glycol in chilled water system

Wondering if there is a rule of thumb on how much a system is derated when glycol is added to a system. Example per say 300 ton chiller with 30% glycol you actually get 225 tons due to the heat transfer characteristics of the glycol.

thanks

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Originally Posted by pipefittermarks

Wondering if there is a rule of thumb on how much a system is derated when glycol is added to a system. Example per say 300 ton chiller with 30% glycol you actually get 225 tons due to the heat transfer characteristics of the glycol.

thanks

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I don't know of any rule of thumb. But most manufactures have charts showing the capacity vs glycol %.

Depends if its Ethylene or Propylene

My experience any thing over 20% is a problem if it was designed for straight water. Approach temperatures increase to where chiller will drop out on refrig temp or pressure while chilled set point not made. Real problem on small DX systems because less engineering seems to be involved. Larger Centrifugal installs chiller more likely to be designed for anti freeze mix

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Originally Posted by Jimmyhat 597

My experience any thing over 20% is a problem if it was designed for straight water. Approach temperatures increase to where chiller will drop out on refrig temp or pressure while chilled set point not made. Real problem on small DX systems because less engineering seems to be involved. Larger Centrifugal installs chiller more likely to be designed for anti freeze mix

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That's a good point. A system designed for use with glycol might have a larger or different evaporator configuration. Larger chillers always get designed as a custom package.

the buiding coils need to be sized for glycol as well. You loose capacity all the way around as well as pump performance.

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Originally Posted by Southern Mech

the buiding coils need to be sized for glycol as well. You loose capacity all the way around as well as pump performance.

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Ah the pumps....:cheers:

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Originally Posted by Healey Nut

Depends if its Ethylene or Propylene

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How do you tell the difference?

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Originally Posted by TheChillerMan

How do you tell the difference?

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Taste;)

depending upon the evaporator design, it can range in the 10-15% area with propylene. This doesnt account for the added horsepower requirement of the pump(s).

You lose approximately 25% of your heat transfer rate in a 50/50 mix. You're gonna run lower suction pressure, or higher head pressure, equipment needs to be selected for expected fluid concentrations, for proper operation.

Bottom line is looking at the SYSTEM. If you add glycol to a closely sized system that was designed for water if could be trouble. The chiller. coils. pumps and concentration of glycol all need consideration.