Glycol use in chill water loop

[lodiroon]

Ran across an interesting quote while browsing some info on chillers that indicated that the use of glycol actually reduces chiller efficiency, while causing higher than normal approach temps. My question is that I have always assumed that the heat transfer capabilities were improved by using the proper amount of glycol-to-water mixture. Any info on the proper mixture and/or the efficiency prperties would be appreciated.

[greybeard]

The easiest thing to do would be to check the original order write up for that chiller. If it was based on X amount of glycol being present no problem , if it was not intended to chill a mixture you would have to find out what type of glycol it has in it as each type would have a different specific heat (how well it transfers heat) and a different specific gravity ( reflected in the pressure drop) and also needed for accurate use of a hydrometer

[freonrick]

i started 2 264ton units a while back and with glycol in it the tonnage is now at 209. this is with 30% glycol. i dont remember which glycol. you do loose capacity. the more glycol the worse. every start up i do with glycol my spec sheet shows the loss that was engineered in to it. so any chiller ordered the sales engineer needs to know whats in it.

[maustin]

We run a 30% solution of Dow Therm SR-1 in our 600 ton comfort cooling system. Dow sampled the water and recommended the correct concentration based on freeze protection and corrosion resistance. Their services were free of charge. I'd look them up and give them a call.

[fat eddy]

I've never heard of a mix that didn't change the transfer rate for the worse, the mix here is usually about 40%, and usually ends up being 50%, Soemtimes this leads to low pressure problems in a chiller,

like a Trane chiller locking out on low pressure every morning at start-up, I mention that one because I see it so often that it is hard to deny.

[hvacker]

Always a loss. Oh ya, and don't use auto antifreeze as it has corrosion inhibiters that can damage seals and other stuff. I remember a injection molding machine that ran 22degF with glycol that went from 17 tons to as I recall 5.5 tons. Part was the low temp but the transfer rate with glycol was poor. I thought ASHRAE Fundamentals had a chart.

[willf650]

Always lose capacity and if your chiller was not specificlly ordered for glycol you generally will have to change the low pressure switches on smaller chillers and the low pressure cut out points on the larger chillers to avoid low pressure trips. If your running low water temps as in ice storage you lose even more capacity.

[tab-tech]

....that capacity loss will always be found when using glycol in a system.
The loss when the mixture is above 30 - 40 % is greatly increased.
Good ol' plain water (no additives like floride, chlorine, etc.) is still the best heat transfer medium available.

[jimp]

Here in FL all the process chillers that I work on are set at a mix to protect down to a temperature, I never base it on percentage of gallons in a system. I just add and use my Misco meter to check for the temp I'm looking for.

[tab-tech]

Originally posted by jimp
Here in FL all the process chillers that I work on are set at a mix to protect down to a temperature, I never base it on percentage of gallons in a system. I just add and use my Misco meter to check for the temp I'm looking for.


.....you are just simply using temperature/color shade as the medium of determination.

[flange]

any system that utilizes glycol will be reduced in capacity. usually at about 35% solution of propylene the ratio is 85% for ethylene its lower i think around 70-75%. as percentage of glycol goes up, efficiency goes down. this can be tracked using the specific heat of a given ratio, but if you are altering a water system to a glycol system there are other factors to be considered as well. Pump head is increase, in addition some older control valves must have their packing replaced. Of course, heat transfer will be effected and the heat transfer components may need upgrading.

[airworx]

you need testing kit and chart for water temp - glycol percent.

[mrhvacmechanic]

Glycol will drop efficiency in any unit. When using glycol the gpm has to be higher than water. Please check with an engineer on capacity in gpm vs. viscosity of glycol.