Energy conservation by retrofitting of dwellings

This article investigates the impact of energy renovation on the indoor environmental quality of apartment building during heating season. 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. Additionally, evaluation of indoor air quality was performed using objective measurements and subjective survey. Thermal environment and concentration of CO2 was measured in bedrooms. Higher concentrations of CO2 was observed in the residential building after its renovation. The concentrations of CO2, in some 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.


Intorduction
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 [2]. 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, was recognized during the second half of the 20th century [1]. 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 energysaving point of view. The aim of the study was to evaluate the impact of basic energy-saving measures on energy demand of the building and indoor air quality in a typical high-rise residential building built in the 1960s in Slovakia.

Building description
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 in recent over the last years in most of the apartments in the building.

Energy demand
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.

Methodology
The first round of the energy consumption and air quality measurements was performed in January 2015 when the building was still in its original condition. 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 [4][5].

Energy consumption
Energy consumption was measured in heat exchanger station, e.g. heat meter, gas meter, water meter, electricity meter.

Fig. 6. Energy consumption measuring
All the measured values had been related to the whole apartment building.

Indoor air quality
The temperature, relative humidity and CO2 concentration, were measured in the bedrooms of the apartments. HOBO U12-012 data loggers and CARBOCAP CO2 monitors ( Figure 4) were used for recording the temperature and CO2 concentration data.
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 rooms 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 [3][4] [5].

Results
In this section the indoor air quality analysis and the energy evaluation results are presented.

Energy efficiency
The energy-saving measures mentioned above decreesd 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).
The renovated and non-renovated residential building were classified into energy classes by the valid Slovak

Indoor air quality results
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 1 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.  The lower CO2 concentration before the renovation resulted in higher AERs in the apartments (average 0.61 h-1). After the renovation, the mean air exchange rate (0.44 h-1) dropped below the recommended minimum (0.5 h-1) ( Table 2).

Discussion
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 [8] [9]. The limitation of the study is its small sample size. The validation of the results on a larger sample size is warranted.
The findings presented in this measurement campaign further support the conclusions of previous studies in Slovakia [2][3][4] that 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 concentrations in the renovated buildings in the winter season.

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.