Study of active technologies for prefabricated multi-active facade elements for energy renovation of multi-family buildings

Sammanfattning: In Sweden, between 1964 and 1975, approximately one million dwellings were raised in the so called million programme. Due to their age and often neglected maintenance regarding both building envelope and installations, in many cases, comprehensive retrofitting is now required. The aim with this study was to theoretically investigate the energy saving potential and cost-effectiveness of integrating active technologies into a prefabricated insulating façade module, when retrofitting a Swedish case-study high-rise lamella multi-family building from the “Million Program”. The active technologies that were found most suitable in the Swedish context were; centralized supply- and exhaust air ducts with heat recovery where the supply air ducts are routed through the multi-active elements as well as facade integrated photovoltaics. To estimate their energy savings potential, various energy simulations were conducted in software tools such as, HEAT2, IDA ICE and Rhinoceros. To estimate the economic feasibility life cycle calculations were carried out. It was found that the heat losses as well as the annual energy losses from wall integrated ducts were minor even without high performing insulation materials applied. Furthermore, the decrease in the supply air temperate during the coldest hour in the year was acceptable. The results showed that by improving the building envelope and reusing the present exhaust air ducts as well as integrating the supply air ducts in the multi-active element the specific energy use can be lowered by 55 %, from 141 to 62.8 kWh/(m²·yr). The combination of heat recovery from the exhaust air as well as the insulating properties of the multi-active elements are the main contributing factors to the energy savings. The multi-active façade solution with complementary energy saving measures (roof insulation, windows and heat recovery) was found to have a higher saving potential compared to traditionally insulate the building with or without a heat pump. Moreover, the integration of photovoltaic modules in the façade have a restricted potential due to limitations in the Swedish tax regulations. This makes the energy savings of installing photovoltaic modules in the façade roughly covering the investment during the lifetime only when the investment subsidy is awarded. The economic analysis showed that improving the building envelope and implementing a multi-active façade solution, resulted in a competitive alternative in comparison to traditionally insulate the building and as well as to previously documented retrofitting projects in Sweden.