Humidifier problem 1

[remp]

Hello

I have an air handling unit with a new steam to steam humidifier. The humidifier is fairly basis and maintains the room level humidity set point pretty good. Only thing is it sometimes sets off the smoke alarm in the supply duct and even in the rooms. Any tips for getting residual steam / water droplets out of the air stream. We used to have HEPA filters on the unit with the old humidifier set up and never had problems them but they are now gone. Looks like the HEPAs took out not only dust particles but also water droplets. Any tips?

B

 

[Drazen]

manufacturer's manual would likely provide better tips than myself.

this can be either matter of adjustment or place of installation. there should be no sensible level of air drops too long downstream. setting too high? duct not insulated? many things are possible, and you should roll the sleeves and check one by one, beginning with manufacturers tips.

 

[MTES93]

Agree w/ Drazen and also check how far downstream the smoke detector is from the humidifier grid/tube. It should be further downstream than the anticipated dispersion distance of the device or better yet upstream of it. It is sometimes setting of the room smoke detector?? "Visible" humidity in the room? If that's the case I would look at the dispersion device.. I don't think it should be doing that.

 

[ChasBean1]

With this problem, the above may already have been accounted for. Modify controls:
1) Put in a fast acting blocking valve that closes upon any AHU shutdown condition.
2) Change the control sequence. Typical humidifier control will alternate full flow and zero flow to maintain a return or exhaust air condition. The lag time in controlling the return/exhaust condition can make for hideous PID control.
Instead, reset the supply RH set point based on the return RH set point. If you want the space to have 30% RH for example, reset supply RH set point between 10 and 70% in the supply to maintain return RH.
In other words, if the space/exhaust RH is 5% RH below set point, have the supply maintain 70%. If the space RH is 5% RH above set point, have the supply maintain 10% RH. Reset the supply RH set point linearly between these two points.

 

[Ziggypump]

Could this be a dispersion pattern problem? Is the smoke detector too close to the humidifier tube? Would installing a dispersion tube with a shorter pattern requirement help?

I'm asking for my own benefit here.

 

[ChasBean1]

Ziggypump, yes. So many of the humidifier vendors sell shorter dispersion distances. <36". 18". 9". These are good under one lab test condition whereas reality might have a wall of varying inlet and outlet temperatures that change the vapor trail substantially.

The supply duct smoke (required per NFPA 90/92 for any supply system >2,000 cfm) should be as far as humanly possibly downstream of the humidifier.

 

[Ziggypump]

I know that lab conditions are one thing, but there are calculations you can perform to get a better idea on what may happen with the field conditions before you start the field testing to see which one will work best.

Even if you get the 9" throw and field conditions show it's actualy 12"; it there's 15" of space, I call that a win and a probable solution.

 

[edithsprouse]

I was also facing the same problem and tried many things like putting fast acting blocking valve that mainly closes upon any AHU shutdown condition but still did not find any solution so atlast contacted air conditioning repair nyc and they really helped me to solve my issue related to it.

 

[ChasBean1]

Here's reality: the humidifier is placed in an AHU just after a device (coil, heat wheel, etc.), that does not have a uniform temperature profile. The bulk air leaving this device may as specified, but the device might have portions of air that are 42°F and other areas that are 67°F.

The wisp of steam entering the 42°F air might show an 8' vapor trail whereas the steam in contact with the 67°F profile has barely a visible profile.

If the bulk airstream were a perfect, uniform 55°F as designed, you'd see the uniform 9" vapor trail as promised... 90% of the time, this is not the case.

 

[Compositepro]

A demister pad may be helpful.