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carlosgw (Mechanical) (OP)
24 Mar 09 12:09
Has anyone used CPVC or PEX for chilled water piping?
Among other issues:
I am trying to find a surface temperature of PEX and CPVC with 45 deg water and no insulation without breaking out my heat transfer textbook.
RossABQ (Mechanical)
24 Mar 09 20:10
My only experience with CPVC in chilled water service was where it was direct-buried.  I didn't engineer the system, it was unfortunately running right thru an area where we were trying to excavate for a new building.  They were uninsulated, 10" lines, and I was assured that insulation was not used because it was uneconomical (no payback on energy loss) and just created problems with soaking up water. CHW temp was 39 - 45 degrees (reset on OSA temp).  Note this was Sch 80 pipe. The supply line outside temperature was pretty cool to the touch, but I suspect the statements about economics for direct bury situations are probably true, depending on the cost of power used for evaluation.

Naturally, it goes without saying that despite a full-time spotter, and extensive staking of the lines' locations, we nicked the lines with a backhoe, not even that hard, and quickly flooded the foundation excavation, costing two weeks' work on that, and another weeks' work to repair the lines.   
ChrisConley (Mechanical)
25 Mar 09 8:53
We've used PEX for chilled water, but only on final connections, and only with radiant cooling systems (where the water is being blended to above dewpoint).

Approximate surface temp should be obtainable if you can get the R value of the pipe, the thickness. Temperatures should be known.

Chris
briand2 (Mechanical)
25 Mar 09 9:25
My rough calculations based on:

Outside diameter 110mm
Wall thickness 8.2mm
Chilled Water 6degC
Surrounding Air 22degC
Draught 0.5m/s

CPVC surface temperature 12.3degC
PEX surface temperature 8.8degC

(CVPV thermal conductivity 0.15W/mK, PEX thermal conductivity 0.46W/mK).

Brian
trashcanman (Mechanical)
25 Mar 09 11:34
No and will not.  See RossABO for a good reason.  Do not use fiberglass either, as it is relatively fragile also.  We are doing several projects for a school district that is actively replacing fiberglass chilled water piping.  It failed too much.  It is hard to beat good old steel.
carlosgw (Mechanical) (OP)
25 Mar 09 16:03
The application would be fan coils with the piping above a ceiling.
If PEX were used at all it would be for branches only to the fan coils.
I have seen it for water source heat pumps. But I have a hard time seeing insulating PEX as practical.
 
Drazen (Mechanical)
26 Mar 09 15:20
You can freely say that there is no generic rule for plastic pipes - you need to see exact manufacturer's data. But I would be bold to say that PE-X shouldn't have any fragility problems.

A brief look in catalogues:

REHAU offers Pe-Xa pipe for heating and sanitary cold water, which means it can be normally used for fan-coils..

HENCO offers multilayer pipe, inner pipe is PE-Xc, and outer pipe is Alumine - explicitely specified for cooling and heating.

Sometimes  I use PP-R as well.

All this pipes have light insulating caracteristics, if you have time you can make input of pipe data in some insulation software and find that couple of mm less insulation thickness is needed compared to  steel pipes.

Usuallly I don't take chances for condensation prevention -I presume ca 5% lower critical air humidity and that's it.

sunshine
 
stevenw (Mechanical)
27 Mar 09 11:30
Office rule - No PEX.

CPVC is ok. Watch them like a hawk so they don't use PVC.
RossABQ (Mechanical)
27 Mar 09 11:56
It should be mentioned that there are increased support costs for any plastic vs. copper or steel.   
AbbyNormal (Mechanical)
27 Mar 09 21:23
chilled water piping here is primarily schedule 80 PVC

sometimes CPVC does not like too much propylene, saw a geothermal job go south when the comcentrations for freeze protection required made the cpvc joints leak

 

Take the "V" out of HVAC and you are left with a HAC(k) job.

Zesti (Mechanical)
1 Apr 09 7:34

Have a look here:

http://www.aquatherm-uk.com

They do a pipe-system that is designed for chilled water, without using insulation.

They should have a tool for you that calculates if condensation will occur under your specific conditions.

 

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