Because of its non-toxicity and its availability steam is frequently used as an energy carrier in industrial processes. Steam is also the by-product of energy intensive processes such as drying, concentration, evaporation and distillation. Although the upgrading concept of open cycle heat pump, commonly called mechanical vapour recompression (MVR), has been known and applied from the beginning of the century, low pressure steam from many industrial processes has traditionally been vented away with its valuable latent heat content.