Chill water pipe insulation

[engineerbrian]

Ok, so long story short.

The building i take care of recently converted existing condenser water piping to chill water piping, and the fiberglass insulation was never upgraded.

The insulation on the "new" chill water piping is only 1" thick, however all of the joints were hit with CP-34 to provide a vapor barrier. So here is the issue. We've noticed lately that quite a bit of the pipe insulation is saturated with water. I'm pretty confident that we dont have a leak so i'm thinking the 1" wall on the pipe cover just isnt up to the job.

So what should the minimum wall thickness be on chill water piping?

Thanks
Brian

[HJ Controls]

usually it is 1 1/2" to 2"

[cnay20]

The amount of insulation will depend on the temperature of the water inside the pipe and the outdoor temperature.

[engineerbrian]

usually it is 1 1/2" to 2"

Thats what i was thinking too. We run our chill water around 45 -47 degrees and all of the piping is inside.

I have a call in to our preffered insulation contractor, so hopefully he can shed some light on this too.

[manny238]

When we usally insulate chilled water lines we use 1" thickness. The tighter the insulation fits on the pipe the less chance you have of leaks. Air is your worst enemy in insulation.

[vangoghsear]

I see from your location that you are in Maryland. Is the space where the piping is run Conditioned space?

You said the piping is interior. How much insulation depends on fluid temperature (45-47) and ambient conditions (interior, exterior, conditioned, unconditioned?). Since the condenser water piping designer chose to insulate the piping within that space with 1", I'm guessing that even warmer condenser water could have caused some sweating.

You are probably right about it needing more. If you have one of those infrared thermometers you can check and see what temperature you have on the outside of your insulation. You need enough insulation so that the surrounding air cannot drop in temperature to its dew point on the insulation. For instance, if the dewpoint of the air is 65 and the pipe insulation is 60, it's going to sweat.

Hope that helps.

[engineerbrian]

I see from your location that you are in Maryland. Is the space where the piping is run Conditioned space?

You said the piping is interior. How much insulation depends on fluid temperature (45-47) and ambient conditions (interior, exterior, conditioned, unconditioned?). Since the condenser water piping designer chose to insulate the piping within that space with 1", I'm guessing that even warmer condenser water could have caused some sweating.

You are probably right about it needing more. If you have one of those infrared thermometers you can check and see what temperature you have on the outside of your insulation. You need enough insulation so that the surrounding air cannot drop in temperature to its dew point on the insulation. For instance, if the dewpoint of the air is 65 and the pipe insulation is 60, it's going to sweat.Hope that helps.

Thanks, thats a good point and easy to check. For the most part the piping is in the mechanical rooms which also serve as the return air plenum. That said its generally in the low to mid 70's

[Octopus]

When I have to insulate and I'm not a professional insulator, I use stink rock which is foam glass and go as thick as possible within reason.

[vangoghsear]

If the dewpoint of the air is in the mid 70's there is a good chance the pipe cover is below that, especially if the dry bulb of the air isn't much above that.

Are the Mech Rooms being used as Return Air and Outside Air mixing boxes, or just Return Air plenums? I've seen that done where the outside air couldn't be ducted to the unit so it is dumped into the mechanical room acting as a plenum to mix. It can add to humidity issues on piping.

I like foam glass. I've used it in mechanical rooms and high pressure steam manholes. It holds up real well, but it is costly.

[engineerbrian]

If the dewpoint of the air is in the mid 70's there is a good chance the pipe cover is below that, especially if the dry bulb of the air isn't much above that.

Are the Mech Rooms being used as Return Air and Outside Air mixing boxes, or just Return Air plenums? I've seen that done where the outside air couldn't be ducted to the unit so it is dumped into the mechanical room acting as a plenum to mix. It can add to humidity issues on piping.

I like foam glass. I've used it in mechanical rooms and high pressure steam manholes. It holds up real well, but it is costly.

Yep, the mechanical rooms are being used as mixing boxes for OA. I spoke to our insulation guy and he ran the numbers and came up with 1 1/2" insulataion

[vangoghsear]

Yeah, that's what I thought. That should do it. 1-1/2 should be fine for mixed air temps.

[HvAckid82]

We used a sub on a project for chilled water piping that had 1/2" armaflex which wasn't doing any good due to age. So he doubled up with 3/4" armaflex and worked well. The chiller/piping is beig demoed this winter and we will replace it with a city multi.