CIBSE is a widely known institution focused on building services and energy efficiency. They are based on UK, but offer services to Europe and all over the world.
One of their main goals is to give advice to engineers designing building services and their integration. Moreover, they fight against the climate change and CO2 emissions by promoting passive and environment friendly solutions. Finally, they connect engineers, graduates and students in different meetings to share their knowledge.
You can find more information in their official website.