Comparison of centralized anddecentralized ventilation in amultifamily building in Stockholm : An LCA-study

Sammanfattning: Construction companies in Sweden has to comply with regulations forboth indoor environment and energy performance in multifamily buildings,and they also face a growing demand for certified green buildings.In order to lower the energy demand, all potential energy savings areof interest. Recent European studies have reported that a decentralizedventilation system might have a lower energy consumption for fansthan a centralized system, and an increasing interest for decentralizedventilation in multifamily buildings has been noted among the buildingcompanies in Stockholm. However, research comparing the environmentalimpact from the whole life cycle seem to be missing. In this thesis,an LCA-comparison of centralized and decentralized ventilation was performedfor a case building in the outskirts of Stockholm, considering alifetime of 50 years. The energy performance was also compared, in relationto Swedish building regulations, and the initial costs were estimatedfor both systems. The LCA-study was carried out in SimaPro, usingEcoinvent 3 as inventory database and ReCiPe 2016 Endpoint (H) asimpact assessment tool. The results showed that if the pressure dropacross supply air diffusers was kept at 70 Pa in the decentralized system,energy for fans was 19% lower than in the centralized system, and ata supply air diffuser pressure drop of 30 Pa the corresponding energysaving was 44%. This led to lower environmental impact on resources,human health and ecosystems for the decentralized system. When theair supply temperature was raised from 16C to 21C, the differences inenvironmental impact increased between the systems due to the fact thatdistrict heating was employed for air heating in the centralized systemwhile Swedish electricity mix was used in the decentralized system. Productionof products only had limited impact on the LCA-results, whiletransports and maintenance had no impact on the results at all. Theenergy performance in relation to Swedish building regulations was bestfor the decentralized system, if air heating was minimized. Both energyand LCA-results were highly dependent on the choice of pressure dropover supply diffusers in the decentralized system, indicating that the systemperformance is sensitive to relatively small changes in pressure dropdue to the low efficiencies of the small fans. The initial costs were estimatedto be 27% higher for the decentralized system, and an increasewith 25 m2 in salable area would be required in the case building to coverfor the higher cost. Further research regarding long-term functionalitywould be valuable in order to evaluate quality aspects and operationaldifferences between the systems. Also, a more thorough inventory of environmentalimpact from district heating generation and a life cycle costanalysis would be welcome.