What percentage of glycol do you use when you have outdoor air-cooled chillers?

[nuuvox000]

These chillers will be serving a 200 apartment hotel. The piping system is 4-pipe so I think they'll want to run it year round just in case someone is hot in their room but I'm not exactly sure if that's common or not. This is in Utah so it can get down to the negative temperatures now and then. All time lows can be -20 F although very uncommon. However, going 50% glycol seems kind of like a waste. Any insight on this is appreciated.

 

[EnergyProfessional]

Look up climate data and freeze and slush points of the typical percentages.
If the chiller would be off during the coldest days (which one could assume apartments) you cna afford the glycol to go slushy. If you need it to run on all days, like in a server room, you can't get it go slushy.

 

[IRstuff]

We've gotten by with 60/40 mixes for military systems specified for -40C; it's admittedly pretty slushy, but's unlikely that there will that much cooling demand at -20F. Note the glycol saps the heat transfer capacity of the fluid, so you want as little glycol as you can possibly get away with.

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[TugboatEng]

Running more glycol might seem wasteful but as you reduce the amount of glycol you increase the amount of water in your system and will now be spending more money on treatment.

 

[EnergyProfessional]

Running higher percentage of glycol than needed for burst or slush protection will unnecessarily reduce thermal properties and increase pump power. Especially for cold applications.
I've never seen a glycol system with chemical feeder. The fluid is for life (whose life?) Water systems have chemical feeders. You will want a glycol fillstation, though.

Also consider if you use PG or EG. For environmental reasons EG is on the way out (it seems).

 

[IRstuff]

EG has ever so slightly better flow at cold, though, but yeah PG is much nicer, particularly with regard to any spillage. PG is also possibly less corrosive with steel, compared with EG.

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[nuuvox000]

Thanks all, I decided to go with 40/60 propylene glycol solution. That should stop any freezing during the winter at my location.

 

[FacEngrPE]

Don't just run glycol in your system. For a 200 apartment hotel, control of the water chemistry can be important. At a minimum the glycol should have an inhibitor package. It may be cost effective to put a monitoring system in place.

See
[ul][li]Section 23 25 00 - HVAC WATER TREATMENT[/li]
[li]Monitoring and Treatment of Closed-Loop Cooling Water Systems (Power Magazine)[/li]
[/ul]

 

[EnergyProfessional]

FacEngrPE: not sure where you are located. but here (US) the glycol you buy has everything included. Manufacturers have specific glycol for geothermal, chillers, solar, heating etc. they all have the (hopefully) appropriate additives to withstand the respective temperatures. For example, solar glycol is rated up to 350°F, while geothermal isn't. All the systems have a glycol fill-station and besides that are sealed. Glycol gets tested, and if pH, etc. are off, fluid gets replaced. Our systems are relatively small (fire station geothermal etc.). I assume for very large systems you could have some sort of manual maintenance of the fluid. but typically it is like a car, you replace if needed. You don't tamper with the fluid.
I wouldn't want the contractor just to start mixing stuff.....