Takes advantage of electronic growth valve to exactly Regulate the move of R290 refrigerant into the evaporator in addition to a four-way valve to divert the refrigerant flow for that defrost operation The refrigerant within an air-source heat pump absorbs heat with the out of doors air and turns right https://purethermal.co.uk/media-news/q4-launch-lithium-large-capacity-r290-ashp-from-pure-thermal-and-enerblue/