Adding glycol to a chilled water system
Adding glycol to a chilled water system
(OP)
I have a 100% water chilled water plant that is going to get new chillers and be filled now with a 40% propylene glycol solution.
I need to check the existing cooling coils on the AHUs to make sure they are adequate to meeting the cooling load with the reduced capacity.
I know from the manufacturer's specific heat data that our Btu/hr = 500 * GPM * dT formula changes to 456 * GPM * dT
But, what about thermal conductivity? Do I need to factor that in? The thermal conductivity of water is 0.336 (BTU/hr*ft^2)(degF/ft). The glycol solution is only .215. Won't this further degrade coil performance?
I need to check the existing cooling coils on the AHUs to make sure they are adequate to meeting the cooling load with the reduced capacity.
I know from the manufacturer's specific heat data that our Btu/hr = 500 * GPM * dT formula changes to 456 * GPM * dT
But, what about thermal conductivity? Do I need to factor that in? The thermal conductivity of water is 0.336 (BTU/hr*ft^2)(degF/ft). The glycol solution is only .215. Won't this further degrade coil performance?





RE: Adding glycol to a chilled water system
The 10% loss in heat capacity is the big one.
Will you be running colder? What about changes in flow (density and viscosity changes will impact pump performance)?
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P.E. Metallurgy, Plymouth Tube
RE: Adding glycol to a chilled water system
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Adding glycol to a chilled water system
RE: Adding glycol to a chilled water system
RE: Adding glycol to a chilled water system
Basically we are putting it in because the Owner wants it. Their property management group is spread thin and they don't want to be bothered with draining and filling the system in the winter to prevent freezing. So they are willing to accept all the trade offs.
I told them we will have to revisit and maybe replace the pumps so we are aware of the head increase.
Sounds like the thermal conductivity isn't THAT great a deal which is mostly what I was worried about.
Thanks!
RE: Adding glycol to a chilled water system
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Adding glycol to a chilled water system
The correct additive package of corrosion inhibitors is also a vital part of this process.
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P.E. Metallurgy, Plymouth Tube
RE: Adding glycol to a chilled water system
RE: Adding glycol to a chilled water system
Make sure the pumps have mechanical seals - packing allows capillary action causing "driping of fluid.
RE: Adding glycol to a chilled water system
Physical props for PPEG solutions required for cooling coil heat transfer and pressure drop calcs are available in text books and maybe on the net also.
RE: Adding glycol to a chilled water system
RE: Adding glycol to a chilled water system
In heating applications, the thermal conductivity was almost a non-issue, but with cooling it was huge!
The best thing you can do is have the coil manufacturer run both conditions and make a comparison.
RE: Adding glycol to a chilled water system