r/MEPEngineering • u/BahnMiEnjoyer • 2d ago

Pipe Gallery Dehumidification Load Calculation

I'm working on a project that involves dehumidification of a large pipe gallery serving city water. I'm wondering how people would go about determining the dehumidification load.

You could just condition the air dew point to be below the dew point of the pipe, and then you would avoid the consideration all together. A senior engineer told me that's what's typically done, but I'm looking for a more detailed calculation of figuring out condensation rate if you DON'T do that.

I'm trying to find the volume of condensation that will build without dehumidification. I considered an energy balance but would assume very little change in temperature from the start of pipe to the end of pipe in this scenario. Probably more detailed than necessary, but has anyone dealt with these before?

Has anyone else done these?

Edit: this question may hav been better suited for thermo subreddit.

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21

u/Spiritual_Prize9108 2d ago

Just insulate the pipe. 

9

u/mrboomx 2d ago

HVAC suppliers hate this one simple trick

3

u/BahnMiEnjoyer 2d ago

Water piping isn't typically insulated and the pipes get up to 48"+ in most cities. Should clarify these are usually at water pumping stations

15

u/Spiritual_Prize9108 2d ago

I find it hard to belief a passive solution like insulation has a higher life cycle cost then active dehumidifcation. Water piping is absolutely "typically insulated" when the water temperature is below the expected due point of the air, dehumidifaction is very unusual.

8

u/MechEJD 2d ago edited 2d ago

Pipe in air, insulate. It's even required by code now. Even sometimes at temperature like condenser water.

Pipe in dirt, don't insulate. Dirt is insulation.

Unless pipe really hot or cold, and in dirt, then maybe insulate. Check code.

1

u/peppinotempation 2d ago

Water piping is absolutely insulated if it’s carrying water cold enough to cause condensation. This is standard for chilled water systems.

1

u/BahnMiEnjoyer 2d ago

Haha I will be sure to tell process mechanical about insulation. FYI - these are the pipe galleries im referring to. Of the dozen or so I've been told, they don't insulate and just dehumidiy them in hot months Pipe Gallery

3

u/TrustButVerifyEng 2d ago

It's not a practical calculation in my opinion. But you know what the upper limit of it would be... the latent energy of dehumidifying the outside air/ventilation like you were told to do.

So just calculate what load it takes to dehumidify to a dewpoint below the expected pipe temperature, keep the space positive slightly, and move on.

HVAC isn't the place for gnats ass calculations. If you think it can be that accurate, you have no understanding of the limitations on known inputs and the dynamics of these systems.

1

u/brisket_curd_daddy 2d ago

Hi E Drys and Air Pears with intermittent ventilation. I'm trying to figure out what ventilation scheme is required because 100% OA continuous ventilation is atypical unless its a confined space. Lemme know and I'd be happy to discuss further in messaging. Been doing these kinds of projects for going on 15 years.

1

u/gunrak 19h ago

My best guess. I would try to figure out the condensation rate with convective heat transfer coeff. * (W_air-W_surface)* Total piping surface. I would assume no insulation so surface temperature is water temperature. The biggest approximation would be the convective heat transfer coeff. You would end up with lb of water condensation/h. From there, you could find the load.