Chiller Questions

[Boiler Guy]

I don’t know how you guys do it. Trying to learn chillers, there is so much to learn. Every compressor/chiller is different, every brand of compressor/chiller is different, all the controls are different. I’ve been to a few chiller classes now between Carrier and Daikin, read lots of manuals, read any books I could find about chillers, and I’ve learned a ton but I still feel like I know nothing.

I’ve got a few chiller related questions that I was going to post in the pro forums but I seem to have lost my pro membership after the website went down. I’m sure I’ll think of some more too. Hope you guys don’t mind answering my (probably stupid) questions.

When doing a full log to assist in troubleshooting, does it have to be done at full load with chilled water at in operating range? This is the only time you’d get an “accurate” log right? Or can it be done at any load, or certain loads? Load is going to affect approaches, discharge super heat, etc, right?

How does a labyrinth pump work on a centrifugal compressor? Is this the same as a labyrinth seal or is it something different? (Question originated from a McQuay centrifugal)

What are the correct methods for testing the accuracy of thermistors and pressure transducers?

What is the best thread sealant to use on chiller/compressor components?

On the CE063 McQuay compressor, what is the plug on the bottom of the gear housing for? (We have one that is leaking?) I have pictures of the cutaway from class and it just looks like an access to the bottom of the gear housing where the oil drain is.

[Boiler Guy]

I was getting the pumping labyrinth and thrust pump confused. How do each of these work?

[jayguy]

I don’t know how you guys do it. Trying to learn chillers, there is so much to learn. Every compressor/chiller is different, every brand of compressor/chiller is different, all the controls are different. I’ve been to a few chiller classes now between Carrier and Daikin, read lots of manuals, read any books I could find about chillers, and I’ve learned a ton but I still feel like I know nothing....

welcome to the party pal. Some days I feel like I know everything and then BAM! I find out I know nothing. Just keep moving forward. No manufacturer has the lock on R22 or R134a or R123 or water flow, etc. If you learn the basics, they will apply to every chiller.

...When doing a full log to assist in troubleshooting, does it have to be done at full load with chilled water at in operating range? This is the only time you’d get an “accurate” log right? Or can it be done at any load, or certain loads? Load is going to affect approaches, discharge super heat, etc, right?...

no, you don’t need to log at full load. Sometimes the problem is occurring ONLY at low loads, or only when the ambient is midrange or whatever. Typically, higher loads show problems better, but not always. Yes, approach will typically rise when the load goes up and at low loads approach problems may be there but hidden to an inexperienced eye. Seeing that comes with time. There is value in “less than full load” logs. Stability of readings is more important.

...What are the correct methods for testing the accuracy of thermistors and pressure transducers?...

do your best to measure at the same location. Sometimes you can’t. Just make a note that you couldn’t verify the accuracy of a particular measurement. That will allow you to look back on your log sheets with care and if that sensor was really a problem, you have a “get out of jail free card” (sometimes).

...What is the best thread sealant to use on chiller/compressor components?...

this is a personal choice and some manufacturers may require a certain sealant.

[Boiler Guy]

jayguy, thanks a ton for the info. There really is no substitute for just working on the equipment. I haven’t gotten to work on them much. Every summer I do some here and there. I’m actually considering a company change to a chiller company just so I can get more hands on.

As far as testing transducers, can you pull them off (the ones on schraders) and test them with a test station/gauge? And the thermistors, can they be tested in ice water or something like that?

[jayguy]

...As far as testing transducers, can you pull them off (the ones on schraders) and test them with a test station/gauge? And the thermistors, can they be tested in ice water or something like that?

I don’t usually pull sensors any longer unless they are acting goofy. I usually use an IR gun (where I can) to see if the sensor is close. Use a trusted gage to verify pressure transducers where possible. NEVER trust the panel until you have verified the sensors first...then feel free then use it exclusively.

[Boiler Guy]

Also on a side note, if anyone has manuals or literature or training material that comes from classes for ANY chiller brand that you can’t download off the internet, I will buy them from you if you don’t need them anymore. Most recent class was Daikin Centrifugal. Before that was Carrier 30 series. If anyone has training manuals or rebuild manuals or whatever that they’d like to sell please let me know!

Or if you have contacts at the factories it’d be awesome to get my hands on some training manuals for other classes I haven’t been able to attend yet.

[Tech Rob]

Typically what I do with sensors and transducers is check them against other ones on the machine, or other ones in the same plant. You very very rarely have to pull sensors out of their wells and test them once you get enough experience around the machines. A bad sensor or transducer sticks out like a sore thumb simply by circulating water through the machine while it's off and comparing saturated temp sensor readings to CHW/CW temp readings, and pressure readings to saturated temp readings, etc. There are obviously times when you do have to verify with a separate instrument, but they are few and far between.

Know how to manipulate the controls on the chiller. Know how to manipulate the plant controls, pumps, valves, etc. in such a way that you don't crash the plant, and the customer never has any interruption in the delivery of cold water. Know how the water flows through the plant. Understand what state the refrigerant is going to be in, in every part of the machine, running or not. These simple things will allow you to have much success in troubleshooting systems.

Logging the machines is important, but even more important is knowing what and how to log. There are tomes of useless arbitrary information scribbled on clipboards all over the world. Make your logs meaningful. Know when it's ok to use the on-board sensors and transducers, and when you have to actually put a gauge on, or stick the probe under the insulation. During annual inspections, I try to get a "design" baseline log for the year. All other inspections, whatever. No load or full load.

I don't know about the plug on the CE063, but I'm going to look at a CE063 tomorrow, so I will get back to you on that.

A labyrinth seal is just a non-contact clearance seal, with a series of grooves, each one designed to create a pressure drop. The pressure drop created by each of those grooves is greater than the pressure differential on either side of the seal.

[nyrb]

I believe the “Pumping Labyrinth Seal” you are referring to is the one located behind the wheel on McQuay compressors. Most Labyrinth seals consist of a series of parallel grooves that reduce the movement of refrigerant and oil between different pressures.

MCQuay uses a pumping seal behind the impeller which is actually threaded to direct flow back to the gearbox. According to what they taught that is their oil return mechanism as opposed to educators found on other machines.

[CHILLERSVCMAN]

All the post are very accurate . As far as thread sealant I will suggest to use a " soft set " non-hardening sealant . Reasons being 1) A sealant which hardens could crack , break , crumble over time and leak . 2) When the threaded object needs to be removed it creates the need to use harsh language when the fitting snaps or rounds off ; this will ALWAYS happen when it is the most difficult to access .

[Boiler Guy]

Another question. Some centrifugal chillers cannot operate at too low of condenser water temperature. If the temp is too high it can cause surging. But I’ve also heard if it’s too low it can cause surging. Is that true? Wouldn’t lower condenser water temp decrease the lift ratio which would be the opposite of what would cause surging? Or am I missing something?

What effects can too low condenser water temp have on a centrifugal compressor?

[Tech Rob]

I've never seen a chiller surge because the condenser water was too cold. Surge is caused by the lift pressure, which is dictated by the thermal lift, exceeding the capacity of the compressor at a specific speed/refrigerant flow rate. Cold condenser water causes a low lift condition which can result in a whole litany of other problems including but not limited to: oil loss/poor oil return, loss of motor, drive, and oil cooling, failure to load, failure to purge out noncondensibles, etc.

[CHILLERSVCMAN]

Surge with low entering condenser water temperature is possible and does happen . it can be confused with ROTATIONAL STALL . A TRANE Centrifugal Mechanic knows the difference . WE WORK LOW PRESSURE .

[CHILLERSVCMAN]

I've never seen a chiller surge because the condenser water was too cold. Surge is caused by the lift pressure, which is dictated by the thermal lift, exceeding the capacity of the compressor at a specific speed/refrigerant flow rate. Cold condenser water causes a low lift condition which can result in a whole litany of other problems including but not limited to: oil loss/poor oil return, loss of motor, drive, and oil cooling, failure to load, failure to purge out noncondensibles, etc.

EXPLAIN LOW END SURGE

[tcy612]

EXPLAIN LOW END SURGE

At the expense of looking like I'm stealing Tech Robs thunder here...

"Low end" surge, as opposed to the much more common "high end" surge, is when a condition which causes a drop in evaporator pressure (below design ranges) such as fouled evaporator tubes, less than minimum evaporator flow, low refrigerant charge, etc which causes the lift across the compressor to exceed its lift capability at those conditions..

Due to improvements in chiller controls, temp sensor, pressure transducer and heat exchanger technology, it's not nearly as common as it used to be with older machines.

[Tech Rob]

EXPLAIN LOW END SURGE

Not going to get into a "measuring contest" here with you guy, as it seems that's what you are looking for... Simply stated, "low side surge" is any surge that is caused by factors in the system that would cause the evaporator pressure to fall to a point where, given a constant condenser pressure which is assumed to be in normal operating range, the lift requirement exceeds the actual capacity of the compressor. This could be caused by low refrigerant charge, low CHW flow rate, oil logging in the evaporator, fouled evaporator tubes, low load and low CHW return temps, control malfunctions related to sensors and inlet guide vanes, etc.

Reduced condenser water temperatures suppress the lift requirements of the system and increase the capacity of the compressor, which is why I stated I have never seen a compressor surge because the condenser water is too cold. Now, have there been chillers at some point in history somewhere in the world that were surging while being supplied with condenser water that is lower than standard ARI conditions? Yes, but they were not surging *because* of the cold condenser water because that's just not how this works.

[Bklyntek]

I've never seen a chiller surge because the condenser water was too cold. Surge is caused by the lift pressure, which is dictated by the thermal lift, exceeding the capacity of the compressor at a specific speed/refrigerant flow rate. Cold condenser water causes a low lift condition which can result in a whole litany of other problems including but not limited to: oil loss/poor oil return, loss of motor, drive, and oil cooling, failure to load, failure to purge out noncondensibles, etc.

Yes,a low end surge, as I used to hear it referred to. which actually means the chiller is in stall. Can sound like a bad bearing or marbles if it is a an older York YT low pressure chiller. Its nice if the particular plant has spares sensors or transducers for checking against if concerned about a reading. Too cold cond water can have similar affect in that the low load conditions involved affects both heat exchangers. evap section due to relatively light load from a cool building envelope and condenser because the lack of sufficient heat build up/transfer from the overall process. good questions Boiler Guy, keep'em coming as we all like to share here when we can.

[Tech Rob]

Yes,a low end surge, as I used to hear it referred to. which actually means the chiller is in stall. Can sound like a bad bearing or marbles if it is a an older York YT low pressure chiller. Its nice if the particular plant has spares sensors or transducers for checking against if concerned about a reading. Too cold cond water can have similar affect in that the low load conditions involved affects both heat exchangers. evap section due to relatively light load from a cool building envelope and condenser because the lack of sufficient heat build up/transfer from the overall process. good questions Boiler Guy, keep'em coming as we all like to share here when we can.

The problem causing the surging in your example is a load that is too low to support the chiller's minimum load requirements. It may be exacerbated by colder CW, but not explicitly "caused by". If you were to raise the CW temp in this case, the surging would get worse, not better.

[CHILLERSVCMAN]

It is called lift differential .

[Core_d]

It is called lift differential .

Dont leave us hanging.. whats the definition?


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[Boiler Guy]

That’s what I thought. Didn’t make sense when someone told me that.