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Anonymous Poster

# The Approach Temperature of a Chiller

11/26/2010 6:20 PM

hi'

It was said:

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I agree with Guest. The aproach temperature of a chiller and the approach temperature of an evaporative condenser are two different things. For a chiller, imagine you have an entering water temperature of 54 F, a leaving water temperature of 44 F, and a saturated refrigerant temperature of 38 F. (To find saturated temperature, measure the refrigerant pressure and find the temperatue equivalent). In this example the Temperature Difference (TD) is 10 F. The approach is 6 F. Temperature difference is a function of water flow, approach is a function of efficiency of the heat exchanger.

Both TD and approach will change as the chiller capacity changes, so an accurate measurement also requires knowledge of capacity at that time. Also the approach will change at the heat exchanger becomes fouled on either the water side or refrigerant side. Rule-of-thumb for American equpment. In the 1980's a typical approach was 10 F. A chiller made today will be more efficient, and have an appreach in the 2-4 F range.

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Hello, it was said here that the approach temperature is 2-4 f,(would you like to buy a pet rock?) and saturated temperature was used. I am still in the 1980'S, and confused! are you saying that the saturated temperature can be 2 degrees above the condensing shell and tube l.w.t.? I think you are confused with sub cooled liquid TEMPERATURE, which is not saturated.

anyone…

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Guru

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21011
#1

### Re: The aproach temperature of a chiller

11/26/2010 6:43 PM

The first person was talking about a chiller; the second about a condenser.

Plate-and-frame heat exchangers can have large areas economically, and thus can achieve closer temperature approaches than most shell-and-tube designs.

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Anonymous Poster
#2

### Re: The aproach temperature of a chiller

11/26/2010 7:00 PM

are you saying that the saturated temperature can be 2 degrees above the condensing shell and tube l.w.t.?

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#3

### Re: The aproach temperature of a chiller

11/26/2010 7:10 PM

Yes, if there is enough surface area in the condenser. In most cases, however, this is not likely to be economical.

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Anonymous Poster
#4

### Re: The Approach Temperature of a Chiller

11/26/2010 7:28 PM

Hello, thank you for your response.

According to what Gadget guy said.

Have you worked or seen a chiller that has a 2 degree approach from the I.W.T and S.D.T.? I work on a lot of them, but have not seem a 2 deg. we are talking about factory, do you still say yes this is true?

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Join Date: May 2009
Location: Richland, WA, USA
Posts: 21011
#5

### Re: The Approach Temperature of a Chiller

11/26/2010 7:33 PM

I haven't personally worked on chillers with that close an approach temperature, but a P/F type exchanger with flooded or recirc refrigerant can surely do this. Just do the LMTD calcs to find what A is needed....

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