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29-05-2009, 05:40 PM #1
Clean Condenser Running too hot??
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?
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29-05-2009, 05:50 PM #2
Re: Clean Condenser Running too hot??
is that with product in the blast chiller or is it empty?
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29-05-2009, 05:53 PM #3
Re: Clean Condenser Running too hot??
any idea what your superheat is??
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29-05-2009, 05:56 PM #4
Re: Clean Condenser Running too hot??
Is the water fed into the condenser from the bottom up or the top down?
What are the water in and out temperatures?
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29-05-2009, 06:00 PM #5
Re: Clean Condenser Running too hot??
good point, i have seen someone pipe a w/c condenser up wrong and it did the same
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29-05-2009, 06:33 PM #6
Re: Clean Condenser Running too hot??
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.
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29-05-2009, 06:35 PM #7
Re: Clean Condenser Running too hot??
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29-05-2009, 07:29 PM #8
Re: Clean Condenser Running too hot??
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?
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29-05-2009, 07:44 PM #9
Re: Clean Condenser Running too hot??
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?
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29-05-2009, 07:49 PM #10
Re: Clean Condenser Running too hot??
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.
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29-05-2009, 07:50 PM #11
Re: Clean Condenser Running too hot??
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?
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29-05-2009, 07:54 PM #12
Re: Clean Condenser Running too hot??
By hot I mean, 135F shell temperature. With 170F hot gas temp. The compressor seams ok and is not running hot.
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29-05-2009, 07:57 PM #13
Re: Clean Condenser Running too hot??
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.
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29-05-2009, 07:57 PM #14
Re: Clean Condenser Running too hot??
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29-05-2009, 08:11 PM #15
Re: Clean Condenser Running too hot??
you won't get a clear sight glass with 404A without sufficient subcooling on liquid line. It is very prone to flashing off
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29-05-2009, 08:14 PM #16
Re: Clean Condenser Running too hot??
See attached
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29-05-2009, 08:16 PM #17
Re: Clean Condenser Running too hot??
I would think the condenser should be able to subcool at least a few degrees, or no?
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29-05-2009, 08:33 PM #18
Re: Clean Condenser Running too hot??
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.
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29-05-2009, 08:44 PM #19
Re: Clean Condenser Running too hot??
You said the liquid was over 120F. Is that a liquid line temperature measurement?
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29-05-2009, 09:02 PM #20
Re: Clean Condenser Running too hot??
yea after the liquid filter the line is 115F.
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29-05-2009, 09:07 PM #21
Re: Clean Condenser Running too hot??
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.
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29-05-2009, 09:08 PM #22
Re: Clean Condenser Running too hot??
I know there is an answer but I'm just stumped on this one.
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29-05-2009, 10:05 PM #23
Re: Clean Condenser Running too hot??
If there were air in the system, then the SCT would be considerably higher than the liquid line temp.
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29-05-2009, 10:20 PM #24
Re: Clean Condenser Running too hot??
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29-05-2009, 10:35 PM #25
Re: Clean Condenser Running too hot??
I found a service manual for this condenser:
http://www.stanref.com/pdfs/Service.pdf
Maybe we can find the answer somewhere in there.
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29-05-2009, 10:47 PM #26
Re: Clean Condenser Running too hot??
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.Last edited by Gary; 29-05-2009 at 10:52 PM.
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30-05-2009, 12:26 AM #27
Re: Clean Condenser Running too hot??
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?
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30-05-2009, 12:52 AM #28
Re: Clean Condenser Running too hot??
I don't understand the reason for the receiver equalizer line. Is there some way to shut it off?
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30-05-2009, 01:15 AM #29
Re: Clean Condenser Running too hot??
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.
Last edited by Gary; 30-05-2009 at 01:22 AM.
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30-05-2009, 02:41 AM #30
Re: Clean Condenser Running too hot??
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
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30-05-2009, 06:30 PM #31
Re: Clean Condenser Running too hot??
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.
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30-05-2009, 06:41 PM #32
Re: Clean Condenser Running too hot??
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?
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30-05-2009, 06:43 PM #33
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30-05-2009, 06:58 PM #34
Re: Clean Condenser Running too hot??
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30-05-2009, 07:33 PM #35
Re: Clean Condenser Running too hot??
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.
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30-05-2009, 07:50 PM #36
Re: Clean Condenser Running too hot??
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30-05-2009, 08:10 PM #37
Re: Clean Condenser Running too hot??
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.Last edited by Gary; 30-05-2009 at 08:15 PM.
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30-05-2009, 09:24 PM #38
Re: Clean Condenser Running too hot??
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?
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30-05-2009, 09:25 PM #39
Re: Clean Condenser Running too hot??
I'm having trouble visualizing the flow
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30-05-2009, 10:48 PM #40
Re: Clean Condenser Running too hot??
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.Last edited by Gary; 31-05-2009 at 06:42 AM.
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31-05-2009, 01:53 AM #41
Re: Clean Condenser Running too hot??
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
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31-05-2009, 05:37 AM #42
Re: Clean Condenser Running too hot??
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.
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08-06-2009, 05:47 PM #43
Re: Clean Condenser Running too hot??
Anything new happening with this system?
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08-06-2009, 08:16 PM #44
Re: Clean Condenser Running too hot??
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.
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08-06-2009, 08:25 PM #45
Re: Clean Condenser Running too hot??
Any chance of getting the temps and pressures I asked for earlier?
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08-06-2009, 08:28 PM #46
Re: Clean Condenser Running too hot??
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08-06-2009, 08:33 PM #47
Re: Clean Condenser Running too hot??
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08-06-2009, 08:35 PM #48
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08-06-2009, 08:42 PM #49
Re: Clean Condenser Running too hot??
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)
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08-06-2009, 08:50 PM #50
Re: Clean Condenser Running too hot??
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