glycol recommendation for an air-cooled chiller exposed to -70 deg F conditions in the winter

[BronYrAur]

I am looking to put an air cooled chiller in Alaska for use during brief periods in the summer. Otherwise, the unit will sit in the elements. Design condition is supposed to be -70 deg F. Draining the unit and letting it sit dry over the winter is apparently not an option. So I am looking into anti-freeze solutions. I would need to have a heater on the chiller and the piping heat-traced I'm sure. And I am thinking I would need to run the pump all the time, or at least below a certain ambient just to keep things from freezing.

The glycol I use in everyday life (not in the arctic) never exceeds 40%. And even then the viscosity and heat transfer property make it difficult to deal with. I can't see any freeze protection down to -70 deg F. with the everyday glycol I use elsewhere. Any recommendations on anti-freeze that would be friendly to an air-cooled chiller and be suitable for pumping and heat transfer?

 

[BigInch]

Put a pump, heater and heat-tracing on the piping. Pump at a slightly higher flow rate needed to prevent freezing.

 

[Compositepro]

Heat tracing all winter when the system is not in use seems very costly. From Wikipedia:

"Most commercial antifreeze formulations include corrosion inhibiting compounds, and a colored dye (commonly a fluorescent green, red, orange, yellow, or blue) to aid in identification.[16] A 1:1 dilution with water is usually used, resulting in a freezing point of about −34 °F (−37 °C), depending on the formulation. In warmer or colder areas, weaker or stronger dilutions are used, respectively, but a range of 40%/60% to 60%/40% is frequently specified to ensure corrosion protection, and 70%/30% for maximum freeze prevention down to −84 °F (−64 °C)."

So standard antifreeze should work for you at 70:30.

 

[blacksmith37]

As I remember, pure glycol freezes slightly above 0 F, so the commercial stuff has a few % water to lower freezing below 0. It seems you will need to know the exact composition for this application.

 

[georgeverghese]

Fig 20-39 in the GPSA in the chapter on gas dehydration also matches the min freeze point value quoted of -80degF for a 70:30 aqueous mix of EG. That would mean poorer heat transfer characteristics at operating circulation temperatures in summer in comparison to a 40% EG mix though.

Switching out to methanol-water may not be a safe option, and also may require corrosion resistant alloy steels.