Clean Condenser Running too hot??

[Chseybold]

Hi guys, I'm new to the forumn but have been around refrigeration for a while. I've been stumped by a problem and hope someone can give me a hand. We commisioned a blast freezer in Suriname and it has been giving us heaps of trouble. The system is using bitzer 2 stage 30hp compressors with a water cooled shell and tube condenser. There are 2 seperate refrigerant circuits per blast room, with each loop having a dedicated evaporator and condenser.
I triple checked all the calculations and everything matches, right size txv valve and condenser has more than 100,000 btuh extra capacity over the point where we want to run it.
We recentely cleaned the condenser and we are still not able to get the system to work how it is supposed to. There is good water flow. The system uses 404a and we are running it at 325psi and still can't get the site glass to clear up and the liquid is over 120F.
There is a liquid reciever installed as well and this has an equalizer line connected to the receiver. To allow good liquid flow from the condeser. I've read all my books and have racked my brain on this but can't figure it out. Any suggestions?

[123-steve909]

is that with product in the blast chiller or is it empty?

[123-steve909]

any idea what your superheat is??

[Gary]

Is the water fed into the condenser from the bottom up or the top down?

What are the water in and out temperatures?

[123-steve909]

good point, i have seen someone pipe a w/c condenser up wrong and it did the same

[Gary]

We also need to know if the system was operating properly before the condenser was cleaned. It is important that the end bells and gaskets were re-installed properly.

[Gary]

good point, i have seen someone pipe a w/c condenser up wrong and it did the same

Indeed, pumping water from the bottom up fills every little nook and cranny, while top down can leave large air pockets.

[123-steve909]

hi gary,
i see what your saying, i have seen a coaxil condenser with the water and refrigerand both going in at the same point and both leaving at the same point so the water contact with the refrigerant was small. the head pressure was really high and once changed the system worked as it should

im interested in your books, where has the link gone?

[Chseybold]

The water is being fed through the bottom of the condenser, there is no product in the machine. The system never really worked right from the beggining as each room has 60hp of 2 stage compressors so it should be cooling a lot better then it is. So it leads me to believe the manufaturer did something wrong in the assembly, I just don't know what and unfortunately they are out of business. The latest test I did, the unit was running around 15 F room temperature with about 25F superheat. Could it be noncondesables in the condenser?

[Chseybold]

The water in is 78F and the out is 90F. The condensers are getting at least 40gpm each. The shell part of the condenser is very hot, maybe I'm not getting a good liquid seal on the bottom? But as u can see the water side seams ok.

[123-steve909]

could be non-condensables in the system, i would be taking a close look at the condenser side of things as it seems to be something wrong there. is the water supply counter flow to the refrigerant?

[Chseybold]

By hot I mean, 135F shell temperature. With 170F hot gas temp. The compressor seams ok and is not running hot.

[Chseybold]

It's shell and tube, so it should be. I just don't understand why I can't add more Refrigerant into the system without the highside pressure going up.

[Gary]

hi gary,
i see what your saying, i have seen a coaxil condenser with the water and refrigerand both going in at the same point and both leaving at the same point so the water contact with the refrigerant was small. the head pressure was really high and once changed the system worked as it should

im interested in your books, where has the link gone?

The link is in my profile under contact info.

[bowral fridgy]

you won't get a clear sight glass with 404A without sufficient subcooling on liquid line. It is very prone to flashing off

[Chseybold]

See attached

[Chseybold]

I would think the condenser should be able to subcool at least a few degrees, or no?

[Gary]

At 122F SCT minus 90F water out temp = 32F approach temp. This is an indicator of heat transfer between the refrigerant and the water and should be no more than 20F.

There is definitely a heat transfer problem in the condenser.

[Gary]

You said the liquid was over 120F. Is that a liquid line temperature measurement?

[Chseybold]

yea after the liquid filter the line is 115F.

[Chseybold]

Could the temperatures be a result of the hot gas going by the liquid seal on the condeser? the condenser is Standard Refrigeration HSE-25a and at 40gpm and 20td it should reject 243,000 btuh when fouled. which is way above what my compressor and circuit need. So what gives?? It also important to note that there is a liquid reciever in the system and the line from the condenser goes up and then down into the reciever and that is why i put a equalizer line in, to get a good flow to the reciever.

[Chseybold]

I know there is an answer but I'm just stumped on this one.

[Gary]

If there were air in the system, then the SCT would be considerably higher than the liquid line temp.

[Gary]

Could the temperatures be a result of the hot gas going by the liquid seal on the condeser? the condenser is Standard Refrigeration HSE-25a and at 40gpm and 20td it should reject 243,000 btuh when fouled. which is way above what my compressor and circuit need. So what gives?? It also important to note that there is a liquid reciever in the system and the line from the condenser goes up and then down into the reciever and that is why i put a equalizer line in, to get a good flow to the reciever.

It's even worse than that. Your TD is 45F. The HSE-25a is rated at about 500,000 btu for that TD.

[Gary]

I found a service manual for this condenser:

http://www.stanref.com/pdfs/Service.pdf

Maybe we can find the answer somewhere in there.

[Gary]

Hmmm... On page 18, your front gasket is #1723. That horizontal bar is very important. If it were missing, part of the water would bypass the condenser. Could this be the case?

Your rear gasket is #2953. If you swapped the two gaskets this could cause big problems.

[Gary]

Here is a link to the product manual:

http://www.stanref.com/pdfs/107_SR.pdf

On page 8 there is a pictorial diagram. Is your condenser piped accordingly? Refrigerant in the top and out the bottom as shown? Water in the bottom and out the top as shown?

[Gary]

I don't understand the reason for the receiver equalizer line. Is there some way to shut it off?

[Gary]

Could the temperatures be a result of the hot gas going by the liquid seal on the condeser? the condenser is Standard Refrigeration HSE-25a and at 40gpm and 20td it should reject 243,000 btuh when fouled. which is way above what my compressor and circuit need. So what gives?? It also important to note that there is a liquid reciever in the system and the line from the condenser goes up and then down into the reciever and that is why i put a equalizer line in, to get a good flow to the reciever.

It seems to me that if the receiver is above the condenser, then an equalizer line would have the opposite effect, eliminating the pressure differential that moves the liquid from the condenser up to the receiver. If the pressures are equal, then the only force left to move the liquid is gravity... and gravity doesn't push upwards.

[Magoo]

Did you clean the pre-pump strainers and basket strainers at tower when cleaning condenser tubes, good water flow does not necessarily mean correct water flow. The manufacturer will publish water pressure differential info across condenser at correct flow rates which includes a fouling factor.
magoo

[Chseybold]

These are all good suggestions, I really appreciate the help guys. I think I'm going to have the following approach. I'm going to shut one of the units down while having pump continue running. After a while I will check the high side pressure and see if it matches with the water temp. This way I can elliminate the possibility of non-condesables. In the loop.

[Chseybold]

It seems to me that if the receiver is above the condenser, then an equalizer line would have the opposite effect, eliminating the pressure differential that moves the liquid from the condenser up to the receiver. If the pressures are equal, then the only force left to move the liquid is gravity... and gravity doesn't push upwards.

Gary, I'm thinking this has a lot do with it. The liquid exits the bottom of the condenser then goes up to a level higher then the shell of the condenser and then down into the top of the reciever and from there it has to exit through a dip tube in the reciever. The reciever and the condenser are at the same level and as you can see no gravity drain. The equalizer was put in between the hot gas line and through a T fitting at the pressure relief port on the reciever. The problem is that with and without the equalizer the system doesn't work right. So eliminate the reciever?

[Chseybold]

Did you clean the pre-pump strainers and basket strainers at tower when cleaning condenser tubes, good water flow does not necessarily mean correct water flow. The manufacturer will publish water pressure differential info across condenser at correct flow rates which includes a fouling factor.
magoo

yea all of these are clean

[Gary]

Gary, I'm thinking this has a lot do with it. The liquid exits the bottom of the condenser then goes up to a level higher then the shell of the condenser and then down into the top of the reciever and from there it has to exit through a dip tube in the reciever. The reciever and the condenser are at the same level and as you can see no gravity drain. The equalizer was put in between the hot gas line and through a T fitting at the pressure relief port on the reciever. The problem is that with and without the equalizer the system doesn't work right. So eliminate the reciever?

Does the sight glass clear without the equalizer line?

I would eliminate the equalizer line, take a new set of pressure and temperature readings, then decide where to go from there.

[Chseybold]

Does the sight glass clear without the equalizer line?

I would eliminate the equalizer line, take a new set of pressure and temperature readings, then decide where to go from there.

The sight glass does clear without the equalizer line but the system still doesn't run right. We have 2 Bitzer S6F-30.2 Compressors on each room, and the room has never gone below -10F. (This is without any load by the way and running for 24hrs) Without the equalizer the unit starts to run on high amprage and it seem the condenser fills with liquid and loses it's capacity. The other problem is that the unit is far away and we'll have to relay the steps for the local tech to do. There are 2 rooms by the way for a total of 4 circuits and all of them have similar symptons.

[Gary]

The sight glass does clear without the equalizer line but the system still doesn't run right...

Without the equalizer the unit starts to run on high amprage and it seem the condenser fills with liquid and loses it's capacity.

Which tells you that the unit is grossly overcharged. Eliminate the equalizer line, then remove refrigerant until the sight glass bubbles... then add a little refrigerant back in to eliminate the bubbles.

[Gary]

An equalizer line is useful when the condenser is cooler than the receiver AND the condenser is above the receiver.

For example: If the condenser is on the rooftop and the receiver indoors, then cold ambient can drop the condenser temperature/pressure, while the receiver is at the higher indoor temperature/pressure.

Equalizing the pressures allows gravity to drain the liquid from the condenser down to the receiver.

Equalizer lines must always have a check valve to prevent reverse equalization when the condenser becomes warmer than the receiver.

[Chseybold]

Which tells you that the unit is grossly overcharged. Eliminate the equalizer line, then remove refrigerant until the sight glass bubbles... then add a little refrigerant back in to eliminate the bubbles.

That is how it was done when we first started the unit. But it still had problems. But you are right about the equalizer. I just read up on it now, it's for assisting gravity flow. But here it is not the case. So the equalizer is wrong then, it just seems there is something wrong with the reciever/condenser set-up. Or have u seen a shell and tube condenser fuction with such a set-up where the liquid has to flow upwards into another vessel where the liquid and gas can seperate. How is the gas removed from the reciever, and what happens when the txv valve closes down?

[Chseybold]

I'm having trouble visualizing the flow

[Gary]

1 psi differential can lift liquid 2.43 ft.

Most condensing units lift the liquid from the bottom of the condenser up to the receiver. The added psi is inconsequential.

[Magoo]

The system is in overload, the enclosure should be at design before any product is introduced. No different than a spiral freezer, all spiral manufacturers stipulate that enclosure has to be at design before product enters. If otherwise you want to pull-down and freeze product at the same time the condenser.., heat of rejection., would be hugely greater than at design conditions. With compounded recips., outside of design pull-down you risk burning them out with high discharge pressures/ temps. the inter-cooler stage has no chance of de-suerheating low stage, so high stage pressures and temps.
magoo

[Gary]

That is how it was done when we first started the unit. But it still had problems.

I don't doubt that the system has other problems, but first we need to deal with the known problem, eliminating the equalizer and adjusting the charge.

Then we need to look at the temps and pressures. These would include:

Low and high side pressures.
Condenser water in and out temps.
Evap air in and out temps.
Liquid line and suction line temps.

[Gary]

Anything new happening with this system?

[Chseybold]

Nothing new, we're in the process of changing the condesate drain line as the going up and down of the line isn't a good arrangement, and I think there might be a gas lock in this area. There is also an intersage take off on this line that shouldn't be there. The pipe size is much larger as well 1 3/8 compared to the 7/8 liquid. I also think that there is no baffel plate at the bottom of the condenser so there is no subcooling in the condser.

[Gary]

Any chance of getting the temps and pressures I asked for earlier?

[Gary]

Nothing new, we're in the process of changing the condesate drain line as the going up and down of the line isn't a good arrangement, and I think there might be a gas lock in this area.

Are you referring to the drip line from the condenser to the receiver?

[Gary]

There is also an intersage take off on this line that shouldn't be there.

Is this referring to the liquid line for the interstage metering device?

[Chseybold]

Are you referring to the drip line from the condenser to the receiver?

Yes this line. The unit is running at 15 degree superheat, 20psi suction, 300psi high side, 75F entering water / 85F leaving water.

[Chseybold]

Is this referring to the liquid line for the interstage metering device?

Yes this line. A whole is drilled/burned into the line at the higher level and it pulls from here. I think that this tube is pulling from around the middle of the line (think of the cross section of the pipe) and it is flashing. So that is one of the reasons I think there is a gas lock in this line. Usually this interstage line is connected to the liquid line (after the reciever in my case)

[Gary]

Yes this line. The unit is running at 15 degree superheat, 20psi suction, 300psi high side, 75F entering water / 85F leaving water.

300psi gives us SCT of 117 - 85 = 32F approach. Same as before. We still have a heat transfer problem in the condenser. Not having the liquid line temp, we can't tell if this is an overcharge problem or not.