Makes use of Digital expansion valve to exactly Handle the circulation of R290 refrigerant into the evaporator as well as a four-way valve to divert the refrigerant movement for the defrost operation The ECOMOD 290HT number of monobloc air source heat pumps come in three chassis measurements and 5 outputs: https://purethermal.co.uk/media-news/q4-launch-lithium-large-capacity-r290-ashp-from-pure-thermal-and-enerblue/