Carrier Chiller Problem

This thing has got to be on a maintenance call-out list. What does the manufacturer have to say on the subject? Do ask, as they have a reputation to uphold!

Is it a micro processer based controlled chiller? If yes in the control panel use proper switch to diagnose the problem .Trouble shooting chart may be available in the Operation and maintenance manual. Following are some of the probable causes.

Defective compressor valves

Shortage of refrigerant

Air or non-condensable gases

Wrong super heat setting and defective expansion valve

Restriction in the refrigeration system

You can also call the manufacturer if it is under warranty period.

Is the refrigerant R-22?

What is the refrigerant fluid? Is it R 134a? What are rated flow rate and entering & leaving temperature of water to be cooled? What is DLWT-Lead/Lag leaving fluid ? Is the compressors are for 30 Ton load each or 60 Ton each? What are rated suction and discharge pressure & temperature of compressor? Trips on what reasons? What do you want from us?

If you answer above questions, you can get desired answer yourself. In the absence of above informations, only I can say that enough evaporation is not taking place which is required to cool water. This can probably be due to one or more of the following in order:

1. Extremely low level of refrigerant fluid (it is leaked or still leaking, please check). If it is flooded evaporator, then water tubes are partially flooded.

2. Clogged evaporator tubes and other reasons mentioned at #2.

Thank you Fredski,

As you assumed we are using R22.

Chiller tripped today also.Alarm indicates it is beacuse of 'High suction Superheat of Circuit A'.Suction superheat at that time was about 45C.Chiller will trip when temp is over 41.7C according to the manual we have.

Probable reasons given by the manual

1. Faulty expansion valve.

2. Low refrigerant

3. Thermistor problems

I noted condensation(dripping) along the expansion valves.The chiller is tripping when the ambient temperature is high.According to our maintenance team expansion valve is OK.

Is there any other reasons for this.I am new to the 'chiller' system and my boss asked me to suggest the reason without the help of maintenance team. How can I confirm the reason for tripping.

Well first off I doubt you're that low on refrigerant based on 2 things. Your head pressure is still very strong and you have sweat accumulation. The thermistor is a definite possibility but it could involve more. The thermistor is the actual small component thats reading a temperature and sending that temperature information to the computer. They're cheap, I'd just change all of them (you have more than one) while you're working on this problem.

On the expansion device....these are tricky devils and I wouldn't just assume your team has it right. You may or may not have one with adjustable superheat. Most of the time they are hard to diagnose without more information. They have several factors that effect their operation. They have a power head on top of them that's attached to a sensing bulb. This in turn is strapped somewhere after the evaporator. They are also influenced by spring pressure in the cage of the valve...this is also where superheat will be adjusted should it be adjustable. It also is influenced by the inlet orifice (the feed of refrigerant into the valve ). This orifice is protected by an inlet screen that can get semi or fully plugged. And finally it's influenced by back pressure from the evaporator itself. If you have any one of these out of whack the valve doesn't perform at it's best.

This isn't really a job for a rookie. If you're feeling ambitious you could Google "superheat testing". If you understand it then just use a thermometer that can be strapped and insulated to the tail end of the evaporator, a reliable set of gauges, and a superheat chart and take a test to confirm the actual superheat. NOTE: Superheat is not an instant thing. It takes up to 20 minutes to get a good reading. So make sure the machine balances out and is running for at least several minutes under a normal load. You don't just take a reading right as it starts and the load on the chiller is high, wait for it to cycle at least once then take a reading when it fires back up and the load is mostly typical. As I said in my earlier post I think you need get "other sources" to take readings of temperature and pressure. Don't assume the readings you have are valid, double check them with known reliable meters.

I have made arrangements for new thermistors.It will be installed with in one or two days.For the time being I would like to calculate the Superheat with the existing setup.i have learned procedure to calculate it as follows

1.Take actual temp at TXV

2.take evaporating pressure at TXV

3.Convert pressure to equivalent temp using charts.

4.Subtract Evoporation temp from actual temp(1-3)

Is this the correct procedure?

I have given all the panel readings that I get from the microprocessor in my first post.Do any of these readings are the same we need to calculate the Superheat?IF I do need extra thermometers what kind of them will work.I have tried it with a IR type, is it reliable and where should I take the readings to make it accurate.

The procedure is correct except for number 1. The temperature for the evaporator needs to be taken at the outlet of the evaporator (return to compressor) at the TXV bulb/or sensing device that meters the TXV. Superheat is to assure proper evaporator saturation.

Read this http://www.stara.co.kr/filedata/sporlan/QT11.pdf

No it isn't correct. You want to take a suction reading as close as possible to the area where the sensing bulb is located. Sometimes theres a port right there. If it isn't right near the bulb get as close as you can to it. You mentioned TXV twice, for a superheat test you don't even have to see the TXV, just the bulb, suction line, suction port. Calibrate your gauge before you begin. Take a suction reading once the system is balanced and running normally, NOT at start up. Take your temperature reading very close to the bulb and make sure your probe is INSULATED so you're reading the line temp and not averaging the line and air temp---very important. Read your gauge in PSIG and convert using the chart. Subtract your temperature reading from your converted temperature reading, this is your superheat.

There are no splits. The condenser entering and leaving are the same equaling no heat rejection so no real capacity and probably flashing the evaporator causing no saturation of the Evap barrel.

Or it is simply low on refrigerant.

check the see all level indicators and open the ends and rod it out.

His head pressures are 286PSI and 302PSI, it would never get that high on a low charge without a valve being shut down.

That would be an incorrect statement......

There is no split in the condenser barrel leading towards fouling or plugged tubes. This would give the impression of over charged or charged correctly since there is no heat transfer = (High Pressures).

There should be at minimum a 10 degree split on the condenser barrel and a 6 - 10 degree approach (with R-22) on the evaporator side of the chiller. Approach is measured by the temperature of the chilled fluid against the temperature of the refrigerants evaporating temperature. The water inlet to a R-22 condenser should be 70 - 80 degrees MAX (higher than that and your tower is too small) leading to a 105 - 110 liquid temperature (no flashing there) @ 225 head for water cooled. The evaporator split should be the same 10 degrees entering and leaving with a 8 - 10 degree super heat. If you are low charged with fouled / scaled or oily (oil will insulate the tubes) tubes you will get exactly the system response the poster has, High head pressure and high suction, with condensation on the TXV, since with a low charge the saturation is happening at the metering device (TXV) rather that in the barrel where it should occur.

Plugged tubes, improper GPM, the wrong size tower or a plugged strainer will all give high pressure readings leading to refrigerant loss due to high system pressures.

There is no "condenser barrel", he said in his post it's AIR COOLED.

Sorry my bad,

However

The same would apply on air cooled. Especially if there is non condensible's in the system. Entering and leaving condenser fluid temperature is the SAME in the OP. again leading to no heat transfer.

Or he could have a head master that is by passing the condenser not allowing suction gas cooling due to high head pressures. Superheat readings are low as well.

As I said in my post to him about an hour ago I don't believe his data and he should confirm it.

Agreed, Agreed, Agreed

Just read you post..

I am going to go work out now!

"The condenser entering and leaving are the same equaling no heat rejection"

At condenser heat rejection is possible even when entering and leaving temperatures are the same because condensing heat transfer is 'latent' for change of state from vapour to liquid. We see the change in temperature only when entering vapour is superheated or leaving liquid is sub-cooled. As OP has not given what refrigerant fluid he is using, we can't say.

HE did it is R-22, and you need heat transfer to efficiently cool the chilled water latent heat (what is left behind) will not properly allow a system to pull down and cool water. Latent heat is better used in a heating calculation when undersizing a heating coil and depending on fenestration or other heat sources to help heat a building.

Yes it was known later that it's R-22.

"latent heat (what is left behind) will not properly allow a system to pull down and cool water"

I don't agree with your above statement. In fact latent heat of vaporization of refrigerant play a major role to cool water in evaporator. Sensible heat is negligible.