We began a series about vacuum condensate units and introduced one of their uses: the reduction of time to bring a building up to temperature after a weekend setback. Today, the R. L. Deppmann Monday Morning Minute (MMM) looks at the second use of vacuum condensate pumps, temperature control.
The modern hydronic boiler systems incorporate temperature set back controls. We understand that fin tube or coils will give out less BTUH if supplied with 140°F water instead of 200°F water. Back in the days where steam systems were common, how did you employ temperature set back controls? A boiler operating at 1 PSIG steam pressure produced steam at 215°F. The only way to supply steam below 212°F was to operate under a vacuum.
If I could create a vacuum in the steam system, I could change the BTUH output of the radiator. In fact, if I change the pressure to 20” of vacuum, I can get water to boil at 161°F. Since the BTUH output of the radiator is directly proportional to temperature difference between the steam and the room air, one could vary the output of the radiator by varying the temperature at which the steam condensed.
In today’s modern heating systems we take night or weekend setback in large office buildings for granted. In the 1930s and 1940s, not so much! Back then, on weekends, these large heating systems were just turned off for a period of time which allowed the building temperature to drop. When Monday morning came around, the office workers would want the building warm so the operator or janitor would come in early during the night to start the system.
From Xylem HOFFMAN HS-203C MANUAL
Bell and Gossett VCD vacuum condensate unit operation from manual TES-375
Many very smart people devised systems to operate under vacuum. Often, the system was named after them. I’ve seen some of these systems still in operation today.
If your system was designed for variable vacuum temperature control and is still operating, don’t assume you can replace the vacuum condensate system with a straight “condensate only” system. Ask your R. L. Deppmann sales engineer to stop by and discuss it with your installing contractor or engineer. If you are not lucky enough to be in the Deppmann territory, Call your Bell and Gossett/Domestic pump representative for their assistance.
Next week we look at a third reason you may have a vacuum condensate pumping system; condensate lift.
Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions that result from this information. Please feel free to contact us if you do have any questions.