/h

Bedroom

Kitchen

Bathroom þ WC

WC only

Supply 1 l/s/m2 <21 m2, 75 m3/h 21e42 m2, 3.6 m3/h.m2 >42 m2 150 m3/h 0.3e0.6 h
1

Supply 1 l/s/m2 <7 m2, 25 m3/h 7e20 m2, 3.6 m3/h.m2 >20 m2 72 m3/h 0.3e0.6 h
1

Exhaust 1 l/s/m2 <14 m2, 50 m3/h 14e21 m2, 3.6 m3/h.m2 >21 m2 or open 75 m3/h Extraction: 100 m3/h

Exhaust 1 l/s/m2 <14 m2, 50 m3/h 14e21 m2, 3.6 m3/h.m2 >21 m2 75 m3/h Extraction: 75 m3/h

Exhaust 25 m3/h

Supply: Hinged window, hatch or door, or fresh air valve. Extraction: 20 l/s (72 m3/h). The air shall be extracted through an extractor hood.

Supply: Hinged window, hatch or door, or fresh air valve. And/or opening to the access. Extraction: 15 l/s (54 m3/h)

Supply: Hinged window,hatch or door, or fresh air valve. And/or opening to the access. Extraction: 10 l/s (36 m3/h)

Exhaust 20 l/s (72 m3/h)

Exhaust 15 l/s (54 m3/h)

Extract flow depends on number of habitable rooms (R). Continuous: 20e45 m3/h Intermittent:: R: 75 m3/h (min 35 m3/h) 2 R: 90 m3/h (min 60 m3/h) 3 R: 105 m3/h (min 75 m3/h) 4 R: 120 m3/h (min 90 m3/h) 5 þ R: 135 m3/h (min 105e135 m3/h) Normal: 40 m3/h (>12 h occupation/day) 60 m3/h (overall air flow) Purge: 200 m3/h (>12 h occupation/day) 200 m3/h (overall air flow) Kitchenet: 40 m3/h (>12 h occupation/day) 60 m3/h (overall air flow)

1 2 3 4 5

Supply fresh air: Hinged window, hatch or door, together with one or more fresh air valves Small dwellings: total clear opening of at least 2.4 cm2/ m2 (nat. vent) 1.2 cm2/m2 (mech.vent) Multi-storey: total clear opening of at least 1.2 cm2/m2 0.5 l/s/m2 (1.8 m3/h.m2)

1.0e1.5 h
1

Min 4.0 l/s/person or 0.7 l/s/m2 floor area (2.52 m3/h.m2)

R: 15 m3/h R: 15 m3/h R: 30 m3/h R: 30 m3/h þ R: 30 m3/h

40 m3/h (>12 h occup./day) 60 m3/h (overall air flow)

Extraction: 25 m3/h

1 R: 15 m3/h 2 R: 15 m3/h 3 R: 15 m3/h 4 R: 30 m3/h 5 þ R: 30 m3/h

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Czech Republic (CSN 73 4301 Residential Buildings, CSN 73 0540 Thermal protection of Buildings) Denmark (DS 418:2002)

Living room

20 m3/h (>12 h occup./day) 30 m3/h (overall air flow)

(continued on next page)

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Table 1 (continued ) Country and Standard/ Regulation reference

Whole building ventilation rates

Living room

Bedroom

Kitchen

Bathroom þ WC

Greece (Greek Legislative Framework Document)

Detached houses, Estimated 5 persons/100 m2 of floor area. Block of Flats, Estimated 7 persons/100 m2 of floor area.

Detached houses and Flats, Min: 8.5 m3/h/p Recommend: 12e17 m3/h/p

Detached houses and Flats, Min: 34 m3/h/p Recommend: 50e85 m3/h/p

Detached houses and Flats, Min: 34 m3/h/p Recommend: 50e85 m3/h/p

Italy (Ministerial Decree 05.07.75) Netherlands(Building Decree) Norway (Norwegian Building Code)

Naturally ventilated dwelling 0.35e0.5 h
1 300 m3/h

Detached houses and Flats, Min: 8.5 m3/h/p Recommend: 12e17 m3/h/p 15 m3/h/p

1.0 h
1

2.0 h
1

0.9 dm3/s/m2 floor area (3.24 m3/h/m2) Supply: Openable window or inlet bigger than 100 cm2 in external wall.

0.9 dm3/s/m2 floor area (3.24 m3/h/m2) Supply: Openable window or inlet bigger than 100 cm2 in external wall.

21 dm3/s (75.6 m3/h)

14 dm3/s (50.4 m3/h)

7 dm3/s (25.2 m3/h)

Extract: 10 l/s þ 20 l/s (from exhaust hood in use) ( 36 m3/h þ 72 m3/h)

Extract: 10 l/s (36 m3/h)

1.0 h
1

1.0 h
1

4.0 h
1

Extract: Min 10 l/s (36 m3/h) (openable window) Max 30 l/s (108 m3/h) 4.0 h
1

Recommend: Not less than 4.0 l/s/person (14.4 m3/h/p)

Extract: Min 10 l/s (36 m3/h) Kitchenette 15 l/s (54 m3/h)

10 l/s (36 m3/h) with openable window or 10 l/s with high speed rate up to 30 l/s (108 m3/h) or 15 l/s (54 m3/h) without openable window

Rapid vent (opening windows): 1/20th of floor area Background vent: 8000 mm2

Rapid vent: opening window Background vent: 4000 mm2 Extract: 30 l/s adjacent to hob or 60 l/s elsewhere or PSV

Rapid vent: opening window Background vent: 4000 mm2 Extract: 15 l/s or PSV

Switzerland (SIA 180, 1988) (SIA 382, 1992)

UK (Building Regs. Approved Doc. F)

Requirements: Rooms shall have continuous 0.35 l/s/m2 floor area (1.26 m3/h/m2) when in use; This corresponds to 0.5 h
1 in a room with height 2.5 m. 12e15 m3/h/person (non-smoking, max CO2 1500 ppm) 30e70 m3/h/ person (smoking) 25e30 m3/h/person (non-smoking, max CO2 1000 ppm) Air change rate in unoccupied rooms more than 0.3 h
1 Rapid vent (opening windows): 1/20th of floor area Background vent: 8000 mm2

Rapid vent: opening window Background vent: 4000 mm2 Extract: 15 l/s or PSV.

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Portugal (NP 1037e1 Standard for natural ventilation) Sweden (Swedish Building RegulationsBBR94)

Not less than 0.5 h
1

WC only

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4.2. Denmark Studies from Denmark performed in homes built in the mid 1980’s indicated that the ventilation rates in naturally ventilated dwellings were lower than 0.5 h
1, which has been the minimum requirement in the Danish building code for more than 20 years. For instance, a study [58] (reported in [59]) carried out measurements in 28 dwellings and found despite the mean value was greater than the required, about 30% of the dwellings had a ventilation rate lower than 0.5 h
1. Similarly, low values were reported by a study that performed ventilation measurements during the winter period (October to March) in 117 single houses built over the period 1984e1989 [60]. The homes were situated in suburban and rural areas in Denmark. CO2 measurements were carried out in 500 children’s bedrooms and the corresponding ventilation rates were estimated [59]. The subset of 500 children was between 3 and 5 years of age and was selected as the second phase of a large investigation, involving 11,120 children, on the impact of the indoor environment on asthma and allergy among children in Odense, Denmark. The 500 children represented 200 symptomatic children (cases) and 300 randomly selected children (bases). The results show that similar ventilation rates for bedrooms were estimated in both cases. The rates were higher while more people sleeping in the measured room. In both groups, 57% of the rooms did not fulfil the minimum requirement of 0.5 h
1. Following this study, the same team [61] analysed the ventilation rates measured previously by some of the most significant variables e.g. room volume (higher rates in smaller rooms), number of people sleeping in the bedroom (higher rates with more people), average window and door opening habits (higher rates with more opening), sharing the bedroom with other family members (higher rates in shared rooms), location of the measured room (higher rates above ground floor), observed condensation on the bedroom

115

window (higher rates at less condensation), year of construction (lowest rates in buildings from early 1970s). The generally low ventilation rates in newer homes may raise concern about whether or not current construction practices meet the ventilation requirements set by the current guidelines. 4.3. Finland A sample of 242 dwellings, with different ventilation systems (natural ventilation, mechanical exhaust and balanced ventilation (mechanical supply and exhaust)) was studied in the Helsinki Metropolitan area over periods of two weeks during the 1988e1989 heating season [51,62]. The air exchange rates had a high variation, but the majority of the dwellings (73%), had rates between 0.2 and 0.7 h
1. The recommended Finnish value (0.5 h
1) was achieved in less than half of the dwellings (48%). The ventilation rates were significantly lower in the houses than in the apartments. However, comparison of the different ventilation systems did not reveal any great differences. Finland is the country with the highest market penetration of mechanical supply and exhaust ventilation in the EU [63]. Almost all new dwellings are fitted with mechanical ventilation with heat recovery (MVHR) systems. Ventilation practice in Finland changed as a result of the changes in regulation in 2003. According to this, guideline ventilation rates increased from 4 to 6 l/s per person and required a minimum of 30% heat recovery from exhaust air. To examine the effect of this system on ventilation, a study was carried out in 102 newly built detached houses in Finland [64]. Air flow rate measurement showed that only 57% of the houses complied with the regulations. The non-compliance was a result of occupants reducing fan speeds to reduce noise. There were complaints of noisy systems, which correlated closely with noise levels in bedrooms. The study revealed that the fan speed was very rarely changed.

Table 2 Ventilation measurements and modelling in European countries. Study

Country

Number of buildings

Ventilation rates

Units (h
1, m3/h, m3/h.m2)

Comments

De Brouwere et al. (2009)

Belgium

1 detached dwelling, modelling study using CONTAM

h
1

A standard I/Airtightness 12 m3/h/m2

h
1

C standard I/Airtightness 12 m3/h/m2

h
1

D standard I/Airtightness 12 m3/h/m2

h
1

D low energy I/Airtightness 3 m3/h/m2 (15-min values) for infiltration for ventilation

h
1

D occupancy I/Airtightness 12 m3/h/m2 (15-min values) EXPOLIS study, Prague, estimated rates from PM2.5 monitoring data analysis Mean

Hänninen et al. (2004)

Czech Republic

50 dwellings, esimates

1.033  0.37 (0.198e2.897, 15-min values) 1.016  0.32 (0.482e2.57, 15-min values) 1.289  0.209 (1.048e1.628, 15-min values) 0.368 for infiltration 0.921 for ventilation 0.603  0.087 (0.503e1.24) 0.142 0.461 0.83  0.24 (0.18e2.24) 0.75  0.43

Kvistgaard et al. (1990; reported in Bekö et al., 2010 Bergsøe (1991; reported in Bekö et al. (2010) and in Øie et al. (1998))

Denmark

28 dwellings

0.67

h
1

Denmark

123 dwellings

0.33 or 0.86

h
1 m3/h.m2

0.55 or 1.37

h
1 m3/h.m2

Andersen et al. (1997)

Denmark

0.59 or 1.44 0.34 (geo.m) 0.37 (ar. m)

h
1 m3/h.m2 h
1

117 single-family one-story houses;

h
1

Single-family houses with natural ventilation, mean Single-family houses with mechanical exhaust ventilation, mean Apartments with exhaust ventilation, mean Winter measurements (October to March). (continued on next page)

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C. Dimitroulopoulou / Building and Environment 47 (2012) 109e125

Table 2 (continued ) Study

Country

Number of buildings

Ventilation rates

Bekö et al. (2010)

Denmark

500 children’s homes

0.46 0.62 0.46 0.62 0.41 0.52 0.76 1.05 0.24 0.31 0.68 0.61 0.58

 2.09 (geo m)  0.56 (ar. m)  2.13 (geo m)  0.59 (ar. m) (geo m) (ar. m) (geo m) (ar. m) (geo m) (ar. m) (a.m)/0.50 (g.m) (a.m)/0.46 (g.m) (a.m)/0.41 (g.m)

0.56 0.63 0.70 0.59

(a.m)/0.41 (a.m)/0.47 (a.m)/0.50 (a.m)/0.45

Bekö et al. (2011)

Denmark

500 children’s homes e ventilation data analysis Notes: *1st phase questionnaire **Home inspection ***parent-recorded during the days of measurements

Units (h
1, m3/h, m3/h.m2)

Comments

h
1

Case study (200 homes)


1

h

Base study (300 homes)

h
1

80% of homes, with windows closed

h
1

19% of homes, with windows open


1

h

1% of homes, with door and window closed

h
1

Volume of measured room (n ¼ 500)** Smaller than 20 m3 (24.8%) 20e30 m3 (49.6%) Bigger than 30 m3 (26.6%) Size of dwelling (n ¼ 496)* 70e89 m2 (12.1%) 90e109 m2 (15.7%) 110e139 m2 (24.6%) >140 m2 (47.6%) Location of measured room (n ¼ 492)* Basement (0) Ground floor (GF) (52.4%) Higher (H) (47.6%) Ventilation in the home (n ¼ 500)** Natural incl. kitchen fan (58.8%) Mechanical exhaust (n ¼ 202) or exhaust and supply (n ¼ 4) (41.2%) Vicinity to road (n ¼ 486)** Highway/heavily trafficked road (66.0%) Quiet road (34.0%) Constr. year of the dwelling (n ¼ 482)* Before 1941 (I) (26.3%) 1941e1960 (II) (21.4%) 1961e1970 (III) (17.2%) 1971e1976 (IV) (10.0%) 1977e1983 (V) (7.3%) 1984e1993 (VI) (6.4%) After 1993 (VII) (11.4%) House type (n ¼ 491)* Family house (69.2%) Row house (18.3%) Apartment (12.5%) Dwelling location (n ¼ 492)* City (43.9%) Suburb (45.7%) Rural area (5.9%) Village (4.5%) No. of people sleeping in the bedroom (n ¼ 500)*** 1 (59.2%) 2 (24.2%) 3 (12.4%) 4 or 5 (4.2%) Sharing the bedroom (n ¼ 486)* Own room of child (59.5%) Shared with siblings (20.4%) Shared with parents (20.1%) Average window opening during night in the measured room (n ¼ 495)*** Closed (80.8%) Ajar (19.2%) Fully open (0) Average door opening during night in the measured room (n ¼ 479)*** Closed (9.6%) Ajar (45.3%) Fully open (45.1%) Condensation in winter on the window of the measured room (n ¼ 473)* None (31.9%) <5 cm (49.3%) >5 cm (18.8%)

(g.m) (g.m) (g.m) (g.m)

h
1

N/A 0.53 (a.m)/0.40 (g.m) 0.70 (a.m)/0.52 (g.m)

h
1

0.59 (a.m)/0.44 (g.m) 0.66 (a.m)/0.49 (g.m)

h
1

0.61 (a.m)/0.44 (g.m) 0.63 (a.m)/0.48 (g.m)

h
1

0.67 0.46 0.54 0.47 0.75 0.72 0.53

(g.m) (g.m) (g.m) (g.m) (g.m) (g.m) (g.m)

h
1

0.63 (a.m)/0.47 (g.m) 0.62 (a.m)/0.45 (g.m) 0.54 (a.m)/0.41 (g.m)

h
1

0.62 0.59 0.63 0.78

(a.m)/0.46 (a.m)/0.44 (a.m)/0.47 (a.m)/0.56

(g.m) (g.m) (g.m) (g.m)

h
1

0.46 0.63 1.08 1.39

(a.m)/0.38 (a.m)/0.48 (a.m)/0.82 (a.m)/1.09

(g.m) (g.m) (g.m) (g.m)

h
1

0.48 (a.m)/0.39 (g.m) 0.60 (a.m)/0.46 (g.m) 1.03 (a.m)/0.73 (g.m)

h
1

0.52 (a.m)/0.41 (g.m) 1.05 (a.m)/0.76 (g.m) N/A

h
1

0.48 (a.m)/0.30 (g.m) 0.55 (a.m)/0.43 (g.m) 0.71 (a.m)/0.53 (g.m)

h
1

0.70 (a.m)/0.53 (g.m) 0.59 (a.m)/0.43 (g.m) 0.54 (a.m)/0.40 (g.m)

h
1

(a.m)/0.50 (a.m)/0.48 (a.m)/0.40 (a.m)/0.41 (a.m)/0.54 (a.m)/0.47 (a.m)/0.45

C. Dimitroulopoulou / Building and Environment 47 (2012) 109e125

117

Table 2 (continued ) Study

Country

Number of buildings

Ventilation rates

Units (h
1, m3/h, m3/h.m2)

Comments

Ruotsalainen et al. (1991; 1992) (also reported in Øie et al., 1998)

Finland

242 dwellings

0.52 (0.07e1.55) 0.45  0.22 0.64  0.30 0.41  0.22 0.46  0.19 0.49  0.26 1.01 1.12 1.26 1.55 1.69 1.52

h
1

3 ventilation systems, mean value (range) Houses Apartments Natural ventilation Mechanical ventilation Balanced ventilation Single-family houses with natural ventilation, mean Single-family houses with mechanical exhaust ventilation, mean Single-family houses with balanced ventilation Apartments with natural ventilation, mean Apartments with exhaust ventilation, mean Apartments with balanced ventilation, mean Houses equipped with MVHR systems

m3/h.m2

0.4

h
1

Finland

102 newly built detached houses 50 dwellings

0.81  0.85

h
1

France

447 bedrooms

27.4 (1e212)

m3/h

19.8 (1e142) 18.0 10.0

m3/h m3/h

94 bedrooms

32.9 (4e210)

m3/h

46 bedrooms 169 bedrooms

23.5 (3e119) 22.7 (3e196)

m3/h m3/h

138 bedrooms

29.6 (1e212)

m3/h

10 houses in West Berlin

1.2 (0.3e3.7) 1.0 (0.2e1.8)

h
1

0.36 0.65 0.78 0.35 0.4 (minimum 0.3) 1.14  1.05 0.74 0.52 Range 0.5e1.5 1.5 0.5 0.21 and 0.28 0.97 and 0.35 1.3  1.1

h
1

Kurnitski et al. (2007)

Finland

Hänninen et al. (2004)

Lucas et al. (2009)

Mailahn et al. (1989)

Germany

Kroob et al. (1997) Reported in BIA (2001)

Germany

Feist et al. (2007)

Germany

Modelling results

Santamouris et al. (2007)

Greece

50 dwellings

Sfakianaki et al. (2008)

Greece

20 dwellings

Bartzis et al. (2009)

Greece

2 flats

Hänninen et al. (2004)

Greece

50 dwellings, estimates

Van der Wal et al. (1991)

Netherlands

14 houses

0.3e0.9 (mean 0.6) 1.05e1.35 (mean 1.2) 0.6 (0.6) 1.7e8.3 0.6e3.1 0.3e0.9 1.5e4.0

h
1

Hasselaar (2002)

Netherlands

38 houses

h
1

De Gids (2004)

Netherlands

86 houses

0.3.
0.3 0.5e0.7 0.5e0.7 0.7 - >1.2 <0.3 <0.5

h
1 h
1

h
1

h
1 h
1

h
1

EXPOLIS study, Helsinki, estimated rates from PM2.5 monitoring data analysis Night-time measurements 1 h e 5 h10 am (peak values) Night-time measurements, average Night-time measurements, median Night-time measurements, median, closed doors and windows Night-time measurements, no ventilation system Night-time measurements, local fans Night-time measurements, mechanical ventilation Night-time measurements, natural ventilation September 1986eApril 1987 Hexafluorobenzene (HFB tracer) Polytetrafluoroethylene (PTFE tracer) Dwellings Rooms with double windows, with sealing Rooms with double windows, without sealing Rooms with highly insulated windows PassivHaus Standard Winter 2004, naturally ventilation Smoking activity (median) Non-smoking dwellings (median) Summer 2005, naturally ventilation Low airtightness level (10 h
1 at 50 Pa) Tight dwellings (4 h
1 at 50 Pa) Winter, natural ventilation Summer, natural ventilation EXPOLIS study, Athens, estimated rates from PM2.5 monitoring data analysis Rotterdam, 4 apartments, naturally ventilated Rotterdam, 4 apartments, mech. balanced ventilated Rotterdam, 2 single houses, naturally ventilated ’s Hertogenbosch, 4 houses, mech. balanced ventilated ’s Hertogenbosch, Kitchen ’s Hertogenbosch, Living room ’s Hertogenbosch, Bedroom (closed windows) ’s Hertogenbosch, Bedroom (open windows) all openings closed; door to circulation area (indoors) open; window open, door closed; window and door open. 10% of houses 33% of houses (continued on next page)

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C. Dimitroulopoulou / Building and Environment 47 (2012) 109e125

Table 2 (continued ) Study

Country

Number of buildings

Ventilation rates

Units (h
1, m3/h, m3/h.m2)

Comments

Balvers et al. (2008)

Netherlands

4 PassivHaus homes

13e20 6.5e23 5.5e15 8e62 62e110

m3/h

Øie et al. (1998)

Norway

344

1.69 1.58 1.84 1.51 0.73 0.69 0.64 0.60 0.75 0.65 0.81 0.51 0.63 1.1 0.8 0.5 1.2 <0.5

m3/h.m2

0.23 (geo m) (0.07e0.54) 0.16 (geo m) (0.06e0.58) 0.83 0.86 1.04 1.19 1.40 1.44

h
1

Ranges of arithmetic means; Bedroom 1 (2 persons); Bedroom 2 Bedroom 3 Bathroom Total air flow Single-family houses, natural ventilation Single-family houses, exhaust ventilation Apartment buildings, natural ventilation Apartment buildings, exhaust ventilation Before 1945, mean 1946e1965, mean 1966e1974, mean 1975e1987, mean 1988e1993, mean Mixed system, summer, mean values Mixed system, winter, mean values Natural ventilation, summer Natural ventilation, winter Winter, healthy building, living room Winter, healthy building, living room Winter, unhealthy building, living room Winter, unhealthy building, living room Summer and autumn (80% of dwellings); Spring (70% of dwellings); Winter (50% of dwellings) Dwellings Shelters (sealed rooms inside the dwellings)

0.68  0.32 0.36 0.35 0.35 0.37 0.48 0.51 0.37/0.34 0.32/0.32 0.44/0.47

h
1 h
1

0.41/0.37 0.30/0.29 0.39/0.42

h
1

0.36/0.34 0.42/0.40 0.32/0.31

h
1

0.31/0.29 0.39/0.38

h
1

Pinto et al. (2006)

Portugal

7 flats

Fernandes (2004)

Portugal

4 flats

Montoya et al. (2010)

Spain

modelling results

Montoya et al. (2011)

Spain

16 single-family dwellings

Stymne et al. (1994) (reported also in Øie et al., 1998)

Sweden

1143 dwellings

Emenius et al. (2004) Bornehag et al. (2005)

Sweden Sweden

540 infants homes 390 children’s homes

h
1

h
1

h
1

h
1

m3/h.m2

h
1 h
1 h
1

Wichmann et al. (2010)

Sweden

18 homes of children (6e11 years old)

0.65  0.27 (0.20e1.31)

h
1

Hänninen et al. (2004)

Switzerland

50 dwellings, estimates

0.83  0.46

h
1

Single-family houses with natural ventilation, mean Single-family houses with mechanical exhaust ventilation, mean Single-family houses with balanced ventilation Apartments with natural ventilation, mean Apartments with exhaust ventilation, mean Apartments with balanced ventilation, mean Apartments and single-family houses, mean Single-family houses, Whole dwelling, mean Single-family houses, Child’s bedroom, mean Raw houses, Whole dwelling, mean Raw houses, Child’s bedroom, mean Multi-family houses, Whole dwelling, mean Multi-family houses; Child’s bedroom, mean Single-family houses, Ventilation system: Natural ventilation; whole dwelling/children bedroom Mechanical exhaust ventilation; whole dwelling/children bedroom Mechanical exhaust/supply ventilation; whole dwelling/children bedroom Single-family houses, Construction period: Before 1960; whole dwelling/children bedroom 1961e1983; whole dwelling/children bedroom After 1984; whole dwelling/children bedroom Single-family houses, Type of foundation: Basement; whole dwelling/children bedroom Crawl space; whole dwelling/children bedroom Concrete on ground; whole dwelling/children bedroom Single-family houses, Number of floors: One floor; whole dwelling/children bedroom >1 floor; whole dwelling/children bedroom 3 with exhaust ventilation, 8 with natural ventilation, 3 with inlet and exhaust, 4 with inlet heated and exhaust ventilation EXPOLIS study, Basle, estimated rates from PM2.5 monitoring data analysis

C. Dimitroulopoulou / Building and Environment 47 (2012) 109e125

119

Table 2 (continued ) Study

Country

Number of buildings

Ventilation rates

Units (h
1, m3/h, m3/h.m2)

Comments

Dimitroulopoulou et al. (2005)

UK

33 dwellings

0.44  0.11 (0.19e0.68) 0.62  0.23 (0.19e1.06) 0.49  0.24 (0.24e0.83) 0.54  0.27 (0.26e0.92) 0.59  0.39 (0.25e1.22) 0.39  0.13 (0.25e0.56) 0.43  0.23 (0.21e0.74) 0.48  0.31 (0.20e1.00) 0.61  0.42 (0.28e1.18) 0.49  0.24 (0.27e0.75) 0.70  0.45 (0.31e1.27) 0.64  0.50 (0.27e1.35) 1.01  0.98 (0.28e2.12) 0.48  0.24 (0.26e0.73) 0.13 0.13 0.16 0.17 0.28 0.25 0.48 0.63 0.32 0.26 0.69 0.48 0.75 0.85 1.08 0.85

h
1

Dwellings built after 1995 Main study, winter Main study, summer

5 dwellings 5 dwellings

4 dwellings

Aizlewood and Dimitroulopoulou (2006)

UK

Flat A1 Flat A2 Flat A3 Flat A4 Flat B1 Flat B2 Flat B3 Flat B4

4.4. France The Indoor Air Quality Observatory (“OQAI” in French), undertook a national survey to assess the air quality in 567 French dwellings, during the period 2003 and 2005 [65]. Following this work, these data, which represent of 24 million primary residences in mainland France Metropolitan, were revisited to establish at the national level, a description as complete as possible of ventilation in dwellings. During the ventilation study, CO2 measurements were carried out for one week in the master bedroom of 447 dwellings, during the night, and the equivalent air change rates have been calculated [66,67]. Half of the residential building stock was built before 1967, i.e. before the first regulations requiring whole-house ventilation, in 1969. Approximately, 70% of the dwellings have mechanical ventilation (35%) and natural ventilation installed (ventilation through lower and higher openings in the walls, passive stack ventilation by ducts or shunt ducts) (34.5%). 9.1% of the dwellings have local fans and 21.45 have no ventilation system. More precisely, natural ventilation is present in older or retrofitted dwellings, while it has almost disappeared from new buildings. It is present in 41% of apartment buildings but only 29% of

h


1

h
1

Peak level study, winter, whole building

h
1

Peak level study, winter, living room

h


1

Peak level study, winter, kitchen

h
1

Peak level study, winter, bedroom 1 (main)

h
1

Peak level study, winter, bedroom 2 (children)

h


1

Peak level study, winter, bathroom

h


1

Peak level study, summer, whole building

h
1

Peak level study, summer, living room

h
1

Peak level study, summer, kitchen

h


1

h
1 h
1 h
1 h


1

Peak level study, summer, bedroom 1 (main) Peak level study, summer, bedroom 2 (children) Peak level study, summer, bathroom HOPE project, spring, living room; bedroom Living room; bedroom

h
1

Living room; bedroom

h
1

Living room; bedroom


1

Living room; bedroom

h
1

living room; bedroom

h
1

Living room; bedroom


1

Living room; bedroom

h

h

individual houses. Mechanical ventilation is equally present in individual houses (35.7%) and apartment buildings (34%). Around 8% of the buildings were built before 1968 and later retrofitted with mechanical ventilation. Around 20% of buildings built after 1975 do not respect the regulation requirements of 1969 or 1982 (i.e. they provide local or no ventilation, instead of whole-house ventilation). 4.5. Germany There are no many measurements of ventilation rates in German dwellings reported in the open literature. Ventilation rates were measured during a program undertaken in West Berlin with VOC sampling in 12 households [68]. The ventilation rates were measured in 10 dwellings during the second half of the campaign (winter period), using the HFB (hexafluorobenzene) technique and comparing the results with those from PTFE (polytetrafluoroethylene) technique [69], applied also in the same dwellings. The mean values using the HFB technique were in the range of 0.5e2.4 h
1, whereas the lowest ventilation rates of were measured during the absence of occupants on vacation. The BIA report from the Institute for Occupational Safety [70], presents some values for air change rates in dwellings, based on an

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C. Dimitroulopoulou / Building and Environment 47 (2012) 109e125

earlier work [71]. These values were used in the calculation methods and model investigations as alternatives to exposure measurement. However, the standard which is currently well known in Germany is the PassivHaus standard [72]. This was developed in Germany and its development was funded by EC between 1997 and 2002 [73], in order to be a leading standard for energy efficient design and construction for cold-climate houses. The PassivHaus Programme, with over 5000 houses built prior to 2005, has promoted development and production of components such as low capacity compact HVAC units, windows and doors and innovative building systems. This standard is used in Germany, Austria and Ireland [74]. The average expected ventilation rates, based on modelling work are given in the PassivHaus Planning Package 2007 [72]. It is recommended that in winter the ventilation rates should be lowered to maintain internal humidity values at acceptable levels [75]. There is a need to demonstrate whether the buildings built under this standard actually perform as well as indicated by the modelled data [76]. 4.6. Greece Measurements of indoor air pollutants were performed in 50 dwellings in Athens, together with measurements of ventilation rates, between December 2003 and April 2004 [77]. The ventilation rates were continuously measured by monitoring CO2 concentration. The research was conducted in low income households located in the poor zones of the city. Almost all the residential buildings in Greece are naturally ventilated, especially during the winter period. During the monitoring period, all openings remained closed. Their results show that 95% of the dwellings had a flow rate below 2 h
1. Airtightness and infiltration measurements were carried out in 20 dwellings, in the Greater Athens Area, during the summer 2005 [78]. For the infiltration measurements, the tracer gas decay method was used. The ventilation rate of dwellings in Athens varied between 0.5 and 1.5 h
1, as a function of the envelope airtightness. During the European BUMA project field campaigns were carried out in five cities across Europe (Milan, Copenhagen, Dublin, Athens and Nicosia) [79]. These campaigns covered, among others, winter and summer weekly ventilation measurements in two public buildings and two private houses in each city, using a tracer gas technique. The results varied a lot due to the different conditions observed, such as absence of occupants and opening of windows. 4.7. Netherlands Indoor air quality was investigated in different types of dwelling in two Dutch cities, in the winter season [80]. The air permeability of the dwellings and the airflows of mechanical air supplies and exhausts were also measured. Based on these, the whole houses air change rates were calculated for 10 and 4 dwellings in Rotterdam and in ’s Hertogenbosch, respectively. The results show that the ventilation rates were generally lower in the naturally ventilated. The mean rates for the whole sample were greater than 0.5 h
1. The majority of dwellings had also similar ventilation rates (>0.5 h
1) in a survey carried out in 86 houses in the Netherlands [81]. A passive tracer gas technique was used and the sampling was undertaken in the living room and the master bedroom, over a period of three months during the heating season. "Ventilation in practice" [82] is also an important source of data and is based on 500 home visits with inspection and interview. The

ventilation rates were calculated for 38 dwellings, based on CO2 concentration logging over periods of 1e10 days per room, under normal weather conditions in April/May and November, and included a diary written by the occupants. The range of values was 0.2e1.6 h
1. There was no correlation between ventilation rates and actual exhaust volume, indicating that the use of windows (cross flow and infiltration) determines the rate rather than the type of ventilation system. Regarding the low energy houses, a study investigated whether the installed mechanical ventilation systems provide sufficient indoor air quality in four Dutch PassivHaus houses [83]. In the Netherlands, a number of houses have been built according to this standard, but the actual performance of these houses has not been thoroughly investigated. The results revealed that the average air flow in use was in all cases lower than recommended by the Dutch Building Code. The questionnaire survey showed the residents played an important role in the level of ventilation and air quality in their own houses; the mechanical ventilation system of all houses was on setting 1, which is the default and should be used when no one is at home. These results indicate that residents must be educated to properly use the PassivHaus ventilation system, in order to improve the indoor environment conditions. 4.8. Norway The total air change rate (h
1) was measured in 344 Norwegian dwellings using the PFT-method (perfluorocarbon tracer gas method), a passive tracer gas method, over a 14-day sampling period [21]. The results show that 36% of all dwellings had rates lower than 0.5 h
1, required by the national building code. The differences between types of dwellings were small. The study revealed that 40% of the single-family houses, 40% of the apartments, and 29% of the detached and semi-detached houses had ventilation rates lower than 0.5 h
1. The ventilation rates between different types of ventilation system did not show substantial differences, either. The dwellings were also categorised according to the construction year. The years 1945, 1965, 1974 and 1987 were major turning points for residential ventilation. After the war, the building techniques and regulations led to more airtight buildings, without, however, simultaneous enhancement of mechanical ventilation, resulting in this way in lower ventilation rates in dwellings. However, in 1980’s, the public awareness increased about the indoor air quality issues and in 1993 the minimum guideline of 0.5 h
1 was introduced. Finally, this study is compared to other Scandinavian studies [62,84,85] and concluded that Norwegian dwellings seem to be better ventilated. The differences in ventilation rates may be due to local climate, inhabitant behaviour with respect to ventilation and selection of population and ventilation rate measurement technique. 4.9. Portugal Ventilation rates were measured and analysed in seven similar flats in a four storey apartment building, using the PFT technique [55]. Six of the studied flats had mixed ventilation (continuous fan driven exhaust system in the kitchen and natural exhaust in the bathroom). For comparison, the seventh flat was naturally ventilated. The measurements were carried out in summer (August 2005) and winter (January/February 2006), in unoccupied flats. The results showed that the average ventilation rates in the flats with a mixed system were always greater than those in the flat with the natural ventilation system. The former were considered by the authors as more “reasonable”, given the high rates in the habitable rooms that are allowed by the Portuguese standards. These rates

C. Dimitroulopoulou / Building and Environment 47 (2012) 109e125

varied slightly with location in terms of height and the orientation of the flats. Within the framework of HOPE project, measurements of ventilation rates were carried out based on SF6 concentration decay [86]. They studied in the living rooms of two flats in naturally ventilated apartment buildings, which were characterised either as “healthy” or “unhealthy”, according to the symptoms reported by the occupants. The results showed that the measurements of ventilation rates alone could not be used to excuse the above characterisation, since in a flat of a healthy building, high CO2 concentrations (>900 ppm) were reported, indicating nonsufficient ventilation. 4.10. Spain Modelling airtighness studies in Spain [87] helped to provide some estimates of ventilation rates, since no experimental data either on ventilation rates or airtightness was not available, until very recently, for Catalan dwellings. The results from these studies showed that the highest ventilation rates were predicted in winter, due to extreme meteorological conditions. The lowest values, under average meteorological conditions were predicted in summer, whereas the lowest values under extreme average meteorological conditions, in autumn. Very recently, some ventilation measurements were performed by the same team in 16 single-family dwellings throughout Catalonia, as well as in sealed rooms inside those dwellings, that could be used as indoor shelters [88]. The dwellings covered different types, years of construction years, floor areas, number of stories, and locations, representing the range of actual dwellings found in Catalonia. All of them had heavy structures, which are typical in Catalonia, i.e. they were built with materials such as concrete, masonry and bricks. The dwellings were naturally ventilated (through windows, doors, and grille vents in kitchens and storage rooms), whereas electrical extractors were only found in kitchens, as required under Spanish law, and in bathrooms without windows. The results show that the Catalan dwellings were airtight, with a geometric mean well below 0.5 h
1. This is probably due to the prevailing construction techniques in Catalonia, which are mainly based on heavy materials. 4.11. Sweden A large Swedish national survey was performed in 1143 dwellings, which is the only representative among the studies in Nordic countries [84]. Their results showed that 85% of single-family houses and 55% of multi-family houses had a ventilation rate below 0.5 h
1 and that these rates are generally low compared to the requirements in Sweden since 1975. A caseecontrol study that was part of the birth cohort study (BAMSE), monitored the homes of 540 infants (cases and controls) of whom 181 were cases for wheezing [19]. Four-week measurements of ventilation and physical parameters were carried out in winter (OctobereMarch). Ventilation rates were measured in all rooms of each infant’s home, using a passive tracer gas technique. Their results showed that in 69% of the homes the ventilation rate exceeded 0.5 h
1. A strong correlation was found between the whole building ventilation rate and the child’s bedroom. The only category of homes, with a mean below 0.5 h
1, was the naturally ventilated single-family homes that were built on crawl space or concrete slab foundation. Ventilation rates were measured in 390 Swedish homes, as part of a large investigation on the impact of the indoor environment on asthma and allergy among children in Sweden [28]. Ventilation rates both of the whole house and bedroom of the children were

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measured during one week in winter (October 2001 and April 2002) with a passive tracer gas method. The sample of dwellings included multi-family and singlefamily houses, either naturally or mechanically ventilated. The measured air change rate in the 390 houses was generally low. The results indicated that more than 55% of multi-family homes and 80% of single-family houses did not meet the national building code requirement of 0.5 h
1. In this study, the mean ventilation rate in the single-family houses were very similar with the ventilation rates in the respective children bedroom. Multi-family houses had higher mean ventilation rates compared to other types. Single-family houses with a mechanical exhaust and supply ventilation system had higher ventilation rates compared to other houses. Dwellings built between 1961 and 1983 had the lowest ventilation rates, together with houses with concrete on ground as foundation. Finally, single-family houses with only one floor had lower ventilation rates than those with more than one floor. Indoor pollutants and ventilation rates were monitored [89], during winter and summer, indoors and outdoors at 18 homes (mostly apartments) of 18 children (6e11 years old), as well as at schools that the children attended. The study was carried out between December 2003 and July 2004. The whole house ventilation rate, were measured using a tracer gas technique (using perfluorobenzene and perfluoromethylbenzene). The rates were measured during day and night in the homes. The houses had different ventilation systems. Unfortunately, this study does not distinguish between the ventilation rates for the various systems. Total ventilation rates for all the types of buildings (both homes and schools) are given, although these buildings have completely different types of building characteristics and use and consequently the ventilation rates should not be mixed up. 4.12. United Kingdom A BRE study [90] investigated the adequacy of ventilation and indoor air quality in homes built since 1995, when the Building Regulations were revised. Measurements of air tightness, ventilation rates, indoor pollutant concentrations, temperature and relative humidity in homes during normal occupancy were performed. The project was divided into a pilot study (NovembereDecember 2001; 4 homes), the main study (January to March 2002; June to September 2002) and the peak level study (January to March 2003; June to September 2003). The total number of homes was 37, monitored twice, in winter and summer. All homes were naturally ventilated but, in bathrooms and kitchens, 34 had extract fans and 3 homes had passive stack ventilators. In the main study, the whole building ventilation rates were measured using the PFT technique over a two-week period. In the peak level study, ventilation measurements were performed in living room, kitchen, bedroom 1 (main), bedroom 2 (children’s) and bathroom. The results of the main study show that in winter (pilot study and phase 1), 68% of homes had a whole house ventilation rate below the minimum design value of 0.5 h
1, which according to BRE research is necessary to avoid condensation [91,92]. In summer (phase 2), 30% of homes had a whole house ventilation rate below 0.5 h
1. Flats seem to be less ventilated than the other types of houses, both in winter and summer. The types of houses with higher ventilation rates are the semi-detached in winter and the centre-terrace houses in summer. However, the statistical analysis shows that there are no significant differences between dwelling types, although a greater sample size may show a significant difference. The peak level study involved further investigation of relative humidity, indoor air quality and ventilation rates in selected homes,

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during the main study (winter and summer months). The selected homes for the peak level study had one or more of the following characteristics: high relative humidity, high indoor air pollutant concentrations, low ventilation rates and occupants reporting the greatest dissatisfaction with air quality during the main study. During the winter peak level study, the highest mean ventilation rates were in kitchens and living rooms and the lowest in bedrooms. In the summer study, the highest mean ventilation rates were in the children’s bedrooms and kitchens. Ventilation measurements were performed in 8 naturally ventilated flats normally occupied (4 flats in two buildings), within the framework of the HOPE project in the UK [93]. The monitoring work was carried out in AprileMay 2004. The ventilation rates in Flats A1 - A4 are at the lowest end of the values measured in the previous study of 37 homes. According to the UK Building Regulations, the trickle ventilators, which are small openings at the top of the window frame, should be left open to provide adequate ventilation. All trickle ventilators were closed in these four flats and consequently, they did not provide the intended background ventilation. The ventilation rates in flats B1eB3 were higher than the minimum design value of 0.5 h
1. The trickle vents in all these flats were fully open (blocked only in Flat B4), although the occupants were not aware of their purpose. The trickle vents provided at least the intended background ventilation. The highest ventilation rates were further explained by open patio doors in the living room and windows in the bedrooms. 4.13. EXPOLIS study The indoor residential and outdoor air PM2.5 concentrations measured in the EXPOLIS study were analysed [94], in order to estimate the infiltration efficiency of PM2.5 particles in four cities (Helsinki, Athens, Basle and Prague). Solving a mass balance equation, the infiltration factor Finf (or Indoor/Outdoor ratio) is as follows:

Finf ¼ I=O ¼ Cinfiltrated =Cgenerated ¼ P a=ða þ kÞ ¼ >a   ¼ kFinf = P
Finf where P the penetration efficiency (dimensionless), a the air exchange rate (h
1), k the decay rate indoors (h
1), The air exchange rates were estimated for the four cities based on PM2.5 decay rates estimated in the US (0.39 h
1) and assuming that the penetration of PM2.5 particles is approximately 1.0. The mean air exchange rate was highest in Athens and lowest in Prague. 4.14. International modelling study An modelling study was carried out in order to investigate the impact of regulations on the house minimum air changes in 15 developed countries, all over the world [95]. Initially, a literature review was carried out on the regulations, standards or guidelines of ventilation requirements for residential buildings of various countries. Then, the minimum air change rates for each country were applied to a model house proposed by the Architectural Institute of Japan in order to compare each other. The model was assumed to have a surface area of 125.9 m2 and a volume of 302.1 m3 and is occupied by a family with 2 children. The estimated whole house minimum air flow rates after the application to the Japanese model house of the regulations for Sweden, Finland, Denmark, Italy and Greece was 0.5 h
1, in the case of Norway and France was 0.7, whereas for Germany and Switzerland were 0.6 and 0.4 h
1, respectively.

The above results show that a large percentage of the dwellings, especially in Northern Europe are under-ventilated with ventilation rates below 0.5 h
1. Furthermore, there is an international effort to reduce CO2 emission by using less energy in the domestic sector, which is expected to further reduce these rates. An extensive review regarding the state-of-the art of highly airtight houses around the world [96] concluded that changes in construction practice lead to highly insulated and airtight structures designed and built with an expectation of a greater use of mechanical ventilation with heat recovering (MVHR) systems. This will have an impact on the quality of air in homes as well as other aspects of the internal environment, such as acoustics and daylight. There are associated risks of declining air quality, but also opportunities for improvement provided that appropriate measures are adopted. It was pointed out the urgent need for research into the performance of highly energy efficient homes with respect to the quality of the internal environment ventilation systems used, and the impact on the health and wellbeing of occupants. 5. Conclusions The major findings from the review on residential ventilation in Europe can be summarised as follows:  Ventilation is increasingly becoming recognised as an important component of a healthy dwelling.  Ventilation is the ultimate strategy to control IAQ. However, modest improvements in construction practice and living conditions, should aim to eliminate first the potential risk of exposure to pollutants due to indoor sources (e.g. to environmental tobacco smoke, to traffic related pollutants that penetrate indoors, to dampness in homes with visible moulds, to volatile and semi-volatile organic compounds due to renovation, painting activities and floorings and to phthalates and chlorine due to the frequent use of cleaning chemical agents) and supply simultaneously with adequate ventilation.  Few conclusive studies were found regarding residential ventilation and its direct association to health effects of vulnerable groups (children and elderly people).  In the studies reviewed here, the value of 0.5 air changes per hour (h
1), which is frequently used in national standards/ regulations in Europe, is reported as a threshold below which associations may occur. However, this value should not be considered as a recommendation for the minimum ventilation level, based on health criteria. On-going European research (HealthVent project) aims at developing health-based ventilation guidelines, considering both health and energy impacts.  Studies in the Nordic countries showed that at ventilation rates greater than 0.5 h
1, there is no direct association between air change rates and asthma or allergy among children. However, at low ventilation rates (lower than 0.5 h
1), allergic symptoms were reported as well as rhinitis and bronchial obstruction. No association was found between ventilation rates and doctordiagnosed asthma. The results from these studies should be seen under the light that there is no commonly accepted set of criteria to identify asthma in epidemiological studies. Studies on asthma, especially in early life (<6 years old), have a high risk of misclassification, since a reliable diagnosis cannot be achieved then.  Certain types of buildings (e.g. relatively new apartments and houses with crawl space/concrete slab foundation) may result in lower ventilation rates and have been reported to be associated with recurrent wheezing in very young children.  Low ventilation can be considered as a risk factor for irritation. Decreased ventilation increases indoor air humidity and

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therefore the risk for dampness in dwellings and the risk of infestation with house dust mites. According to WHO guidelines, remediation of dampness can reduce adverse health impacts. Ventilation requirements receive major attention in building regulations, across Europe. The ventilation standards tend to cluster around common values for recommended ventilation rates. The Nordic countries adopted the minimum requirement of 0.5 h
1 for the whole building ventilation rates. Rates greater than 0.3 h
1 have also been adopted in some countries (e.g. Switzerland and Italy). Ventilation in practice is often poor, resulting in increased concentration of pollutants and hence exposure to health risk. The ventilation measurements in the Nordic countries showed that a large percentage of the monitored dwellings did not fulfil the minimum requirement of 0.5 h
1 (up to 60% in Denmark, about 50% in Finland, 30%e40% in Norway). In Sweden, different samples of dwellings showed contrary results, although the large national study reported 55% of multiple and 85% of single dwellings having ventilation rates lower than 0.5 h
1. The Norwegian dwellings seem to be better ventilated than the other Scandinavian ones. Ventilation rates greater than 0.5 h
1 were reported in the Netherlands as well as in the Mediterranean countries (Greece and Portugal), which had rates greater than 0.5 h
1 and up to 1.5 h
1 in Greece and 1.2 h
1 in Portugal. The naturally ventilated British dwellings were better ventilated in summer (70% > 0.5 h
1) than in winter (68% < 0.5 h
1), showing that the occupants behaviour (window opening in the warmer months) affects the whole building ventilation. Higher ventilation rates were measured in the mechanically ventilated dwellings compared to the naturally ventilated dwellings in a number of countries (e.g. Netherlands, Portugal, Sweden). There is an international effort to reduce CO2 emissions by using less energy in the domestic sector. As a result, low energy houses have been built according to the German PassivHaus standard for energy efficient design and construction for coldclimate houses. Surveys in some houses showed that the occupants should be educated to use properly the ventilation system, whereas measurements are needed to demonstrate if the buildings built under this standard perform as good as indicated by the modelling studies. The residents play an important role in the ventilation level in their own homes. Surveys of occupants showed that people generally think ventilation is important, but their understanding of the ventilation systems in their houses is low. The chain of activities from design through execution to use and maintenance, especially of mechanical ventilation systems, shows weak links. Higher set points required to achieve adequate ventilation are not often used due to the noisy fans. Thus, poor use and lack of knowledge from the occupants seem to be the main problems for the under-ventilated homes.

Acknowledgements This work was carried out as part of the EPHECT project. EPHECT is a European collaborative action, which has received funding from the European Union, in the framework of the Health Programme. The author would like to thank Prof. Peder Wolkoff, NCRWE, Denmark, for his constructive comments and for providing material for this review and Prof. Eduardo de Oliveira Fernandes, IDMECFEUP, Portugal, for his valuable comments.

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