Overall environmental impacts of nZEBs are substantially lower than conventional buildings. This is the conclusion of a new AZEB study in which the environmental performance of 3 AZEB case studies was evaluated using life cycle assessment (LCA).
The combination of LCA with optimization methods facilitates decisions to minimize environmental impacts of nZEBs, while keeping the costs as low as possible.
It is recommended to use LCA from the early design phases, when decisions have the largest influence on the environmental performance of the building.
Since nZEBs have the goal to drastically reduce the energy consumption in the maintenance and use phase, this automatically leads to less environmental impact in this stage too.
Consequently, the impacts for nZEBs are somewhat higher in the construction and renovation stages, because of thicker insulation layers, use of triple glazing and possibly solar collectors.
But this is compensated by lower impacts in the use stage thanks to energy saving and renewable production.
The aim of LCA
The objective of Life Cycle Assessment (LCA) is to evaluate the environmental impacts of a product from its fabrication until its end of life, including possible recycling [EN ISO, 2006].
In general, three areas of protection are considered: human health, natural environment (also named ecosystems), and natural resources.
Example set of objectives and related indicators
(Example objectives - Example indicators):
- Preserve raw materials - Abiotic resource depletion
- Save energy - Cumulative energy demand
- Save water - Water used
- Manage land use - Land occupation, Transformation
- Limit toxic emissions - Damage to health
- Protect the climate - Greenhouse effect (100 years)
- Protect fauna and flora - Damage to biodiversity
- Protect forests - Acidification
- Protect rivers and lakes - Eutrophication
- Improve outside air quality - Photochemical ozone production
- Reduce waste - Waste production
- Reduce radioactive waste - Radio active waste
3 AZEB case studies
Three different types of buildings were studied:
1- Single family house in Bulgaria
The building is a single family house, which was designed according to the passive house standard. The high performance envelope is complemented with efficient equipment and photovoltaic electricity production, allowing to reach a nearly zero energy balance. LCA has been performed in order to evaluate the environmental performance of the project. Thermal simulation allowed also checking the thermal comfort in the building.
2- Social housing building in Spain
The studied project (new construction) is a social housing building. The building has 8 storeys and corresponds to 171 inhabitants. Due to the sloped ground, there are accesses on two different levels. Three storeys are partly underground: -3 is only for parking, -2 for parking and dwelling and -1 for storage rooms and dwelling. The other storeys (ground floor up to 5th floor) include only dwelling. There are 32 apartments in total.
3- Primary school in Italy
The building is a primary school located in northern Italy (climate zone E); it is characterised by an L-shape, with a covered surface area around 1970 m2 and a total volume of 20685 m3. The presence of 15 classrooms allows a maximum capability of 375 students. Both the branches of the building have three storeys above ground level, which are served by the same entrance, located at the corner. In the north-west corner it is located the gym
Affordability two-fold term
The AZEB methodology has its main focus in reaching affordability for high energy performance buildings, to become attractive for a broader group of clients. The affordability is defined as a two-fold term:
- Life-cycle costs are reduced and
- The value for the customer is increased
The value for the customer is connected with sustainability and creating environmentally-friendly buildings for the future.
Therefore, the application of the methodology allows to define the requirements and costing practices in such a way, that investment of additional costs in reduction of environmental impact will be considered as contribution to the value of the building.
The exact parameters and weights have to be defined separately in each project. For assessment of the environmental impact different performance indicators need to be measured.
The AZEB methodology proposes a set of them to use the life cycle assessment method.
Environmentally-friendly or more cost-efficient design
When LCA is combined with optimization analysis, it allows to define parameters which can be changed in order to achieve either a more environmentally-friendly design, or a more cost-efficient design, while holding e.g. the energy performance constant.
AZEB showed that when doing optimization and improvement proposals, the topic of uncertainty should always be considered – a good solution today might not be that optimal in 10 years.
This is crucial for a building with a life-span of 80 years.
Use simple tools with user friendly interface
The LCA study helps also for the optimization of low cost solutions with minimum environmental impact.
While LCA studies can be expensive and time consuming, the AZEB methodology encourages to use simple LCA tools with a user friendly interface so that such a study does not require too much time, while providing a correct sensitivity to design parameters.
The multicriteria nature of LCA can lead to a complex study that imply many trade-offs or interactions among criteria.
Estimated cost and time
The cost of the studies presented in this report (except for the uncertainty and robustness analysis) corresponds to one day for data collection, two days for input and calculations, and one day for interpretation and report per case study.
It seems therefore acceptable in practice, especially for public projects, where the objective of setting good examples for sustainability and future-proof solutions should play an important role.
Start but limit LCA
LCA is still not common practice in most European countries.
Therefore, some environmental indicators may be difficult to understand and interpretation of results might not be easy.
In a first step, it is proposed to limit the LCA to a small number of indicators, which can correlate with those shown in AZEB methodology e.g. CO2 emissions, non-renewable primary energy consumption and the reference time period.
LCA facilitates decisions
AZEB recommends to consider the environmental impact in the set of requirements for any nZEB project.
How ambitious the goals will be depends on the client. But the integration of the life cycle perspective throughout the building process is important for creating a sustainable vision and project set-up.
Together with the life cycle costing, LCA should facilitate making decisions to minimize environmental impacts of nZEBs, while keeping the costs as low as possible.
The goal is to take the best available options. Depending on the project phase, different levels of details for LCA evaluation can be pursued, but at least key indicators like CO2 emissions over the whole life cycle of a building should be considered.
Include all life cycle stages
Adding a threshold only regarding products (i.e. fabrication, transport, implementation, replacement and end of life) may constitute a barrier against energy saving and renewable energy techniques that induce impacts during their fabrication.
Because such indicator does not account for the use stage during which impacts are reduced. It is therefore recommended to include all life cycle stages in the targets.
The advice of AZEB is to use LCA from early design phases, when the decisions have the largest influence on the ultimate environmental performance of the building.
Horizon 2020 program
AZEB has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 754174.