Energy Consumption and Indoor Environmental Quality of a Residential Building Before and After Refurbishment

The study was performed in one residential building before and after its renovation. Energy auditing and classification of the selected building into energy classes were carried out. This study investigates the impact of energy renovation on the indoor environmental quality of apartment building during heating season. Evaluation of indoor air quality was performed using objective measurements and subjective survey. Concentration of CO2 was measured in bedrooms, and sampling of total volatile compounds was performed in the living rooms of the selected apartments. Higher concentrations of CO2 and TVOC were observed in the residential building after its renovation. The concentrations of CO2, and TVOC in some of the cases exceeded the recommended maximum limits, especially after implementing of energy saving measures on the building. The average air exchange rate was visible higher before renovation of the building. The current study indicates that large-scale of renovations may reduce the quality of the indoor environment in many apartments, especially in the winter season.

Keywords: Carbon dioxide concentration; Energy renovation; Indoor environment quality; Volatile organic commands concentration

Most of the residential buildings in Slovakia that were built in the 20th century do not satisfy the current requirements for energy efficiency presented in the national building code. Nationwide remedial measures have been taken to improve the energy efficiency of these buildings and reduce their energy use (Földváry V., Bekö G., Petráš D. (2014)). However, since the impact of these measures on indoor air quality is rarely considered, they often compromise indoor air quality due to the decreased ventilation and infiltration rate.

The highest development in the housing stock, as a result of economic changes and population growth, has been recognized as taking place during the second half of the 20th century (Jurelionis A., Seduikyte L. (2010)). The majority of housing in Central and Eastern Europe was constructed from panel technology. The degradation of its quality, which has led to its renovation, has become one of the most important measures from an energy-saving point of view.

The aim of the study was to evaluate the impact of basic energy-saving measures on indoor air quality in a typical high-rise residential building built in the 1960s in Slovakia.

Building description and building energy

The residential building investigated (Figure 1) is located in Šamorín, Slovakia. It was built in 1964 from lightweight concrete panels. The building was naturally ventilated. Exhaust ventilation was only used in sanitary rooms, such as the bathrooms and toilets.  Renovation of the building was carried out in 2015 and included the following measures: insulation of the building envelope using polyethylene (80 mm), insulation of the roof using mineral wool (120 mm) and hydraulic balancing of the heating system. New plastic frame windows had already been installed over the last years in most of the apartments in the building.(Földváry V., Bekö G., Petráš D. (2015)).

Table 1. Heat transfer coefficients of the structures.

The heat demand was calculated for the non-renovated and renovated condition. The highest energy-saving is provided by the thermal insulation of the external walls. This can be explained with the large heat exchange surface of the walls. On the Figure 2, is clearly indicated the heat demand for the structures for square meter and the solar and heat gains for both types of residential building. The figure shows that the heat demand for the insulated part of the building significantly decreased and for the calculated air exchange rate (AER) and gains remained the same.

The renovated and non-renovated residential building were classified into energy classes by the valid Slovak legislation: Decree of the Ministry of Transport, Construction and Regional Development No:300/2012.

The energy-saving measures mentioned above decreased the energy consumption by 55%. In accordance to our law on energy efficiency of buildings, the original dwelling belonged to the ‘E’ category (159 kWh/m²a), after refurbishment to the ‘B’ category (74 kWh/m²a).

Figure 3. Energy certificate of the non-renovated building.

Figure 4. Energy certificate of the renovated building.

Methodology

The first round of the measurements was performed in January 2015 when the building was still in its original condition, and the second round was performed in January 2016 after energy saving-measures had been implemented. Twenty apartments were selected across the residential building; they were equally distributed on the lower, middle and highest storeys of the building. The same apartments were investigated in both winter seasons over a period of eight days (Földváry V. (2016); Bekö G., Földváry V., Langer S., Arrhenius K. (2016)). The temperature, relative humidity, CO2 concentration, and volatile organic compound concentration (TVOC) were measured in the bedrooms (the TVOC concentration in the living rooms) of the apartments. HOBO U12-012 data loggers and CARBOCAP CO2 monitors (Figure 5) were used for recording the temperature and CO2 concentration data.

Figure 5. Hobo data logger and Carbocap CO2 monitor (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

For the TVOC concentration Perkin-Elmer adsorption tubes (Figure 6) with 200 mg Tenax TA were used. The measurements were performed according to ISO 16017-2. All the devices were calibrated before the measurement campaign began. The data were recorded at 5-minute intervals for eight days in each apartment. The locations of the instruments were selected with respect to the limitations of the carbon dioxide method (Földváry V., Bekö G., Petráš D. (2015))

Figure 6. Perkin-Elmer adsorption tube.

Each unit was placed at a sufficient distance from the windows and beds to minimize the effect of the incoming fresh air or the effect of the sleeping occupants. The space between the furniture and the room corners was avoided. The CO2 concentration was used to calculate the air exchange rate over eight nights in each bedroom. The occupants CO2 emission rate was determined from their weight and height as set out in questionnaires (Földváry V., Bekö G., Petráš D. (2015); Földváry V. (2016)).

The calculation of the air exchange rates was performed using the following mass balance (Persily A. K. (1997)):

Ci(t) = (Co − Ca) · e(−λ · ti) + Ca + (E ·103 λ ·VR · (1−e−λ · ti) )

Ci(t)=   concentration at time t, ppm(V)

Co   =   concentration in the beginning (at time t=0), ppm

Ca   =   outdoor concentration, ppm

λ     =   air exchange rate, 1/h

E     =   estimated metabolic CO2 generation rate per person in the zone, h−1

VR   =   volume of the room, m³

ti     =   time, h

A questionnaire survey was used to determine the subjective evaluations of the quality of the indoor environments. The questionnaire survey was carried out along with the objective measurements. Two types of documents were prepared (for the unrenovated and renovated building).

The questionnaire contained 6 main parts:

1.    Basic information about the occupants

2.    The state of the building

3.    The ventilation habits of the occupants

4.    Sick building syndrome symptoms

5.    Perceived air quality

6.    Thermal comfort

Results

The results of thermal comfort, the measured values of CO2, AER, and the TVOC parameters and the questionnaire survey are as follows:

A. Thermal comfort

The measured values of temperature and relative humidity are presented in the following text.

From the measured data is obvious that day and night average temperature was higher in the renovated building than in the non-renovated (Figure 7, Table 2).

Table 2. Indoor air temperature before and after renovation.

1)    Before renovation (N=20)

2)    After renovation (N=20)

The relative humidity was very similar in both types of residential building (Figure 8, Table 3).

Table 3. Relative humidity before and after renovation.

1)    Before renovation (N=20)

2)    After renovation (N=20)

Both measured values fulfils the requirement of the Slovak standard STN EN 15 251( T: T>20°C; T<24°C; RH: RH>30%; RH<70%).

Figure 7. Average temperatures in the apartments before and after complex renovation.

Figure 8. Average relative humidity in the apartments before and after renovation.

B. Carbon-dioxide concentration and Air exchange rate

The CO2 concentrations before and after the renovation of the building are shown in Figure 9. Most of the CO2 concentration data points were within the acceptable limit (green line) before the renovation (blue line), while significantly higher concentrations were measured after the renovation (red line). Table 4 and Figure 10 present the descriptive statistics of the day and night-time CO2 concentrations before and after the renovation of the residential building. The grand average was 1205 ppm, and the median was 1190 ppm before the renovation.

After implementing the energy-saving measures, the CO2 concentration visibly increased. The mean was 1570 ppm, and the median was 1510 ppm. Table 5 shows the percentages of the average day and night-time CO2 concentrations above four cut-off values in the residential building before and after its renovation. A higher number of the apartments exceeded 1500 ppm and the upper concentrations during both the day and night-time after the renovation than before the renovation.

The lower CO2 concentration before the renovation resulted in higher AERs in the apartments (average 0.61 1/h). After the renovation, the mean air exchange rate (0.44 1/h) dropped below the recommended minimum (0.5 1/h) (Table 6 and Figure 11).

Figure 9. Example of CO2 concentration in one selected apartment during two days out of the whole measurement period before and after the renovation. (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

Table 4. Day- and night-time CO2 concentrations before and after renovation of the residential building. (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

1)    Before renovation (N=20)

2)    After renovation (N=20)

Figure 10. CO2 concentration before and after renovation as a statistical output (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

Table 5. The fractions of the apartments where the average CO2 concentration exceeded 1000, 1500, 2000 and 2500 ppm during the day- and night-time. (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

a)    Before renovation (N=20)

b)    After renovation (N=20)

Table  6. AER before and after renovation (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

Figure 11. Air exchange rate before and after renovation as a statistical output (Sánka I., Földváry V., Petráš D. (2016); Sánka I., Földváry V., Petráš D. (2017))

C. Concentration of volatile organic compounds

In both cases (before and after the renovation) the volatile organic compound (TVOC) concentrations were above the maximum limit value (300 µg/m³) Even higher concentrations were measured in the apartments after refurbishment (Table 7). In some cases, concentrations of TVOC were measured as very high (>1000 µg/m³), which are illustrated by the green dots on Figure 12. Table 8 contains the percentages of the measured values exceeding the threshold values.

Table 7. TVOC concentration before and after renovation.

Figure 12. TVOC concentration before and after renovation as a statistical output (Sánka I., Földváry V., (2017))

Table 8. TVOC concentration before and after renovation (Sánka I., Földváry V., (2017))

D. Results of the subjective measurements

The results of the questionnaire survey are based on the responses of the occupants of the evaluated residential building. The results below characterize the ventilation habits of the occupants, the perceived air quality, and the acceptability of the indoor air quality.

The residents labelled the acceptability of the indoor air on a scale from −1 to +1. The following figure shows the acceptability of the indoor air quality in the bedrooms and living rooms of the unrenovated and renovated building. The boxplot value of -1 represents poor air quality, and the value 1 represents good air quality.

Figure 13. Acceptability of the indoor air as statistical output.

The changes in the ventilation habits of the inhabitants before and after the renovation are presented in Table 9. The first part of the table shows the percentage characterizing the frequency, while the second part contains the duration of the ventilation.

The results indicate that the inhabitants did not change their ventilation habits after the renovation. Most of them ventilated the living room once a day, and the ventilation time was 7.5 min.  The occupants ventilated bedrooms daily or almost daily but not every day. After the renovation, the ventilation time slightly increased but not significantly. 

Table 9. Ventilation habits of the inhabitants.

The boxplots in Figure 14 shows the relationship between the duration of the ventilation and the air exchange rate, as well as the relationship between the duration of the ventilation and the acceptability of the indoor air.

The results clearly show a linear relationship between the duration of the ventilation (AER) and the acceptability of the indoor air.

Discussion

Indoor air quality is a dominant contributor to total personal exposure because most people spend a majority of their time indoors (N. Klepeis, W. C. Nelson, W. R. Ott el al. (2001). The findings presented in this measurement campaign support the conclusions of previous studies in Slovakia (Földváry V., Bekö G., Petráš D. (2014)) in which deterioration of indoor air quality follows energy renovations. In this study, the implementation of the energy-saving measures was not combined with measures to improve the indoor environmental quality, which explains the lower AERs and higher CO2 and TVOC concentrations in the renovated buildings in the winter.

Many international studies have also attributed this phenomenon to the fact that older buildings are leakier and newer ones are more air-tight as a result of improved construction techniques and stricter regulations (Kotol M., Rode C., Clausen G., Nielsen T. R. (2014); Bekö G., Toftum J., Clausen G. (2011)). The limitation of the study is its small sample size. The validation of the results on a larger sample size is warranted. The study is ongoing, and additional results will be available in the near future.

Conclusion

A key goal of the implementation of an energy renovation strategy is to achieve the improved energy efficiency of buildings. However, the effect of these programs has not been systematically assessed. The effects on indoor air quality and well-being of the occupants is often ignored. There is an urgent need to assess the impact of the currently applied building renovation practices on the residential indoor air quality on a nationwide scale.

References

Jurelionis A., Seduikyte L. (2010): Assessment of indoor climate conditions in multifamily buildings in Lithuania before and after renovation. 2nd International conference on Advanced Construction. Kaunas, Lithuania.

Földváry V., Bekö G., Petráš D. (2014): Impact of energy renovation on indoor air quality in multifamily dwellings in Slovakia. Proceedings of Indoor Air 2014, Hong Kong, Paper No. HP0143. Arash Rasooli, Laure Itard, Carlos Infante Ferreira, “Rapid, transient, in-situ determination of wall’s thermal transmittance,” in Rehva Journal, vol. 5, 2016, pp. 16-20.

Földváry V., Bekö G., Petráš D. (2015): Seasonal variation in indoor environmental quality in non-renovated and renovated multifamily dwellings in Slovakia. Proceedings of Healthy Buildings Europe 2015, Eindhoven, Paper ID 242.

Földváry V. (2016): Assessment of indoor environmental quality in residential buildings before and after renovation. Doctoral thesis. Bratislava, Slovakia.

Bekö G., Földváry V., Langer S., Arrhenius K. (2016): Indoor air quality in a multifamily apartment building before and after energy renovation. Proceedings of the 5th International Conference on Human-Environment System, ICHES 2016 Nagoya, Japan.

Persily A. K. (1997): Evaluating Building IAQ and Ventilation with Indoor Carbon Dioxide. ASHRAE Transactions. 103, Vol. 2.

N. Klepeis, W. C. Nelson, W. R. Ott el al. (2001): The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants. Journal of Exposure Analysis and Environmental Epidemiology. 11, pp. 231–252.

Kotol M., Rode C., Clausen G., Nielsen T. R. (2014): Indoor environment in bedrooms in 79 Greenlandic households, Building and Environment, Vol. 81, pp. 29-36.

Bekö G., Toftum J., Clausen G. (2011): Modelling ventilation rates in bedrooms based on building characteristics and occupant behaviour. Building and Environment, Vol 46, pp. 2230-2237.

Sánka I., Földváry V., Petráš D. (2016): Experimentálne meranie CO2 a intenzity výmeny vzduchu v bytovom dome. (Experimental measurements of CO2 concentration and air exchange rate in a residential building) TZB-Haustechnik, Vol 25, 5/2016, pp. 46-49.

Sánka I., Földváry V., Petráš D. (2017): Evaluation of Indoor Environment Parameters in a Dwelling Before and After Renovation. Magyar épűletgépészet Vol, 65, pp. 29-33.

Sánka I., Földváry V., (2017): Experimentálne meranie toxických látok vo vnútornom vzduchu pred a po obnove bytového domu. (Experimental measurements of toxic substances in the indoor air before and after renovation) TZB-Haustechnik, Vol 26. 2/2017, pp. 32-35.