Minimising energy demand in commercial buildings is fundamental to achieving greater energy independence from fossil fuels and meeting future European environmental requirements. The Annex 59 project focuses on HVAC systems. It aims to develop efficient systems by minimising heat transfer losses at the various levels of the system chain, but also to minimise the electrical consumption of auxiliaries (pumps, fans, etc.): 1. Losses due to multiple temperature differences between external heat sources or heat sinks (for example, the temperature difference between the surface of a floor heating system and the indoor ambient air) 2. Losses due to flow mixtures at different temperatures (e.g. blowing air from outside to inside by mechanical ventilation) 3. Losses from humidification and dehumidification processes 4. The electrical consumption of the pumps and fans used in the air and water circuits connecting the external heat sources and heat sinks and the emitters located inside the building. Reducing temperature differences, for example for refrigerating machines, should reduce the machine's electricity consumption. Moreover, minimizing these temperature differences encourages the use of renewable energy sources.