propylene glycol in an oil fired boiler system

 
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Post by coalkirk » Thu. Apr. 05, 2018 5:04 pm

I need some advice from those of you who are oil fired boiler guys. I encountered a system today where the owner, an engineer, drained his system and filled it propylene glycol. It's a hot water baseboard system only. Is that ok? There was no backflow preventer on the boiler feed so I did call that out as a problem. Thanks!


 
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Post by Rob R. » Thu. Apr. 05, 2018 5:12 pm

propylene glycol is less toxic than ethylene glycol, but I think having a backflow preventer would be a good idea (and probably required by code anyway, even without the glycol). I don't see any issue with it in the right application, other than the normal issues that come with using any type of glycol (leaks, btu transfer, need to monitor chemistry).

 
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Post by scalabro » Thu. Apr. 05, 2018 5:53 pm

Ive often wondered why a hot water heater (baseboard) system is generally not either ethylene or propylene glycol and just completely isolated from the potable water supply in a home...

 
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Post by hotblast1357 » Thu. Apr. 05, 2018 6:14 pm

Most of your outdoor wood boiler are glycol based, for obvious reasons of freeze prevention. I’ve heard of several people doing it around here in their normal inside boiler, so that if there away from home on vacation or something and something happens to the heating system, it won’t freeze.

 
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Post by rberq » Thu. Apr. 05, 2018 7:03 pm

Heat transfer efficiency is lower with propylene glycol so costs money every day. And it is expensive to buy and install, and expensive to recover and re-fill if the system must be drained. But I do know people who have baseboard systems with pipes inside exterior walls, who have had pipes freeze.

 
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Post by lsayre » Thu. Apr. 05, 2018 7:12 pm

Although it is less toxic than ethylene glycol, propylene glycol is still toxic. It also has the issue of being capable of carrying (delivering) only about 63% of the heat of water when used at 100% concentration. Zones will need to circulate almost 60% longer to deliver the same overall amount of heat, since 1/0.63 = 1.59

It is as if the boiler has only 63% of the BTUH vs. the same boiler with pure water. On the coldest days of the year you may find that you do not have enough boiler to heat your house. If a boiler is rated for an output of 90,000 BTUH with water, it will be rated at 56,700 BTUH output on pure propylene glycol.

The same phenomenon exists for a radiator in a car, whereby if running on straight propylene glycol it will only remove 63% of the engine heat of straight water. And straight ethylene glycol is way worse, since its specific heat value is only about half that of water, as opposed to 63%.

 
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Post by Lightning » Thu. Apr. 05, 2018 7:19 pm

Seems like that deficiency of BTU carrying ability could be fixed just by just circulating the fluid faster. Is that right?


 
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Post by lsayre » Thu. Apr. 05, 2018 8:04 pm

Lightning wrote:
Thu. Apr. 05, 2018 7:19 pm
Seems like that deficiency of BTU carrying ability could be fixed just by just circulating the fluid faster. Is that right?
I would initially intuitively believe so, with no problems until you run into velocity noise. Another issue is that circulators only deliver what they deliver, and they stay on their curves. Sufficient additional GPM flow would require a whopping circulator upgrade in some cases to overcome what would be a massive rise in friction head.

But then oddly enough, if you look at published data for fintube radiators, they don't change much in their BTUH per foot delivery rate when the flow through them goes from 1 GPM to 4 GPM, so this has me wondering. See fintube chart at the attached link below. Lastly (for now) intuition generally makes for bad science.

http://www.slantfin.com/images/stories/Technical- ... ne30_r.pdf

 
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Post by McGiever » Thu. Apr. 05, 2018 9:57 pm

Plenty of foods, skin care products, pharmaceuticals and e-cigarettes vapes contain propylene glycol as an ingredient.

 
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Post by VigIIPeaBurner » Thu. Apr. 05, 2018 10:29 pm

McGiever wrote:
Thu. Apr. 05, 2018 9:57 pm
Plenty of foods, skin care products, pharmaceuticals and e-cigarettes vapes contain propylene glycol as an ingredient.
Yes, with the food grade "USP" PG which meets FDA regs. Terry - what grade did the engineer use? He might have access to some industrial grade. Could get iffy then without documentation.

From the charts on this link, it appears that a 30-40% by weight PG:Water blend would carry 89-94% of the BTU content as plain water. Freezing point approaches 0 F and boiling point is a little higher. With a higher boiling point, would the pressure rise as the temperature does? IDK but I think not. So if you run hotter you push the BTU content up, right?

 
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Post by Lightning » Thu. Apr. 05, 2018 10:31 pm

lsayre wrote:
Thu. Apr. 05, 2018 8:04 pm
But then oddly enough, if you look at published data for fintube radiators, they don't change much in their BTUH per foot delivery rate when the flow through them goes from 1 GPM to 4 GPM, so this has me wondering.
Ah, so the only way to fix the lacking BTUs would be to raise the fluid temperature.

 
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Post by lsayre » Fri. Apr. 06, 2018 5:27 am

McGiever wrote:
Thu. Apr. 05, 2018 9:57 pm
Plenty of foods, skin care products, pharmaceuticals and e-cigarettes vapes contain propylene glycol as an ingredient.
But it is toxic at about 2 grams of intake. The world health organization has established the maximum amount of propylene glycol that can be ingested in a single day and it is 25mg/kg.

 
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Post by lsayre » Fri. Apr. 06, 2018 5:33 am

VigIIPeaBurner wrote:
Thu. Apr. 05, 2018 10:29 pm

From the charts on this link, it appears that a 30-40% by weight PG:Water blend would carry 89-94% of the BTU content as plain water.
It's not bad at that concentration range, but you do not want to push it to 100%.

 
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Post by lsayre » Fri. Apr. 06, 2018 5:37 am

Lightning wrote:
Thu. Apr. 05, 2018 10:31 pm
Ah, so the only way to fix the lacking BTUs would be to raise the fluid temperature.
Yes! Or keep the percentage of propylene glycol lower as was pointed out by VigIIPeaBurner.

 
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Post by hotblast1357 » Fri. Apr. 06, 2018 6:20 am

Well it’s a good thing we drink our boiler water! Lol


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