Propylene glycol in hydronic heating loops

Gordon

Greetings from the plumbing shop at Central Washington University in Ellensburg, WA.

Many of the buildings on our campus are hydronically heated, and most of these must be treated with glycol to protect against freezing. A few of our older loops are treated with ethylene glycol, but most of the newer buildings have propylene glycol in their heating systems. Anyway, we've begun having problems with deterioration of the glycol in some of our buildings. Typically, we're finding lower pH, high residual phosphate levels (probably from the original cleaning process), and high levels of dissolved metals, espacially Cu and Fe. We've checked with several water chemistry "experts" and have gotten almost as many answers as to why the glycol is breaking down in some of our systems.

Specifically, our questions are:
1) Is it advisable to use glycol with rust inhibitors? We've been told that the additives used by different manufacturers may not be compatible and can cause problems when mixed.
2) Are the rust inhibitors added to commercially available glycol sufficient for a building hydronic loop (we've been told they're not), or should we augment the solution with our own concoction? If so, what chemical additives are best and what is generally considered and ideal concentration of these additives?
3) How often should we have the fluid in these loops analyzed and what should we be looking for? Are there any test kits available that we could use to routinely check the condition of our glycol systems?
4) What is a reasonable "life expectancy" for proplylene glycol in a building heating loop?
5) Is there an industry standard for cleaning and treating hydronic loops in new buildings? We've found some variation in approaches by different water chemistry firms we've dealt with.

Any information you could provide us would be greatly appreciated. Thanks.

hr

All the right questions

I've talked to many and have found Dow tech assistance the best. The have two great "free" tech manuals on for propylene and one for ethylene.

The ph is one of the numbers to watch 9.5- 10.5 is ideal. When it drops to 8 time to add boost packages. Below 7, time to start over, it's had it.

Dow will do an analysis for free on large systems. Mail a sample to them. It goes a lot further than a simple field test. 1-800-447-4369 will get you to Dow to request the free enginnering manuals, test kits, sample bottles and any other questions.
Good luck.
hot rod

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canuckDale

Glycol is The Engineer's Savior

100% O/A. OK..you need it in cold climates. Um sometimes. That is if you design the system that way.

Greetings from a northern Canadian School System. I have >460 mixed HWH/STM/CHW systems. Some with glycol, mostly new. Some without, mostly old. Engineers here use glycol to add a cushion to their design/reputation. IMHO, it's not necessary. Controls, good return mix and proper freeze-stat location works well too.

The glycol...It naturally degrades over time. It degrades to form aldehydes, then to acetic acid. That's why the pH drops. You can buy it inhibited or uninhibited. Buy inhibited, and it comes loaded with phosphates. The science is that the phosphate coating on the piping is the corrosion protection and the buffering agent to guard against the pH drop. Obviously, over time, the phosphate depletes and you lose the buffering capacity. That phosphate also contributes to disolved solids - conductivity. Which grinds the hell out of pump seals.

We chose uninhibited. Of course our water treament program is closely (in-house by two steam engineers) monitored. The premium choice is molybdate based anodic treatment with azole cathodic inhibitors. Some older systems are nitrite treated because moly inhibitors weren't available then. I refrain from converting them to moly. Some studies say that nitrosamines can form and they are carcinogenic.The glycols are tested each fall. pH is adjusted with sodium meta-borate as the buffer.

The company we use is Betz Dearborn. Now GE Betz Dearborn. Formerly Grace Dearborn. Like any treatment supplier, the value is dependant upon the expertise/support of the staff at any given time.

Whoever is the 'best' local supplier usually earned that confidence through other institutions/universities/colleges like yours. Betz, Nalco or other companies must be in your area just dying to help you save and protect your equipment?
The ones you don't want are the ones that know nothing about your systems but will come in cold and claim to "Save you significant dollars".

John Ruhnke1

I NEVER design a system for anti freeze........

To me, if the system needs anti freeze, its a poor design. Unless of course it has snow melt. Even then I like to use a heat exchanger and keep the anti freeze from moving through the rest of the system. I hate anti freeze. I have seen too many good systems destroyed by it. If a system already is poorly designed and you need antifreeze, I will work with it and mantane the system. I will test the anti freeze once a year and put in additives to increase PH. The problem comes in when the people decide to skip the mantenence or maybe they switch plumbers and the new guy doesn't test the system. Then the problems start........ What a mess!! I have seen some major disasters out there! Radiant floor leaks, leaks in walls, boilers destroyed and more!

JR

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hr

Glycol yes or no?In cold climates

I know contractors in Montana and Alaska that use glycol in every system they install. They do a lot of remote homes and cabins. Some acessible only by snowmobile of snowshoes (in the winter These buildings can sit for months without anyone checking them. A very good application for glycol.

You are right John, maintenance is a must. Generally not an issue in a commercial setting with full time maintenance staff. On residential it really is up to the installer and owner to assure this check up. I install bright yellow stickers on the boiler noteing this requirement. You wouldn't install an oil fired boiler and just walk away without pointing out the importance of clean and check yearly maintenance, would you?

Same for glycol systems. I use my slow times to go around and do glycol checks. It's always good to do a drive by on all your jobs once a year. Heck they may even want to buy some more from you! It's good PR and an opportunity to see how your jobs are working. More than once I 've tweaked some things on a job after the first season. Heck I have even repiped some things after learning better methods here on the wall!

Customers are alway impressed when you do a free call to check on them and their equipment.

hot rod

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canuckDale

Go North!

Come north John! We need more here like you!

Didn't mean to dis' engineers.

It's incredibly frustrating when some of them load up a 10,000 gallon HWH system in a high school with that stuff for the only reason that "that's what we always do". Five years down the road, the CV's started leaking and the cheap isolation valves didn't hold....We got by for a while by forcing water back up the drops, freezing the pipe and making the repairs.$$$$$$$!!!!! We had to get special permission from the local boiler safety authority to for-go boiler blowdown because that stuff can't go down the sewer. Which meant annual instead of biennual inspection. And that meant R&R 800 gal X two boilers each year! More $$$$$$! The end result was $35,000 to properly dispose of the glycol, install better return air blenders and add a few strategically placed freeze-stats. Five years and many -35*F days and have not lost a coil.

Now for the hypocrite part. I glycolled all my chilled systems. ~:-P Smart huh?? LOL! I increased the load on the chillers by 25% because of the loss of heat transfer. But it saves me the maintenance money from having to drain/purge hundreds of coils in the fall and refill in the spring.