Ice storage is not only beneficial in economic terms, it is also energy-saving, noise-free and helps extend the life of the systems. It consists in keeping a certain amount of ice, as a way of storing "cold", in order to use it later. It was initially restricted to water chillers, but has been used more recently in centralized air-conditioning systems using variable refrigerant flow or volume (VRF/VRV), in Japan where, unlike in Europe, peak electricity consumption period is in the summer because of AC. Ice storage generates savings as it can shift AC systems electricity to cheap rate hours as the ice can be used during peak hours. Full ice storage refers to systems in which refrigerating units are cut off completely during peak times during which refrigeration is provided thanks to the stored ice. Partial ice storage refers to systems in which refrigerating units run continuously and the ice storage is used as a supplementary cold source when needed. Ice storage also generates energy savings since it enables compressors to operate permanently at their nominal rate (at which their energy efficiency is optimal) regardless of external temperature. Storing ice is also more efficient than storing chilled water because of its latent heat.