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Re: COP and Superheat - does is it help?
Peter sorry for stepping on your toes! Not my intention!
Coolpack and the like in my opinion is to used by those who understand the refrigeration process. So the issue of what the superheat is, is determined by the knowledge on the person imputing the data.
I agree you can almost insert what ever data you want and it will calculate it.
The areas in Coolpack that I use, do not reference the load itself, (ie room temp), so that being the case, they level of superheat useful or not, can be what ever you want, coolpack also does not give warnings about very discharge temps (even though is does calculate the temp), which is also a practical issue
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Re: COP and Superheat - does is it help?
MF, no you didn't step on my toes, not at all, I only have sometimes doubts if I understand correct what I read.
Ever tried Solkane?
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Re: COP and Superheat - does is it help?
Honeywell link http://www.honeywell-refrigerants.co...mber_108269853 very similar to Coolpack but more graphics
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Re: COP and Superheat - does is it help?
Peter - I downloaded a copy of Solkane and it is very nice stuff, lots of respect for the authors.
When I put the numbers in that I use it came back with exactly the same answers so very pleased with that agreement.
So at this point I cant yet see where SH improves the COP and as MAD points out if you enter the wrong data into Coolpack it will give the wrong answer. It does not seem to check if what you are trying to do is reasonable. Solkane is also similar in it allows unrealistic SH to be added although the COP remains pretty constant. The basic reason seems to be neither consider the box temperature which in a real scenario is essential.
The main idea of this thread is to find out if SH ever increases COP and is not intended to show up Coolpack or Solkane but as a corrollary to the thread it does appear that care should be exercised in their use.
So my only intention is determine if SH ever improves COP and so far I have not seen any conclusive evidence.
Now there may be many reasons why SH is a good thing but that can be looked at later.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
desA
Right then, Chef. Please set the example/s & lets get cracking.
Ready when you are.
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Re: COP and Superheat - does is it help?
Hi folks,
Apologies for my late entry into the debate. Have been frenetically busy of late. I'll review the post above & make comments along the way. Fascinated to see how Peter's trials work out in practice.
What Peter & Chef's (& hopefully MF's) systems will be able to provide is the following vital information:
1. What happens to Te,sat / Tc,sat / Tc,disch when ONLY evap SH is altered?
2. How does the METHOD of altering SH affect Te,sat / Tc,sat / Tc,disch?
2.1 For instance, if SH is altered by trimming refrigerant mass flow?
2.2 If SH is altered by adjusting evap fan speed?
2.3 If SH is altered by other means?
If Peter / Chef / MF could provide practical, experimental data, then this would be the place to begin the COP calculations.
From my own work in my Laos lab, I noted that as SH was adjusted, that other variables in the system automatically re-set themselves, as the system balanced itself. An adjustment of one part, affects the whole system.
I would also agree with the discussion of 'useful' SH. In other words, the SH rise has to come from useful evaporator effect ie. extraction of energy from atmosphere - NOT heat-ingress along the suction line.
Anyway, I feel that the experimental feedback will be absolutely vital, before going into detailed calcs via Coolpack / Solkane / etc.
[at]Peter : Pam says 'Hi'... Please send our regards to Kristien. :)
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Re: COP and Superheat - does is it help?
Ah DesA - I have already posted the paramters to use for the comparisons.
Also put up my results for the 3C and 8C SH cases and it pretty well shows the COP falls off with increases in SH.
"Anyway, I feel that the experimental feedback will be absolutely vital, before going into detailed calcs via Coolpack / Solkane / etc."
I think we have to get away from the experimental feedback, the complexity of a test rig to produce results reliable enough to determine COP would be an awesome rig with massive amounts of sensors. SO experimental is out and lets stick to hear say or gut feel.
Detailed calcs in Coolpack/Solkane? How detailed can you get in those programs!
Lets see what you come up with to support your ideas and then we can compare.
Oh and fans on the evaporator are not allowed but changing the mass flowrate or even the charge is fine. Whatever you choose.
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Re: COP and Superheat - does is it help?
Chef,
My thoughts are as follows:
1. Performing a purely academic exercise on a fixed set of values may not be representative of what happens in real life.
2. Obtaining feedback from the real rigs out there - Peter, MF, your systems - will allow us to set more realistic calculation regime, for comparison.
I'm pretty eager to have more solid feedback from the real-world rigs, before we can proclaim a 'cast-in-stone' result of precisely how COP does vary, in reality. Apologies if this was not they way you wanted to go.
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Re: COP and Superheat - does is it help?
DesA - This is my initially posted question.
"So far I have not been able to show this increase in COP and so ask if anyone knows of a good example/article that describes it."
Really that is all I want and comments and points of view along the way are very illuminating, but your continued insistance on testing is unfounded. I cannot ask anyone to go to the lengths of running real life tests to satisfy such a simple question.
Of course it is an interesting question.
Your comment that performing acedemic calculations would be invalid without testing, seems, presumptuous at best.
If we are not able to calculate, predict and understand theoretical results what qualifications do we have to interpret and make conclusions about test data.
More to the point "if" it was decided to do testing to prove a theory, one must already have a premise to base the test upon, ie we must already have some insight into how the test parameters are to be set to prove the concept either way.
Maybe you could propose such a test schedule and your reasons for such a test.
You never know - with some some promising paramters to work to I may even update my capillary test rig.
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Re: COP and Superheat - does is it help?
Hi,
"First" "Mads Rig", ah is not longer a test rig, is chunking away nicely cooling milk on a farm.
However I understand both of your concerns, measuring a test, is only any good, if you know what your measuring against, but us in the praactical side, also know that steady state theory does not really apply to any great extent to what really happens.
Also care has to be taken, in understanding what your require from the system. Peters example (my understanding, please correct me if I am wrong), was focusing on the heating side of the loop (even though the cooling is still important).
Back to practical testing, it would be difficult with engineers tools and test gear to accurately see some of the changes you would hope to see. (either the machine needs to be really large, or test equipment needs to be of very high quality (My test gear was better than most ref engineers would have but not up to the equipment that full test labs have.
I think that DesA should throw some calcs into the mix (using his expertise in heat transfer, which may have more of an influence, than just small changes is superheat) I think that could give a starting point, us dummies, then could apply some of our practical knowledge and observations.
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Re: COP and Superheat - does is it help?
[at]Chef : My recommendation for linking the proposed cycle operating points to reality, is that a purely academic review (dead easy to perform) will presume certain parameters to remain constant, whereas, in reality they move as the SH 'raiser/lowerer' will affect the rest of the system. No single variable remains locked as SH is altered, in reality.
Presuming parameters to remain constant, when in fact they change, may (will) lead to incorrect final conclusions.
This was the reasoning behind my suggestions. No problem if this is ignored - feel free - it is your thread, after all. But, don't complain when the final 'comparisons' turn out to be implausible, in practice. :)
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Re: COP and Superheat - does is it help?
It's a pitty I never made this test rig http://www.refrigeration-engineer.co...retical+sensor
This could have been very useful now. I found after this post someone who could program this alll and send it via ZigBee to a laptop and then project it with a beamer
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
Peter_1
My rig was very similar, using a SCADA, I did not have all the inputs going into it ( i am thick when comes to electronics)
What i was lacking was high end "energy measurements" and "refrigerant mass flow devices".
So it was excellent for see change, but not good enough to give definitive performance (estimate +/-5%)
I would tie the figures in with the comp manufactures data.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
desA
[at]Chef : My recommendation for linking the proposed cycle operating points to reality, is that a purely academic review (dead easy to perform) will presume certain parameters to remain constant, whereas, in reality they move as the SH 'raiser/lowerer' will affect the rest of the system. No single variable remains locked as SH is altered, in reality.
I do not know what the acedemic reviews presume till I read them But as it is dead easy to perform we hope to see some good stuff posted
Presuming parameters to remain constant, when in fact they change, may (will) lead to incorrect final conclusions.
It is a bit of a circular comment, if parameters remain constant how can they change.
This was the reasoning behind my suggestions. No problem if this is ignored - feel free - it is your thread, after all. But, don't complain when the final 'comparisons' turn out to be implausible, in practice.
Of course your testing idea has merits, lets imagine I want to upgrade to a new gas so you would propose testing all available gases till a good one is found and ignore the massive amount of data provided by the manufacturers/suppliers.
Or better still I have to install a split into a new build in Raynes Drive. So rather than suppliers selection information coupled to weather and solar data I have to buy a house and test various splits over the seasons to make sure I have the right unit. Seems right to me!!!!!
:)
Oh and I wont complain if the results are of the mark but if you can possibly make a contribution it would be appreciated.
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Re: COP and Superheat - does is it help?
Quote:
Peter mentioned:
It's a pitty I never made this test rig
http://www.refrigeration-engineer.co...retical+sensor
This could have been very useful now. I found after this post someone who could program this alll and send it via ZigBee to a laptop and then project it with a beamer
[at]Peter:
When you say 'program this all', do you mean as in generate a computer simulation?
If so, than this may help us to establish the movement of variables with our modification of SH. This could possibly also then assist to settle the COP discussion. Not sure mind you, unless the author manages to correctly model compressor efficiency changes, evap & condensor changes, as the cycle changes.
Would be nice to see in action.
I had also in mind trying to locate a dynamic simulator for an hvac system. This may, however, also suffer from the same inaccuracies.
This is where a simple circuit will be so useful. (My heat-pump lab is currently in moth-balls in Laos. Would have run some hard trials & sorted most of this out by now... :) )
Peter, or MF, are you perhaps able to run some trials with your rig/system/s? It should take one day, at most, to determine what we need - at least, close enough for us to clarify Chef's dilemma.
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Re: COP and Superheat - does is it help?
Quote:
Chef commented:
Oh and I wont complain if the results are of the mark but if you can possibly make a contribution it would be appreciated.
SH is never controlled directly, but indirectly. Other parameters e.g. TXV, fan speed, etc are controlled, or adjusted directly.
Once we have established the system settling point (Te,sat; Tc,sat; Td,comp; compressor power input etc) (via tweaking of a direct variable), we will be able to compute COP & track it against SH. That will then provide some level of answer to your question. No?
What will also be important is the adjustment methodology:
1. Adjust controlled variable;
2. Leave system to settle into steady-state operating point;
3. Take readings;
4. Repeat, as required.
At that point, I'll be calculating away, you betcha... :)
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Re: COP and Superheat - does is it help?
I have a little program that pretends it is a fridge. A pretty simple one with the condenser at the back, a plate inside as the evaporator, a capillary tube and compressor. No HX.
The inputs are ambient, box contents, temp setting of the thermostat and Temp cycle (on/off temps)
Other inputs that define the fridge are more or less fixed for that model like compressor characteristics, evaporator and condenser dimensions, heat transfer coefficients, heat leakage rates etc insulation, even convection constants.
The outputs are mainly time based and position based. So with a stable and cycling fridge turning on and off the results show, for instance, box temp v. time or any system variable v. time but more importantly and what I really want is the refrigerant mass in each component.
So as the fridge cycles on and off one sees a nice drop in box temp and in the off cycle a slower rise as heat is lost. Now a snap shot every minute (or whatever) shows where the refrigerant is located and how it migrates around the system during cooldown and warm up.
By changing the thermostats temp cycle for instance from 5C down to 1C shows an increase in the number of cycles and all is as one would expect. At some point the cycle is so short that pressure equalisation cannot be achieved and so starting loads become large.
Throw in 4 litres of warm water and cycle times now extend (after a longer initial cooldown period)
Now in changing system charge, or some of the fridges components sizes and especially the cap tube the SH can be varied and the response of the whole system can be studied, BUT many sources suggest more SH increases the COP and so far all I have seen is a decrease in COP.
So if it is true that COP falls as SH rises it helps to have more confidence in the programs results, but if that assumption is wrong then I need to find out where the problem lies and fix it.
Hence my question
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Re: COP and Superheat - does is it help?
Thanks Chef for a very, very interesting review of your fridge simulator.
If I may ask, does your simulator determine an evap SH / Te,sat / Tc,sat / Tcomp,disch?
If memory serves correctly, you are something of a guru on setting up pretty realistic simulators using EES platform.
I could possibly assist on the evap heat-transfer (condenser, as well), if this would assist in modeliing the Te,sat / SH characteristics of the evap. Once these are in place, then the simulator may be able to give us even deeper insights into the expected system balance points.
I'd say that publishing of the various simulated system parameters for critique, would allow a few folks to assist towards a better understanding of what is really going on. We'd all benefit from the experience, I'm sure.
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Re: COP and Superheat - does is it help?
I would tend to look at this another way.
Imagine the rig, is steady state, -20C box temp, Te -26C sh 6K (100% useful, no more useful available)
So it must be that a part of the evap is only used superheating.
So this then brings in DesA (you chose a evap), what would be the new Te if the SH was only 1K "the net cooling load remain constant"
Ignore other system changes at this point.
I think this will prove the practical point about SH
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1 Attachment(s)
Re: COP and Superheat - does is it help?
Yes it does Te, SH, Tc Tcompdisch etc plus a few more.
Input and output variables include, Uc, dTc, ambient at condenser, convection constant, condenser dimensions, Qc, dPc, SC, RMc (refrigeration mass cond) heat transfer coeff air side.
Evap variables are similar and also include velocity versus evap position, boiling scheme, Ue V. position, dPe V. position, Qe V. position, RMe V. position ......etc
Other inputs include pressure drops in suction line, valves in comp, discharge line. Line dP can either be input or calculated from system conditions and pipe dimensions and K factors for fittings.
Comp efficiency V. Te/Tc and SH
Cap tube length, diameter, coil size and number of coils, Isenthalpic or adiabatic expansion, Fanno recovery efficiency, # of tubes, K Epsilon vorticity, kinematic relaxation, . Too much output data to list here really.
System wide variables include insulation heat transfer properties, fridge size, thermal mass, box contents and thermal mass and heat transfer properties.....etc
It is a pretty long list really and not sure it will help discover a solution to the SH question.
MAD - With a box of -20C and SH=1C all available used I get Te=-21C but the Qe goes up and so I cant keep the load consatant or the same as with Te=-26
Also have to change the cap tube or it will not even allow that to happen.
Here is a fun plot of the fridge inside temperature distribution, plate is at the top of course and blue is cold.
Attachment 9487
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Re: COP and Superheat - does is it help?
Very cute.
I would suspect that, in order to answer your original question/s, & check your simulator realism, you'd be better off building a test fridge & comparing variable responses... Anything else may end up being pure speculation - honestly. :)
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Re: COP and Superheat - does is it help?
DesA - I believe this is an important topic and deserves a proper hearing.
There appear to be many engineers looking for a resolution on this topic.
Please do not keep repeating an old mantra that has been shown to be outside the scope of a discussion thread.
Also there seem to be outstanding questions for you to answer that may go along the right track to progress the answer.
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Re: COP and Superheat - does is it help?
Hi Chef
you certainly pick interesting topics, beyond me
but from my limited understanding without the calcs
the lower the superheat the higher the cop
as mass flow through the compressor increases with lower superheat
the condenser does less de-superheating, resulting in more subcooling
resulting in more cooling effect through the evaporator
gonna be a long learning curve rewiring my brain if you's now say thats not the case ?
R's chillerman
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Re: COP and Superheat - does is it help?
Chillerman - lower SH and higher COP is what I see as well so not trying to get you to relearn.
Increased mass flow at lower SH and less desuperheating are two good points. Also there may be increases in compressor efficiency and steeper slopes on the specific entropy curves adding to the mix.
You also mention more SC also adding in there.
There may also be a reduction in pressure losses but I would have to study that more but from intial thoughts dP will fall as SH falls because dP is a function of velocity squared compared to just density.
So we have at the moment
- Increase in mass flow
- drop in desuperheating
- increase in compressor efficiency
- decrease in specific entropy
- increase in SC
- Decrease in pressure drops
Nice one Chillerman, may be fun to which one is more influential
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1 Attachment(s)
Re: COP and Superheat - does is it help?
Here is a snip from a paper that makes it even more complex, it seems it can decrease or increase or not affect the COP.
Attachment 9488
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Re: COP and Superheat - does is it help?
Quote:
Chef:
DesA - I believe this is an important topic and deserves a proper hearing.
There appear to be many engineers looking for a resolution on this topic.
Agreed.
Quote:
Please do not keep repeating an old mantra that has been shown to be outside the scope of a discussion thread.
I suspect that we'll - with respect - have to agree to disagree. :)
Quote:
Also there seem to be outstanding questions for you to answer that may go along the right track to progress the answer.
There certainly are a lot.
What I'd like to suggest first off is that you reveal a lot more of the software platform you are developing. This can then form the substantive basis for discussion & comparison, in the absence of a robust comparative test platform.
What will also be of major interest in the 'why' of high superheat leading to increased COP is precisely how the condenser operates & how heat is extracted. In this regard, MF can contribute an immense amount of experience, based on his earlier heat-pump projects.
In other words, in raising evap SH - if it leads to 'increased' Tc,sat , will almost certainly have a COP reduction impact. If raising SH, allows a technology 'tweak' to be used such that Tc,sat is lowered, then COP rises.
In order for your simulator to reflect this, you will need to model the condenser in split form.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
Chef
Here is a snip from a paper that makes it even more complex, it seems it can decrease or increase or not affect the COP.
Attachment 9488
I suspect that this may be due to the enthalpy (h) response with pressure - more accurately as enthalpy difference response with pressure. The effect at low P (evap side), may be different to the high P (condenser side), affecting COP response - as the cycle migrates over its range of operation.
Interesting perspective...
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Re: COP and Superheat - does is it help?
DesA - here are the outstanding questions from previous posts that would help, if we keep leap frogging and missing stuff out we will lose vital comments and information.
Quote:
Originally Posted by
mad fridgie
I would tend to look at this another way.
Imagine the rig, is steady state, -20C box temp, Te -26C sh 6K (100% useful, no more useful available)
So it must be that a part of the evap is only used superheating.
So this then brings in DesA (you chose a evap), what would be the new Te if the SH was only 1K "the net cooling load remain constant"
Ignore other system changes at this point.
I think this will prove the practical point about SH
Quote:
Originally Posted by
desA
[at]Chef : My recommendation for linking the proposed cycle operating points to reality, is that a purely academic review (dead easy to perform) will presume certain parameters to remain constant, whereas, in reality they move as the SH 'raiser/lowerer' will affect the rest of the system. No single variable remains locked as SH is altered, in reality.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
desA
I suspect that this may be due to the enthalpy (h) response with pressure - more accurately as enthalpy difference response with pressure. The effect at low P (evap side), may be different to the high P (condenser side), affecting COP response - as the cycle migrates over its range of operation.
Interesting perspective...
I dont really understand what you are saying here, maybe you could rephrase it so we can understand what the article is alluding to.
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Re: COP and Superheat - does is it help?
I better clear up the evap proposal.
as an example the box requires 500w of cooling (steady state), this being achieved with an evap (simple) which is running at -26C and 6K SH.
We could say that 20% (as an example) of the surface area of the evap is being used for superheating. (in my opinion poorer heat transfer)
So if we reduce the superheat to 1K, then for example only 4% of the surface area is used for superheating. So we now an additional 16% which is wetted and has better heat transfer.
So to maintain our 500w steady state will the evap temperature in increase to reach the 500w equalibrium.
(at this point I have excluded all other parts of the system) So for example the evap temps goes from -26C to -24C (no clacs done)
Now lets look at the rest of the system, to ensure the equalibrium of 500 watts and the new Te, then the system mass flow would reduce (by means of reduction in comp swept volume) Do we know get a better efficiency?
Or if the system remain the same, would we end up with a new equalibrium point, lets say Te being -25C, but we now have a net cooling duty of 520w.
What would these figures do to the system COP.
So it all comes down to what effect SH has on an existing evap performance. Then we can determine if SH on an energy level is beneficial or detrimental.
In depth knowledge on heat transfer coefficients, is not my field. (a little knowledge may be dangerous???)
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Re: COP and Superheat - does is it help?
I'm not sure I understand the dilemma.
If the load is held steady, then the only way the SH at the evaporator outlet can be increased is to reduce the mass refrigerant flow... thus dropping the saturation temperature and reducing the COP.
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Re: COP and Superheat - does is it help?
According to the TECHNISOLVE program, as increase the superheat decrease the cop except r12.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
moideen
According to the TECHNISOLVE program, as increase the superheat decrease the cop except r12.
Thankyou moideen, a result, what kind of result do you get for R12.
I do not know TECHNISOLVE so by how much and a few conditions.
So far it seems that COP goes down as SH is increased but ther are are also some exceptions. This is exactaly what we are looking for so thanks.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
mad fridgie
I better clear up the evap proposal.
as an example the box requires 500w of cooling (steady state), this being achieved with an evap (simple) which is running at -26C and 6K SH.
We could say that 20% (as an example) of the surface area of the evap is being used for superheating. (in my opinion poorer heat transfer)
So if we reduce the superheat to 1K, then for example only 4% of the surface area is used for superheating. So we now an additional 16% which is wetted and has better heat transfer.
So to maintain our 500w steady state will the evap temperature in increase to reach the 500w equalibrium.
(at this point I have excluded all other parts of the system) So for example the evap temps goes from -26C to -24C (no clacs done)
Now lets look at the rest of the system, to ensure the equalibrium of 500 watts and the new Te, then the system mass flow would reduce (by means of reduction in comp swept volume) Do we know get a better efficiency?
Or if the system remain the same, would we end up with a new equalibrium point, lets say Te being -25C, but we now have a net cooling duty of 520w.
What would these figures do to the system COP.
So it all comes down to what effect SH has on an existing evap performance. Then we can determine if SH on an energy level is beneficial or detrimental.
In depth knowledge on heat transfer coefficients, is not my field. (a little knowledge may be dangerous???)
Very clever MAD but having a variable speed compressor does not really fit the original specs for the problem.
OK it was not specifically excluded but it makes it more complex and how are we going to get peer results from other contemporary programs, non of them have variable speed compressors as the input.
I dont know if that can be included - but if it does indeed show a COP increase it would be interesting.
Have you got any more results that show this is possible?
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
desA
What I'd like to suggest first off is that you reveal a lot more of the software platform you are developing. This can then form the substantive basis for discussion & comparison, in the absence of a robust comparative test platform.
If you are conversent with macro, finite element methods, finite difference time slices and Newton Raphson derivatives and second order approxamations for N+1 setups it may help.
Eulerian flows in tetrahedral elements would be even beter.
The program is written to discover where the refrigerant mass is located in a cycle and how it moves plus to show efficiency with varying charge, cap tube dimensions etc.
My results so far show COP always decreases with SH increasing which is not in line with some published data and so this is the question. Has anyone got any evidence COP increases with SH.
What will also be of major interest in the 'why' of high superheat leading to increased COP is precisely how the condenser operates & how heat is extracted. In this regard, MF can contribute an immense amount of experience, based on his earlier heat-pump projects.
You have lost me there, the bit about how the condenser operates? Please advise on this one.
In other words, in raising evap SH - if it leads to 'increased' Tc,sat , will almost certainly have a COP reduction impact. If raising SH, allows a technology 'tweak' to be used such that Tc,sat is lowered, then COP rises.
This is a 4 component fridge in its simplest form, no technology tweaks allowed, but if you are saying raising the SH can raise the COP - as you state above - what is the basis for this and some reference would be nice.
In order for your simulator to reflect this, you will need to model the condenser in split form.
What is a split form condenser???????????
Seems you have a way to raise COP with increased SH - sounds interesting.
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Re: COP and Superheat - does is it help?
Quote:
Chef:
DesA - here are the outstanding questions from previous posts that would help, if we keep leap frogging and missing stuff out we will lose vital comments and information.
??? :eek: :eek:
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1 Attachment(s)
Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
Chef
Thankyou moideen, a result, what kind of result do you get for R12.
I do not know TECHNISOLVE so by how much and a few conditions.
So far it seems that COP goes down as SH is increased but ther are are also some exceptions. This is exactaly what we are looking for so thanks.
dear chef,
find the attachment.in the technisolve program using r12 the cop increase slightly as increase the SH.
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Re: COP and Superheat - does is it help?
Quote:
DesA:
What I'd like to suggest first off is that you reveal a lot more of the software platform you are developing. This can then form the substantive basis for discussion & comparison, in the absence of a robust comparative test platform.
Quote:
Chef:
If you are conversent with macro, finite element methods, finite difference time slices and Newton Raphson derivatives and second order approxamations for N+1 setups it may help.
Eulerian flows in tetrahedral elements would be even beter.
One sincerely doubts that your simulation would require the use of Eulerian flows modeled on a tetrahedral mesh. FE/FD methods are well known - as is Newton Raphson convergence techniques. (Not always the most stable, mind you - fairly dated by now). That is, unless you're attempting to accurately model two phase flow evaporation/condensation regimes. You may want to save some level of energy, by reading up varous legacy books on the topic (e.g Collier/Thome & Thomes' later works).
I suspect that you're attempting to show off a tad... gotcha... :)
Back onto topic, then, dear fellow.
Quote:
Chef:
The program is written to discover where the refrigerant mass is located in a cycle and how it moves plus to show efficiency with varying charge, cap tube dimensions etc.
Useful. Try experimenting with RefSim (Technisolve). May prove to be a useful back-check. This software will balance the system temps, as various process parameters are adjusted. Even allows real compressors - performance tables & all, to be used. There are ways to tweak the parameters further, in order to study what you are looking for. Allows TXVs.
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Re: COP and Superheat - does is it help?
Handbags at dawn????????
But back on the subject.
We have to be careful that we are using the superheat for. As Des has stated increased suction superheat can improve the benefits for a heat pump application, where the heat side becomes the priority, but my understanding of the original question was related to the cooling side, but in either case w change on aspect of the cycle then it follows that all other areas change as well. So it still my belief it may not be the software that wrong, but how any data is in putted.
Also we have to consider why require superheat (normally to stop chance of liquid flood back and/or compressor oil dilution, so should the superheat that is required, be useful "direct", non useful (energy directly picked up from out side the refrigerate envelope, or just a pressure drop.
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Re: COP and Superheat - does is it help?
Quote:
Originally Posted by
chillerman2006
Hi Chef
you certainly pick interesting topics, beyond me
but from my limited understanding without the calcs
the lower the superheat the higher the cop
as mass flow through the compressor increases with lower superheat
the condenser does less de-superheating, resulting in more subcooling
resulting in more cooling effect through the evaporator
gonna be a long learning curve rewiring my brain if you's now say thats not the case ?
R's chillerman
Glad you jumped in before me C.M.
Read the comments. "Chef" continues to ask: is there proof that increased (useful or not) superheat increases C.O.P? I don't qualify for this level of discussion however, any amount of superheat, say 15K on a cooling cycle cannot increase C.O.P. as there is less duty performed by the volume of saturated refrigerant in the evaporator to start with. Increase S.H = less work done and longer running cycles. Negates C.O.P. During any duty cycle.
Maybe you are thinking, if the increased discharge temperature is raised with higher superheat, then the transfer of heat through the condenser is maximised, increasing performance. (Oversized condenser)
If one were to use increased superheat in a reverse cycle situation, then my answer is yes.
Just my humble response guys.