anti-freeze & galvanized pipes

[afm]

I’ve got an old run-around-coil heat-recovery system, which is handling about 12 cu m/sec of air. Heat is extracted from the exhaust air streams with 4-row coils and the water is pumped to 6-row coils to heat the supply air. The system seems to recover about 50% of the available heat, when it runs in winter.

The original system had a ‘summer cooling’ mode that cooled the air with cold water pumped through the supply coils from a cold water storage tank. I abandoned this feature because it is now illegal and was never a good idea.

The problem is that, because the system once handled domestic cold water, all the existing pipework is galvanized. It has always been filled with plain water and the supply coils have frozen several times. I now want to put anti-freeze into the system. I understand that the usual anti-freeze mixtures (ethylene or propylene glycols) will usually have di-potassium phosphate corrosion inhibitor, which will react with the zinc.

Can anyone suggest any different antifreeze solutions which are compatible with the zinc, or will I have to replace all the old pipework? I tried a couple of large chemical suppliers, but they were not helpful. Any other bright ideas would be welcomed.

TIA

 

[meintsi]

Why not just drain the line?


Remember...
"If you don't use your head, your going to have to use your feet."

 

[romke]

Antifreeze can be obtained in various forms. Most of them contain anticorrosion packages that are designed for use in automotive applications and therefore may contain substances that are not compatible with zinc. It is however also possible to obtain just the antifreeze, which means just ethylene or propylene glycol.

Since you do not need the anticorrosion properties you could use just the glycol with water and all should be fine.

Chemical suppliers should be able to sell this to you - just make vary clear you do not want any additves in it, just the base product.

 

[afm]

The heat recovery system still works and I want to keep it in use, with a fluid in it.

Does anyone know if it is just the corrosion inhibitors which re-act with the zinc, or will glycols (ethylene or propylene) re-act with the zinc as well?

Thank you both.

 

[saxon]

AFM, Here is an emprical method that you can use to test how corrosive the glycol/water mixture is on zinc. Weigh and measure (with a mic.) a zinc corrsion test coupon, place the coupon in a beaker of the glycol/water mixture for a period of time (say 3 months)pull the test coupon, reweigh and remeasure it (once a month)and log the data. At the end of 3 months you will have available data on the corrosion rate of zinc in glycol/water solution.

As for running glycol/water solutions in galvanized pipe I have seen this done extensively in industrial chiller loops without major degradation. Check with the manufacturer of the glycol for their recommendations for galvinized pipe service. The anti-corrosion additve packages can be formulated to specific requirements.

saxon

 

[ChrisConley]

I don't really have anything additional to add to the discussion, other than to state that most antifreeze manufacturers will have a very good idea of how their product reacts to various metals. That being said, the part of your post that really attracted my attention was:

-The old system had a 'summer cooling' mode.......I abandoned it because it is now illegal and was never a good idea.

First off: What makes the system illegal? Secondly cold storage is something that we're using up here in Canada (8 months of winter means we can get all the cold we need), why do you not like the idea?