Effects of ethylene glycol on piping

[tchvacman]

I visited a site in Oregon and have a couple of questions. The design uses sch. 80 PVC in the upper floors of the building and black pipe in the basement.

The units in the building are water source heat pumps.

The engineer called for 50% glycol in the system. I am not sure if a rust inhibitor was installed.

There are several PVC fittings that are coming apart at the glue joints. They also have a real bad rust problem in the system. The great part is that no strainers were installed so there were multiple failures of units.

My questions:

1. What are the effects of ethylene glycol to metal pipe?
2. What are the effects of ethylene glycol to pvc pipe?
3. I have always seen just 25% glycol used. Is 50% normal?
4. Have you ever seen a glycol system used with a cooling tower?

Thanks for any help.

 

[quark]

1. Ethylene glycol can be quite troublesome for carbon steel piping if corrosion inhibitors are not used. Further, some kind of bacteria feed on iron corrode pipes. If you find gelatinous sludge then that is due to bacteria.

2. PVC is OK

3. 50% may be for freeze protection

4. Glycol system with a cooling tower??? Needs some explanation before making comments. Where exactly it is used?

 

[tchvacman]

Thanks for the info Quark.

The building has water source heat pumps. They are using glycol in the condenser water for freeze protection I am assuming.

I have only seen this done if they are using a heat exchanger and using the glycol in a closed loop system

They do have a boiler that they will fire up and use in the winter to maintain 70 to 85 degrees in the system. This is the only time the system becomes a closed loop . They valve off the cooling tower and drain it in the winter.

Kind of negates the need for freeze protection in my opinion.

The pipe started rusting and sending the particles to all the control valves. They had no strainers installed except for on on the pump.

Hope this helps brighten the picture a little.

Any comments would be appreciateed.

 

[quark]

You mean they are using the glycol in open loop system (i.e for cooling tower instead of water?

Are you sure?

 

[tchvacman]

Absolutely positive. I couldn't believe it either. They only have a closed loop when they shut the tower down in the winter and run the system through the boiler.

 

[quark]

OK. One more question in that case. Do they have evaporative cooler type one or do they spray ethylene glycol into the cooling tower?

The second seems to be unbelievable still, for I am not sure how they dilute the solution to the required concentration, after the evaporation process in the cooling tower. In any case, this is a wrong practice (no.2) and there are plenty of chances that EG picks up all kinds of contaminants, possibly existing, and makes the pipeline life miserable.

As for corrosion, it is better to install corrosion coupons and check the system periodically.

If there is no problem of freezing, then 50% is overkill. Anyhow, it is better to check the temperature of cold fluid during winter conditions (i.e fluid going into boiler). You can get freezing point vs concentration data from Perry's. One of the comembers at HVAC forum of eng-tips developed a spreadsheet for pressure drop calculation and freezing point data comes as a bonus with it. Check at,

http://mysite.wanadoo-members.co.uk/pressure_drop2

 

[tchvacman]

This is some really good info Quark. Thanks

In response to your question. They have a BAC cooling tower. They are not spraying the EG into the tower. From what I can tell, as they test the water every month, they add more glycol as needed. They ran this system for several years with no rust inhibitor or water testing.

They started having trouble with rusting and then hired a testing company to come out. They have been watching the PH, alkalinity and such since Feb. this year. It appears they are finally getting the right levels, but the EG levels change often.

Some of the things they found were no makeup water, high levels of iron in the system and no strainers.