Ground Source Heat Pump Loop (geothermal) anti-freeze

[carlosgw]

I have used ethylene glycol mix for a system is the past.
It has been suggested to use methanol or ethanol. Is this a common use?
Any issues to be concerned about?
Are there propriety products (like Dow for ethylene glycol)?

 

[ProcessHVAC]

glycol is toxic, so depending on your local regulations they might not allow you to use it for ground source. Some of those proprietary products for ethanol are actually good, and they can help with engineering and figure out O&M procedures and planning.

 

[NegativeZero]

why would use glycol in the ground loop?

but Propylene glycol is food grade

 

[GMcD]

Nobody in the HVAC world has been using ethylene glycol for 20 years. Propylene Glycol (Dowfrost as a brand name) is the go-to antifreeze additive. Methanols and ethanols are also good because they don't thicken and have better viscosity at cold temperatures, but local environmental regulations and taxes on the alcohol based antifreeze solutions make them hit or miss depending on local conditions.

I wonder about the geo system design if it's running so low that antifreeze is required. Using antifreeze for an undersized geo field in a heating dominated climate is a recipe to create permafrost. There are a lot of examples of geo fields that have turned into permafrost in Canada from poor geo system design (generally too small a field and over-optimistic soil conductivity assumptions).

 

[EnergyProfessional]

Typically propylene glycol is used Ethylene glycol is outlawed in many locations due to toxicity.

If you need it depends on your soil temps and field size/load. Here in WI it is common.

 

[carlosgw]

I'm trying to get information on the properties of ethanol mixtures. I am getting mixed information. Some of which suggests that it has a higher viscosity than propylene glycol mixtures.
???????

 

[IRstuff]

That seems hardly plausible. PG turns to slush around -30ºC in a 50:50 mix.

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[EnergyProfessional]

Ethylene glycol is less viscous (less pressure drop) than PG. Both are more viscous than water.
Low temperature make all fluids more viscous (look at your engine oil when cold). Your pressure drop calcualtion has to account for that!
In hot systems (i.e. solar thermal) the viscosity of glycol mixtures is almost the same was water, no big deal. But when cold, you have more pressure drop and your pump performance drops in addition. Grundfos, BG etc. have software calculators and you can enter temp and mixture to get the aproppriate curve.

I've seen designs that just used the standard water (@60°F) for design calcs in groundsource systems and they failed since they ignored the cold, the mixture and reduced pump performance.

 

[NoHtPp]

Great HKL !

That is sooooooooooo important even at spec'd 24% glycol in Northern Loops frequently LW to the ECL, gle ground loop, is 30f to 27f (yikes) and a 50% "pump penalty is in place at the charts...
What is meant by that is if I want total circulation and GEOTHERMAL unit heat exchangers and all connected fittings (ALL, that means ALL)

I will look at wanting 22 ft TDH water on a pump chart but at the 33ft TDH p-glycol mark and see what GPM I will likely end up with. REM: an oem is at the mercy of water coil PERFECTION by their charts...(!) You can find just 3.1/2 to 5ft tdh water coils in some GTHP OEM's as has been since the early 80's, too.

Also several reasons for over 20% p-glycol , if any used ( I used to think 18% was fine ) and not because your loop is not entering above 34f. [Energy Star(tm) is rated at 32f x 3pm per rated -ton (which is ~ 3.3gpm per compressor label actual-ton)].
But I think you will find some other bugs and properties of P-Glycol is requiring that minimum by vol.

Methanol is great! and at just 16% I only adjust about a third away from the water charts to 40%.

We have had food grade p-glycol require maintenance as in radiant systems and waxing impellers and volutes and cavitation can occur more easily, so kick around certain additives, please.

In zones 4 on up, common loops residentially sized, 4500 to over 7000 deg day, are guarranteed only 34f or more returning to the GTHP at ~ 2.7 GPM per rated "size-ton"
then: ~ 3GPM per compressor-in-box label-ton. Notice that W:W specs having size and tons of actual compressor, like Water Furnace and Hydro-Temp Corp of AR does, are equal to the labeling on the ARI rated compressor... but double check all forced air/ READ the heats of absorption and go from there, please. Vertical boreholes in residential loading only approach ~ 42 to 44 btuh per standard grouted x 3/4" PE dr-11 loop foot at 34f return and ~ 30-29.1/2 going out to the Earth Coupled Loop, ECL, gle.

 

[NoHtPp]

We have commercial library loops (1997 installation) that never get below 38f, nor above 88f, back to GTHP...[average 220 f per block loaded cooling ton Trane calculator, then in 120ft water below grade in 300ft 1" pe dr-11, enhanced grout, 17ft apart boreholes ] but I would always have some 16% something as a starting point if I thought it leaving below 37f, for sure.

That is standard North-GT Earth-Coupling.

We have added cross-over 6 gpm/ton - circulators on 50f well systems, discharging 32.1/2f to 34.1/2f all the time, but controlled refrigerant and water temp sensors are redundantly set up. The water coil ices and changes the pressure drop quickly in 1/2" ID re-enforced (ss-wrapped-wire-clad) heat exchanger tubing, - also for great water-only process cooling requirements hitting almost exactly 32f, very carefully, continuously too.

 

[EnergyProfessional]

before you go too deep into ethanol/methonal, please check if all the materials are compatibel, and if you have regualtory requirements to meet. Ethanol burns, casues corrosion etc. glycol comes certified with stabilisator, corrision inhibition, pH bufffer etc. Do you even have an ethanol manufacturer that produces that for HVAC? Please tell me you don't jsut to go to the liquor store and buy some alcohol...

so maybe this is a non-starter right here. My question is, why would you want to explore ethanol/methanol? Do you think it is cheaper? Soemoen always will suggest something, mostly those suggestions coem from non-engineers.

Regarding viscosity, either you find some values googling or from manufacturers. I wrote a little prgram for PG, EG etc. i cna see if one could use ethanol/methanol. but thsi is only part of the equation. You get more pressure drop in the system. but your pump performance also degrades and I don't know if BG, Grundfos etc. give you pump performance for ethanol/methanol.