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Deep energy renovation

Buildings represent the largest energy consumer in Europe. Deep energy renovation of the existing stock to reduce its energy consumption seems to be the most appropriate measure and a key policy to achieve emissions reduction targets. The largest part of the European building stock was built way before strict energy requirements were set and, given the long life span of buildings, it is expected that between 85 -95 % of the existing stock will be still under use by 2050 [1]. Given the importance of the global climate change and the commitments under the Paris agreement, the European Union, (EU), has proposed in the Climate Target Plan 2030 to reduce the greenhouse gas emissions by at least 55% by 2030 compared to 1990 (2). 

Figure 1: Deeply renovated residential buildings in Leida, Spain (7). The Spanish demo of Bellpuig consists of a recently built multifamily house with poor performance. The east-oriented main façade is retrofitted by installing timber prefabricated façade modules, including new windows with shading system, decentralised ventilation machines with heat recovery and PV panels. 

 

However, according to a recent study performed on behalf of the European Commission (3), ‘the average total annual energy renovation rate of residential buildings, namely the sum of all different levels of energy renovation depths from “below threshold” to “deep renovations”, for the period 2012-2016 based on floor area is estimated to be at around 12% for EU28 as a whole. For residential buildings, the annual weighted energy renovation rate was estimated close to 1% within the European Union. This is in line with other estimations of the European Commission (0.4-1.2% depending on the Member State) and highlights the insufficient progress in the building sector in terms of moving towards decarbonisation of the building stock’. Therefore, the weighted annual energy renovation rate in the EU is as low as 1% while the annual rate of deep renovation is only 0.2% and 0.3% in residential and non-residential buildings, respectively (3). To break down the energy renovation barriers, the Commission introduced the Renovation Wave strategy (2), which aims to at least double the annual energy renovation rate by 2030 and to foster deep renovation. 

Figure 2: Energy renovation of a building in Bulgaria (8). The project involves renovation of the existing envelope including additional insulation and high quality windows, new HVAC systems and a better ventilation and control system. 

 

The Energy Performance of Buildings Directive (EPBD, 2010/31/EU) is the main legal tool to enhance the energy efficiency in buildings across the EU (4). To support the implementation of the Renovation Wave strategy, the Directive was revised in 2021. The proposal defines deep renovation as a renovation that transforms buildings into Nearly-Zero Energy Buildings (NZEBs) in a first step. As of 2030, deep renovation will transform existing buildings into Zero-Emission Buildings (ZEBs) (5). 

Figure 3. Energy renovation of a commercial building in Germany (9). The building comprises a single volume with four rectangular courtyards and a publicly accessible ground floor that provides a new pedestrian connection between downtown Munich and the museum district. Floor-to-ceiling windows and a smart spatial organization allow employees to have visual connection to their colleagues throughout the building, while various open areas act as meeting spaces where people can collaborate across departments. Thanks to a holistic approach to sustainable design, the new building consumes 90% less electricity and uses 75% less water than its predecessor. Heating, ventilation, and air conditioning systems can be adjusted by employees, and thanks to the company’s smart building technology, data from 30,000 points allow for a comprehensive insight into the daily energy performance of the building. 

 

The deep or NZEB renovation level vary across the Member States. Common measures identified in deep renovation include thermal insulation to achieve U-values of 0.10 – 0.20 W/(m²K) for walls and 0.10 – 0.20 W/(m²K) for roofs, passive technologies (shading devices, natural ventilation, night cooling, thermal mass), active technologies (mechanical ventilation with heat recovery, condensing boilers, district heating) and renewable energy from photovoltaics (PVs) and solar thermal (6). 

 

The main purpose of this document is to provide knowledge, information and a reference for the city decision makers, building professionals and building stakeholders to implement appropriate energy renovation measures across the EU Member Countries.   

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