Uses Digital growth valve to exactly control the stream of R290 refrigerant in to the evaporator in addition to a 4-way valve to divert the refrigerant movement with the defrost operation They set to work and at the end of the day had eradicated Nearly all the outdated machines.From there https://purethermal.co.uk/media-news/q4-launch-lithium-large-capacity-r290-ashp-from-pure-thermal-and-enerblue/