I think I might have an answer to your question. I started a topic to answer it and joined this forum as well to that end. I am now a retired ME but early in my carrer I was the engineering and maintenance manager for two large processing facilities. We required 8.7 megawatts to run these factories simultaneously but our steam driven generator was only capable of making 5.2 megawatts as I recall. I assume that you are using a barometric condenser to pull your vacuum. What I think is happening is that because you have an open system, you are pulling more heat away than is possibly necessary. Also, once you have established your boiling point, energy is being removed from the boil thus requiring more energy input. When your solvent or ethyl alcohol is condensed, it indicates an open system. You might want to look up designing a barometric condenser. Later in my carrer, I was in upper management. When I interviewed some engineers for a Vice Presidents job I would ask them why specific volume was important to have in the steam tables by Keenan and Keys provided my spelling of their names is correct the steam tables are amazing pieces of work.
i hope this helps to answer your question.
