I recently conducted a steam survey at a major medical school that was heated by 100 PSIG steam generated at the university’s boiler plant. Steam was reduced to 30 PSIG inside this building. Here are some of my significant findings. All of them were contributing to poor heating performance, failed steam coils, and an enormous waste of costly steam!
This aging building had numerous make-up air units. When these units were replaced several years ago, the new make-up air units were piped incorrectly. Some units which originally had two coils were replaced with units with four steam coils. Because of apparently sketchy drawings (I was never able to actually see them – nobody seemed to know where they were), poor installation by the contractor and extremely cramped equipment spaces, some of these four steam coil units were piped to a single trap! Such group trapping is a definite violation of good piping practice! Incredibly loud and serious water hammer was occurring as a result.
A second major cause of water hammer was steam unit heaters that had been installed in the attic equipment room as part of the recent retrofit. The 30 PSIG unmodulated steam condensate from these unit heaters them was discharging into the same condensate return main serving the make-up air units. One of these five unit heaters had no steam trap at all. Consequently, 30 PSIG steam was literally short circuiting through this unit heater into the single condensate return main which also served the 30 PSIG steam drip traps and steam humidifiers that I was told had never worked properly. This 30 PSIG steam was overpressurizing the single condensate return main causing further water hammer for the make-up air unit steam coils which sounded like someone was inside them wailing away with a sledge hammer.
With all these problems, Jack Ames, P.E. was able to identify simple cost effective solutions to major piping problems. These problems included:
- Individually trap steam coils on all six make-up air units. Because of limited access, this will be the most difficult recommendation to implement.
- Install vacuum breakers on each coil of these same units. This will be easy!
- Disconnect the five unit heaters in the attic equipment rooms. This will be easy! This is possible because the sprinkler system in the attic has already been converted to a dry system and thus could never freeze. Secondarily, there is sufficient heat loss from the floor below the attic that even stagnant chilled water lines should never freeze.
- The reason the steam humidifiers did not work properly was because their drip traps were tied into the single pressurized condensate main. For these humidifiers to work properly, their drip traps had to be discharged directly into floor drains where there would be no back pressure. This will be easy to implement! The amounts of unreturned condensate resulting from repiping these drip traps will be insignificant.
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