When flash steam is generated and vented to the surroundings a considerable amount of energy is lost
If a condensate receiver in a steam distribution system is vented to the surroundings, flash steam will be generated and evacuate, and a considerable amount of energy will be lost.
The amount of flash steam generated depends on the initial and final pressure before and after condensate traps for heat exchangers. In the example - calculating generated flash steam - 0.11 kg flash steam is generated per kg condensate from a heat exchanger with 5 bar gauge pressure.
In other words 11% of the condensate is lost to the surroundings and must be replaced by new water feeded to the system.
Feeding more water requires morel heat energy and additional water treatment increasing the total operating cost for the system.
To improve system efficiency, and to reduce operating cost, it is common to limit the flash steam energy loss by using some kind of low pressure flash recovery system where the flash steam condensates in low temperature consumers - like feeding water heat exchangers, air heaters or similar.