Results 51 to 93 of 93
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23-07-2008, 12:21 AM #51
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23-07-2008, 02:38 AM #52
Re: Mass Flow Rate with Big Condenser
Hi, Mike.
I agree with you.
There are 2 types of optimization. Optimum design and optimum operation. Optimum design is the foundation of optimum operation. However, optimum operation is the final goal of energy saving process. Two steps should be done for optimum operation.
1. Determination of optimum set points and operating strategies for different ambient conditions and different refrigeration loads. Very often we just guessing about these points and strategies. This is the most difficult part of optimization. However, how we can reach the goal if we don't know what is it.
2. Implementation of optimum set points and optimum operating strategies. Sometimes, we don't know how to implement these set points.
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23-07-2008, 02:56 AM #53
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23-07-2008, 02:57 AM #54
Re: Mass Flow Rate with Big Condenser
Originally Posted by Sergei
Optimization is completely different than balanced equipment selections.If all else fails, ask for help.
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23-07-2008, 03:01 AM #55
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23-07-2008, 03:09 AM #56
OK, it's offical..you're whacked again.
Originally Posted by GXMPLX
The way I approach this is once I know the loads, I look at the weather profiles. If the wet bulb temperature moves around like a bell curve I have a lot of hours available for low condensing temperatures. That's number 1.
Number 2 is determined by the lowest reasonable condensing temperature I can expect to run; somewhere around 45-50°F (7.2-10°C) during the low ambient condition. That's well within the margin for supplying hot gas for defrost.
Number 3 is to look at the load profile. If you don't know how the load acts, you can't design for it.
Next step is to determine the highest possible evaporating temperatures for each cooling load. AND, don't use back-pressure regulators...they are expensive to install, maintain, and pay for with operating costs.
Next step is to find the right mix (sizes and types) of compressors to match the load profile.
Next...talk to some guys who really understand control systems.
And lastly, get a contractor who can install it right.
Please bear in mind I'm talking about big ammonia systems, but the same logic applies to others also.Last edited by US Iceman; 23-07-2008 at 03:10 AM. Reason: edit
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23-07-2008, 03:18 AM #57
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23-07-2008, 03:28 AM #58
Re: Mass Flow Rate with Big Condenser
Optimize
a) to enhance the effectiveness of something
to make something function at its best or most effective, or use something to its best advantage
b) write program concisely
to write computer programming instructions for a task in as few lines as possible to maximize the speed and efficiency of program execution
To me;
a = make sure the system is able to operate at any condition with the lowest energy use
b = follow the KISS principle
PS. I saw your note, but it disappeared on my last view. Send me a PM and I will see what I can do, OK?
If all else fails, ask for help.
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23-07-2008, 04:34 AM #59
Re: Mass Flow Rate with Big Condenser
Ok I admit my English is not nearly as good … but I don’t confuse optimize with optimum.
Optimize is the necessary process for reaching an optimum.
I’ll use calculus to explain it, in a typical scenario with your good practices you may have 4 TXVs to choose (2 types of charge) , 4 compressors (2 screw 2 recip), 3 condensers, and 2 evaporators.
The possible combinations are 4 x 4 x 3 x 2 =96.
With heuristics you can reduce them to half your experience to 1/3 but if you don’t check the remaining 32 combinations you may not be near an optimum.
You still need to check these at different working conditions.
For me an optimum design is yet to be seen and I’ve seen lot’s of big America’s main brands! If I can change one component to reduce energy consumption the design is not optimal.
It doesn’t mean they are bad! I'm pretty sure your designs are very good! ... or at least as good as mine!
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23-07-2008, 05:09 AM #60
Re: Mass Flow Rate with Big Condenser
Yeah, and if you run the permutations on a big ammonia system you end up having to use exponents to describe the number!
I think it's simpler than that, but it's difficult to put into words. For some reason I just do it in my head and it seems to be OK. The logic I offered earlier is about the simplest way I can explain it.If all else fails, ask for help.
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23-07-2008, 05:20 AM #61
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24-07-2008, 06:02 PM #62
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24-07-2008, 06:10 PM #63
Re: Mass Flow Rate with Big Condenser
Majo, waar werk jij ergens als ik u dit vragen mag?
Your knowledge surprises me. Few at your age pose the questions you do. You're thinking further than most do.
Try also to understand what's the big benefit of lowering the HP.
I'm a teacher at Syntrawest (part-time evening classes) and I think I say this at least 10 times during the year: try to get those needles (HP and LP) as close tot each other as technical possible and allowable.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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24-07-2008, 06:48 PM #64
Re: Mass Flow Rate with Big Condenser
Tuurlijk mag je dit vragen... ik werk nu bij ClimaTronix (gentse), verdelers van Thermotron environmental in de benelux. Ik heb sinds afgestudeerd aan nog niets anders gewerkt dan klimaatsimulatie, al was het de vorige jaren bij een ander merk
Kheb nog jong en heb nog veel te leren maar ik ben zeer geinteresseerd in het vak en vind dat er nog teveel mensen niet snappen hoe die koeltechniek echt in elkaar zit. Daarom dat ik ook graag lees wat mensen zoals jij te schrijven hebben. This is a great forum.
I understand about trying to get those needles as close as possible... but didn't ever thought about that close. 4bar is pretty new to me
sintrawest is dit antwerpen?
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24-07-2008, 07:37 PM #65
Re: Mass Flow Rate with Big Condenser
I bet I know that company ..W...s
Look also once in our section CPU overclockers. This is something which may interest you, especially the autocascade systems.
Syntrawest in Kortrijk and Oostende http://www.syntrawest.be/FOLDERS/I000000534.PDF sorry, all in DutchLast edited by Peter_1; 24-07-2008 at 07:39 PM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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24-07-2008, 08:42 PM #66
Re: Mass Flow Rate with Big Condenser
hmm indeed w...s
hmmz... nemen jullie ook de examens af voor de certificering dan?
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24-07-2008, 09:38 PM #67
Re: Mass Flow Rate with Big Condenser
I was the sole teacher for the first Flemish session for the certification, held in Kortrijk and the chairman for the first exams. All (10) succeeded but I doubt a little bit the usefulness of this new legislation, at least the way we're approaching this in Belgium.
I think you already read articles of me in Cool&Comfort. Look once in an old edition of C&C.
How I know W...s? We have a client in Bruges with a small environmental chamber and they gave price to install the condensing unit just outside the building. (because we proposed this to reduce internal heat load) I think they use/install golden tubes because we could do it for 1/3 of their price.
They needed a new liquid tank due to the longer lines: +/- 2 or 3 m 3/8 tube, new expansion device, new gas,....
Also another condenser, also due to the longer lines.
I was always interested in low temperature applications.
We made a cascade with ethylene and propylene, we service some Polycolds, serviced also in the past some environmental chambers at Siemens (can't remember right now the brand name),....Last edited by Peter_1; 27-07-2008 at 10:21 AM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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25-07-2008, 12:03 AM #68
Re: Mass Flow Rate with Big Condenser
Originally Posted by majo
However, the high side can move a lot before you see problems. Peter is absolutely correct though. Get the pressures as close as you can to each other. That's the best advice...If all else fails, ask for help.
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25-07-2008, 10:19 AM #69
Re: Mass Flow Rate with Big Condenser
I will take a look, C&C is my favo magazine by far
Hehe... w***s always uses golden tubes, very pricy indeed, a bit over the top!
Former Siemens is this the company in Oostkamp, near the E40? Could be EADS or Tyco, they have a large amount of environmentals.
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25-07-2008, 11:53 AM #70
Re: Mass Flow Rate with Big Condenser
That's the one, but I'm talking of many years ago.
Isn't EADS their military section?It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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25-07-2008, 04:16 PM #71
Re: Mass Flow Rate with Big Condenser
Yes indeed it's military
was it a w***s you serviced?
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26-07-2008, 06:55 AM #72
Re: Mass Flow Rate with Big Condenser
No Majo, it was a...xxx (the years, names are the first erased on my HD), there were as far as I remember 2 x 4 DWM/Copelands cascades in it (or 2 x 2), serving an enclosure of +/- 1.5 x 1.5 x 1.5 (3 x 3 x 3 ft)
The compressors were on the left side of the chamber.
I had some copies of the electrical circuit and refrigeration circuit but I don't know where starting to search for this.Last edited by Peter_1; 26-07-2008 at 09:39 AM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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26-07-2008, 10:45 AM #73
Re: Mass Flow Rate with Big Condenser
hmm...I've never seen a chamber of that capacity over there... maybe shredded.
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26-07-2008, 05:01 PM #74
Re: Mass Flow Rate with Big Condenser
Hey everyone have to chime in on this one. Well said Iceman. But there are really to many other variable that I have encountered here at the plant I work at. First they will always try and up the load hence your hp goes up. We have 6 Bac,4 Imeco, and 2 risto condensors atm and we need more. But even the best designed systems have problems some of are condensors take more of a heat load then the rest. Air in the system etc etc. The biggest problem is when we get to about 185lbs hp we start to lose 1st and second stage so nothing gets froze. So imo bigger is better. And as we all know its always the reffer guys fault.
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26-07-2008, 05:08 PM #75
Re: Mass Flow Rate with Big Condenser
Originally Posted by Poodzy
This sort of highlights a second issue; you can pick all of the right equipment, however the installation procedures can cause you to receive less benefit from the equipment.If all else fails, ask for help.
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26-07-2008, 05:12 PM #76
Re: Mass Flow Rate with Big Condenser
That's sometimes frustrating: both companies are offering the same equipment but the final result can be so different.
Then try once to explain why your higher price is justifiedIt's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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26-07-2008, 05:59 PM #77
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26-07-2008, 08:12 PM #78
Re: Mass Flow Rate with Big Condenser
Originally Posted by GXMPLX
Originally Posted by meIf all else fails, ask for help.
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26-07-2008, 10:24 PM #79
Re: Mass Flow Rate with Big Condenser
As Big Brother once said:... Here we go again!
No, I think they are absolutely different.
One thing is to flood the condenser with liquid and require a higher pressure to discharge it so you get a bumpy high pressure. You solve this with a siphon.
Another completely different is to divert more gas refrigerant through a condenser that has low pressure drop in parallel with another of higher pressure (until Pdrop on both branches equal) causing one small condenser not to be able to condense all refrigerant going through it and discharge superheated vapor. You solve this one with an INVERTED siphon.
Do you think they are the same because they are both pipework issues?
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26-07-2008, 10:27 PM #80
Re: Mass Flow Rate with Big Condenser
Last edited by GXMPLX; 26-07-2008 at 10:29 PM. Reason: (my first translation did not sound right, sorry)
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26-07-2008, 10:48 PM #81
Re: Mass Flow Rate with Big Condenser
OK, let me try this a different way...
If the intention is TO flood the condenser for winter pressure control, this is something different.
If you have multiple condensers in parallel then the only way you can GRAVITY DRAIN them is to ensure the outlet pressures of EACH outlet branch connection exist at the same pressure. However you have to do this to make the condensers attain their rated heat rejection capacity is what is required.
And...more often than not, incorrect piping practices cause this.If all else fails, ask for help.
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26-07-2008, 10:59 PM #82
Re: Mass Flow Rate with Big Condenser
I was thinking of flooding as a problem not as a solution too.
In order to gravity drain in all condensers with different pressure drops across would need inverted siphons on the ones with less pressure drop.
Maybe you design your systems too good and never had these problems us mere mortals with smaller systems do.
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26-07-2008, 11:08 PM #83
Re: Mass Flow Rate with Big Condenser
Originally Posted by GXMPLXIf all else fails, ask for help.
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26-07-2008, 11:36 PM #84
Re: Mass Flow Rate with Big Condenser
I like simple questions they lead to simpler answers: Not using the sense of smell, of course!.
If you want place a sight glass on each output.
I see you optimize too much, try a hypothetical problem: Installing an air cooled with one circuit in parallel to a cooling tower (refrigeration side of course), both with the same capacity, different pressure drop.
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26-07-2008, 11:56 PM #85
Re: Mass Flow Rate with Big Condenser
Originally Posted by GXMPLX
I agree with what you're saying about the two different types of condenser. There the pressure drop could be considerably different between the two.
But... it's the same problem on evaporative condenser coils also. And there the low pressure drops found can cause excessive liquid back-up in the condensers and cause you to loos heat rejection capacity.
Same problem, just different devices...If all else fails, ask for help.
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27-07-2008, 12:08 AM #86
Re: Mass Flow Rate with Big Condenser
OK, fine for me. Check CP though.
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27-07-2008, 07:53 AM #87
Re: Mass Flow Rate with Big Condenser
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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27-07-2008, 07:54 AM #88
Re: Mass Flow Rate with Big Condenser
Like this one with 1 condenser double the size as the other one.
Last edited by Peter_1; 27-07-2008 at 08:56 AM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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27-07-2008, 10:21 AM #89
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27-07-2008, 10:31 AM #90
The 2 parallel condensers were for a replacement of the old pack I made around 1989.
Perhaps for the young techs amongst us: no oil floats, no oil separators, no oil tanks, no interconnection between the compressors.
As long you respect the proper guidelines, you don't need all these fancy tricks.
We made several this way and this is the first one we replaced. The pack ran the last 5 years almost at 100% due to expansion of the company
The black ones (still the original Prestcold compressors) were chosen in a mathematical row 1 - 2 - 4 - 7.5 Hp. The PLC then could chose ramp up capacity in steps of 1 HP, sometimes 0.5 HP.
So no VFD needed and still able to regulate a preset LP very precise.
The two grey ones (DWM/Copeland) are for the freezer and those were replaced a year before the replacement.Last edited by Peter_1; 27-07-2008 at 10:33 AM.
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27-07-2008, 07:29 PM #91
Re: Mass Flow Rate with Big Condenser
Great congratulations! But I think you must count luck in your side too, I wouldn’t recommend this though obviously can be done!
Of this you don’t have to convince me!
DISCLAIMER: I am not talking against VSD/VFD in the following (they do have several advantages):
VFD/VSD vendors always compare their system application in a refrigeration system that is grossly oversized and it is obvious ANY form of capacity control would improve efficiency too!
Never seen a study of one compressor with VSD against a rack, or compressor with VSD against a compressor with capacity control. I don’t think these studies haven’t been done.
Not letting head pressure float or suction pressure float may be energetically inefficient. It does have other important advantages like simplifying control, correcting power factor, and in some situations save energy too, etc.
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27-07-2008, 10:14 PM #92
Re: Mass Flow Rate with Big Condenser
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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27-07-2008, 10:31 PM #93
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