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Monitoring of the energy delivered to multifamily residential buildings

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The actual use of energy for heating in residential buildings is usually different to that calculated using reference values. The reason for this is the influence of inhabitants on the energy use. They can overheat or underheat their dwellings, apply different ventilation strategies and install individual retrofit measures such as replacement windows.

Monitoring of the energy delivered to the building, according to principles given in prEN 15603, is a very useful method to establish actual energy use. It is particularly suitable when there is a lack of data concerning energy use.

This article describes work to compare monitored and calculated energy consumption of large multifamily residential buildings in Warsaw.

Energy performance and thermal retrofitting of existing multifamily buildings in Poland

Multifamily residential buildings built before the economical transformation at the end of the last century were poorly insulated. The process of retrofitting energy efficiency measures to these buildings is a lengthy one, individual measures being applied incrementally. To date this lengthy process remains incomplete. In order to improve the calculation method used for estimating energy economies due to retrofitting measures (elaborated on the national level before the approval of EN 832 and EN 13790) a research project was initiated in 2004 at the Polish Building Research Institute (ITB).

Energy monitoring of multifamily residential buildings in Poland

In this project energy usage was monitored in two similar large multifamily residential buildings (each with over 100 dwelling units) located in Warsaw. The buildings were built almost 40 years ago and had a similar design. Both were connected to a district heating network and both were partly retrofitted. In one, windows had been partly replaced. In the other the district heating system had not been replaced by individual systems and only one external wall had been additionally insulated.

One building was monitored in the winters of 2004 and 2006 (see Figure 1). Daily energy usage was measured. In the other building energy monitoring was performed only once (in 2005) using weekly energy usage measurements (see Figure 2). The seasonal heat use for heating measured in these experiments was almost the same as the result from calculation – the difference not exceeding 3%.

This means that energy monitoring is a credible method for estimating energy needs for heating of a building. Deviations of heat consumption in particular periods from the trend line are caused by changes of weather conditions and the influence of inhabitants.

Conclusions

  • Energy monitoring is a credible method for estimating the actual energy needs for the heating of a building and the results of applied retrofitting measures.
  • The method is useful for determining energy economies due to single retrofit measures when retrofitting operation is incremental.
  • The minimum time interval for the estimation of energy needs for heating in the case of large multifamily residential buildings with significant heat capacity is one week.