A steam generation unit includes a heat exchanger that has a shell, end plates for receiving a process fluid in a volume defined by the shell and the end plates, and channels for a working fluid. The shell and the channels define at least a first heat exchange zone, a second heat exchange zone, and a third heat exchange zone each having a respective pass of the channels for preheating the process fluid, for boiling the process fluid, and for superheating the process fluid, respectively. The process fluid is heated sequentially from the first to the second to the third heat exchange zone. A heating, ventilation, air conditioning, and refrigeration (HVACR) system includes a refrigerant circuit with a compressor, a steam generation unit, an expander, and an evaporator fluidly connected.