Propylene Glycol vs Heat Trace

[tlhoo]

Designing a job in Wash, DC area, with exposed chilled water piping (air cooled chillers on grade). Intially planned to use heat trace, but was directed to use propylene glycol due to the "reliability" problems with heat trace.

Anyone have any experience with heat trace failures?

Any thoughts on this matter in general?

Thanks in advance.

 

[KenRad]

Heat trace certainly can fail. To detect when it does, we install indicator lights at the end of each run. Checking that the lights are on are part of the plant checks for our maintenance technicians during the winter months. If there is a break anywhere in the run, one of the lights will go out.

Glycol is certainly more fail-safe, but you must be willing to deal with the environmental concerns when draining fluid from the system. You also pay a penalty in pumping energy and heat transfer. Our plant decided years ago that we were better off going glycol free, especially with all of the draining and refilling we do as a result of system changes.

---KenRad

 

[Yorkman]

One thing to consider with heat trace is if you don't have power you have no protection. (unless you tie the heat trace into an emergency power system.) Propylene glycol is considered none toxic by all accounts, although dumping issues may be regulated by your local authorities.
What KenRad brings up is a very important but often over looked point. Propylene glycol is going to reduce the specific heat of your cooling medium, thus affecting your cooling capacity. You may have to lower your chilled water setpoint or increase the chilled water flow to be able to make system load requirements. Lowering setpoints brings about it's own set of issues, because the heat transfer is not as good with glycol the approaches are going to suffer on the chilled water bundle. Depending on the setpoint you might experience low evap. pressure trips.
The solution I see having the most success with glycol is to increase the chilled water flow rate, if the pump is on a V.F.D. this may not be too hard, provided the motor can handle the increase in amps. If it's a standard starter you're looking at increasing the impeller size. Again motor amperage would need to be considered.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[CESSNA1]

YORKMAN: Do you have any figures on how much glycol changes the specific heat? I had a test run many years ago on a diesel engine test I was doing as part of a waste heat system. The results were that a 50/50 ethylene glycol/water mixture had a specific heat of 0.99 as opposed to 1 for water. The other side is that I in my first car - a '66 Impala with a 327 engine - I changed the anti-freeze (ethylene glycol) twice a year. Anti-freeze/water in the winter and rust inhibitor/water only in the summer. The engine ran consistently 20 Deg F hotter in the winter than in the summer. 200 deg F. in the winter and 180 deg F in teh summer. I attribute that not so much as a change in specific heat, but as an insulting film that the ethylene-glycol put on the cast iron water passages in the engine.

To TLHOO's basic question, heat trace and glycol are equally valid, as the other respndents note. It is a matter of choice unless you have a heat exchanger and run just water through one side of it, and then a heat trace is the way to go. You can also do both.

Regards
Dave

 

[Yorkman]

Cessna1
I have an old chart I got in some start up literature from York;
Ethylene glycol by volume @ 40 degrees
15% SpHt .929 Density 63.98 Freeze 22.7 Degrees F
25% "" .891 64.96 14.7
30% "" .861 65.65 3.5
40% "" .817 66.59 -12.7
50% "" .770 67.47 -34.7

Propylene glycol by volume @ 40 degrees
15% SpHt .958 Density 63.63 Freeze 22.9 Degrees F
25% "" .929 64.32 14.7
30% "" .910 64.66 8.5
40% "" .872 65.21 -6.7
50% "" .830 65.67 -28.8

Chapter 21 in the A.S.H.R.A.E. Fundamentals handbook have some detailed tables for Ethylene and Propylene solutions. Hope that helps



I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[ONEPOINT]

Hi,

I have to do a sizing(how many tracers and diameter)for a ethylene glycol heat tracing system for 12", 20" and 24" piping. Does anybody out there know what calculation steps shoud I take?

Best regards,

Bogdan

 

[ONEPOINT]

Hi,

I have to do a sizing(how many tracers and diameter)for an ethylene glycol heat tracing system for 12", 20" and 24" piping. Does anybody out there know what calculation steps shoud I take?

Best regards,

One Point

 

[lilliput1]

tlhoo
Can the system be design to use outdoor air economizer cycle so the chiller would not run and therefore can be drained during winter. Provide shutoff valves indoor as close as possible. Provide vents & drain valves to completely drain the outdoor piping including the chiller evaporator.
Check requirement of your state. Use of food grade propylene glycol may be required. This is more viscous and less thermally efficient as ethylene glycol but it has no environmental hazard concern.
lilliput1

 

[sterl]

Onepoint:

Both Chromalox and Raychem have tremendous design stuff on teh Web...For pipes that size, you will want to look at your "geometrically odd" portions, especially what won't be insulated, such as upper valve bonnets...or maybe whole valves?