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Steam (Boiler) Humidifier.....how much pressure/temp needed?

JUGHNE Member Posts: 11,074
Our hospital has steam heat via HXC to glycol HW system. The only steam that leaves the boiler room is for humidifiers in surgery.
The boilers are running at 12 PSI. I have tried to convince the maint man to consider lowering them, he was reluctant, just because that is where they have always been.
Today working there on plumbing, I noticed steam coming from the small 3/8" port on the 2 1/2" pop off valve.
I told him you are getting close to the 15 PSI opening level and we should lower the pressure. I set it down to a 4 to 7 range.
He said he had talked to the pneumatic service man, (who has been around this stuff for 40 years). He cautioned about dropping the pressure too much might give them problems with the steam humidifiers.

The best explanation maint man could give was if the water was not hot enough that the "trap" would dump water into the ductwork and he would have a mess.
Can anyone familiar with a system like this explain things to me??

Also we have to run steam heating/glycol in July & August because they have "cold deck/hot deck air handlers" and need to go thru the reheat process for cooling from the chiller water/glycol. Any simple explanations or remedies for that scenario??


  • Jamie Hall
    Jamie Hall Member Posts: 23,419
    For the cold deck/hot deck -- it is a simple and easily controlled way to hit a target humidity. You run the cold deck to drop the air to the desired dew point -- whatever that may be -- and then reheat to bring the sensible air temperature to where you want it. Not, perhaps, the most energy efficient way to do it -- but it works like a charm.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 15,607
    Cold deck/hot deck your out of luck. It has to be run that way. Seems wasteful but hospitals always are. Heat and cold "fight" to maintain an accurate temperature and humidity. My understanding is this type of system can only be used in a hospital, lab, or some process job that requires tight control.

    Safety valve sometimes are not accurate and will weep when operated near 15 psi.

    The humidifiers are usually ordered for a specific steam pressure. Maybe you can get a model # and check with the mfg. I see no reason that a lower pressure would cause duct flooding but may cause a capacity loss. They usually have a built in trap at the humidifier to catch any water before it enters the humidifier tube

    Don't know what temp they need for sterilizing. Possibly they need high steam press for this??
    JUGHNE Member Posts: 11,074

    Thanks for replies.
    They have a separate electric sterilizer unit.
    The steamers used to do DHW.
    I installed two HTP Phoenix WH's (with cross over piping for isolation if needed) to eliminate their 360 gallon tank with steam insert coil. (all original from 1971, as we cut the tank up for removal we could see the internal coating starting to fail).
    June was a non steamer month. July and Aug needed some reheat, at least the boiler room temp did not match the DHW temp delivered as before.
    I was hoping for more energy savings than achieved but this was also a pro-active change out for DHW system.
    They have 2 steam boilers but had only one DHW tank/source.

    I'll have to investigate the humidifier a little more.
    They have scheduled surgery for about 1/2 day per week.
    That is when they need humidity in heating and reheating in cooling.