Comparison of a hybrid ventilation system and a mechanical ventilation system with heat recovery through life cycle assessment : A case study of a modern Danish office building

Sammanfattning: The building sector is responsible for 36% of the energy usage and 39 % of all CO2- emissions in European union (EU). Therefore, it is of great interest to investigate how the building sector can become more energy efficient and lower the environmental impact. It is reported that 80-90 % of a building’s total energy usage occurs during the operational phase. The energy usage is mainly due to lightning, technical equipment and the heating, cooling and ventilation system (HVAC-system). During the last century the energy efficiency in lightning developed significantly meaning the energy used in the HVAC-system becomes increasingly significant. As EU aim to increase the energy efficiency and the ratio of renewable energy in the grid, one can assume that the importance of other phases in the HVAC system lifecycle will be increasingly interesting as for example the manufacturing process and material usage which can be evaluated through life cycle assessment (LCA).This thesis presents a comparison between the environmental impacts of a hybrid ventilation (HV) system and a mechanical ventilation system with heat recovery (MVHR) system through a LCA perspective designed for an office building in Lystrup, Denmark. The office building in Lystrup, Denmark was chosen as the HV system is implemented there. The HV system consists of an automated natural ventilation (NV) system and a mechanical exhaust air ventilation (MEV) system. The environmental impact from the NV was provided through environmental products declarations provided by the company dimensioning the NV system. The data was lacking for the MEV system and that system was therefore dimensioned and evaluated through LCA. The mechanical ventilation system chosen for comparison is a mechanical ventilation system with heat recovery (MVHR) decided by the commissioner of the project, Sweco AB. The MVHR system was dimensioned as well. The project was significantly affected by lack of data resulting in many assumptions. The system boundary of the life cycle was set to cradle to grave excluding the energy usage of producing the ventilation components. The assumed lifetime is 25 years. Gabi Education software was used for calculating the LCA results. The impact categories chosen are global warming potential (GWP), ozone depletion potential (ODP), acidification potential (AP), eutrophication potential (EP), photochemical ozone depletion potential (PODP), abiotic depletion potential (ADP) elements and ADP fossil which are used in the EN15804 standard when conducting LCA for construction components. The CML2001-IA 2001 IA method was used for the life cycle impact assessment in the LCA software which also is recommended according to EN15804.The LCA results were compared between the systems and interpreted through contribution analysis were the result was divided in the following categories; Energy usage (use phase), transportation, material usage (including raw material extraction and material processing) and end of life treatment. The two systems score similarly on all environmental impacts categories except for the global warming potential (GWP) and the abiotic depletion potential (ADP) fossil were the MVHR system scores approximately 3 times higher than the HV system. The MVHR system consumes approximately 3 times more energy during the use phase. The contribution analysis showed that the energy usage (use phase) dominated the contribution in almost all environmental impact categories. Further, the environmental impact caused by the material usage was compared between the MVHR - and HV system and the MVHR system scored higher in all categories except ADP elements.The conclusion drawn from this report is that the HV system is better if one looks to GWP and ADP fossil. The HV contributes less to climate change which is an important environmental concern. Further, the energy usage during use phase contributed most to environmental impacts for both the MVHR - and HV system. The environmental impact of the material usage is less for the HV - compared with the MVHR system.