OK you drop your SST and starve the coil "increasing the super heat." But do you understand what happens to the rest of the system with excessive superheat
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I have thought for many hours about that one before, that is not how I would drop SST, but that would work.
Could you give me an example of when lowering the SHR does not reduce overall system EER?
Even fitting heat pipes before and after the evap coil adds air resistance and lowers circuit COP.
Others have spent time explaining the way these things go - but still no one knows why...
http://en.wikipedia.org/wiki/Capillary_action
That is often the first place to start if it is a service matter. If your SCT is at design and your condenser capacity is at max, say max fans at max speed, then you cannot drop it any significant amount without some radical addition or modification to the plant - say atomized spray water.
If you were going to modify the plant to drop SST but maintain or even reduce SH then adding a mechanical subcooling circuit would do a great job and you'd regain efficiency overall - the two bits of plant combined will have a higher EER.
Interesting comment - you've got me all excited now. Tell me more?
I would have thought the increased vapour pressure (raised dew point) would result in weak molecular attraction level of forces causing the water to condense into the paper and ink in the paper. As the wiki link say - water's intermolecular forces are weaker than the forces between the molecules and the paper and so when the ink is taken back into solution with water the waters attraction to the paper causes it to run with the ink.
But I'm not saying much - I'm now out of my league - I'm more comfortable sticking to HVACR.
I have attached a couple of photo's from a data center cooling system I consulted on doing all the load calcs, equipment selection, controls philosophies and pipework (distribution) design and so forth. In other words a real life example of what we are talking about - the importance of understand SHR.
So some questions to entertain your intellect :)
What do you think is my designed SHR and how would energy be wasted if it is not commissioned to design intentions but rather is naively commissioned only to design spec?
air, moisture, products (including SHR)
Think of air as a sponge, it is dry and sitting on the bench, 0% RH, dunk totally in water, 100% RH.
Squeeze the sponge a bit (which means either increased air pressure or cooling down, basically both are contracting the mass), what comes out , "water" what is the present RH 100%, now release it in the air, what is the RH (between 0 and 100%, depends upon how much you squeezed) no place on the bench, leave for a minute, lift up what will you see, water because the water had more pressure excerted than the bench pushed up (in this case gravity)
I love thermodynamics so I have developed what I believe to be a lecture with methods of explanations better than none other to impart to others an uderstanding of psychrometrics.
Dalton law of partial pressures is required first. But only after I have rid people minds of the catasrophy of the spunge analogy which actually detracts from peoples ability to develop an understanding of psychrometrics. I have attached an example slide randonly selected from about 10 slides I use to convery this first principle that is mean to dispense with the spunge analogy.
Sorry - hit the submit button rather than the manage attachments button...
Here is the slide...
Problem is matey ...... your over enthusiastic, overwhelming "love" for thermodynamics has tended to cause a lot of peeps to yawn and ask the question ....Why are we listening to this?
It's not required at the moment... You seem to have gotten lost in your own world of over egged responses to an in field problem with a total loss vent system that isn't working.
Go back to the begining of this thread and read what the poor OP was asking in the first place.
He needed some help, not a rant on the mysteries of thermodynamics.
I feel sorry for you in some respects because I can understand how you want to give up the knowledge you hold so dearly, to those who aren't so fortunate to have the ability that you quite clealy have. I can see you're something of a very talented chap. You can quote garrulously with technical and philosphically sounding arguements. You hold a magical esteem of yourself which comes over something a tad pompous, and I suspect because of this challenging nature that you exude there have been a few people willing to run with you for a while. However, I wouldn't be suprised if the original poster has gone off wondering why he ever bothered .... because he didn't get any help from reading your pontifications about the benefits of SHR's
It would, in all fairness to willsmithiraq, been better to have moved your lectures over to another thread where you could discuss the flavour of the cheese in the moon to your heart's content. :D
I am standing in defence of the proposition that knowledge of SHR is useful. You may very right about everything you say about me - you may be wrong - I am not interested in which, if any, it is - and whatever it happens to be it would still be irrelevant to the question "Is there any need for a commissioning engineer to have a good understanding of SHR control?".
You have gone silent on that quest? Are you avoiding it?
The ad hominem fallacy is committed when an antagonist brings into the discussion an irrelevancy.
If someone argued that we should not take seriously the findings of a medical scientist who had researched the beneficial effects of jogging on the cardiovascular system on the grounds that the scientist was overweight and probably could not even run 100 yards then a matter utterly irrelevant to the topic at hand would have been introduced to the discussion. The antagonist might just as well have stated that in Spain it rains mainly on the plains for all it adds to the topic at hand. Because the two claims can be true at the same time. They are not mutually exclusive. The one does not contradict the other and nor is the one contrary to the other. In which case the antagonist has merely changed the subject to an irrelevance.
As I say, you might even be right about your claims of me but this is not actually the time nor place to discuss such matters so I'd rather we get back onto the the other very unrelated topic of the benefits of understanding SHR manipulation.
You see, I am not asking people to take my claims on faith or on testament but instead by analysis of the evidence and argument I present. And anyway even if you were right about me none of that necessarily detracts on its own from any value my testament might have if it was mere testament rather than argument and evidence I was offering.
If someone is introducing an irrelevancy then it is good enough simply to remind them that they have changed the subject and that you would like to finish the discussing the topic at hand before moving on the other topics.
I cannot see how the original poster would be dished a disservice by all of the ensued technical speculations. You are introducing greater irrelevancies than I might have done in the first place - fighting fire with fire doesn't always word - sometimes it merely amounts to two wrongs.
Cynics, skeptics, pessimists and relativists.
Cynics suggest nothing matters, skeptics keep and open mind, pessimists throw their arms in the air and claim it's all pointless and relativists are willing to swing in any direction.
Skepticism is healthy if it is inquiring skepticism - if it is participatory skepticism. Over the ages the many intellectually liberating antimonies - particularly those of Sextus Empiricus, Descartes, Hulm and Kant.
I am a strong skeptic - I challenge - break apart - then rebuild - every synthesis of information that comes my way.
It's only the cynical pessimists that are averse to technical speculations. There was a time - it seems nearly a decade back now - when I once started a forum category called "Technical Speculations" and speculating there but anywhere else too was quite an accepted past time. unfortunately there are too few constructive skeptics in our industry.
And I still don't see the relevance of SHR to service.
If I know the required temp and RH, I can make it happen without evaluating or knowing anything about the SHR.
It's all about the condition of the supply air.
Way off topic. I give up. Unsubscribing the thread.
I'm about to go north 3 hrs drive for a few days so I shall leave you in peace.
I will probably be barred from accessing these forums again shortly anyway :)
I'm also not sure what relevence SHR has to service except to say that in the same way a tech knows more about a system if he/she understands the dynamics of Subcool he/she knows more about the system if he/she understands the dynamics of SHR (i.e. ADP)
But I will say that if you tried to answer my question put further up this thread on the data centre SHR commissioning to design intention versus commissioning to spec then you might gain an appreciation of SHR with regards to being a good commissioning engineer.
Then come back and explain what you mean by "It's all about the condition of the supply air" and how this somehow excludes any SHR implications.
Then read Malcolm Gladwell's Book called Blink and the power of thin slice thinking and how it is increased with learning but the learning must not cloud the actual on site real situation analysis - but that on site situational analysis is vastly improved with leasure-time studying of the topic material to as great a depths as possible.
Also, as Socrates say in the Theatatus "How do you know you have found what you are looking for if you do not know what you are looking for?" Which direction do you head in search of it if you don't even know what it is - how do you know it is not your problem if you don't even know what it is?
With 20% of the required knowledge we can fix 80% of the problems. All added knowlege comes with diminishing returns. And if everyone knows only the same 20% then anyone who knows more seems out of kilter and since everyone get's along facing the same 80% of problems leaving the systems 80% good who's going to care about the 20% missing performance or longivity especially if no body is even aware of its possibilities.
Later Gary - also - check your mail :)
No not avoiding it at all, but it was your question that you were ranting on about not the one from the OP. We should be staying on topic and helping the guy to solve a problem, not adding confusion to the issue.
I can just imagine Winston Churchill trying to get the bouncing bomb into a mission and some boffin (aka yourself) arguing that there were some fundimental issues covering the triple point of water in Norway on a winter's night, that needed to be adressed and may have some bearing on the way the bomb may or may not bounce.
;)
I Give up :confused:
I'm still waiting for the OP to return with further info, so we can get back to his problem.
Gary,
I fear he's long gone. . . He's enough on his plate without trying to read through all of the above ... not helpful really. I'm as guilty as anyone for contributing.
Happy Sunday ... tomorrow's Monday . yippee
I doubt seriously that we chased him away with our riveting discussion of SHR.
More likely he is busy with other things and hasn't gotten back to the system in question yet... or he figured it out and moved on.
I did not say antagonistic - I said antagonist
Antagonist: a person who is opposed to, struggles against, or competes with another; opponent; adversary.
Antagonistic: hostile; unfriendly.
If you think I meant antagonistic then maybe that has more to do with your own perception of yourself.
If you were to try square the implicitly invoked generalisations of the above argument universally then you would be being inconsistent if you did not equally assert that system total air volume flow and zone air volume flows are preset at design so you cannot see how a commissioning engineer is able to make any corrections to these factors.Quote:
Originally Posted by nevgee
No system meets perfectly the design parameters - in the UK CIBSE give percentage tolerances that ought to be met and that ought to be stated in the specifications.
With regard to SHR's - comfort cooling systems are more forgiving of deviations from design.
With data center close control systems enormous amounts of electrical energy is wasted when the CRAC SHR's are lower than the Rack Hall's SHR on account of excessively cold chilled water temperatures causing continuous unnecessary operation of the humidifier bottles. On the Global Switch project I was involved with - the biggest data centre in Europe - such ignorance during commissioning would amount to tens of thousands of £'s wasted monthly.
You should be able to count 26 1.5MW Air Cooled Chillers on the roof here...
http://maps.google.co.uk/maps?hl=en&...01629&t=h&z=20
In an asymmetric persuasion dialogue the person making the claim bares the burden of proof. This is when a protagonist makes a claim and the antagonist simply denies the acceptability of the argument and evidence offered. An example here is Me versus Gary. Gary has not made a counter claim - he has merely expressed skepticism and so bares no burden of proof.
In the persuasion dialogue between you and I we have both made claims - me for and you against - this is thus a symmetrical persuasion dialogue - you share equally a burden of proof for your claim as I do for mine. I am still waiting for your argument and evidence. You may yet turn out to be right but so far your argument is weak and your evidence is none.
Getting hold of the designers intentions would help. When is the system to operate in heating and when in cooling (What ambient temps) and what are the peak heating and cooling TD's and dT's.
In the case of the 100% fresh air system for high but inactive occupancies you will over cool the occupants with normal supply air to return air dt's. Thus the high BPF but with maintained SHR.
On the other hand face and bypass over and around a coiling coil is for SHR variation.
We are in the presence of a very well educated member (a compliment)
How ever you must be able to impart your knowledge in a way that those of us who are not as educated or skilled within your feild, that either is above our present knowledge levels, or a way that does not make us feel inferior.
Going Back, SHR, the "TERM" is used commonlly in Air conditioning, but is very rarely used in refrigeration (I know that they are basic the same side of the coin) Rightly or wrongly thats another question.
SHR is calculated figure, normally in refrigeration, the design engineer normally gives the tech, a set of criteria that the on site engineer should be aiming for, which if dealing with air could always be calculated SHR figure. what comes first the SHR or the onsite tech data.
So when passing my design data to engineers, I would give them a set of data that should occur under certain conditions.
"Air on" conditions, "Air off", refrigeration details, air pressure drops, and so on.
For this reason the guy on site does not need to use SHR as his main method of proving performance, even though if you used and calculated his collected data he would actually have a SHR figure.
Using SHR% as starting point is irrelevent unless you have pretermined reference points.
Moving off slightly I understand your point about your data centre and the humidity bottles, As I have mentioned, more use of enthalpy sensors should be used.
I'm willing to accept the compliment so long as you are able and willing, if necessary, to provide justification - perhaps backing it up with evidence - after also demonstrating you are qualified to issue such compliments - just kidding :)
I don't know about the not as educated or skilled references - after all - to go through the motions of imparting knowledge one implicitly assumes, at this level of sharing, those listening are sufficiently educated but just per chance not in the know of this particular take of the spectrum.
I was also cruising along explaining stuff quite plainly up until the point a claim was made against me in a manner that implicitly suggested that person could underpin the claim with argument and evidence. I called the person's bluff and invited the argument and evidence. None came and at the same time I am not going to do their work for them by providing in full with every detail my own argument and evidence in defense. We have a right to assume that a person making a claim against a notion we propose will have valid and sound reasoning for doing so and will be also most willing to demonstrate that reasoning in an articulate manner - otherwise how can they themselves be sure of their own claims.
I have given a brief clue as to some of the SHR issues arising with Data Centre design and commissioning but there is a little more still to it. The photo's I posted of my recent consulting project is of a project where the matter of SHR is the very central foundational point upon which everything else, design wise, pivots.
If anyone wants to convince me that there is no point in a commissioning engineer understanding how to manipulate system SHR then they will have to first demonstrate to me they are qualified to draw such conclusions otherwise for all I know they could be sharing some old mistaken knowledge they were taught by some guy who was in turn taught by some other equally mistaken guy ad infinitum.
DTLarca, could you explain how this sensible heat ratio has relevance to origional posters problem when he has not had the equipment running long enough to have a coffee break? He did not manufacture the parts, just there to put it together and make some customers request happen. It seems to me op may not have had the luxury of time to discuss above events, probably now working through component parts capacity with manufacturer or whoever supplied the equipment. thats what i would do... mike.
It has no immediate relevance - there are more serious concerns this far.
The discussion on SHR springs from this inherently self defeating set of statements "Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens."
To manipulate the condition of the supply air (specifically wetbulb) as a means of controlling humidity levels is to manipulate the SHR, but needn't be thought of as a manipulation of the SHR, and needn't be couched in terms of SHR%.
It could simply be thought of as manipulating humidity, and the ends achieved without referring to SHR%.
To my mind, SHR% seems an unnecessary complication.
I am no specialist on Data centres.
But lets have a go without looking for external Data.
I presume you are talking about a high energy density area (compact electronics) So all the load from these items is sensible energy, possibly at little latent load from people and the required amount of fresh infiltration/makeup.
We want to ensure that static electricity is not produced, therefore the humidity entering the process has to be high enough, that when the air picks up the load sensible energy that the humidity s still high enough to ensure static is not produced.
Now we have our return air/load.
how is it to be chilled, it is a dedicated chiller (water or DX), Ok is a perfect world, a floating set point on supply fluid/SST to meet the load profile whilst being high enough to ensure required high exiting humidity levels. On a multi use system, the working fluid/sst, must meet the lowest common requirement, so using a floating set point to control a modulating valve. if the area(s) are zoned, use of a air transducer and VSD to match the air requirment profile. Final introduce free cooling, based upon the enthalapy difference, allowing for cooling without the need for additional moisture (unless the moisture producing device is more econimical to run than the refrigerant plant.
All contolled by logic based upon wet/bulb conditions.
Are you on the right page MAD?
Good effort there Mad Fridge.
Gary just does not want to admit that SHR is a better description of what he's talking about :)