I think Sergei already knows based on some our past discussions. I also think what seems like divergent views are a lot closer than we might want to admit also.;)Quote:
Originally Posted by wambat
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I think Sergei already knows based on some our past discussions. I also think what seems like divergent views are a lot closer than we might want to admit also.;)Quote:
Originally Posted by wambat
I think that X is optimum size of condenser. What is the optimum? The optimum is the size of condenser when total(compressors, condensers, evaporators) power use per unit of refrigeration is minimum. If condenser is oversized we should reduce capacity(and energy use) of this condenser. So capacities of compressors and condensers should balanced to keep total power use at minimum level. This balancing should be done at different ambient conditions and different refrigeration loads. Sometimes optimum condensing pressure is low and we have a barriers to keep it low. However, every barrier has a solution. The longer we run plant at optimum condensing pressure, the better efficiency of this plant.
Didn't know "X" would make such a fuzz!
Optimums are hard to get at, when we are more like searching for feasible solutions! ... like not having our fuses blown!
I certinaly don't think anyone is getting their fuses (or fuzzes) blown.:D
What we see with this discussion is the many different ways people look at topics and how they attack them to develop solutions.
It is also important to recognize that any topic will have differing viewpoints because the posters all have different skill sets and experience levels.
So...a simple question on over-sizing condensers went from theoretical to optimization to practical in the span of only several posts. How cool is that?!:cool:
Ok, didn't think it was able to work at these low pressures, I'll take a look.
But If you have such a huge condensor with pressures as low as these. When working in a chamber at e.g. 10°C, with outside temps of -10° for example, you could have major problems with head pressure and need to keep your pressures up, no?
Sorry I didn't have enough time to answer these, my way.
Thanks wambat I think this is a wise post! And it was in response to Sergei's below.
The only problem with it is that it implies that an optimum is somewhere in the middle and if I interpret Sergei right it's what he's after.
Unfortunately I've never seen a system designed so that it minimizes power per unit refrigeration.
The big problem is this is impossible to do in the field you can calculate it and we better do, but it is done after the system is built not before.
This is exactly what people in NASA should do with good computer models and crystal clear objectives and lots of computing resources, and maybe then build the system.
YOU ARE ABSOLUTLY RIGHT WANTING THIS OBJECTIVE but I'm afraid we are far from it!
Yes, the balancing is done depending on ambient and cold room conditions but with a different objective an that is comply with demand.
The primary objective of the system is to do the cooling what it is supposed to. All optimizations that I know are done are on component basis, not on system basis because it is impossible to stretch the condenser 5 inches to reach a better working condition.
What you do is once you have the system (or at least selected componets) you do all optimization possible like adding capacity control maybe add a VFD but your system may be far from working at any optimum.
A big one and very cost effective is heat recovery, that's why it has become a must with all big brands!
Some system designers have programs to work in this direction but their own components cannot be assembled in such a way that you can make enough combinations to get even close to an energy use optimum like you want, THAT I KNOW OF!
This is what I do for a living. If you are lucky to do this before the system is built it is so much easier. If you have to do it after installation it is a lot of work.Quote:
Originally Posted by GXMPLX
There is an optimum for each operating condition. The real trick is to find these operating points and match the system response to these with the most cost effective method of operation.
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.
Hi Sergei. I sort of thought you might since we have talked about this before.:DQuote:
Originally Posted by Sergei
Optimization is completely different than balanced equipment selections.
:off topic: OK, it's offical..you're whacked again. :p
Well...if you think I'm using calculus for this your crazy!:DQuote:
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.
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?
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!:D
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.
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.
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 :D
sintrawest is dit antwerpen?
I bet I know that company ..W...s:p
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 Dutch
hmm indeed w...s
hmmz... nemen jullie ook de examens af voor de certificering dan?
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),....
The highest you can get the low pressure is based on the temperatures required for cooling. That means you have a relatively fixed range the low side can operate in.Quote:
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...
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.
That's the one, but I'm talking of many years ago.
Isn't EADS their military section?
Yes indeed it's military :)
was it a w***s you serviced?
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.
hmm...I've never seen a chamber of that capacity over there... maybe shredded.
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.
That's not the condensers fault, but it could be the system designers. This is in part., two issues. The piping may not be correct which allows liquid to hang up in the condenser. This reduces the heat rejection capacity of the condensers. Air is a problem for the purgers to work on.Quote:
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.
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 justified :mad:
Yes this is very true and it relates to this:Quote:
Originally Posted by GXMPLX
Sometimes the problem is not related to just selecting a bigger condenser, but making those you have work.Quote:
Originally Posted by me
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?