Which Glycol?

[DavidNJ]

In the summer, not necessary. But the chiller will be outdoors all winter, and the storage tank maybe, and 2 of the air handlers will be in a currently unconditioned attic.

Are there choices other than an Ethylene Glycol like Dowtherm 4000 or a Propylene Glycol like Dowfrost HD? All seem to reduce system efficiency. I'm told disposal costs have made ethylene glycol less attractive.

What is the best practice? How do you account for it in coil, pump, and chiller sizing? How do you determine its impact on the air handler efficiency?

[pecmsg]

Any glycol solution is going to reduce capacity from 5 to 10% or more, plus it can screw up water treatment.

Coils exposed to outside air can be drained the glycol pumped thru and drained again.

Keeping the chillers and piping above 55*f is your best bet.

[dean557]

Ethvl Methyl bad stuff... as stated reduction in efficiency is the key.. both protect.. but the disposal and leakage is the key...

[DavidNJ]

Any glycol solution is going to reduce capacity from 5 to 10% or more, plus it can screw up water treatment.

Coils exposed to outside air can be drained the glycol pumped thru and drained again.

Keeping the chillers and piping above 55*f is your best bet.


Air cooled chiller and unconditioned attic for the fan coils. Just can't control or guarantee the water temp.

[amickracing]

I guess it's a bit foreign to me to see a water system (chiller or boiler) that doesn't have any glycol in it around here.

I know it will kill efficiency, but generally speaking it seems like the equipment is usually over sized to some degree anyway so I wouldn't think it'd effect it too much.

Just curious, what temp are you planning on protecting it down to? Around here we usually shoot for 25-30% in most systems. A few places that have crappy power and horrible winter weather we bump it up a bit higher.

[Randy S.]

The "specific heat" or ability to carry a BTU, drops off rapidly above 30%.

[DavidNJ]

At 50F water has a specifc heat of 1.0015 btu/pound/F, 30% propylene glycol is .898, 40% .852, 11.5% and 15% less respectively.

At 150F water is 1.0003 btu/pound/F, the propylene glycol mix is .935 and .900 at 30% and 40% respectively. That is 6.5% and 10% less respectively.

The issue may be thermal conductivity. Water ranges from .561 W/mK at 32F to .679 at 212F. Meanwhile 30% is .434 at 50F and .4846 at 150F. That's about 30% less.

The heat capacitance could be handled by more fluid. The thermal conductivity would require a revised evaporator and water coils.