Passivhaus is an international energy efficiency standard, the only standard proven to ensure design intent translates to real life measured performance. Energy in-use is reduced to the minimum within carefully considered economic and practical constraints - energy use could be reduced to zero, but this would not be widely economically viable. In the UK, the PH standard typically represents a 90% energy use reduction. This is achieved through high levels of insulation, reduction of air leakage through the walls/roof/floor, triple-glazed windows/doors, and a whole building ventilation solution which recovers heat from extracted air (wet, smelly air being exhausted out from bathrooms or kitchens).
The Passivhaus approach is focused on reducing our dependence on carbon emitting fuels, BUT it also enables other important outcomes. Firstly, the risk of internal condensation is removed, eliminating potential mould growth, and improving internal air quality significantly. Asthma or hay-fever sufferers will notice the difference. Secondly, the constant supply of fresh air to every habitable space, coupled with no internal draughts, ensures very high levels of thermal comfort. Thirdly, fuel poverty is eliminated - imagine no-one ever having to worry about meeting the costs of an annual heating bill, or as a social landlord being able to offer space heating within the rental charge (known as warm rent) because the cost is that minimal.
Finally, Passivhaus is a mark of quality and must be independently checked using the PHPP energy modelling software. So no greenwash, no eco babble, just a rational approach to building that is kind to our environment and to us.