Ejectors typically use steam passing through an expansion nozzle to entrain a secondary flow of water vapour from an evaporator vessel at low pressure and raise its pressure at the ejector discharge. The driving energy is heat to raise the steam that drives the compression process. There are therefore few moving parts and the system can be powered by waste heat or even solar energy. A major disadvantage is the low efficiency of ejectors which leads to low overall COPs (coefficient of performances). The University of Nottingham has built a prototype system that has been installed in a building in Leicestershire using solar panels and a back up gas fired boiler. Its COP is only around 0.3 but this does not matter when the system is being powered by solar energy. More crucial is the high capital cost of the prototype although the University is investigating how ejectors may be moulded from plastic which should reduce the cost of manufactured systems. 
 

Figure 1 an Expansion-cooling Module