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## Negative condenser approach?

I have a couple of water cooled chillers running for about 6 years now, I have never been involved in the operation or maintenance of them until recently, and have noticed that the condenser approach is actually a negative figure. I dug out the commissioning documents from when the factory engineer started them on site, and they have been running a negative approach from day 1 it seems.

Over the 3 chillers the approach varies from -2.3 to -6.2 degrees C. In my mind this is an extremely efficient condenser. But how is it possible for the approach to be negative? How is it that the liquid refrigerant is cooler than the condenser leaving water. And is it normal or acceptable for this to be happening.

As some additional information, these chillers are running single 245 ton offloading screw compressors, and they have a desuperheater factory installed providing preheated water to potable water heat exchangers.

2. How can you have negative #’s
The refrigerant would be cooler the the condenser water.

Not Possible!

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Originally Posted by pecmsg
How can you have negative #’s
The refrigerant would be cooler the the condenser water.

Not Possible!
Well that's why I'm asking, because that is what is happening. The liquid line exiting the condenser is cooler that the water exiting the condenser. I took the readings multiple times to be sure using 3 different probes. Liquid line temperature readings were taken in the sensor well with the controller refrigerant temperature sensor.

Cond. No. 1: Liquid Line=32.2 C Cond. Leaving Water=40.4 C Approach= -8.2 C
Cond. No. 2: Liquid Line=33.3 C Cond. Leaving Water=39.2 C Approach= -5.9 C
Cond. No. 3: Liquid Line=32.2 C Cond. Leaving Water=37.5 C Approach= -5.3 C

4. Originally Posted by kris84
Well that's why I'm asking, because that is what is happening. The liquid line exiting the condenser is cooler that the water exiting the condenser. I took the readings multiple times to be sure using 3 different probes. Liquid line temperature readings were taken in the sensor well with the controller refrigerant temperature sensor.

Cond. No. 1: Liquid Line=32.2 C Cond. Leaving Water=40.4 C Approach= -8.2 C
Cond. No. 2: Liquid Line=33.3 C Cond. Leaving Water=39.2 C Approach= -5.9 C
Cond. No. 3: Liquid Line=32.2 C Cond. Leaving Water=37.5 C Approach= -5.3 C
If I am reading this correctly, you used three different probes to recheck the leaving water temp.. However, the liquid temp. was from the controller refrigerant temperature sensor which is part of the original equipment and would have given the readings for the commissioning.

Was a calibration of the controller refrigerant temperature sensor possibly required during the original installation?

5. Another possibility.

All three units were built custom at the same time. They were supposed to have 3K thermistors for the controller refrigerant temperature sensors, but 2.2K thermistors were installed in error. This would give refrigerant temperature readings below what they actually are.

6. Originally Posted by David Goodman
Another possibility.

All three units were built custom at the same time. If They were supposed to have 3K thermistors for the controller refrigerant temperature sensors, but 2.2K thermistors were installed in error. This would give refrigerant temperature readings below what they actually are.
There should have been an “if” included.

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Just curious, what is your entering condenser water temp?

8. More efficient than the basics laws of physics - now That is some damned fine efficiency! <g> You would think those HX makers would want to patent their construction method !

Joking aside: it seems that you have a measurement / sensing disparity. It is not possible to have even a 100% efficient heat exchange process. And yours is 100+% ? <g>

You have a sensing issue in there somewhere - now you have to find it. Are all your readings taken independently? Or are you relying on the unit's control panel readouts?

PHM
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Originally Posted by kris84
I have a couple of water cooled chillers running for about 6 years now, I have never been involved in the operation or maintenance of them until recently, and have noticed that the condenser approach is actually a negative figure. I dug out the commissioning documents from when the factory engineer started them on site, and they have been running a negative approach from day 1 it seems.

Over the 3 chillers the approach varies from -2.3 to -6.2 degrees C. In my mind this is an extremely efficient condenser. But how is it possible for the approach to be negative? How is it that the liquid refrigerant is cooler than the condenser leaving water. And is it normal or acceptable for this to be happening.

As some additional information, these chillers are running single 245 ton offloading screw compressors, and they have a desuperheater factory installed providing preheated water to potable water heat exchangers.

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Do you have an economizer on the liquid line? The new Trane Agility mag bearing chiller has a plate frame heat exchanger on the liquid line where the liquid passes through one side of the heat exchanger on to the EXV feeding the evaporator and the other side of the heat exchanger is fed by another EXV which is fed with liquid teed off from the main liquid line and after going through the heat exchanger it’s vented to suction. This cools the liquid down below leaving water temp.

10. If you have a restriction in the liquid line, and it acts as a metering device, you could have a colder temp than the water itself. But, I'm with Mikey on this. I think you have a sensor issue.

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And yet again, a question where make, model, and serial number would help.