Employs electronic growth valve to precisely Manage the stream of R290 refrigerant in to the evaporator in addition to a 4-way valve to divert the refrigerant stream with the defrost Procedure The Haier Air to Drinking water Heat Pump variety works by using cost-free renewable Power from the surface air https://purethermal.co.uk/media-news/q4-launch-lithium-large-capacity-r290-ashp-from-pure-thermal-and-enerblue/