Short Life of Compressor on Air Chiller

Take a look at this. It's from the Mcquay site. Tip #6 caught my eye.

What is failure mode of compressor?

A very pertinent question from Dvicars! an answer will definitely help in resolving the issue.

I presume it is reciprocating compressor. There could be many causes for compressor failure. Few of them are short cycling,moisture in the system, inefficient condensers ( As it is air cooled), defective controls, etc. need to be checked based on log sheets and filed condition and diagnose the problem.

I had incountered similar problem in Riyadh and compressor fail in short period of time after repair.

Source of failure is the closed proximity of coil in the wall which causes high inlet air temp to the coil,.

Action taken; if unit can't be relocated, the following task are required:

1. Install air filter at the coil side (similar with air cooler at GCC country)

2. Install a dripping water at top of the filters and interlock with condenser pressure and small pump with automatic float valve to maintain water level at thench collection pond

3. Check if compressor has stages of loading to insure the design pressure are maintained based on load condition.

For more info/claricifation, please feel free to contact me.

Nelson

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Any chance you can provide a few pictures of this installation? I especially would like to see this 4' extension you installed and its relationship to the wall. Depending on the type of blades used most air being discharged leaves the top of the unit at a roughly 45 degree angle. The misconception is that the air is travelling straight up, it isn't. You may actually be creating a vortex and are defeating your intent. Again, a picture would really help. I don't quite understand the theory about the walls and radiant heat. I'd like to know (see) where the air that enters the condenser is being supplied from. It almost sounds like your unit is in a pit. If that's right then your original design is flawed. Here in California building designed that want to "hide" large equipment have large screen/louvers put into screening walls next to or very near the condenser air intake. I will tell you if your condensers do get direct sun that will defiantly effect head pressure and lower your heat rejection capacity.There are a few adjustments you can make if that's the case.

One of the answers suggested a load shifting approach. I think having a stored reserve is a nice idea but I doubt your roof will handle the excess 42 tons each that the filled tanks will exert. Before you go out and buy two 10,000 gallon tanks you might want to check if your roof can handle an additional 84 tons of live load.

Do you know the actual failure of the compressors, was it the same thing? Did they fail electrically? Did they have a mechanical failure? Has there been a history of any oil issues to the compressors? Have they ever kicked out the oil protection circuit? You always want to determine what causes a premature failure. I wont go into the possible list of failures but it is a lengthy. Without knowing what the nature of the failure is you're just guessing how to prevent it from reoccurring.

I'll keep this thread open for a few days. If you get the pictures I can tell you more about your installation and offer a few ideas on what to look for or change. Good luck.

It was ASSUMED that the tanks would be mounted at grade, near the chiller. I fully agree that most roofs do not have the structural capacity to support that level of "active" loading at any time without a whole lot of long support beams to spread out the load- and then you have the wind load factor.

I liked your answer. I just don't know if he has space for 84 tons of load at his site. That's a pretty substantial amount of weight and area requirement.

His description is a bit confusing. That's why I asked for pictures. He may or may not have room for a storage system that would help him to increase capacity and shift compressor workloads to later in the day. It sounds like he has a tight situation that wouldn't allow for more equipment. He made no note of having extra space adjacent to his installation. Maybe he does? I don't think capacity address's why his compressors are failing prematurely. If he has a design or installation issue I would rather address that first before attempting to increase capacity. Without seeing exactly what he has it's hard to give a concrete answer. From what little information he provided I would want to know more about the air being provided to the condenser as well as it's discharge. And of course knowing the nature of the compressor failure goes a long way in correcting his problem. If he has a slugging or electrical issue increasing capacity doesn't address his problem of losing the compressor. Increasing his capacity would however help him to keep his building cooler for a longer period of time. As well as allowing the system to store chilled water at night when the system can work under less load and possibly lower electrical rates.

I think you offered a well thought out answer to increase his capacity and address his lack of cooling on part of his building. In order to chill 20,000 gallons he'd be further increasing the workload on the compressor(s) to keep that water chilled. But as I said if he has other issues with installation of design those have to be addressed or he'll lose compressors even faster with the increased capacity of the system.

My initial issue is that the compressor that had failed is apparently cycling fairly frequently- 13,000 starts during a 30,000 run hours is less than 2.5 hours per start. That is why i questioned the OP's statement that the system was too small to support its load. Compressors do not cycle off during heavy loads.

My solution was a way to keep the compressors running for a significant period- 8 hours at night (and cut operating costs at the same time) and then essentially one compressor running constantly for the other 16 hours without the high cost of an ice storage system and the corresponding challenges associated with same.

A 10,000 Gallon tank is about 8 foot diameter and 28 feet long. Installed, it would need a 10x10 foot pad (the 887 PSF loading will be no problem for adequately compacted earth), so a 20x10 foot pad will support both tanks. NOT usually a large amount of space at an industrial site. Likely the end of a building. Another option would be to bury the tanks with connections at low left and top right and use either PVC or fiberglass piping.

Thanks to all for the feedback.

Attached are a couple of pictures of the installation that Fredski requested.

The FAULT code when tripping out read: motor start fault. It would trip off on motor start fault on an occasional basis and we couldn't pinpoint the exact cause until it also made some mechanical noise as it tried to start. When we checked it more thoroughly it showed it was shorted to ground internally on the compressor and are now in the process of replacement of compressor #1.

The PVC line toward the top of the air intake grill is to mist some water in the air to help keep the temps down a little, along the line of a "swamp cooler". There is a noticeable difference in performance when the outside air temp is high and the water is misting. We have room around the enclosure to add addtional equipment/tanks if that is a way we would choose to go.

Your willingness to provide more information, as in the photographs, is very helpful. Even more information would be even better. I am not familiar with the brand you are using, but certain general characteristics may be relevant. The apparent short cycle time, combined with the comment that the system was designed to small for the heat load, and the comments about the noise at attempted start up with the error code suggests that the problem was a long term one, with the offset field coil switch on the electric motor of the failed unit arcing and burning out the starting field switch. Perhaps this unit does not even have such a switch, but if it does, this would explain everything. The apparent short cycle time is from the multiple attempts to start before finally achieving start up, making an apparent occasional load out of a heavy load situation. If both units were attempting to start at approximately the same time, the extra demand load might be causing a drop in available voltage, causing an even greater current demand on the starting switch. The apparent air flow problems (the intake is too close to the building - perhaps the units should have been installed with intakes away from the building, etc) combined with heavy usage would cause a general running hot condition which would exacerbate the electrical problems. It sounds like what you needed was a new motor or motor component, not the compressor. But then, I do not know this brand.

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