Thermal Improvement in Residential Buildings in View of the Indoor Air Quality – Case Study for Polish Dwelling

K e y w o r d s : Indoor air quality; Airtightness measurement; Exhaust air flow measurement; Natural ventilation; Numerical simulation. 3/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 121 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 3/2018 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 8 0 4 4 M . B l a s z c z o k , A . B a r a n o w s k i 122 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 3/2018 Thermal improvement involves: • Extra thermal insulation for outdoor parts (both walls and a roof), • Window replacement, • Central heating improvement. Window replacement, being one of the major aspects in thermal refurbishment, frequently results in the deterioration of indoor environment conditions. Modern windows with a low heat transfer coefficient are airtight and lead to insufficient air exchange in buildings [5] as well as the rise in relative humidity and CO2 concentration. The air quality in rooms depends on the air parameters, including air temperature and relative humidity. In winter conditions inside the buildings thermal comfort is achieved when temperatures range between 21÷23°C, and relative humidity: 40÷70%. While getting the comfort temperature inside the room is not a problem due to the operation of central heating installation, than maintaining the relative humidity can be troublesome. RH inside the heated rooms very often falls below the recommended value, because the heating results in drying of air. Unless there is insufficient air exchange, with large internal moisture gains (washing, cooking), RH can reach high values. A parameter influencing the air quality in the room is also the concentration of CO2 which is produced by humans. When the air exchange inside a building is not enough the CO2 concentration increases, which can lead to bad mood, sleepiness, headaches, etc. The concentration of carbon dioxide is easily measurable and therefore often used in measurements as an indicator of air quality [6]. According to Polish Standard PN-83/B03430/Az3:2000 [7] in a multifamily building of up to 9 stories, natural or mechanical ventilation can be used. Higher buildings should have mechanical exhaust ventilation or supply-exhaust ventilation. The standard specifies the minimum ventilation air stream in a dwelling (the sum of exhaust air streams from auxiliary rooms): • For kitchen with external window, used gas or coal cookers – 70 m3/h, • For kitchen with external window, used electric cookers, in apartments for up to 3 people – 30 m3/h, – in apartments for more than 3 people – 50 m3/h, • For kitchen without external window, used electric cookers – 50 m3/h, • For bathroom (with or without toilet) – 50 m3/h, • For separate toilet – 30 m3/h, • For auxiliary room without windows – 15 m3/h. Thus, in case of the most common dwellings in Poland, the total exhaust air stream amounts to 120 m3/h (kitchen with external window, used gas cookers, bathroom) or 150 m3/h (dwellings with separate toilet). Pursuant to Journal of Laws Dz.U. 2002.75.690 [8] special supply ventilation units or mechanical ventilation should be used if the airtight window frames render the external air infiltration impossible. The above mentioned regulation [6], as amended, applies to construction or extension of a building. Thermal improvement, window replacement in particular, are renovation works and as such are not governed by the regulation in question. Tilt and turn windows are most often used in the improved buildings. Such windows have the microventing option, which makes the airtightness lower, yet it is hardly ever used in winter so as not to cool the premises. The research [5] done in Polish multifamily buildings showed that the exhaust air streams from the dwellings amounted to 10÷105 m3/h, which is only a fraction of the required values determined by PN83/B-03430/Az3:2000 Standard. The measurements described in [9] and carried out in winter in a few Polish naturally ventilated dwellings located in a 5 and 11-storey buildings proved that the exhaust air stream was much lower than the one specified by the standard. In case of a 5-storey building the stream was 32÷105 m3/h (the required value was 150 m3/h). It was even worse in the 11-storey building, where the exhaust air stream was 0÷63 m3/h for closed airtight windows and 18÷83 m3/h for widows with the microventing option. The problem of insufficient air exchange in improved buildings across Poland and the Czech Republic was indicated, inter alia, in [10]. France was fraught with similar problems during 1980s, when trickle vents had been used until mechanical ventilation was introduced. The air permeability is the air parameter that influences the air exchange in a building. It is characterized by n50 coefficient that specifies the number of air exchanges within 1 hour with the outdoor and indoor pressure difference amounting to 50 Pa. The airtightness of the building envelope (or the airtightness of the dwelling), should be in accordance with PN-EN 12831 standard [11] (Table 1). THERMAL IMPROVEMENT IN RESIDENTIAL BUILDINGS IN VIEW OF THE INDOOR AIR QUALITY – CASE STUDY FOR POLISH DWELLING E N V I R O N M E N T e 3/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 123 As proved by research [5], the values are frequently not reached in case of Polish dwellings, especially if they are equipped with airtight windows. Regarding the dwellings with modern windows the n50 coefficient amounted to 1.5 h-1, whereas as regards old and mixed windows the n50 coefficient was 2.7÷3.8 h-1. The results show that the dwellings equipped with old windows are classified as medium airtight while the ones with modern windows – demonstrate high airtightness (Table1). When assessing air exchange in a building/dwelling, air exchange rate is often applied. According to Polish Standard PN-EN 12831:2006 [11] the minimum air change rate in dwellings should be 0.5 h-1. The same standard applies in many European countries. The research carried out in European countries [12] shows that the air exchange rate of 0.5 h-1 is not always reached. (Denmark –in 60% of the examined dwellings n<0.5 h-1, Finland – 50%, Norway – 30÷40%). In addition, the data contained in [13] show that the air exchange rate in Swedish detached houses and dwellings is lower than 0.5 h-1 (0.47 h-1 for dwellings, 0.33 h-1 for detached houses). A similar low air exchange rate is observed in Catalonia, Spain due to heavy structure of the buildings [14]. The situation looks much better in Mediterranean countries – n=1.5 h-1 in Greece [15, 16], n=1.2 h-1 in Portugal [17]. Thus, air exchange rate depends on the outdoor climate, buildings are not so airtight in warm climate. The impact of outdoor climate on opening the windows was observed in Great Britain, where the air exchange rate in 70% of the dwellings was over 0.5 h-1 in the summer and in the winter in 68% of the dwellings, it did not exceed 0.5 h-1 [18, 19]. In a similar way, the research done in four different regions of various climates across the USA showed that the air exchange rate dropped to 0.42 h-1 in winter [20] whereas in warm climate regions (California, New Jersey, Texas) it amounted to n =0.71 h-1 [21]. The air exchange rate of n=0.5 h-1 is insufficient as shown by the research in European countries [12] and results in health problems of the part of the residents. Too little amount of fresh air in rooms brings about an increase in indoor pollutants as well as humidity and can result in SBS and allergy (mite build-up). In over 55% of the dwellings and 80% of the detached houses in Sweden the air exchange rate did not exceed 0.5 h-1 [22, 23]. The readings in Denmark are comparable to the ones in Sweden [24, 25]. The studies [26] carried out in Danish children’s bedrooms (4÷5-year olds) demonstrated that in 57% of the case, the air exchange rate was lower than 0.5 h-1. The average CO2 concentration was below 1000 ppm in 32% of the bedrooms while in 23% of the dwellings it reached 2000 ppm, and in 6% of the rooms exceeded 3000 ppm. Lower CO2 concentrations were recorded in rooms where a parent slepts together with the children, which suggests that the rooms were ventilated more often. It seems that ignorance on the part of the residents over insufficient fresh air amount plays a crucial part. The research done in Polish bedrooms [27] demonstrated periodical increase in CO2 concentration exceeding 3800 ppm. The research in question showed the average CO2 concentration in the examined bedrooms to range from 535 ppm to 2755 ppm within 8 hours. In two out of three cases CO2 rise did not exceed the recommended Ashrae Standards 62.1-2010 [28] of 700 ppm above CO2 concentration in outdoor air. The same was true for spacious rooms, with the cubic capacity of approximately 25 m3 for one person. The literature shows the issue of inadequate air exchange rate to be a common problem in many European countries. With energy saving in mind and low awareness of air exchange, residents frequently end up with low quality of indoor air.