# NZEB Renovation Definition in a Heating Dominated Climate: Case Study of Poland
## 7 Conclusions  
The calculations enabled the identification of a definition of cost-optimal and NZEB renovation in a heating-dominated climate of Poland. The propositions refer well to the one of general definition on NZEB renovation characteristics [12]: \"The primary energy consumption of the building after renovation is reduced by 75% as comparing to the pre-renovation status\". The defined requirement for energy need for heating for NZEB renovation is the same as unofficial indicator for low-energy residential buildings in Poland (QH \(\leq\) 40 kWh/(m\({}^{2}\) year) [64]. However, many NZEB renovation definitions are much more ambitious than proposed in the study:  
* QH \(\leq\) 18 kWh/(m\({}^{2}\) year): Belgium (Brussels); and
* QH \(\leq\) 15 kWh/(m\({}^{2}\) year): Slovenia. The open question is if such ambitious standards can be widely used in reality and how they correspond to real cases. Examples from Poland show that it is possible to reach a level of energy demand for heating of 24.5 kWh/(m\({}^{2}\) year) [65] or reduce the final energy demand by 90% [66]. Although the reduction in energy demand was very significant, unfortunately it does not translate into a very good economic result in terms of investment. The cost was much higher than in the study. From this perspective the use of lower requirements seems to be reasonable. The calculation shows that the index of primary, non-renewable energy Q\({}_{\text{P}}\) demand for cost-optimal renovation variants was higher than required for a new NZEB single-family house in Poland. Such results confirm that the requirements used for existing buildings should be different from those for new ones. Reaching NZEB standards in case of existing buildings can be technically complicated (implementation of mechanical ventilation with heat recovery) and also very expensive. Final results show that cost-optimal level depends strongly from the energy price. In a case of very cheap fuel renovation can be economically ineffective. People in Poland use very often two or more energy carriers and buy cheap, low quality coal. There are also some examples of garbage burning. From this perspective it is very important to introduce regulations that will forbid the use of cheap, low-quality fuel. A higher cost of energy sources stimulates the renovation process. In contrast to definitions using only maximum level primary energy demand, two indicators were proposed in the study: heating energy demand and percentage of reduction of the primary, non-renewable energy. Such a solution is appropriate for existing buildings because it prevents the situation in which only RES (with low PEF) will be implemented in order to reduce the primary, non-renewable energy demand. Additionally, according to BPIE [67] the use of PEFs to calculate the energy performance of a building is often incorrect or leads to perverse effects. For example, dual fuel boilers, burning both biomass and coal, are very common in some Member States, e.g., Poland. According to their energy characteristics, these buildings claim to use biomass but, in reality, they are burning a high proportion of coal, resulting in a real energy consumption (and CO\({}_{2}\) emissions) significantly greater than the calculated consumption. Expected energy saving targets are, therefore, only met on paper, not in reality. BPIE [67] proposes an alternative way of determining and setting requirements for the building energy performance: using the calculated delivered energy as one of the main building performance indicators rather than primary energy. Primary energy alone does not provide useful information about the energy efficiency of buildings, but is more a political indicator. It depends on the generation mix and efficiency of the system rather than the actual performance of the building. Using delivered energy can make the calculation independent from the PEF.